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The opening of Cook Strait: Interglacial tidal scour and aligning basins at a subduction to transform plate edge
Abstract
Cook Strait, the central seaway through the axial ranges of New Zealand, has many inferred origins. A compilation of marine geological and geophysical datasets suggests that Cook Strait developed when five sedimentary basins at a rapidly changing, obliquely convergent, plate boundary were moved into line and were linked by strong tidal scour in middle Pleistocene times. The basins relate partly to oblique subduction north of Cook Strait and partly to intercontinental transform to the south. Prior to opening, muddy, subduction pull-down and foreland basins in the northwest were separated from equally quiet water, rotating, forearc to transform basins in the southeast. The land barrier between them narrowed and was finally breached as subduction-related basins migrated southwards and transform-related basins extended northwards in response to rotation and divergent branching of a major transcurrent fault.Following breaching, a history of alternating scour and quiet water deposition is recorded by a series of deep, irregular unconformities in muddy basin fill. Scour is correlated with interglacial periods of high sea level when land barriers were submerged and strong tides, caused by a 140° phase difference at either end of the strait, eroded muddy sediments deposited in glacial periods when an emergent landbridge limited tidal exchange.
... The Cook Strait is the narrow (20 -60 km wide) oceanic passage between the North and South islands (Te Ika a Māui and Te Waipounamu) of New Zealand/Aotearoa, connecting the Tasman Sea/Te Tai o Rehua on the west to the Pacific Ocean/Te Moana nui a Kiwa on the east. The Cook Strait has been shaped by a complex combination of tectonic, climatic and oceanographic processes (Harris, 1990;Lewis et al., 1994). ...
... Tidal currents are known to play a major role in shaping the seafloor in the Cook Strait (Carter, 1992;Lewis et al., 1994). Elevated bed shear stresses related to strong tidal currents in the nearby Cook Strait are also regarded to represent a major forcing mechanism in the western Marlborough Sounds (Walters et al., 2010), and is therefore likely to strongly influence the seafloor geomorphology and grainsize distribution within QCS and TC. ...
... We suggest that the complex coastal geometry characteristic of much of the Marlborough Sounds is causing localized intensification of tidal currents, which results in QCS and TC having notably contrasting morphologies. Patterns of seafloor erosion related to currents interacting with complex shoreline geometry is observed elsewhere in New Zealand and globally for example, the Narrows, Cook Strait (Carter, 1992;Lewis et al., 1994;Lamarche et al., 2011;Longhitano, 2018), Portland Bill, southern United Kingdom (Bastos et al., 2002), the Minas Passage, Bay of Fundy (Shaw et al., 2012), the San Juan Channel sand wave field in the San Juan Archipelago (Greene et al., 2017) and in Boundary Pass and Haro Strait in the Georgia Basin, on the Pacific margin of Canada (Barrie et al., 2005(Barrie et al., , 2009). ...
The shallow marine environment represents a region of high biological productivity, ecological diversity, and complex oceanographic conditions, and often supports various human activities and industries. Mapping of the seafloor in shallow marine environments reveals seafloor features in detail, shedding light on a range of natural and anthropogenic processes. We present a high-resolution (2-m) multibeam dataset, combined with geologic samples that reveals a complete map of the seafloor from the land-water interface to ∼350 m water depth within Queen Charlotte Sound/Tōtaranui (QCS) and Tory Channel/Kura Te Au (TC), Marlborough Sounds, New Zealand. These data reveal that the seafloor geomorphology and distribution of natural and anthropogenic features varies spatially from the inner QCS to the Cook Strait. Tidal currents play a large role in the erosion, transport, and deposition of sediments in QCS and TC. The distribution and depth of seafloor scouring suggests that tidal flow is locally intensified by coastal geometry and bathymetric barriers, resulting in concentrated scouring where tidal flow is restricted or redirected. In addition, superimposed bedforms reflect localized variations in flow direction that have likely developed across a range of spatial and temporal scales. Evidence for extensive seafloor fluid expulsion is preserved in > 8500 pockmarks mainly located within the inner and central QCS. The size and spatial distribution of pockmarks suggest multiple fluid sources in the region. The cumulative anthropogenic footprint on the seafloor within QCS represents 6.4 km² (∼1.5%) of the total seafloor area and is predominantly related to maritime activities including anchor dragging (47.5%) and mooring blocks (24%). This study provides a unique example of the information that can be revealed by a comprehensive survey programme that mapped from the land-water interface to the subtidal zone. Results presented in this study form a robust basis upon which to develop improved hydrodynamic models and benthic habitat maps and to assess the full extent of anthropogenic activities in the shallow marine realm.
... The plate boundary structure changes at the northern end of the South Island to a set of strike-slip faults in prominent valleys with intervening parallel ridges, the Kaikōura ranges (Fig. 1a, b;Little and Jones, 1988). The on-land faults of both islands are linked through a complex faulted subsidence zone beneath the now-submerged Cook Strait between the islands (Lewis et al., 1994;Begg and Johnston, 2000;Lee and Begg, 2002;Rattenbury et al., 2006;Nicol, 2011). ...
... 1a, 2b, 3a). Wairau River sediments have contributed to thick sedimentary deposits of the Wairau basin in Cook Strait ( Fig. 3a; Lewis et al., 1994). The Motueka River in the northern South Island flows northwards in a structurallycontrolled depression between two uplifted basement blocks, and this topography has formed above the southwestern extent of the subduction zone (Figs. ...
... This recent divergence timeframe is also supported by regional genetic analyses of upland terrestrial invertebrate species (Trewick and Bland, 2012). The strait formed during structurally-controlled subsidence within the tectonic transition zone (Lewis et al., 1994;Little et al., 2009), resulting in formation of the two separate islands that persist to the present (Fig. 8b, c). The topography of the transpressional zone of the northern South Island was already established at this stage and was dominated by long-lived structurally-controlled valleys along principal faults, with intervening upland ridges (Fig. 8b, c). ...
... Cook Strait bisects central New Zealand and features intricate submarine canyons and ocean circulation patterns (Bowman et al., 1983;Proctor & Carter, 1989;Lewis et al., 1994). Complex and temporally variable geography and currents in the region have contributed to many differing patterns of phylogeographical structure in a range of marine invertebrates with various life-history strategies (Stevens & Hogg, 2004;Waters & Roy, 2004;Ayers & Waters, 2005;Goldstien et al., 2006;Knox et al., 2011;Veale & Lavery, 2011. ...
... During some glacial maxima of the Pleistocene, a land-bridge connecting Whanganui and Golden Bay closed Cook Strait (Fleming, 1979;Proctor & Carter, 1989;Lewis et al., 1994). Between the onset of the Last Glacial Maximum (LGM) roughly 25 kya (Sandiford et al., 2002), and its more gradual end roughly 7 kya (Lambeck et al., 2002), eustatic sea levels dropped to as much as 120-130 m lower than at present (Fleming et al., 1998;Lambeck et al., 2002). ...
... The shallowest possible connection between the North and South Islands, along Farewell Rise/Egmont Terrace, presently has a maximum depth of between 94 and 100 m (Bowman et al., 1983;Lewis et al., 1994). Admittedly, little is known of the rates of uplift and subsidence on the Farewell Rise, or rates of sedimentation from the Whanganui catchment or via west-wind drift from the north-western South Island (Lewis et al., 1994). ...
Cominella maculosa and C. virgata are common whelk species that inhabit rocky shores around much of the North Island of New Zealand, the northern South Island and, for C. maculosa, the Chatham Islands. This study used DNA sequences from the mitochondrial gene CO1 to examine the phylogeographical structure of populations of both species in areas that have not previously been sampled. Collections of both species were made from sites in the Cook Strait region, C. maculosa from the Chatham Islands and C. virgata from the northern North Island. Both species were found to have a considerable degree of genetic differentiation, but genetic diversity and phylogeographical patterns differed greatly between regions. South Island populations of C. virgata may have originated, or been supplemented, by human-mediated translocations. Phylogenetic analyses were conducted using the mitochondrial genes CO1 and 16S rRNA, and the nuclear gene 18S rRNA. The northern subspecies C. virgata brookesi did not form a monophyletic lineage and is synonymized with C. virgata. A lectotype is designated for Buccinum lineolatumQuoy & Gaimard, 1833, of which C. virgata is a replacement name.
... Marine inundation once again became a characteristic of the New Zealand landscape during the Pliocene and Pleistocene, but on a more regional scale, and this time due to sea-level changes driven by glacial cycles (Lewis et al. 1994;Worthy and Holdaway 2002). During the Pliocene, the lower North Island was inundated, with the formation of the Manawatu Strait, which separated present-day Taranaki/Hawke's Bay from the Nelson/Marlborough region of the South Island (Bull and Whitaker 1975;Rogers 1989;Worthy and Holdaway 2002). ...
... During the Pliocene, the lower North Island was inundated, with the formation of the Manawatu Strait, which separated present-day Taranaki/Hawke's Bay from the Nelson/Marlborough region of the South Island (Bull and Whitaker 1975;Rogers 1989;Worthy and Holdaway 2002). The Pleistocene saw the formation of Cook Strait (separating North Island and South Island) and Foveaux Strait (separating South Island and Stewart Island) and the presence of an island archipelago in the Northland region (Lewis et al. 1994;Stevens et al. 1995;Worthy and Holdaway 2002). Sea-level fluctuations (up to 135 m below present levels) associated with Pleistocene glacial cycles result in the intermittent presence of land bridges across Cook Strait and Foveaux Strait and the reconnection of previously isolated regions of Northland (Lewis et al. 1994;Stevens et al. 1995;Worthy and Holdaway 2002). ...
... The Pleistocene saw the formation of Cook Strait (separating North Island and South Island) and Foveaux Strait (separating South Island and Stewart Island) and the presence of an island archipelago in the Northland region (Lewis et al. 1994;Stevens et al. 1995;Worthy and Holdaway 2002). Sea-level fluctuations (up to 135 m below present levels) associated with Pleistocene glacial cycles result in the intermittent presence of land bridges across Cook Strait and Foveaux Strait and the reconnection of previously isolated regions of Northland (Lewis et al. 1994;Stevens et al. 1995;Worthy and Holdaway 2002). ...
New Zealand has a diverse lizard fauna, comprising diplodactylid geckos and skinks and over 100 recognised species or taxa. Geckos are thought to have colonised New Zealand during the Eocene or Oligocene (40.2–24.4 mya), prior to the ‘Oligocene drowning’ event. In contrast, skinks reached New Zealand during the Miocene (~18.3 mya) via long-distance overwater dispersal from New Caledonia along the Lord Howe Rise and Norfolk Ridge. Investigations of the biogeography of New Zealand lizards have long been hampered by two key factors: recent range contractions and local extinctions following the successful establishment of 31 exotic mammalian species and taxonomic gaps and a limited grasp on the true diversity of the endemic lizard fauna. However, subfossil records have improved our understanding of the prehuman distributions of several previously widespread species, and intensive taxonomic activity over the last two decades has provided a more accurate estimate of lizard diversity. This enhanced knowledge has enabled the key historical processes responsible for the diversification of lizards within New Zealand to be identified. These include sea-level changes during the Pliocene–Pleistocene in northern New Zealand, the Pliocene marine inundation of the lower North Island, the impact of water barriers such as Cook Strait (separating the North and South Islands) and Foveaux Strait (separating the South Island and Stewart island), tectonic activity along the Alpine Fault and regional north–south differentiation within the South Island. We provide an updated list of 22 biogeographic categories for New Zealand lizards. We highlight that the essential framework is now in place with which to investigate the biogeographic patterns evident in the New Zealand lizard fauna and examine the processes that have created them.
... Previous palaeogeographic maps of central New Zealand for the late Neogene (c. last 5 Ma) have invoked extensive strike-slip faulting, contraction and block rotation in North Island on the basis of previously published tectonic reconstruction models of the New Zealand micro-continent (e.g. Wellman 1985;Kamp 1986;Lewis et al. 1994;Beu 1995;King 2000;Bunce et al. 2009). For many years it was assumed that large-scale strike-slip faulting (several hundred kilometres) and tectonic rotations of similar magnitude to those inferred for South Island also occurred in North Island (e.g. ...
... The estimated timing of formation of Cook Strait at c. 500 ka (Lewis et al. 1994) suggests that the Wellington area was, until this time, still connected to Marlborough via a low-relief land bridge between areas of mountainous topography. This land was likely to have been relatively narrow with sedimentary basins on its northwestern and eastern sides. ...
... The present form and disjunction between New Zealand's 'North' and 'South' islands is geologically a very young feature (B0.5 Ma; Lewis et al. 1994). For much of the late Neogene (c. 8 Ma) parts of the Wellington area have been part of a 'South Island' rather than a 'North Island', linked to the south by low-lying land across what is now Cook Strait. ...
... Major active faults cannot be traced across Cook Strait, and basement terranes are offset by ∼140 km across it, indicating that it is a major structural discontinuity (Walcott, 1978;Carter et al., 1988). These observations suggest that the inactive, rotated, termination of the Alpine-Wairau Fault may run through Cook Strait (Walcott, 1978;Lewis et al., 1994); differential motion across this structure may explain the later apparent initiation of rotations in this part of the margin, compared to those documented on the North Island. ...
... The most likely position for this rotation boundary is in Cook Strait, which appears to represent a major structural discontinuity (Walcott, 1978) (Fig. 7.11a). The faults of the NIDFB cannot be linked across Cook Strait to those in the Marlborough Fault Zone (Carter et al., 1988), and Mesozoic basement terranes (e.g. the Esk Head subterrane, Fig. 7.11a) are offset by 140 km across what is interpreted to be the eastern termination of the Wairau Fault, which is bent clockwise through Cook Strait (Walcott, 1978;Lewis et al., 1994). This dextral offset probably occurred in the early Neogene, before the eastern Wairau Fault was isolated by development of the Southern Inversion Zone on the western North Island at 10 Ma ( Fig. 7.10a), became inactive, and began to rotate with the rest of the Hikurangi margin to the north (Fig. 7.11b). ...
... This dextral offset probably occurred in the early Neogene, before the eastern Wairau Fault was isolated by development of the Southern Inversion Zone on the western North Island at 10 Ma ( Fig. 7.10a), became inactive, and began to rotate with the rest of the Hikurangi margin to the north (Fig. 7.11b). It is unclear whether structures are preserved in Cook Strait that might have accommodated this rotation; extension associated with the Late Miocene Wairau Basin (Lewis et al., 1994) was probably important, but the deformation style associated with most Late Miocene-Pliocene faulting is poorly constrained (Barnes and Audru, 1999). Barnes and Audru (1999) according to Little and Roberts (1997). ...
Vertical-axis rotations are an important component of Neogene deformation in the New Zealand plate boundary region, and potentially offer fundamental insights into the rheology of continental crust. Extensive paleomagnetic sampling along the Hikurangi margin, on the East Coast of the North Island, has provided new insights into the patterns, rates and timings of tectonic rotation, and also an improved understanding of the magnetic signature of New Zealand Cenozoic mudstones. Rigorous field tests reveal numerous late remagnetizations, which haveoften formed several million years after deposition and can be irregularly distributed within an outcrop. Scanning electron microscopy and rock magnetic analyses indicate that the remanence carrier is predominantly the ferrimagnetic iron sulphide, greigite, which is present as a mixed population of single domain and superparamagnetic grains that are characteristic of arrested authigenic growth. Strong viscous overprints are the result of later, usually recent, oxidation of these sulphides. The recognition of late-forming magnetizations leads to a completely new view of the Neogene tectonic evolution of the Hikurangi margin, with no tectonic rotations being evident prior to 8–10 Ma; coherent rotation of most of the Hikurangi margin since that time refutes the existence of the independently rotating ‘domains’ that were inferred from earlier paleomagnetic data. This pattern is more consistent with the short-term velocity field, and allows all Neogene rotation to be more simply explained as a large-scale response to realignment of the subducting Pacific plate. Tectonic rotations have been accommodated by a variety of structures since 10 Ma; in the Late Miocene and Pliocene, rates of tectonic rotation were 3–4 times faster than presently observed and possibly involved a much larger region, before initiation of the North Island Dextral Fault Belt and the Taupo Volcanic Zone at 1-2 Ma instigated the current tectonic regime. Collision of the Hikurangi Plateau in the Late Miocene is interpreted to have caused both the initiation of tectonic rotation, and the widespread remagnetization of sediments, making it a key event in the Neogene evolution of the plate boundary region.
... The KMFS is associated laterally with onland structures that have previously been identified as potential earthquake sources (e.g., Manawatu Anticlines [Te Punga, 1957;Melhuish et al., 1996]) and previous paleoseismic studies in southern North Island have identified a number of onshore active faults [Smith and Berryman, 1986;van Dissen and Berryman, 1996;Stirling et al., 1998Stirling et al., , 2002b. These predominantly land-based studies, however, have failed to take into account the late Quaternary activity of offshore faults because structures in the marine environment have only been mapped previously at basin-wide scales using lowresolution geophysical techniques [Anderton, 1981;Carter et al., 1988;Lewis et al., 1994]. This is likely to result in a slight underestimation of the seismic hazard in southern North Island, as was observed previously by Wesnousky [1986] in a study offshore California. ...
... [9] Offshore, the northern extension of the Wairau Fault from the northern part of South Island has been postulated to lie across western Cook Strait and to the west of Kapiti Island (Figure 1) [Carter et al., 1988;Moore and Francis, 1988], perhaps linking with the Rauoterangi Fault in onshore Manawatu (Figure 2) [Lewis et al., 1994]. The Wairau Fault represents the oldest extension of the major intracontinental strike-slip Alpine Fault, which is the largest single geological structure in New Zealand ( Figure 1). ...
... Seismic penetration was generally good in these areas (often >25 ms). These units represent Plio-Pleistocene sediments [e.g., Lewis et al., 1994] that at certain localities lie on irregular unconformities, commonly marking the upper surface of underlying acoustically opaque basement rocks. In addition, on the seaward side of the Mascarin Fault, which is marked by a bathymetric break-in-slope on the inner shelf at water depths of 40-80 m, a thickening wedge of possibly mainly post-last glacial sediment with vertical stacking of several channel sequences is also apparent (Figure 3d). ...
... In the late Miocene, after the New Zealand cicada lineages had become established, substantial structural changes took place on the North Island, including volcanism and the creation of mountains and basins during the late Miocene (McGlone, 1985;Lewis et al., 1994). Strike-slip movement occurred throughout the Pliocene (5-2.6 Ma) and eventually led to flooding from the north into the Taupo region (Lewis et al., 1994;Bunce et al., 2009), creating a sea strait that covered much of southern North Island. ...
... In the late Miocene, after the New Zealand cicada lineages had become established, substantial structural changes took place on the North Island, including volcanism and the creation of mountains and basins during the late Miocene (McGlone, 1985;Lewis et al., 1994). Strike-slip movement occurred throughout the Pliocene (5-2.6 Ma) and eventually led to flooding from the north into the Taupo region (Lewis et al., 1994;Bunce et al., 2009), creating a sea strait that covered much of southern North Island. The northern boundary of the strait moved progressively southwards during this epoch (Fig. 2). ...
... The Taupo Line has been drawn at various locations between 38.5°and 39.5°S (Fig. 1b). Hypotheses for the existence of this ill-defined line include Pliocene sea-strait flooding (McGlone, 1985;Lewis et al., 1994;Chapple et al., 2009), tectonic uplift throughout the Pleistocene (McGlone, 1985), volcanic activity (Wilson et al., 1984(Wilson et al., , 1995 and Pleistocene glacial cycles (Buckley et al., 2010). The discrepancies in its placement may be due to the idiosyncratic responses of different species to these factors, the gradual southward migration of the Pliocene sea strait (Fig. 2) and/or the speed of recolonization of different taxa southwards. ...
Aim
Comparative biogeographers question the extent to which codistributed species respond similarly to environmental change. Such responses should create similar, appropriately timed patterns of cladogenesis among codistributed taxa compared to evolutionary independence, which may limit the predictions that can be made for unstudied species. Here, we compare phylogeographical patterns across ecologically divergent, codistributed taxa in the light of New Zealand's palaeohistory.
Location
North Island, New Zealand.
Methods
Mitochondrial DNA from six codistributed cicada species ( Kikihia ochrina , K. cutora , K. laneorum , K. cauta , K. scutellaris and K. dugdalei ) was analysed using phylogenetic methods and molecular dating techniques. We analysed phylogeographical distributions using analysis of molecular variance ( AMOVA ) to determine the significance of hypothesized biogeographical boundaries for clade differentiation and spatial distribution of genetic diversity.
Results
Five species ( Kikihia ochrina , K. cutora , K. laneorum , K. cauta and K. scutellaris ) show various degrees of intraspecific concordance with biogeographical boundaries found in previously studied taxa – the Kauri Line, the Northland Line and the newly identified Cockayne's Line. Clade splits of forest species correlate with the Kauri Line and/or Northland Line, whereas splits of scrub/hill species correlate with Cockayne's Line. Four species ( Kikihia ochrina , K. cutora , K. laneorum and K. cauta ) diversified before the Last Glacial Maximum ( LGM , 20 ka), whereas two species ( K. scutellaris and K. dugdalei ) show only post‐ LGM diversification.
Main conclusions
Despite species idiosyncrasies, we see the imprint of shared palaeoclimatic/geological events. We distinguish between (1) the importance of biogeographical lines as the demarcation between older genetically diverse and newer genetically depauperate populations, and (2) the importance of lines as biogeographical boundaries between sister clades. We also stress the importance of dating clade splits to ensure consistency with explanations for the biogeographical lines in question. We suggest that the Taupo Line has been overemphasized as a biogeographical boundary, whereas the importance of the mountain axis running north‐east to south‐west (‘Cockayne's Line’) has been overlooked.
... Phylogeographical disjunctions across Cook Strait, which opened 500 000 years ago and separated the North and South Islands during interglacial high sea stands (Lewis et al., 1994), also occur in many taxa, including but not limited to: fish and insects (Craw et al., 2019), plants (Haase, 1992;Rawlence et al., 2021), molluscs (Efford et al., 2002) and birds (Miller & Lambert, 2006;Robertson & Goldstien, 2012;Boast et al., 2019). At the same time, some genetic linkages straddle Cook Strait, notably in freshwater fish and marine invertebrates (Allibone, 2002;Apte & Gardner, 2002;Ayers & Waters, 2005;Apte et al., 2007), reptiles (O'Neill et al., 2008) and birds (e.g. ...
... In the first scenario, early divergence of the wattlebird family occurred on the proto-North Island during the Miocene. Progressive uplift caused the North Island to expand in a southward direction (Lewis et al., 1994;Bunce et al., 2009). Marine seaways became narrow enough ~3 Mya to permit dispersal, allowing the ancestral forms of the South Island kōkako and saddleback to colonize the South Island. ...
The biogeographical origins of the endemic birds of New Zealand (Aotearoa) are of great interest, particularly Palaeogene lineages such as Callaeidae, a passerine family characterized by brightly coloured wattles behind the beak and, in some cases, extreme sexual dimorphism in bill size and shape. Ancestral representatives of Callaeidae are thought to have split from their closest relatives outside New Zealand in the Oligocene, but little is known about the timing of divergences within the family. We present a fully dated molecular phylogeny of Callaeidae mitogenomes and discuss the biogeographical implications. Our results suggest that formation of Pliocene marine seaways, such as the Manawatu Strait, are likely to have played a significant role in the differentiation of North Island and South Island kōkako (Callaeas spp.) and saddlebacks/tīeke (Philesturnus spp.).
... Retention of this deep phylogeographic structure, despite subsequent intermittent emergence of a low-lying land-bridge (Walton et al. 2019) between the North and South Islands during glacial maxima suggests there may have been little or no gene-flow between these clades since their divergence. North/South Island lineage divergence estimates pre-dating formation of the Cook Strait (500 kya; Lewis et al., 1994) are observed in a wide-variety of other terrestrial taxa (Baker et al., 1995;Efford et al., 2002;Greaves et al., 2007;Liggins et al., 2008;Lloyd, 2003). ...
... obs.). Conversely, shallow genetic divergence between the remaining North Island, and northern South Island populations of H. duvaucelii implies widespread population connectivity during periods of eustatically-low sea levels (up to 130 m; Lewis et al., 1994); with subsequent isolation (0.32-1.03 Mya and 0.47-1.48 ...
Methodological and technological improvements are continually revolutionizing the field of ancient DNA. Most ancient DNA extraction methods require the partial (or complete) destruction of finite museum specimens, which disproportionately impacts small or fragmentary subfossil remains, and future analyses. We present a minimally destructive ancient DNA extraction method optimized for small vertebrate remains. We applied these methods to detect lost mainland genetic diversity in the large New Zealand diplodactylid gecko genus Hoplodactylus, which is presently restricted to predator‐free island and mainland sanctuaries. We present the first mitochondrial genomes for New Zealand diplodactylid geckos, recovered from 19 modern, six historic/archival (1898 to 2011) and 16 Holocene Hoplodactylus duvaucelii sensu latu specimens, and one modern Woodworthia sp. specimen. No obvious damage was observed in post‐extraction micro‐CT reconstructions. All ‘large gecko’ specimens examined from extinct populations were found to be conspecific with extant Hoplodactylus species, suggesting their large relative size evolved only once in the New Zealand diplodactylid radiation. Phylogenetic analyses of Hoplodactylus samples recovered two genetically (and morphologically) distinct North and South Island clades, probably corresponding to distinct species. Finer phylogeographic structuring within Hoplodactylus spp. highlighted the impacts of Late‐Cenozoic biogeographic barriers, including the opening and closure of Pliocene marine straits, fluctuations in size and suitability of glacial refugia, and eustatic sea‐level change. Recent mainland extinction obscured these signals from the modern tissue derived data. These results highlight the utility of minimally destructive DNA extraction in genomic analyses of less well studied small vertebrate taxa, and the conservation of natural history collections.
... The split between Kikihia subalpina (Hudson, 1891) (NI) and Kikihia 'flemingi' (SI) was estimated to be ~0.5-1.0 Mya , when rising sea levels in interglacial periods of the Mid-Pleistocene Transition narrowed the land bridge connecting NI and SI (Lewis et al., 1994) (see also Fig. 1). ...
... Cold temperatures and glaciers were at their most extreme during the LGM, exposing vast areas of the continental shelf of Zealandia when sea levels became 100 m lower than what they are today (McSaveney, 2007). The Cook Strait gap, which typically divides NI and SI, was substantially narrowed (Lewis et al., 1994), increasing the possibility of Rhodopsalta overwater dispersal between islands. ...
Why do some genera radiate, whereas others do not? The genetic structure of present-day populations can provide clues for developing hypotheses. In New Zealand, three Cicadidae genera are depauperate [Amphipsalta (three species), Notopsalta (one species) and Rhodopsalta (three species)], whereas two have speciated extensively [Kikihia (~30 species/subspecies) and Maoricicada (~20 species/subspecies). Here, we examine the evolution of Rhodopsalta, the last New Zealand genus to be studied phylogenetically and phylogeographically. We use Bayesian and maximum-likelihood analyses of mitochondrial cox1 and nuclear EF1α gene sequences. Concatenated and single-gene phylogenies for 70 specimens (58 localities) support its monophyly and three described species: Rhodopsalta cruentata, Rhodopsalta leptomera and Rhodopsalta microdora, the last taxon previously regarded as uncertain. We provide distribution maps, biological notes and the first descriptions of diagnostic songs. We show that both R. cruentata and R. microdora exhibit northern and southern genetic subclades. Subclades of the dry-adapted R. microdora clade show geographical structure, whereas those of the mesic R. cruentata and sand-dune specialist R. leptomera have few discernible patterns. Genetic, bioacoustical and detailed distributional evidence for R. microdora add to the known biodiversity of New Zealand. We designate a lectotype for Tettigonia cruentata Fabricius, 1775, the type species of Rhodopsalta.
... According to this scenario, P. maculata inhabited NZ waters before the end of the last glacial maximum (LGM) when sea levels were low and NZ was a single land mass [77,78]. At some later time, most likely following the LGM (~22,000 years ago), large benthic habitats became available [79,80], and this may have facilitated population expansion possibly from north to south and fragmentation aided by warming temperatures and rising sea levels [81]. ...
... The split time (ca. 8 kya) estimated for the north and south P. maculata populations suggests that the genetic differentiation between the populations might have happened recently following creation of the present coastline after the last glacial maximum [77,89]. The north-south disjunction identified for P. maculata can be explained by oceanographic barriers specific to NZ, but also with an isolation-by-distance model. ...
Pleurobranchaea maculata is a rarely studied species of the Heterobranchia found throughout the south and western Pacific – and recently recorded in Argentina – whose population genetic structure is unknown. Interest in the species was sparked in New Zealand following a series of dog deaths caused by ingestions of slugs containing high levels of the neurotoxin tetrodotoxin. Here we describe the genetic structure and demographic history of P. maculata populations from five principle locations in New Zealand based on extensive analyses of 12 microsatellite loci and the COI and CytB regions of mitochondrial DNA (mtDNA). Microsatellite data showed significant differentiation between northern and southern populations with population structure being associated with previously described regional variations in tetrodotoxin concentrations. However, mtDNA sequence data did not support such structure, revealing a star-shaped haplotype network with estimates of expansion time suggesting a population expansion in the Pleistocene era. Inclusion of publicly available mtDNA sequence from Argentinian sea slugs did not alter the star-shaped network. We interpret our data as indicative of a single founding population that fragmented following geographical changes that brought about the present day north-south divide in New Zealand waters. Lack of evidence of cryptic species supports data indicating that differences in toxicity of individuals among regions are a consequence of differences in diet.
... Finally, SNI + NSI split during the formation of Cook Strait some 10-500 thousand years ago (i.e. t-Cook) (Lewis et al. 1994;Craw et al. 2019). Scenario (ii) was similar to scenario (i), with a first splitting event of an ancestral population into NNI and SNI + NSI + SSI during the Plio-Pleistocene. ...
... Low lying areas between northern and southern portions of the main axial ranges may have acted as barriers to dispersal, as well as Cook Strait, which first formed ∼500,000 years ago (i.e. sea barrier during interglacial and low lying land-bridge during glacial periods; Lewis et al. 1994;Craw et al. 2019). ...
Island ecosystems can be severely affected by climate change as
they provide limited opportunities for species to track their
habitat. Studying the population dynamics of keystone species
from these ecosystems can shed a light on climate – ecosystem
interactions. Southern beeches are such keystone species in New
Zealand with beech forests constituting the most abundant forest
cover on the two main islands. Here we use 2.4 kilobase pairs of
chloroplast genetic markers from four species of southern beech
across their geographic distribution to help elucidate the
Pleistocene history of New Zealand forests, and the processes that
led to the present-day distribution of southern beech diversity.
Broadly concordant phylogeographic patterns were observed
across all beech species analysed. The centre of genetic diversity
in silver beech was in the northern South Island, with unique
haplotypes in the southern South Island, and southern and
northern North Island, separated by known ‘beech gaps’.
Significantly less genetic diversity was evident in the subgenus
Fuscospora (red, hard, black/mountain beech). All three species
shared a single haplotype in the southern South Island, and a
unique haplotype north of the central South Island ‘beech gap’.
Our study indicates that the present-day distribution of southern
beech diversity in New Zealand is largely a result of Plio-
Pleistocene environmental changes, with survival in cryptic
southern South Island and multiple North Island in situ
microrefugia throughout recent glacial cycles. By contrast, the
northern South Island was likely the only New Zealand region that
supported large (silver) beech populations throughout the
Pleistocene. With beech species in New Zealand being keystone
forest species, the distribution of the genus throughout the
Pleistocene provides a proxy for forest cover at different times. It
helps understand the ecological challenges the New Zealand
forest fauna and flora were exposed to during the climate
oscillations of the ice ages.
... Cook Strait, the passage of water separating the North Island and South Island of New Zealand, is particularly well-known for extreme weather systems, characterised by high winds and swell (Lewis et al. 1994). Wellington's south coast, from Sinclair Head to Breaker Bay (Gardner et al. 2008), is adjacent to Cook Strait, and heavily impacted by winds and swell from the Southern Ocean (Bowman et al. 1983, Harris 1990. ...
... The Wellington south coast in New Zealand is exposed to the Cook Strait and typically experiences strong, prevailing westerly winds and large swells generated by storms in the Southern Ocean (Bowman et al. 1983, Harris 1990, Lewis et al. 1994. Storms reaching the Wellington south coast can travel quickly up the South Island of New Zealand, with little to no obstruction, causing an increase in significant wave height of three metres in three hours (Laing 2001). ...
Disturbance is a fundamental process that affects the structure and dynamics of populations. Wave action is an important agent of disturbance in coastal marine systems, and the frequency and severity of wave-associated disturbances is forecasted to increase with climate change. Understanding the effects of waves on coastal marine ecosystems, and the ability of organisms to adapt to wave action, is of growing importance. This is particularly true for intertidal/shallow subtidal species that are subjected to varying, sometimes intense, wave action. Most studies to-date have focused on species with limited mobility (e.g., algae and invertebrates), and have used estimates of wave dynamics that are not always relevant to the spatial scales of these organisms and their home ranges. My thesis focuses on the common triplefin, Forsterygion lapillum, an abundant benthic marine fish inhabiting shallow subtidal and intertidal rocky reefs throughout New Zealand. I develop and implement a protocol to characterise wave climates on an ecologically relevant scale. I evaluate the effects of waves on abundance, phenotype, performance, and behaviour of a reef fish.
In Chapter 2, I develop and implement a protocol to characterise wave climate at an appropriate scale. The Wellington south coast is exposed to storm waves that develop in the Southern Ocean and propagate up the east coast of New Zealand. I deployed low-cost HOBO acceleration loggers at two depths within each of six locations along the Wellington south coast to record a time series of wave action at twelve sites. Data from my loggers showed substantial spatial and temporal variation in water acceleration due to interactions between waves and local topography. I used a clustering analysis to characterise my 12 sites as either ‘exposed’ or ‘sheltered’. Assignments to these exposure categories did not match with a priori predictions of exposure, suggesting that wave forces experienced by organisms in the shallow subtidal environment may be difficult to assess from surface-based observations of waves. Data were generally well-correlated with an offshore buoy at all sites, and these correlations were stronger for more exposed sites.
In Chapter 3, I explored variation in fish density and phenotype through time and as a function of wave exposure. Densities peaked in summer (corresponding to seasonal recruitment) and declined over winter (consistent with increased losses during high-wave periods), and were generally greater at sheltered locations. While body condition was generally highest for fish sampled from exposed sites (consistent with a density-dependent effect on condition and/or enhancement of foraging with increasing water acceleration), other morphological characteristics did not consistently vary with wave exposure.
In Chapter 4, I used otoliths to reconstruct of growth histories of individuals to further elucidate the influence of wave exposure on triplefin phenotypes. Recent growth was not influenced by wave exposure, but this was confounded by strong seasonal variation in growth rates. Lifetime growth rate also did not differ with wave exposure, and was strongly influenced by hatch date. I used mixed effects models to appropriately account for the potentially confounding effects of other features on growth, and found that daily growth rates were slightly positively correlated with site-specific daily measures of wave action. This result can potentially account for the elevated body condition of fish at exposed sites (Chapter 3), and it has important implications for fish inhabiting wave exposed coasts.
In Chapter 5, I conducted a lab experiment to evaluate feeding ability in relation to simulated wave action. I used fish of a range of sizes, sampled from either a wave-sheltered or a wave-exposed site, and measured their consumption of prey in calm (low flow) conditions, disturbance (high flow) conditions, and immediately following a period of disturbance. Fish consumed fewer prey during disturbance, and more prey during calm conditions (and a similar consumption rate was observed for fish that were assayed after a period of intense wave action). While this pattern held for fish sampled from both populations, fish from wave-exposed sites consumed more prey than fish from sheltered sites, suggesting phenotypic traits (e.g., behavioural or morphological) that shape their feeding efficiency.
Collectively my results suggest that organisms that inhabit wave-exposed coastlines may be intimately linked to wave climate. Waves may have direct effects on numbers (reducing densities via induced mortality) and/or indirect effects on the traits, foraging opportunities, and/or body condition of survivors. Species such as the common triplefin may exhibit plasticity in phenotypic traits that enable them to adapt to dynamic and unpredictable environments. Overall, this thesis provides insight into the ability of an intertidal/shallow subtidal species to cope with variable wave action. Such species may exhibit resilience with increasing wave action due to climate change.
... Some biologists have suggested that the evolution of wing-reduced insect populations (and species) may take substantial time (>10,000 years; Donald 1985), a factor which may explain the difference in the number of wing-reduced lineages between the North and South Island (see above). Suitable alpine habitat has only existed in the lower North Island for about 1 Ma (Lewis et al. 1994), with most of the axial mountains in the southern region of the North Island not forming until the mid-Pleistocene (ca. 500,000 years ago; Trewick and Bland 2012). ...
... This similar pattern across the two taxa may suggest that genetic divergence was driven by a single evolutionary event. We suggest that S. helsoni and S. prasina once had relatively continuous distributions across central New Zealand (Nelson/Marlborough -Taupo) until North Island and South Island populations were separated by either the formation of Cook Strait (500 Kya; Lewis et al. (1994), or by peripatric divergence following the rapid tectonic uplift of the Tararua Range over the last 1Ma (Trewick and Bland 2012). A similar molecular divergence timeframe is also suggested for freshwater-limited headwater fish populations separated by the Cook Strait (the widespread Galaxias divergens; Waters et al. 2006;Craw et al. 2008). ...
Stenoperla helsoni is an endemic New Zealand stonefly characterised by distinctive sexually dimorphic wing loss. Previous distribution records indicated that this species was restricted to the South Island's Southern Alps, although our recent collections of wing-reduced specimens from a site in the Tararua Ranges suggest that this species may extend into the lower North Island. We amplified the mitochondrial COI gene to confirm the identity of North Island specimens, and to assess phylogeographic structuring within the species and genus. North Island specimens were confirmed as S. helsoni, indicating that this species has a much wider geographic range than previously thought. This broad distribution, combined with low levels of intraspecific divergence, suggests that female S. helsoni may be strong fliers, despite males being flightless. Distinct North Island and South Island populations were identified, with a 1.5% divergence between the two populations.
... According to this scenario, P. maculata inhabited NZ waters before the end of the last glacial maximum (LGM) when sea levels were low and NZ was a single land mass [77,78]. At some later time, most likely following the LGM (~22,000 years ago), large benthic habitats became available [79,80], and this may have facilitated population expansion possibly from north to south and fragmentation aided by warming temperatures and rising sea levels [81]. ...
... The split time (ca. 8 kya) estimated for the north and south P. maculata populations suggests that the genetic differentiation between the populations might have happened recently following creation of the present coastline after the last glacial maximum [77,89]. The north-south disjunction identified for P. maculata can be explained by oceanographic barriers specific to NZ, but also with an isolation-by-distance model. ...
Pleurobranchaea maculata is a rarely studied species of the Heterobranchia found throughout the south and western Pacific–and recently recorded in Argentina–whose population genetic structure is unknown. Interest in the species was sparked in New Zealand following a series of dog deaths caused by ingestions of slugs containing high levels of the neurotoxin tetrodotoxin. Here we describe the genetic structure and demographic history of P. maculata populations from five principle locations in New Zealand based on extensive analyses of 12 microsatellite loci and the COI and CytB regions of mitochondrial DNA (mtDNA). Microsatellite data showed significant differentiation between northern and southern populations with population structure being associated with previously described regional variations in tetrodotoxin concentrations. However, mtDNA sequence data did not support such structure, revealing a star-shaped haplotype network with estimates of expansion time suggesting a population expansion in the Pleistocene era. Inclusion of publicly available mtDNA sequence sea slugs from Argentina did not alter the star-shaped network. We interpret our data as indicative of a single founding population that fragmented following geographical changes that brought about the present day north-south divide in New Zealand waters. Lack of evidence of cryptic species supports data indicating that differences in toxicity of individuals among regions are a consequence of differences in diet.
... The two rarest taxa, L. hamiltoni and L. pakeka, are restricted to single insular island populations located off the northern South Island. Based on bathymetry and late Quaternary sea-level reconstructions, these populations have probably been isolated for the past 14 000 years (Gibb, 1986;Lewis, Carter & Davey, 1994;Bishop et al., 2013;Thurlow, 2015) (Fig. 1d). ...
... Leiopelma auroraensis should, therefore, be retained as a distinct taxon, as demonstrated by our multivariate analyses and Worthy's (1987b) osteological descriptions. Likewise, glaciation may have driven the morphological differentiation observed between L. markhami populations in the western and northwestern South Island, whereas the geographical separation of the North and South Island L. markhami, L. hamiltoni and L. hochstetteri populations may have occurred more recently when post-glacial sealevel rise fractured land-locked islands of the South Island's Marlborough Sounds at least 14 000 BP (Gibb, 1986;Lewis et al., 1994). The nearshore island populations of L. hamiltoni also became isolated at this time (Thurlow, 2015). ...
The taxonomic status of some of New Zealand's endemic and threatened leiopelmatid frogs has been debated for decades. Clarifying this uncertainty is vital to their conservation, especially given the risk of extinction of cryptic taxa. We reexamined leiopelmatid diversity through multivariate analyses of the skeletal and external morphology of extinct and extant Leiopelma to determine morphological differentiation. Our results suggest that the morphological distinction between extinct taxa is greater than in modern extant taxa. While size ranges of postcranial elements overlapped within extant species, maxillae shape discriminated some extant taxa. We confirm the morphological distinctiveness of the extinct taxa recognized to date but identify latitudinal and altitudinal variation in postcra-nial element size and shape within the widespread Leiopelma markhami and L. waitomoensis, which suggest possible post-human extinction of cryptic taxa. Furthermore, the lack of morphological and osteological differentiation between L. archeyi and the insular extant L. hamiltoni and L. pakeka leads us to question the taxonomic distinctive-ness of these three taxa. Future genetic research using modern and ancient DNA is recommended to enable species limits within Leiopelma to be tested in more detail to provide an evidence-based assessment for their conservation management.
... Disjunct distributions can also arise when populations are divided plunges eastwards to 3000 metres in the Hikurangi Trough. Tectonic activity associated with the Australian-Pacific continental plate boundary caused rapid uplift of mountain ranges in the area during the last 1 million years (Lewis et al. 1994;Trewick & Bland 2012). Uplift in what is now southern North Island gradually closed older seaways further north, and in effect drove subsidence southward. ...
... Uplift in what is now southern North Island gradually closed older seaways further north, and in effect drove subsidence southward. By late Pleistocene interglacial periods the landscape was configured much as it is today, but during the last glacial maximum global sea level was sufficiently low to allow land connection of North and South islands (Lewis et al. 1994;Trewick & Bland 2012). ...
The evolutionary significance of spatial habitat gaps has been well recognised since Alfred Russel Wallace compared the faunas of Bali and Lombok. Gaps between islands influence population structuring of some species, and flightless birds are expected to show strong partitioning even where habitat gaps are narrow. We examined the population structure of the most numerous living flightless land bird in New Zealand and the world, Weka (Gallirallus australis). We surveyed Weka and their feather lice in native and introduced populations using genetic data gathered from DNA sequences of mitochondrial genes and nuclear β-fibrinogen and five microsatellite loci. We found low genetic diversity among extant Weka population samples. Two genetic clusters were evident in the mtDNA from Weka and their lice, but partitioning at nuclear loci was less abrupt. Many formerly recognized subspecies/species were not supported; instead we infer one subspecies for each of the two main New Zealand islands. Although currently range restricted, North Island Weka have higher mtDNA diversity than the more wide-ranging southern Weka. Mismatch and neutrality statistics indicate North Island Weka experienced rapid and recent population reduction while South Island Weka display the signature of recent expansion. Similar haplotype data from a widespread flying relative of Weka, and other New Zealand birds revealed instances of North Island - South Island partitioning associated with a narrow habitat gap (Cook Strait). However, contrasting patterns indicate priority effects and other ecological factors have a strong influence on spatial exchange at this scale. This article is protected by copyright. All rights reserved.
... During sea level low-stand periods (i.e. during the last ice age c. 20,000 years BP), the erosion and sediment deposition within most global canyon systems were dramatically enhanced. We expect this to also be true for the Cook Strait Canyons (Lewis et al. 1994;Mountjoy et al. 2009). We infer that the geomorphic evidence for landslides observed in the canyons post-dates the start of sea level rise (i.e. the start of the current interglacial period) as this is inferred to have coincided with a dramatic reduction in canyon forming downslope sediment processes. ...
... Indeed, one of the dated landslides occurred prior to this date. During the sea level low-stand, a land bridge formed between the northwestern South Island and Taranaki, creating a large tidal embayment through Cook Strait (Lewis et al. 1994;Proctor and Carter 1989). This land bridge breached approximately 15,000 years BP as sea level rise initiated, likely releasing a large amount of sediment resulting in a short period of intense down-canyon sediment transport. ...
Cook Strait Canyon is a submarine canyon that lies within ten kilometres of Wellington, the capital city of New Zealand. The canyon walls are covered with scars from previous landslides which could have caused local tsunamis. Palaeotsunami evidence also points to past tsunamis in the Wellington region. Furthermore, the canyon’s location in Cook Strait means that there is inhabited land in the path of both forward- and backward-propagating waves. Tsunamis induced by these submarine landslides pose hazard to coastal communities and infrastructure but major events are very uncommon and the historical record is not extensive enough to quantify this hazard. The combination of infrequent but potentially very consequential events makes realistic assessment of the hazard challenging. However, information on both magnitude and frequency is very important for land use planning and civil defence purposes. We use a multidisciplinary approach bringing together geological information with modelling to construct a Probabilistic Tsunami Hazard Assessment of submarine landslide-generated tsunami. Although there are many simplifying assumptions used in this assessment, it suggests that the Cook Strait open coast is exposed to considerable hazard due to submarine landslide-generated tsunamis. We emphasise the uncertainties involved and present opportunities for future research.
... During sea level low-stand periods (i.e. during 9 the last ice age c. 20,000 years BP) the erosion and sediment deposition within most global canyon 10 systems was dramatically enhanced. We expect this to also be true for the Cook Strait Canyons 11 (Lewis et al., 1994;Mountjoy et al., 2009). We infer that the geomorphic evidence for landslides 12 observed in the canyons post-dates the start of sea level rise (i.e. the start of the current interglacial 13 period) as this is inferred to have coincided with a dramatic reduction in canyon forming downslope 14 sediment processes. ...
... Indeed, one of the dated landslides occurred prior to this date. During the sea level low-stand, a land 18 bridge formed between the northwestern South Island and Taranaki, creating a large tidal 19 embayment through Cook Strait (Lewis et al., 1994;Proctor and Carter, 1989 To derive an overall magnitude/frequency relationship for landslide occurrence in the canyons we 4 divide equation (1) by the inferred time period over which they occurred. That is, the annual 5 probability of getting a landslide of minimum size V somewhere in the upper Cook Strait Canyon is: 6 ( > ) = 1 = 3.28 −1.53 15,000 ...
Cook Strait Canyon is a submarine canyon that lies within ten kilometres of Wellington, the capital city of New Zealand. The canyon walls are covered with scars from previous landslides which could have caused local tsunamis. Palaeotsunami evidence also points to past tsunamis in the Wellington region. Furthermore, the canyon’s location in Cook Strait means that there is inhabited land in the path of both forward- and backward-propagating waves. Tsunamis induced by these submarine landslides pose hazard to coastal communities and infrastructure but major events are very uncommon and the historical record is not extensive enough to quantify this hazard. The combination of infrequent but potentially very consequential events makes realistic assessment of the hazard challenging. However, information on both magnitude and frequency is very important for land use planning and civil defence purposes. We use a multidisciplinary approach bringing together geological information with modelling to construct a Probabilistic Tsunami Hazard Assessment of submarine landslide-generated tsunami. Although there are many simplifying assumptions used in this assessment, it suggests that the Cook Strait open coast is exposed to considerable hazard due to submarine landslide-generated tsunamis. We emphasise the uncertainties involved and present opportunities for future research.
... Molecular estimates of the divergence times between many of these North-South Island species pairs have been dated to the Plio-Pleistocene (5.3-0.012 Mya) and may have been promoted by the intermittent formation and closure of marine straits between the two landmasses, including the Manawatu Strait (3-1 Mya; Trewick & Bland, 2012) and the Cook Strait (0.5 Mya; Lewis et al., 1994). Molecular divergence dating suggests that takahē and moho diverged from their respective common ancestors ~2-2.5 Mya (Garcia-Ramirez & Trewick, 2015). ...
Many avian species endemic to Aotearoa New Zealand were driven to extinction or reduced to relict populations following successive waves of human arrival, due to hunting, habitat destruction and the introduction of mammalian predators. Among the affected species were the large flightless South Island takahē ( Porphyrio hochstetteri ) and the moho (North Island takahē; P. mantelli ), with the latter rendered extinct and the former reduced to a single relictual population. Little is known about the evolutionary history of these species prior to their decline and/or extinction. Here we sequenced mitochondrial genomes from takahē and moho subfossils (12 takahē and 4 moho) and retrieved comparable sequence data from takahē museum skins ( n = 5) and contemporary individuals ( n = 17) to examine the phylogeny and recent evolutionary history of these species. Our analyses suggest that prehistoric takahē populations lacked deep phylogeographic structure, in contrast to moho, which exhibited significant spatial genetic structure, albeit based on limited sample sizes ( n = 4). Temporal genetic comparisons show that takahē have lost much of their mitochondrial genetic diversity, likely due to a sudden demographic decline soon after human arrival (~750 years ago). Time‐calibrated phylogenetic analyses strongly support a sister species relationship between takahē and moho, suggesting these flightless taxa diverged around 1.5 million years ago, following a single colonisation of New Zealand by a flighted Porphyrio ancestor approximately 4 million years ago. This study highlights the utility of palaeogenetic approaches for informing the conservation and systematic understanding of endangered species whose ranges have been severely restricted by anthropogenic impacts.
... Whilst global sea level rise at c. 140 ka and c. 20 ka is an important factor controlling Late Pleistocene and Holocene marine transgression in Tasman Bay (cf. Maier et al. 2023), long wavelength subsidence affecting the South Taranaki and Wanganui basins in the last 5-4 Ma and extending southward to the northern South Island is ultimately driven by backarc flexure above the W-dipping Pacific plate (Stern and Davey 1989;Holt and Stern 1994;Lewis et al. 1994;Hayward et al. 2010;Nicol 2011). The subducted Pacific Plate is presently located at depths 40-75 km from north Marlborough to eastern Tasman Bay ( Figure 15) (Williams et al. 2013;Seebeck et al. 2014). ...
... At the WBs eastern margin, we envision braid plains, delta fronts and gravelly beaches to have developed during sea level low stand, locally incising through the previous HST, as evidenced by delta type architecture above undulating surfaces of erosion within eastern margin conglomerate deposits (Fig. 17). Nearby land was likely deforested and sediment input particularly high (Beu et al. 1981;Lewis et al. 1994 Low stand deposits were later scoured and eroded during transgressive ravinement, reworked into shelly gravel dunes at inner-most shelf depths (Abbott 1998). Local preservation of low stand deposits in eastern WB (Abbott 1992), suggests transgressive ravinement was either not as destructive or that low stand incision was more pervasive along the eastern basin margin. ...
... Taking into account that the Alpine Fault passes through the Marlborough Sounds region, I suggest that at the very least the evolutionary history of the tararua-species group and its migration to the South Island were associated with the regional development of the landmasses of the Alpine Fault and the evolution of Cook Strait. Apparently, the members of the group reached the South Island before the formation of Cook Strait, which only appeared in the mid Pleistocene (Lewis et al. 1994). The formation of Cook Strait split the range of the most northern species of the group, N. tararua, between the Islands. ...
Species of flightless litter ground beetles of the tribe Anillini, genus Nesamblyops, from the North Island and from the north-eastern part of the South Island are revised. Eight new species are described and one previously known species, Nesamblyops oreobius (Broun), is re-described. Nesamblyops oreobius, the only hitherto recorded species from the North Island, is most similar to the group of two new species from the South Island, N. confusus n. sp. (type locality: New Zealand, Marlborough Sounds, Mount Stokes) and N. lescheni n. sp. (type locality: New Zealand, Marlborough Sounds, D’Urville Island), based on the structure of the male genitalia. The second species of the genus known from the North Island, N. tararua n. sp. (type locality: New Zealand, Wellington, Tararua Range) represents another lineage, based on the structure of the male genitalia, and is closely related to a group of three new species from the South Island, N. brouni n. sp. (type locality: New Zealand, Canterbury, Southern Alps, Lewis Pass), N. distinctus n. sp. (type locality: New Zealand, Marlborough, Richmond Range, Fabians Valley), and N. townsendi n. sp. (type locality: New Zealand, Marlborough Sounds, Tennyson Inlet). Nesamblyops carltoni n. sp. (type locality: New Zealand, Nelson, Richmond Range, Dun Mountain) and N. parvulus n. sp. (type locality: New Zealand, Marlborough Sounds, Mount Stokes), both from the South Island occupy an isolated position among the examined species. All species are illustrated with digital images of habitus, body parts, and drawings of genitalia. Distribution maps for all species are also provided. Geographical evidence of Nesamblyops dispersal to the North Island is discussed, based on distributional data.
... However, other species that exhibit similar barriers to gene flow south of Cook Strait have divergence times between lineages of between 200,000 and 300,000 years ago (Goldstien et al., 2006). The Cook Strait region underwent major topographical and hydrological shifts during this long period, and it is difficult to identify a particular historical event that would have produced the observed genetic structure (Lewis et al., 1994). It is surprising that such a genetic discontinuity could be maintained over multiple generations after a historical barrier has broken down (Landguth et al., 2010), particularly in a data set of microsatellite markers, which are believed to represent a more contemporary scenario due to their high mutation rate (Selkoe and Toonen, 2006). ...
Understanding how ocean currents affect larval transport is crucial for understanding population connectivity in sessile marine invertebrates whose primary dispersal opportunity occurs during the pelagic larval stage. This study used Lagrangian particle tracking experiments to examine population connectivity in New Zealand green-lipped mussels (Perna canaliculus) at the national scale. Predicted patterns of larval dispersal were compared to published multi-locus microsatellite data of observed population genetic structure. Estimates of oceanographic circulation correlated significantly with FST, and we conclude that hydrodynamic processes are important in driving genetic connectivity. However, no evidence was found for an oceanographic barrier to gene flow south of Cook Strait, an important feature of genetic structure observed across several marine invertebrate species. Discrepancies between genetic and biophysical data may be explained by several factors including the different timescales of connectivity described by the two methods and the impact of localised ecological conditions and corresponding adaptations in genetic structure not captured by the bipohysical model. Population genetic analyses provide empirical data on realised connectivity and Lagrangian particle tracking experiments reveal information about directionality and asymmetry of connections that often cannot be determined by molecular analyses alone, thus a multidisciplinary approach is recommended.
... There is geographic structuring present in the genetic data, whereby populations that grow closer together are often more closely related, although this pattern is not universal. Five populations from Western Nelson in the South Island and coastal Taranaki in the North Island are united genetically (WELT SP100460, WELT SP100462, WELT SP090542, WELT SP090544 and WELT SP090540); these land areas would have been connected during the last glacial maxima (Lewis et al. 1994); so, this can be interpreted as a geographic pattern. No morphological characters were found to unite these five populations. ...
A taxonomic revision of the southern hemisphere pygmy forget-me-not group (Myosotis L.; Boraginaceae) is presented here. Climate-edaphic niches are modelled and compared for five species in the pygmy group, namely, M. antarctica Hook.f., M. brevis de Lange & Barkla, M. drucei (L.B.Moore) de Lange & Barkla, M. pygmaea Colenso and M. glauca (G.Simpson & J.S.Thomson) de Lange & Barkla, and one unnamed putative taxon, M. “Volcanic Plateau”. In this case, niche-modelling data mostly do not aid species delimitation, but morphological and genetic data provide evidence for recognising the following three species within the group: M. brevis and M. glauca (both endemic to New Zealand), and an enlarged M. antarctica (native to New Zealand, Campbell Island and Chile). Myosotis antarctica is here circumscribed to include M. antarctica sens. strict., M. drucei and M. pygmaea. The following two allopatric subspecies of M. antarctica are recognised on the basis of minor morphological differences: subsp. antarctica (formerly M. antarctica from Campbell Island and Chile, M. drucei and M. “Volcanic Plateau”) and subsp. traillii Kirk (formerly known by New Zealand botanists as M. pygmaea Colenso, an illegitimate name). For all three species, which are considered Threatened or At Risk, most of their genetic variation is partitioned between rather than within populations, meaning that conserving as many populations as possible should be the priority to minimise risk of extinction.
... Other sections of the isosurface can be linked to known tectonic features of New Zealand. These include a notch in the backstop related to Cook Strait (Lewis et al., 1994), deep depressions related to Taranaki basin (e.g., King & Thrasher, 1996) and Whanganui basin (e.g., Carter & Naish, 1998), and a collection of shallow depressions throughout the Taupō Volcanic Zone (Wilson et al., 1995(Wilson et al., , 2009. These upper-plate tectonic features are discussed in more detail in Chow et al. (2022). ...
Seamounts are found at many subduction zones and act as seafloor heterogeneities that affect slip behavior on megathrusts. At the Hikurangi subduction zone offshore the North Island, New Zealand, seamounts have been identified on the incoming Pacific plate and below the accretionary prism, but there is little concrete evidence for seamounts subducted beyond the present‐day coastline. Using a high‐resolution, adjoint tomography‐derived velocity model of the North Island, we identify two high‐velocity anomalies below the East Coast and an intraslab low‐velocity zone up‐dip of one of these anomalies. We interpret the high‐velocity anomalies as previously unidentified, deeply subducted seamounts, and the low‐velocity zone as fluid in the subducting slab. The seamounts are inferred to be 10–30 km wide and on the plate interface at 12–15 km depth. Resolution analysis using point spread functions confirms that these are well‐resolved features. The locations of the two seamounts coincide with bathymetric features whose geometries are consistent with those predicted from analog experiments and numerical simulations of seamount subduction. The spatial characteristics of seismicity and slow slip events near the inferred seamounts agree well with previous numerical modeling predictions of the effects of seamount subduction on megathrust stress and slip. Anomalous geophysical signatures, magnetic anomalies, and swarm seismicity have also been observed previously at one or both seamount locations. We propose that permanent fracturing of the northern Hikurangi upper plate by repeated seamount subduction may be responsible for the dichotomous slow slip behavior observed geodetically, and partly responsible for along‐strike variations in plate coupling on the Hikurangi subduction interface.
... nov. was alive (Lewis et al. 1994;Worthy and Holdaway 2002). Thus, its descendants potentially could have walked between these landmasses before the current physical isolation between the islands occurred. ...
We describe Apteryx littoralis sp. nov., a new species of kiwi based on a 1-million-year-old tarsometatarsus from shallow marine sediment in the North Island of New Zealand. The fossil is very similar to the tarsometatarsi of living kiwi species, most closely resembling Apteryx rowi and A. mantelli in size and shape, but differs in being stouter, with proportionally narrower proximal and distal ends. The new fossil is the second oldest known record of kiwi. It demonstrates a relatively conservative kiwi morphology since the mid-Pleistocene.
http://zoobank.org/References/cefc907d-0c1d-44dc-83c5-5799f5d6d3d2
... In fact, bottom temperature and satellite surface Chl a were also important variables to explain the differences in species composition of isopods between the two regions, while grain size (%sand) dictated the composition at family level (Fig. 7). In addition, historical vicariant and dispersal processes can also be responsible for observed distributional patterns; that is eastern (Chatham Rise) and western (Challenger Plateau) communities have been biogeographically separated since the formation of Cook Strait, which has only recently re-opened (10-5 kya) to its current extent (Lewis et al., 1994;Stevens et al., 1995). Previously, the dispersal of species was only possible via northern or southern routes around New Zealand's main islands, which was probably hindered by environmental constraints (with specimens crossing different temperature and productivity regimes; Knox et al., 2012bKnox et al., , 2020. ...
As part of the New Zealand government Ocean Survey 20/20 programme (OS 20/20, 2006–2013), samples from the Chatham Rise and Challenger Plateau collected in 2007 were analysed to determine the effects of key environmental parameters, in particular sediment and water mass properties, on spatial changes in the community structure (abundance, diversity and community composition) of bathyal asellotan isopods. Benthic collections were obtained in Austral autumn (May/June 2007) and included a total of 20 epibenthic sledge samples taken from the upper slope between 218 and 1,239 m. Due to the contrasting environmental settings between the Chatham Rise and Challenger Plateau, in terms of surface productivity and habitat heterogeneity, we expected the abundance, regional (or gamma-) diversity and community composition of benthic isopods to significantly differ between the two regions, and furthermore local (or alpha-) diversity and abundance (density) to decrease with increasing depth. Consistent with our assumptions, multivariate PERMANOVA analysis revealed a clear distinction in species composition between the Chatham Rise and Challenger Plateau with satellite surface chlorophyll (Chl) a and bottom temperature being the main environmental drivers. In contrast to previous benthic studies from the same sampling campaign, however, differences in isopod density and diversity between the two regions were not significant, either at species, or generic and family level. In addition, no depth-related changes in abundance and diversity could be observed at any hierarchical level. Instead, isopod densities at species and generic level were positively correlated with satellite surface Chl a and %silt, whilst species and generic diversity could be positively linked to the amount of total organic matter (TOM) in surficial sediments. In total, 97 asellote species in 54 genera and 15 families could be identified from both regions, of which 90.7% were likely new species. Species diversity was average to high when compared to other regions in the Northern and Southern hemispheres. However, neither for Chatham Rise nor for the Challenger Plateau did the species accumulation curves reach an asymptote, indicating that additional samples are required to provide more robust diversity estimates.
... The most prominent genetic break corresponds to the divergence among populations located around 42°S, at 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 12 the north of the South Island near Cape Farewell (Ayers and Waters 2005, Goldstien et al. 2006, Ross et al. 2009). The origin of this break has been associated with the historical of sea-level changes which closed the Cook Strait region during glacial periods (most recently 15-24,000 y ago; Lewis et al. 1994), and may be maintained by a sharp present-day thermal gradient acting as an environmental barrier to gene flow (Ayers andWaters 2005, Goldstien et al. 2006). Several studies have also observed a west/east genetic divergence at the northern tip of the North Island (Jones et al. 2008, Ross et al. 2009, Veale and Lavery 2012, where the strong southward oceanic splits into the eastern and western arms of the Auckland Current, which may strongly limit gene flow across this region. ...
... The North and South Islands were connected until about 500 Kya (Fleming, 1979;Lewis, Carter, & Davey, 1994), ...
In parasites that strongly rely on a host for dispersal, geographic barriers that act on the host will simultaneously influence parasite distribution as well. If their association persists over macroevolutionary time it may result in congruent phylogenetic and phylogeographic patterns due to shared geographic histories. Here, we investigated the level of congruent evolutionary history at a regional and global scale in a highly specialised parasite taxon infecting hosts with limited dispersal abilities: the microsporidians Dictyocoela spp. and their amphipod hosts. Dictyocoela can be transmitted both vertically and horizontally and is the most common microsporidian genus occurring in amphipods in Eurasia. However, little is known about its distribution elsewhere. We started by conducting molecular screening to detect microsporidian parasites in endemic amphipod species in New Zealand; based on phylogenetic analyses, we identified nine species‐level microsporidian taxa including six belonging to Dictyocoela. With a distance‐based cophylogenetic analysis at the regional scale, we identified overall congruent phylogenies between Paracalliope, the most common New Zealand freshwater amphipod taxon, and their Dictyocoela parasites. Also, hosts and parasites showed similar phylogeographic patterns suggesting shared biogeographic histories. Similarly, at a global scale, phylogenies of amphipod hosts and their Dictyocoela parasites showed broadly congruent phylogenies. The observed patterns may have resulted from covicariance and/or codispersal, suggesting that the intimate association between amphipods and Dictyocoela may have persisted over macroevolutionary time. We highlight that shared biogeographic histories could play a role in the codiversification of hosts and parasites at a macroevolutionary scale.
... The most prominent genetic break corresponds to the divergence among populations located around 42°S, at the north of the South Island near Cape Farewell (Ayers and Waters 2005, Goldstien et al. 2006, Ross et al. 2009). The origin of this break has been associated with the historical changes of sea-level which closed the Cook Strait region during glacial periods (most recently 15-24,000 y ago; Lewis et al. 1994), and may be maintained by a sharp present-day thermal gradient acting as an environmental barrier to gene flow (Ayers andWaters 2005, Goldstien et al. 2006). Several studies have also observed a west/east genetic divergence at the northern tip of the North Island (Jones et al. 2008, Ross et al. 2009, Veale and Lavery 2012, where the strong southward oceanic current splits into the eastern and western arms of the Auckland Current, which may strongly limit gene flow across this region. ...
Molecular studies have reported the co‐existence of two species of Agarophyton in New Zealand: the newly described A. transtasmanicum with an apparently restricted distribution to some sites in the North Island, and the more wide‐spread A. chilense. Here we compared the distribution, genetic diversity, and structure of both Agarophyton species throughout the archipelago using sequences of the nuclear Internal Transcribed Spacer 2 (ITS2) marker. Agarophyton chilense’s distribution was continuous and extensive along the North and South Islands, Stewart Island, and Chatham Island, and the genetic clusters were mostly concordant with boundaries between biogeographic regions. In contrast, specimens of A. transtasmanicum were collected in four sites broadly distributed in both the North and South Islands, with no clear spatial structure of the genetic diversity. Populations where the species co‐occurred, tended to display similar levels in genetic diversity for the two species. Demographic inferences supported a post‐glacial demographic expansion for two A. chilense genetic clusters, one present in the South Island and the eastern coast of the North Island, and the other present in northern South Island. A third genetic cluster located on the western coast of the North Island had a signature of long‐term demographic stability. For A. transtasmanicum, the skyline plot also suggested a post‐glacial demographic expansion. Last, we developed a new molecular tool to quickly and easily distinguish between the two Agarophyton species, which could be used to ease future fine‐scale population studies, especially in areas where the two species co‐exist.
... The North Island has experienced some geologically recent, substantial orogeny in the south-east, but is better known for the influence of destructive geological events. These include the expansion of the sea strait over the southern part of the island and submersion of the Auckland Isthmus during the Pliocene sealevel rise (McGlone, 1985;Lewis et al., 1994;Chapple et al., 2009), volcanism in the central North Island, particularly from the Pleistocene to present (Wilson et al., 1984(Wilson et al., , 1995a, and extreme cool-dry periods in the southern portions of the North Island during Pleistocene glacial maxima (Buckley et al., 2010). ...
New Zealand has a complex recent history of climatic and tectonic change that has left variable signatures in the geographic distribution and genetic structure of the region's flora and fauna. To identify concordant patterns, a broad range of taxa must be examined and compared. In New Zealand's North Island, a consensus is forming as to the dominant biogeographic barriers in the region although obligate freshwater taxa have not been considered in this framework. We use single-nucleotide polymorphisms to investigate phylogeography in the widespread obligate freshwater fish Gobiomorphus basalis on the North Island. Phylogeographic patterns within G. basalis reveal biogeographic disjunctions that are in some ways consistent and in other ways at odds with established patterns, providing insight into the processes that have shaped the islands' biogeography. We also use phylogeography to delineate species boundaries within the entire New Zealand radiation of Gobiomorphus and find that it contains several morphologically cryptic species. We resolve two clades within G. basalis that correspond to areas north and south of the Taupo Volcanic Zone. We confirm the distinctiveness of Gobiomorphus alpinus relative to Gobiomorphus cotidianus, as well as the presence of two lineages within Gobiomorphus breviceps that were previously identified based on mitochondrial data.
... In the present day, the West Coast current feeds the D'Urville current (Carter et al. 1998;Chiswell et al. 2015), which swings from NE to SE around the northern South Island and is diverted through the Cook Strait (Carter et al. 1998;Chiswell et al. 2015) (Fig. 1; INSET). It is proposed that the Cook Strait opened and closed over many eustatic sea level cycles linked to glacial and interglacial periods (Lewis et al. 1994;Alloway et al. 2007). A relatively weaker remnant of the West Coast current continues north to the northern Taranaki area, where present-day currents are reported as weak and variable (Rad, 2015;Chiswell et al. 2015) ( Fig. 1; INSET). ...
Three-dimensional (3D) seismic data reveal the complex interplay between the surface topography of a c. 4405 km ³ mass transport deposit (MTD) and overlying sedimentary packages over approximately the last two million years. The data image part of the Pleistocene to recent shelf to slope to basin-floor Giant Foresets Formation in offshore western New Zealand. The MTD created substantive topographic relief and rugosity at the contemporaneous seabed, formed by the presence of a shallow basal detachment surface, and very large (up to 200 m high) intact slide blocks, respectively. Sediments were initially deflected away from high-relief MTD topography and confined in low areas. With time, the MTD was progressively healed by a series of broadly offset-stacked and increasingly unconfined packages comprised of many channel bodies and their distributary complexes. Positive topography formed by the channels and their distributary complexes further modified the seafloor and influenced the location of subsequent sediment deposition. Channel sinuosity increased over time, interpreted as the result of topographic healing and reduced seafloor gradients. The rate of sediment supply is likely to have been non-uniform, reflecting tectonic pulses across the region. Sediments were routed into deep water via slope-confined channels that originated shortly before emplacement of the MTD.
... Little is known about the influence of ocean currents on seafloor morphology and sediment transport along the Hikurangi Margin. Tidal currents are exceptionally strong through Cook Strait (Lewis et al. 1994) and documented to play a significant role in transporting sediment into canyons (Mountjoy et al. 2013). ...
Submarine landslides occur on continental margins globally and can have devastating consequences for marine habitats, offshore infrastructure and coastal communities due to potential tsunamigenesis. Therefore, understanding landslide magnitude and distribution is central to marine and coastal hazard planning.
We present the first submarine landslide database for the eastern margin of New Zealand comprising >2200 landslides occurring in water depths from c. 300–4000 m. Landslides are more prevalent and, on average, larger on the active margin compared with the passive margin. We attribute higher concentrations of landslides on the active margin to tectonic processes including uplift and oversteepening, faulting and seamount subduction. Submarine landslide scars are concentrated around canyon systems and close to canyon thalwegs. This suggests that not only does mass wasting play a major role in canyon evolution, but also that canyon-forming processes may provide preconditioning factors for slope failure.
Results of this study offer unique insights into the spatial distribution, magnitude and morphology of submarine landslides across different geological settings, providing a better understanding of the causative factors for mass wasting in New Zealand and around the world.
... The Wellington south coast (North Island, New Zealand) is exposed to the Cook Strait, which frequently experiences strong winds and large swells generated by storms in the Southern Ocean (Bowman et al., 1983;Harris, 1990;Lewis et al., 1994). Storms can travel quickly up the South Island of New Zealand to cause a 3-m increase in significant wave height in as little as 3 h (Laing, 2001). ...
Wave action shapes species distributions and ecological interactions within the intertidal- and shallow-subtidal zone. Empirical estimates of wave exposure within these zones are limited by logistical constraints and/or cost. Hydrodynamic models of wave action poorly resolve fine-scale heterogeneity in wave energetics that are important for biology. We used cost-effective accelerometers to continuously measure fine-scale wave exposure across 12 locations (i.e., two depth strata at each of six sites), over sixteen consecutive months. We categorised wave exposure at each of our sites a priori (as ‘exposed’ or ‘sheltered’) based on shore topography. We compared in situ measurements of acceleration with a nearby wave rider buoy and evaluated variation in water acceleration and frequency of large wave events among sites and between depths. Wave height data significantly correlated with accelerometer data confirming accelerometers sufficiently measure wave action. Our analyses indicate significant fine-scale variation in acceleration, and differences in timing and frequency of large wave events during the study period. In situ acceleration had limited correspondence with shore-based (a priori) assessments of wave exposure. These results demonstrate the spatial and temporal differences in water acceleration on the Wellington south coast and highlight the limitations of surface topography to predict fine-scale wave action. This study also emphasizes the need for fine scale wave action measurements to better explain patterns in intertidal/shallow subtidal organism traits.
... Intense bioturbation and burrowing occurs in the siltstone below this shellbed. and sediment input particularly high (Beu et al. 1981;Lewis et al. 1994). Low stand deposits were later scoured and eroded during transgressive ravinement, reworked into shelly gravel dunes at inner-most shelf depths (Abbott 1998). ...
The Waitapu Shell Conglomerate is an important marker horizon in the eastern Whanganui Basin, occurring within a Pleistocene volcaniclastic record that contains early eruption products from the Taupo Volcanic Zone. The unit comprises a cross-bedded pebbly-shell conglomerate containing the first influx of Kaukatea Pumice (c. 0.9 Ma) within the Rangitikei succession. We document soft sediment deformation structures that occur in close stratigraphic proximity to the Waitapu Shell Conglomerate and other laterally equivalent units within the basins Castlecliffian outcrop belt. Soft sediment deformation structures formed through a combination of liquefaction and fluidisation, triggered by a range of mechanisms, including evidence of high sedimentation rates, loading, slope instability and potential for wave and earthquake-induced seismicity. Lateral changes in depositional style toward the basins eastern margin relate to relative position on the paleo-shelf, reduction of accommodation space, intermittent preservation of low stand deposits and proximity to the uplifting paleo-axial range.
... Conversely, the divergence between the two recent adzebill species coincides closely with the formation of an isthmus (1.5-2 Ma) across the Manawatu Strait, which persisted until the modern Cook Strait formed around~0.45 Ma [99,100]. Thus, it is likely that adzebills survived in the larger South Island of New Zealand-from which the fossil adzebill A. proasciarostratus has been described (16)(17)(18)(19) Ma)-and only dispersed into the North Island after the Manawatu land-bridge formed. ...
The recently extinct New Zealand adzebills (Aptornithidae, Aptornis spp.) were an enigmatic group of large flightless birds that have long eluded precise taxonomic assignment as they do not closely resemble any extant birds. Adzebills were nearly wingless, weighed approximately 16–19 kg, and possessed massive adze-like reinforced bills whose function remains unknown. Using hybridisation enrichment and high-throughput sequencing of DNA extracted from subfossil bone and eggshell, near-complete mitochondrial genomes were successfully assembled from the two Quaternary adzebill species: the North Island Adzebill (Aptornis otidiformis) and South Island Adzebill (A. defossor). Molecular phylogenetic analyses confirm that adzebills are members of the Ralloidea (rails and allies) and are sister-taxon to the Sarothruridae, which our results suggest comprises the Madagascan wood rails (Mentocrex, two likely sp.) in addition to the tiny (<50 gram) rail-like Afro-Madagascan flufftails (Sarothrura, 9 spp.). Node age estimates indicate that the split between adzebills and Sarothruridae occurred ~39.6 Ma, suggesting that the ancestors of the adzebills arrived in New Zealand by long-distance dispersal rather than continental vicariance. This newly identified biogeographic link between physically distant New Zealand and Afro-Madagascar, echoed by the relationship between the New Zealand kiwi (Apterygiformes) and Madagascan elephant-birds (Aepyornithiformes), suggests that the adzebill’s near relatives were formerly more widespread. In addition, our estimate for the divergence time between the two Quaternary adzebill species (0.2–2.3 Ma) coincides with the emergence of a land-bridge between the North and South islands of New Zealand (ca. 1.5–2 Ma). This relatively recent divergence suggests that North Island adzebills are the result of a relatively recent dispersal from the South Island, from which the earliest (Miocene) adzebill fossil has been described.
... This maps show a complex pattern of sediments in the strait that is likely related to a combination of modern transport processes involving strong tidal-and wind-mixing (Heath 1978;Harris 1990;Stevens et al. 2012), and frequent earthquakes (Mountjoy et al. 2009). There are also relict sedimentary features from before Cook Strait opened during the last glacial c. 20,000 years ago (Lewis et al. 1994). The centre of Cook Strait, the 22 km-wide 'Narrows', has very low mud and sand and very high gravel content (Figure 2A-C; S5A-C; Lewis and Mitchell 1980), with moderate carbonate percentages ( Figure 2D; S5D). ...
This paper provides new maps of the surficial sediment distribution on the continental shelf (0∼150 m water depth) of New Zealand based on a new database – nzSEABED. The maps of percent mud, sand, gravel and carbonate, are compared with previous research to provide a comprehensive update of the surficial sediment distributions on the continental shelf, together with a review of the main environmental (oceanographic and climatic), geomorphological and geological processes and human activities that have influenced sediment deposition. Continental shelves are dynamic regions that are in a constant state of flux from floods, storms, tides, waves, earthquakes and volcanic activity. While some of these events may be captured by individual samples, the compilation of >23,000 samples collected and analysed over 60 years provides a long-term average distribution of sediments on the continental shelf that can inform future research and coastal management.
... Ginsberg and Perillo, 1999). They also can be relict in the topography of transgressed shelves (Belderson et al., 1982;Liu et al., 1993;Lewis et al., 1994). ...
The Gulf of Guayaquil, Southern Ecuador, is the largest tidal system of the Pacific margin of South America. The
incipient oceanic tide has a tidal range of over 1m and is amplified on the continental shelf, which is widened in
this area by the tectonic activity related to the northward escape of the North Andean Block. The head of this
embayment connects to the Guayas River, roughly running along the dextral strike-slip fault bounding the North
Andean Block. The Guayas River connects to the Gulf of Guayaquil through a tide-dominated delta, the supratidal
part of which is composed of mangroves drained by a network of tidal channels. The river channels
merge into the Jambelí Channel, a subtidal valley forming the main distributary channel of the delta. Very high
resolution seismic profiles collected at the junction between the Jambelí Channel and the Gulf of Guayaquil show
the architecture of several depositional sequences preserved in the first 0.1 s twt beneath the sea bed. These
sequences mainly consist of a lowstand to transgressive systems tract comprised of fluvial to estuarine channels
topped by a highstand systems tract of prodeltaic muds. The progradational muds volumetrically dominate the
stratigraphic record and characterize the Guayas delta facies. By contrast, the near bed features close to the
mouth of Jambelí Channel show the present dominance of tidal scour, forming hollows up to 50m deeper than
the surrounding area, reworking the underlying deposits and forming levees or, inside the subtidal valley, tidal
ridges. The prodeltaic muds may reach and cover the tidal scour hollows during the late highstand only, in favor
of a damping of tides due to the reduction of the tidal prism caused by the advance of the Guayas delta. The
sequences preserved in the outer part of Jambelí Channel pinch out toward a hinge line located along the Puná -
Santa Clara fault system. This fault system is responsible of the uplift and emergence of a topographic barrier at
the entrance of the Jambelí Channel. As a result, the Estero Salado was progressively disconnected from the Gulf
and the tidal flows were concentrated in the Jambelí Channel, bringing about tidal scour hollows. In the
meantime, the tidal prism was maintained and subsidence took place in a sub-basin located landward of the
uplifting barrier. This caused the Jambelí Channel to remain subtidal during most of the past sea-level highstands,
in spite of the large amount of sediment supplied by the Guayas River.
... While large areas of the South Island (up to 30%) were covered by glaciers during the Pleistocene, the North Island was not subjected to any extensive glaciation (Newnham et al. 1999;Carter 2005). Despite the post-Oligocene topographic makeover of New Zealand, episodes of regional marine inundation have still occurred during the Pliocene (Manawatu Strait [the inundation of the lower North Island]) and Pleistocene (Northland, Cook Strait [separating the North Island and South Island]; Foveaux Strait [separating the South Island and Stewart Island]) (Lewis et al. 1994;Worthy and Holdaway 2002). ...
... that the sequence dips gently southward towards a depocentre located offshore (Anderton 1981). The emergence of the northern Whanganui Basin has been associated with uplift, offlap and southward migration of the basin depocentre through the Quaternary (Lewis et al. 1994;Nicol 2011). ...
Plio-Pleistocene sediments exposed in the dissected hill country of the Lower Pohangina Valley and Manawatu Saddle provide a unique record of sedimentation adjacent to the actively uplifting main axial range, North Island, New Zealand. Located in the eastern Whanganui Basin, which has formed behind the active Hikurangi subduction zone, renowned for one of the most comprehensive Quaternary stratigraphic records in the world. The oldest beds in the succession, unconformably overlying Torlesse Group, comprise Mangapanian (3–2.4 Ma) very fine conglomerate, sandstone and mudstone of the Komako Formation. Subsequent deposition of Konewa Formation continued through to late Nukumaruan time (2.4–1.63 Ma), including large tracts of conglomerate now preserved across the Manawatu Saddle, clearly visible from the Saddle Road. Takapari Formation consists of early Castlecliffian (1.63–1 Ma) sediments characterised by a sudden influx of primary volcanic and reworked volcaniclastic material. Distinctive rhyolitic marker beds and molluscan bio-events provide a means of correlating and dating the succession from the Lower Pohangina Valley across the Whanganui Basin. We present the geology of the Lower Pohangina Valley on a 1:30,000 geological map, accompanying cross section and 3D model. A new stratigraphic framework is presented, integrating work in the Komako District, Pohangina Valley with Whanganui Basin stratigraphy through the application of tephrochronology and biostratigraphy. The Lower Pohangina Valley succession provides evidence for marine conditions prevailing across what is now part of the main axial range of New Zealand from c. 3 to 1.6 Ma. An influx of conglomerate, eroded from Torlesse Group, into the sedimentary record during early Nukumaruan time (2.4 Ma) is attributed to an early phase of tectonic uplift along the North Island Dextral Fault Belt (NIDFB), before closure of the ‘Manawatu Strait’ commenced in early Castlecliffian time (1.63 Ma).
... Uplift in the last half million years has exposed the Plio-Pleistocene sequence and underlying Mesozoic Torlesse Supergroup basement (Kamp et al. 2004;Furlong and Kamp 2009). During the Plio-Pleistocene, seaway connections existed between the Whanganui and East Coast basins, becoming progressively limited and eventually cut off as the protoaxial ranges emerged during the Pleistocene (Lewis et al. 1994;Bunce et al. 2009;Trewick and Bland 2012). ...
A 66 m thick Pleistocene succession (Konewa Formation) exposed in southern Pohangina Valley, New Zealand, records predominantly coarse terrigenous clastic deposition in a wave-dominated fan delta and nearshore to offshore shallow marine environments. Depositional environments are interpreted from facies associations based on sedimentary features and biostratigraphy. The fan delta environment is characterised by sub-aerial to subaqueous, plastic or pseudoplastic, clast-rich debris flow deposits. These are consistent with debris flows initiated during partial collapse of steeply dipping, unstable delta foresets, and avalanching of sediment building up at the top of the delta system. The fan delta facies are interpreted to represent a Gilbert-style fan delta with a fluvial signature in beds deposited within the delta plain, steeply dipping foresets in the delta front, and a marine signature to beds deposited in the pro-delta zone. The Konewa Formation provides valuable insights into the potential connection between Whanganui Basin and Hawke's Bay, a region now separated by tectonic uplift forming the North Island axial ranges. Biostratigraphy of deposits associated with the prograding delta system places a potential phase of tectonic uplift in the northern Ruahine Range within early Nukumaruan time (c. 2.4 Ma).
... The archipelago of New Zealand has had a dynamic geological and climatic history. Shifting tectonic plates pushed up mountains, volcanoes wreaked havoc on surrounding landscapes, sea levels fluctuated, and vast glaciers carved out valleys (McGlone, 1985;Isaac, Herzer & Brook, 1994;Lewis, Carter & Davey, 1994;Suggate & Almond, 2005;Alloway et al., 2007;Naish & Wilson, 2009). The effects of these historic events in New Zealand's calamitous past have stretched into the present, leaving a mark on the current geographic distribution and genetic structure of species (reviewed in Wallis & Trewick, 2009;Trewick, Wallis & Morgan-Richards, 2011;Buckley, Krosch & Leschen, 2015). ...
Historic geological and climatic events such as tectonic activity, volcanism and glaciation have significantly impacted the distribution and genetic signature of organisms. In New Zealand, glacial cycles during the late Pliocene and throughout the Pleistocene caused the loss of large areas of forest habitat and many species are proposed to have been restricted to refugia during this period. Here we use mitochondrial DNA (COI, COII) to reconstruct phylogenetic relationships between haplotypes in association with several hypothetical biogeographical lines to determine the impact that past climatic conditions had on the giraffe weevil (Lasiorhynchus barbicornis), an endemic brentine weevil found in native forests across New Zealand. Our analyses revealed that populations in northern New Zealand have higher genetic diversity than those in the south. We compared evidence for genetic structure in relation to four biogeographical lines: Northland Line, Kauri Line, Taupo Line and Cockayne’s Line. Although, there was significant difference in genetic variation north and south of all the proposed biogeographic lines, we found most support for the Kauri Line. These results support our hypothesis that giraffe weevils had a restricted range during the Pleistocene, predominantly pushed north into refugia, which was followed by range expansion following glacial retreat.
... The 20-40 km-wide Cook Strait, between the North and South islands of New Zealand, represents the only water passage from the Tasman Sea to the Pacific Ocean between 35°S and 47°S, with consequent strong tidal currents and a distinctive pattern of sedimentation (Carter, 1992;Lewis et al., 1994) (Figure 1a). Coupled with being part of the Pacific-Australian plate boundary (Carter et al., 1988), Cook Strait has been the focus of significant study including acquisi-tion of multichannel and high resolution seismic reflection data, which provide information on the upper 1500 and 50 m subsurface, respectively, as well as large number of sediment cores, and seafloor photographs and grab samples. ...
Backscatter reflectivity from multibeam echo-sounders provides a powerful tool to efficiently characterize seafloor substrates. A comprehensive EM300 bathymetric and backscatter survey has been completed of Cook Strait, in central New Zealand. This paper presents a detailed analysis of the realtime corrections applied to the raw EM300 multibeam data and additional corrections required to compute angular variations of the backscatter strength. The corrections, including the local absorption coefficient, the influence of seafloor topography and sound refraction in the water column, are determined for different Cook Strait seafloor substrates. Modifying MB-System software code, we extracted the backscatter signal parameters in order to quantify the raw backscatter strength and apply additional processing. Profiles of backscatter strength versus incidence angle were computed for a variety of sites characterized by flat seafloor and homogeneous substrates, and for which ground-truth data were available. For each homogeneous site, different but characteristic backscatter profiles are observed that can be interpreted in terms of sediment facies. To analyze heterogeneous substrates, we present a statistical technique, based on a 3-dimensional distribution of (incidence angle, backscatter strength) couples that preserves geological information of the substrate components. This analysis, using backscatter data acquired on a submarine volcano, north of New Zealand, clearly differentiates soft sediments and lava flows within a heterogeneous substrate.
... Most of the studies (33%) reported a north-south split around the southern region of the Cook Strait (the body of water that separates the north from the south Island), at about 42°S. For some species, such as Perna canaliculus and Patiriella regularis, the reported divergence time between north and south Island populations dates to approximately 1.3 Ma ago (Apte & Gardner 2002;Ayers & Waters 2005), which corresponds to a period of hydrographic change across the region which was later on to form the Cook Strait (Lewis et al. 1994). In contrast, the contemporary north and south Island lineages of each of the three endemic intertidal limpets Cellana ornata, Cellana radians and Cellana flava diverged approximately 200 000 to 300 000 years ago (Goldstien et al. 2006). ...
Both historical and contemporary processes influence the genetic structure of species but the relative roles of such processes are still difficult to access. Population genetic studies of species with recent evolutionary histories such as the New Zealand endemic scallop Pecten novaezelandiae (<1 Ma) permit testing of the effects of recent processes affecting gene flow and shaping genetic structure. In addition, studies encompassing the entire distributional range of species can provide insight into colonisation processes. Analyses of genetic variation in Pecten novaezelandiae (952 individuals from 14 locations, genotyped at 10 microsatellite loci) revealed a weak but significant regional structure across the distributional range of the species, as well as latitudinal gradients of genetic diversity and differentiation: estimates of migration rates supported these patterns. Our results suggest that the observed genetic structure and latitudinal gradients reflect a stepping-stone model of colonisation (north to south) and emerging divergence of populations as a result of ongoing limitations to gene flow and insufficient time to reach migration-drift equilibrium. The low levels of inter-population and inter-regional genetic differentiation detected over hundreds of kilometres reflect the recent evolutionary history of Pecten novaezelandiae and stand in contrast to patterns reported for other evolutionary older species at the same spatial scale. The outcomes of this study contribute to a better understanding of evolutionary processes influencing the genetic variation of species and provide vital information on the genetic structure of Pecten novaezelandiae. This article is protected by copyright. All rights reserved.
New Zealand is home to 30 recognised endemic mite harvestman species and subspecies, 26 of which were described by Ray Forster in 1948 and 1952. These species comprise three genera: Rakaia Hirst, 1926, Neopurcellia Forster, 1948, and Aoraki Boyer & Giribet, 2007. Here, we focus on the diversity and distribution of Aoraki: we describe A. grandis Boyer, Tuffield & Dohr, sp. nov. and A. meridialis Boyer, Hahn & Ward, sp. nov. and we synonymise A. granulosa (Forster, 1952) with A. tumidata (Forster, 1948), bringing the total of named species and subspecies to twelve, and extending the southern range of the genus by over 100 km. Our phylogenetic analysis revealed three major lineages within the genus characterised by differing levels of granulation of the male fourth tarsus. We report striking variation in the range size and level of genetic structuring present within currently recognised species and subspecies of Aoraki, and propose future studies to address evolutionary, biogeographic and taxonomic questions in the group. urn:lsid:zoobank.org:pub:BDD4D61C-B099–44D5–949C-34AD217A016F.
Three-dimensional (3D) pre-stack depth migrated seismic data are used to analyse the geometry and growth of shallow faults associated with tectonic shortening in four (4) prominent thrust anticlines off Nankai, SE Japan. The four thrust anticlines show a trench-ward increase in horizontal shortening and deform the seafloor at present. They shortened the overburden strata by 7143 m in the Late Quaternary, reflecting a horizontal shortening of 32.9% in response to plate subduction. A significant number of closely-spaced and segmented fault arrays is observed in their hinge regions. We show that vertically segmented fault arrays with local throw maxima between 5 and 14 m relate to the existence of more competent (strong) intervals, or layers. Incompetent (weak) intervals where record relatively small throw values between 2 and 5 m. The observed mechanical layering is likely to continue at depth to control stress accumulation in faults posed to reactivate during seismic events. We show that the presence of closely-spaced, segmented fault arrays at shallow stratigraphic levels can have a significant impact on local stress distribution, controlling near-seafloor strain in accretionary prisms as Nankai's.
Knowledge about the population genetic structure of species and the factors shaping such patterns is crucial for effective management and conservation. The complexity of New Zealand’s marine environment presents a challenge for management and the classification of its marine biogeographic areas. As such, it is an interesting system to investigate marine connectivity dynamics and the evolutionary processes shaping the population structure of marine species. An accurate description of spatial and temporal patterns of dispersal and population structure requires the use of tools capable of incorporating the variability of the mechanisms involved. However, these techniques are yet to be broadly applied to New Zealand marine organisms.
This study used genetic markers to assess the genetic variation of the endemic New Zealand scallop, Pecten novaezelandiae, at different spatial and temporal scales. A multidisciplinary approach was used integrating genetic with environmental data (seascape genetics) and hydrodynamic modelling tools. P. novaezelandiae supports important commercial, recreational and customary fisheries but there is no previous information about its genetic structure. Therefore, twelve microsatellite markers were developed for this study (Chapter 2).
Samples (n=952) were collected from 15 locations to determine the genetic structure across the distribution range of P. novaezelandiae. The low genetic structure detected in this study is expected given the recent evolutionary history, the large reproductive potential and the pelagic larval duration of the species (approximately 3 weeks). A significant isolation by distance signal and a degree of differentiation from north to south was apparent, but this structure conflicted with some evidence of panmixia. A latitudinal genetic diversity gradient was observed that might reflect the colonisation and extinction events and insufficient time to reach migration-drift equilibrium during a recent range expansion (Chapter 3).
A seascape genetic approach was used to test for associations between patterns of genetic variation in P. novaezelandiae and environmental variables (three geospatial and six environmental variables). Although the geographic distance between populations was an important variable explaining the genetic variation among populations, it appears that levels of genetic differentiation are not a simple function of distance. Evidence suggests that some environmental factors such as freshwater discharge and suspended particulate matter can be contributing to the patterns of genetic differentiation of P. novaezelandiae in New Zealand (Chapter 4).
Dispersal of P. novaezelandiae was investigated at a small spatial and temporal scale in the Coromandel fishery using genetic markers integrated with hydrodynamic modelling. For the spatial analysis, samples (n=402) were collected in 2012 from 5 locations and for the temporal analysis samples (n=383) were collected in 2012 and 2014 from 3 locations. Results showed small but significant spatial and temporal genetic differentiation, suggesting that the Coromandel fishery does not form a single panmictic unit with free gene flow and supporting a model of source-sink population dynamics (Chapter 5).
The importance of using multidisciplinary approaches at different spatial and temporal scales is widely recognized as a means to better understand the complex processes affecting marine connectivity. The outcomes of this study highlight the importance of incorporating these different approaches, provide vital information to assist in effective management and conservation of P. novaezelandiae and contribute to our understanding of evolutionary processes shaping population structure of marine species.
Cook Strait separates North Island and South Island of New Zealand. It contains the Wairau and other sedimentary basins, which have sedimentary thicknesses of up to 4 km. The Strait overlies part of the Australia–Pacific plate boundary where subduction below the North Island changes to strike-slip motion through the South Island. Strike-slip faults are well documented in the South Island and less so in the North Island. Cook Strait has been surveyed by a variety of shallow penetration seismic in the past, and this has resulted in various models and uncertainty about how major faults join across the strait. The shallow-penetration data image numerous fault traces close to the sea bed, most of which can be traced for only a short distance. Gaps between individual fault traces are common. In recent years, a growing body of research, government and oil company seismic data has imaged structures much more deeply and is the subject of this paper. The Wairau Basin structural style is one dominated by normal faulting, with expansion of basin area and progressive eastwards shift in depocentres with time. A steep structural gradient or faulted margin to basement subcrop and outcrop on the North Island margin indicates a significant north-northwest to northwest component of fault control in this area of Neogene development. The seismic interpretation of this deeper data suggests there are continuous seismogenic zones underlying the discontinuous young seafloor fault scarps. Such discontinuities have led to a perception that Cook Strait faults are not connecting through, that fault rupturing across Cook Strait is improbable. Fault connections across Cook Strait along seismogenic zones have recently been interpreted from historical records. These indicate that the October 1848 earthquakes involved mainshock (M w 7.4–7.7) displacement on the Awatere Fault in the South Island and probable aftershock displacement on the Ohariu and Wellington faults in the North Island. The January–February 1855 earthquakes (mainshock M w ∼8.2–8.4) occurred on the Wairarapa Fault in southern North Island, Wharekauhau, Nicholson Bank faults in Cook Strait, Vernon and Awatere faults in the South Island, and Needles Fault off the NE Marlborough coast. These interpretations are supported by recent seismic data that indicate underlying basin-defining seismogenic zones connect across Cook Strait, with movements that date back at least to the top Paleogene.
Nearly 17 years wave records from deep water and shore‐based stations are used to describe the ocean wave characteristics around New Zealand. The wave environment is dominated by west and southwest swell and storm waves generated in the temperate latitude belt of westerly winds. As a result, the west and south coasts are exposed, high energy shores, the east coast is a high energy lee shore, and the northern coast from North Cape to East Cape is a low energy lee shore sheltered from these winds and waves. South of New Zealand, wave energies are extremely high; the prevailing deep water wave is 3.5–4.5 m high and has a 10–12 s period, with a slight increase in wave heights in winter.The west coast wave environment is mixed, and consists of locally generated westerly and southerly storm waves, and swell waves generated to the south. The prevailing wave is t.0–3.0 m and 6–8 s period. There are no strong seasonal rhythms, only shorter period cycles of wave height (5 day) associated with similar quasi‐rhythmic cycles in the weather.The east coast also has a mixed wave climate with southerly swells, originating in the westerlies south of New Zealand, and locally generated southerly and northerly storm waves. The prevailing wave is 0.5–2.0 m and 7–11 s period. A short period rhythmic cycle, similar to that on the west coast, is superimposed on a weak seasonal cycle. The seasonal, cycle results from an increase in the frequency of local northerly waves in summer.The prevailing wave on the north coast is a northeasterly, 0.5–1.5 m high and 5–7 s period. Subtropical disturbances and southward‐moving depressions generate a mixed wave environment and a possible seasonally reflecting a winter increase in. storminess.
The scallop Chlamys (Zygochlamys) delicatula (Hutton) now lives mainly in the subantarctic area south of New Zealand, and is common only as far north as Otago Peninsula. The limits of its northward migration during early Nukumaruan (late Pliocene or early Pleistocene) glacial periods are defined by scattered localities in the lowlands of Hawke's Bay and Wanganui, and in the northern Ruahine Range. Five new localities near the northern limits of its northward migration are reported: Ashcott Hill, Ruataniwha Plains; crest of the northeastern Ruahine Range west of Big Hill; western side of Mt Kohinga, near Kuripapango, Napier-Taihape Road; eastern side of Gentle Annie Hill, near Kuripapango; and summit of Te Rakaunuiakura, Mangaohane limestone plateau, western Ruahine Range east of Taihape.That most of the elevation of the Ruahine Range occurred during the last 1 million years (i.e., since early Castlecliffian time) is demonstrated by 3 lines of evidence: the widespread outliers of Nukumaruan marine rocks on the northern Ruahine Range; the simultaneous appearance of large quantities of Mesozoic clasts, derived form the Ruahine Range, in Castlecliffian conglomerate on both sides of the range; and the faulting of Castlecliffian rocks against Mesozoic basement along the eastern Ruahine Range. The mean rate of uplift of the range was at least 1.3 mm per year.
A Late Miocene to Pliocene/Lower Pleistocene sedimentary sequence is located 3–15 km west of the New Zealand Alpine Fault and north-west of Lewis Pass. Rappahannock Group is non-marine, and formations are based on the pebble content of conglomerates which are interbedded with sandstones and carbonaceous siltstones. Evidence for the timing of transcurrent movement on the Alpine Fault is provided by provenance studies of pebbles in these conglomerates. The basal Frog Flat Formation and overlying Spargo Formation contain conglomerates with 58-87% arenite pebbles. These arenite pebbles are characterised mainly by a quartz modal count of generally < 10 and are thought to be of Caples/Pelorus origin. Pelorus rocks on the western side of the Alpine Fault, north of Rappahannock Group, are rejected as the arenite source area as there is no evidence of Pelorus pebble transportation south to the Rappahannock Group. The Caples terrane is a more probable source area and is thought to have been located across the Alpine Fault adjacent, and to the east of, the depositional basin during the Late Miocene. Approximately 420 km of subsequent dextral shift on the Alpine Fault has resulted in the locating of the Caples terrane in its present position in west Otago/Southland.Supporting evidence for large scale dextral shear on the Alpine Fault in the Late Cenozoic is provided by the deformation of Rappahannock Group into a zigzag en echelon fold pattern. A progressive change in the trend of the northern fold axis, from the base to the top of the sequence, suggests folding was synchronous with deposition.Schist pebbles in Devils Knob Formation, uppermost in Rappahannock Group, are derived from both the Alpine Schist Belt and the Otago Schist. Schist pebble content rises from 5% at its base to 91% at the highest existing level. Metamorphic grade of the pebbles rises from chlorite and biotite schists in the loiwer part of the sequence to garnet schist at the top. These trends reflect southward movement of the Otago schists and continued uplift of the Alpine Schist Belt east of the Alpine Fault supplying increasing quantities of schist and exposing schist of higher grade.The depositional and deformational record of Rappahannock Group supports both extensive uplift and 420 km lateral shift on the New Zealand Alpine Fault since the Late Miocene.
An analysis of the wave climate within Cook Strait, New Zealand, and wave refraction diagrams for the Marlborough coast between Rarangi and Cape Campbell, identify two littoral cells. Cloudy Bay in the north is dominated by a northward movement of foreshore sediments under southerly swell waves. Clifford Bay in the south is dominated by a southward movement of material under locally generated northerly seas. Beach morphology and the longshore sediment distribution, measured at 16 stations, reflect the dominance of sections of the coast by either the southerly or northerly wind/wave régimes.
The ironsand component (ilmenite, titanomagnetite, and/or magnetite) of surficial sediments on New Zealand's western continental shelf is highest on the inner-middle shelf between Auckland and Taranaki where the mean concentration is x 0304; = 3.85% by weight. Sediments off Westland and Nelson contain only x 0304; = 0.17% ironsand. The subsurface distribution of ironsand, as revealed in piston cores, resembles that at the surface except that subsurface concentrations are markedly lower (e.g., x 0304; = 0.77% for Auckland-Taranaki)Textural and compositional data from the Auckland-Taranaki shelf suggest ironsand was originally concentrated under littoral conditions during the Holocene transgression and was dispersed north and southeast of the main primary source, the Egmont volcanics. The ironsand and host sediment are now approaching equilibrium with the modern hydraulic regime of waves and storm-induced currents and, therefore, are regarded as palimpsest.Any ironsand concentrated on the Westland-Nelson shelf during a lower stand of sealevel is now covered by ironsand-poor modern sediment; the Auckland-Taranaki shelf has a far lower modern sediment supply and, thus, the ironsand has remained exposed.
Data on the semidiurnal tide around the coast of New Zealand, and on neighboring islands are summarized, and interpreted using World, and a large scale, numerical models, and an analytical island-shelf model. The island-shelf model consists of a circular island (representing New Zealand) surrounded by a parabolic shelf, and a deep ocean of constant depth. The basic feature of the semidiurnal tide is a complete range of phase (0 degree -360 degree ) around the New Zealand coast, with large changes in the age of the tide from region to region, and an approximate threefold amplification in tidal amplitude over the deep sea at the coast.
The Geology of New Zealand, edited by R. P. Suggate, G. R. Stevens, and M. T. Te Punga (1978), contains a near-complete set of references up to 1970, and, to cover a printing delay, a less complete set up to 1976. For brevity and where appropriate, we use “Geology NZ” with page and figure numbers for references up to 1970. New Zealand stratigraphy is ordered into stage divisions that have unique two-letter symbols, and have been set out with a time scale by Stevens (1980). The letter symbols are used below in parentheses when appropriate.
The Taranaki Basin has undergone a complex sedimentary and tectonic history since the late Oligocene, reflecting the impingement of deformation associated with the evolving Pacific and Australian convergent plate boundary. At various times through the Neogene, elements of a passive continental margin, retro-arc foreland basin, foreland fold and thrust belt, inverted subbasin, back-arc rift and back-arc contractional basin have been variously displayed within the Taranaki Basin. -from Authors
The character of sedimentation in northeast Marlborough changed markedly during the Miocene, when long-established, dominantly calcareous deposition gave way to an influx of clastic detritus. Conglomerate, breccia, olistostromes, sandstones and turbidites then predominated and are described from the coastal section of the shallow fold and fault belt, between the Kekerengu and Waima Rivers. The change in sedimentation was preceded by submarine volcanism and accompanied by rapid tectonic uplift, a marked increase in sedimentation rate, exposure of older indurated undermass rocks and localized sedimentation of the very coarse clastics. These often chaotic deposits, collectively referred to as the Great Marlborough Conglomerate, formed from partly coalescing submarine slides and debris flows. The sequence is conformable, with substantial variations in thickness of the clastic units and interfingering of the rudites with sandstones, turbidites and mudstones. Localization of the type and size of megaclasts is a conspicuous feature. The Conglomerate is restricted to the major fault-angle depressions and thickens rapidly towards the faults. Massive slope failure of the rising fault blocks supplied the coarse debris to the fault-controlled basins. A transition from marine to non-marine deposition through the Miocene is seen from the southeast to the northwest. Sedimentation continued into the Pliocene, after which the covering strata were subjected to imbricate thrust faulting and folding along a northeast trend, parallel to the oblique-slip margin. Subsequently, dextral faulting on the same trend has rotated the covering slab of the shallow thrust and fold belt, which was uncoupled from the undermass as a tectonic décollement in the Ben More block. This décollement is related to a major dextral fracture—the Kekerengu Fault. Another décollement is postulated to occur over the northernmost sector of the Clarence Fault. A transition occurs in the Marlborough region from late Oligocene subduction and compression to Miocene normal faulting, Pliocene–early Pleistocene normal oblique-slip and late Pleistocene–Recent reverse oblique-slip. The Miocene–Recent movements have been concentrated on the major faults of the region: Wairau (Alpine), Awatere, Clarence, Hope and Kekerengu.
High concentrations of fine-grained and probably wind-blown quartz with
an Australian provenance have been mapped in Holocene sediments in the
southwest Pacific. During the last glacial maximum a narrow zone of high
eolian input, as reflected in a higher abundance of quartz, extended
more than 20° longitude farther east than today. This zone, which
was significantly farther north than at present, is centered around lat
30° S but curves around the northern tip of New Zealand. These
quartz distributions imply that the westerly winds that blew the
airborne quartz over the southwest Pacific had shifted considerably to
the north under the influence of intensified atmospheric circulation
during the last glacial maximum.
Late Quaternary sediment pathways through the deep ocean, east of New
Zealand, were determined using sand-sized mica tracers in conjunction
with physical oceanographic, seismic, and stratigraphic data. Results
indicate that in glacial times, micaceous sediment, derived mainly from
low-grade metamorphic rocks of the eastern South Island, was delivered
by rivers directly to Bounty Trough. Here turbidity currents transferred
the sediment 1000 km eastward to the Bounty Fan on the 4500 m deep
Southwest Pacific Basin. A western boundary current (WBC), flowing over
the fan, redirected the sediment 1000 km to the north and northwest
where it eventually accumulated as a drift deposit near Hikurangi
Trough. The drift also received mica that had been transported 700 km
along Hikurangi Trough from mainly plutonic sources on the northwestern
South Island. Interglacial episodes witnessed a major change in
transport paths. River-borne sediment was diverted away from Bounty
Trough which became a site of predominantly calcareous pelagic
sedimentation. Denied the lateral injection of terrigenous sediment, the
WBC nevertheless continued to supply small quantities of mica to the
drift through erosion of existing glacial deposits on the Bounty Fan.
The paucity of interglacial mica on the drift indicates it is also
receiving little terrigenous sediment by way of Hikurangi Trough.
Three Mini-Sosie™ seismic reflection profiles across part of southern Wairarapa, North Island, with a combined length of 22 km roughly normal to the main structural trend, reveal shallow crustal structure down to a depth of 1.5 km in upper Cenozoic strata hidden below upper Quaternary gravel deposits. Our stratigraphic correlation of the seismic data is based on the closest mapped outcrops, as there are no deep drill-holes. (™ Trademark of Societe Nationale Elf Aquitane). A profile across the Huangarua Valley, 5 km southeast of Martinborough (Line 101,3 km long) defines an asymmetrical syncline verging southeastward and formed during the last one million years, as previously described from geological outcrop.
Profiles across the Wairarapa Plain, intersecting Highway 2 at a point 3.5 km southwest of Masterton (Lines 201 and 202, combined length c. 19 km) reveal the following structures south-eastward from the Alfredton Fault at the north-western edge of the Wairarapa Plain.
1. Chester Anticline formed in upper Miocene-basal Pliocene strata, buried under the north-west flank of the Taratahi Syncline (see below).
2. Taratahi Syncline, 7 km wide, its north-west flank unconformably overlying Chester Anticline, its bottom flat and nearly level for 5 km, and its south-eastern flank rising in a concentric curve to the adjacent Peter Cooper Anticline.
3. Peter Cooper Anticline and on its south-east side the complementary Fern Hill Syncline, both concentric folds, and strongly developed in Upper Miocene and Pliocene strata, but weakly developed in Quaternary strata.
We have mapped in outcrop two growing structures at the south-east side of the Wairarapa Valley (south-east end of Line 201) as the active Gladstone Anticline and Huangarua Syncline, which are well displayed in the profile. Subsidence of the region commenced near the beginning of Late Miocene time, c. 10 million years bp. There was a brief folding event in latest Miocene and/or earliest Pliocene time. There was little tectonic activity other than regional subsidence during most of Pliocene and early Quaternary time. An increase of the folding rate of nearly an order of magnitude commenced in the middle of the Quaternary, c. 1 million years ago, and continues at the present day.
Current‐meter observations at three sites in the narrows of Cook Strait over individual periods of 30–82 days confirm the dominance of the semi‐diurnal tidal flow. The major semi‐diurnal constituent, the M2 tide, has near degenerate ellipses aligned through the Strait with amplitudes decreasing towards the west. Daily mean currents are dominated by flows with 2 and 4 weekly periods which are correlated with the wind (mainly the through Strait component) and possibly associated with the fortnightly MSf (4–9 cm s∼') and monthly Mm (4–7 cm s) tides (mainly the across Strait component). Mean currents over the observational periods were directed through the Strait, with a southward component at about 4cms on the western side and a 5–14 cm s northwards component on the eastern side. An appreciable (1–12 cm s) 6.2 hour M4 tide is also present with flow directed mainly across Cook Strait. The Mm, MSf, and M4 compound tides are probably associated with a response to interaction of the non‐linear field acceleration of the semi‐diurnal tide producing flow across the sloping sea floor.
The phases and amplitudes of the M2 and S2 constituents of tidal elevation in Coiok Strait may be adequately described as an open mouth reflection of tidal waves advancing from the east and west coasts of New Zealand and reflecting near the latitudes of Titahi Bay and Cape Campbell (a distance of approximately 60 km). Other reflection conditions give amplitude and phase distributions different from those observed. Best fits to the observed phases and amplitudes for the M2 tide elevation arise from non‐rotational one‐dimensional solutions which allow for the bathymetry. If rotation is introduced in the form of Kelvin Wave solutions, the result is a two‐dimensional phase‐distribution pattern qualitatively similar to that observed, with the change in phase more rapid and the tidal amplitude smaller on the eastern than on the western side of Cook Strait.The solution for the S2 tide also fits closest to the observed tidal elevations for the non‐rotational one dimensional solution, but the introduction of rotation leads to a two‐dimensional phase‐distribution pattern qualitatively similar to that observed. The ratio of the amplitude of the wave (£) advancing from the northwest into Cook Strait to that (A) advancing from the southeast is substantially greater for the S2(B/A = 11) than for the M2(B/A = 2) tidal constituent and leads to the region of most rapid phase change for S2 being shifted further to the south than that for M2.
Two-dimensional and three-dimensional gravity models of the Mesozoic basement topography in the Wairarapa show that the major feature is the Wairarapa Trough, aligned SSW—NNE through the area. The Trough has two arms, one north of Eketahuna and the other south of Carterton. All three features are fault-angle depressions, bounded to the west by the West Wairarapa, Wellington, and Dry River Faults, respectively, and reaching their greatest depths at these faults. A structural contour map of the Mesozoic surface in the Wairarapa shows that the basement is covered by more than 3000 m of Cenozoic material.The West Wairarapa Fault is shown to be reverse in the south, with a dip as low as 15°. The other faults are apparently near-vertical.
Widespread shell beds and occasional coarse gravel layers were deposited on the western continental shelf of New Zealand during late Pleistocene to early Holocene low sea levels from 19,700 to 10,600 years ago. Some molluscan species present in the shell beds suggest cooler waters during this time, and most are typical of the inner shelf environment. The gravel layers represent near shore deposits. The data presented are consistent with estimates of late Glacial age eustatic sea levels from other parts of the world though the possibility of local downwarping is not excluded.
Cotton (1955, Footnote 10, pp. 70–1) states, when discussing subsidence and submergence in the Marlborough Sounds, “This makes no allowance for a probable north-easterly tilt of the whole Marlborough Sounds block of country. . . .First a tectonic subsidence took place with down-warping or tilting of the whole block towards the north-east, deeply drowning a mountainous landscape (Plate VII, Fig. 1) so that ridges and spurs taper to points and plunge beneath Cook Strait. This movement was followed, perhaps considerably later, by the submergence due to postglacial eustatic rise of ocean level, causing drowning to about 300 feet and producing the intricate shoreline pattern”.
Four benches of the Last Interglacial, and the Present Interglacial bench are identified on most parts of the south-east coast of the North Island. Inferred ages for the back of the benches are 125 000, 100 000, 84 000, 80 000, and 6000 years. The heights of the benches define a pattern of folds and faults which can be traced inland by contouring the summit heights. In the coastal belt the summit height surface is similar in pattern, but twice as high as the 100000-year surface. It is found that the best overal1 fit with the 100 000-year surface is by assuming an age of 200 000 years for the summit height surface. It is thought that uplift was smal1 until 200 000 years ago and then increased to the average rate for the last 100 000 years. Rates are compared in a combined isobase map, and the uplift rates and flank tilt rates for the main anticlines and synclines set out in a table for the last 6000 years, 100 000 years, and summit-height surface. On the marine benches uplift rates range from 0 · 75 m to 4 · 0 m per thousand years for the growing anticlines, and from 0 · 5 m to 2 · 2 m per thousand years for the growing synclines. For the summit height surface, uplift rates on the anticlines range from 3 · 0 m to 4 · 5 m per thousand years. In terms of classical description, there are three phases in the uplift history of the district: an epeirogenic phase (very slow subsidence without much folding) from 14 mil1ion years (m.y.) to 1 · 3 m.y.; a phase of tectogenesis (folding with low rate of uplift) from 1 · 3 m.y. to 0 · 2 m.y.; and an orogenic phase (folding and intense uplift) from 0 · m.y. to the present day.
Abundant and well preserved Foraminifera in turbidites of Upper Miocene (Kapitean) age, at Cleland Creek, were compared with Foraminifera in four different depth biofacies of about the same age. The turbidites were deposited in depths certainly greater than 2,000 ft, and probably between 4,000 and 6,000 ft, and were derived from all shallower depths up to about 400 ft or less. Fragile shells and large shells are less common in turbidites than in non-turbidites, and many shells are considered to have been destroyed during transport. The basal layer of each turbidite rhythm is considered to consist of “slumped” neritic sediment with little intermixed deep-water sediment, the intermediate layer to have been deposited by a swift turbidity current, and the upper layer to have been deposited from suspension after the turbidity current ceased flowing. No trace of autochthonous sediment was found between turbidite rhythms.
The lithology and foraminiferal content of a faulted outlier of Pliocene conglomerate, sandstone, and mudstone at Makara in the south of the Wellington Peninsula are evidence of an important marine transgression during the Opoitian, The beds have the characteristics of deposits in a wide-mouthed embayment, with a basal shallow-water conglomerate and, in the upper part of the sequence, mudstone deposited probably deeper than 50 fathoms. As the rocks are 200 ft thick, the relative rise of sea level was more than 500 ft. The abundance of delicate thin-shelled Foraminifera, and the absence of Miliolidae and thick-shelled shallow-water forms, which are being transported widely throughout Cook Strait sediments by strong turbulent currents at the present day, indicate that a strait was not then in existence. The deposit does, however, provide evidence that makes possible a correlation of the lime and mode of development of Cook Strait with the Manawatu Gorge.
Magnetic concrete, composed of crushed ironsand and cement, was used as an artificial tracer mineral in an experiment designed to estimate the sedimenttransporting power of the bottom currents in the central part of Cook Strait, New Zealand. The results show that these currents are capable of transporting sand grains at least 1½ mm in diameter.
The Hikurangi Margin is the active subduction complex on the east coast of the North Island and the northern South Island of New Zealand that lies between, and structurally links, the Tonga- Kermadec subduction zone with the Alpine Fault. The current deformation of the Hikurangi margin is well determined from seismicity and geodetic strain observations. Extension in the north perpendicular to the plate boundary zone changes to shortening in the south so that present-day rotation of the margin as a whole is indicated: such rotation is observed paleomagnetically. The amounts and rates of rotation vary with time and location but on average the margin has rotated at about 4 degrees/Ma for at least the last 10Ma. Although the rotation is not uniform over the margin as a whole, it is so over discrete parts of it. These parts are termed domains and are of the order of 100kms in lateral dimension; they appear to have rotated in a coherent, uniform manner. The overall rotation of the margin is considerd to record a progressive change in orientation of the underlying subducted plate and such a rotation is inferred from plate tectonic reconstructions. Two domains are rotating rapidly today, in excess of 5 degrees/Ma and behind them the back-arc region is itself deforming in one case by spreading and the other by simple shear on a set of major transcurrent faults. In the middle of the margin is a domain that apparently has not rotated in the last 2Ma and it is bounded in the back-arc region by a block that has been relatively stable over the period. The driving mechanism of rotation is the rotation of the underlying slab, itself a natural outcome of the particular configuration of plate boundaries of the region.
The South Wangartui Basin lies in central New Zealand between the South Taranaki Graben and the axial ranges of the North Island. Hili the area of the basin lies offshore beneath northern Cook Strait and the South Taranaki Bight. Four thousand kilometres of CRP seismic reflection profiles, resulting from petroleum exploration in the basin and adjacent areas, have been interpreted to determine the structure and evolution of the basin. The basin is a broad half-graben trending NNE. It contains up to 4000 m of marine Plio-Pleistocene sediments and has developed by progressive subsidence and onlap to the south combined with emergence and offlap in the north. Most of the subsidence occurred during the late Pliocene and early Pleistocene when the depocentres were aligned along the southern continuation of the Taupo Graben trend.The western boundary of the basin is formed by basement highs oriented en echelon and bounded by major pre-Pliocene wrench faults (Flaxmore, Manaia, and Taranaki Faults). The eastern boundary of the basin is marked by NNE-trending probable wrench faults related to basement block movements during Plio-Pleistocene sedimentation. Together with a set of northeast-trending faults across the basin, the boundary faults show a regional pattern of divergent and dextral wrench deformation. To the north the transition to the older North Wanganui Basin is not clear. To the south the Pleistocene sediments onlap the basement rocks of Marlborough Sounds.
Analysis of the structure and sedimentary geology of W New Zealand has identified a middle Eocene to early Miocene continental rift system, 1200km long and 100-200km wide, named here the 'Challenger Rift System'. Four phases of rift development occurred: 1) infra-rift subsidence; 2) active axial trough subsidence; 3) expanded rift subsidence involving collapse of the rift shoulders; and 4) incipient sea-floor spreading.-from Author
Egmont Terrace west of Cook Strait has been built, principally during times of lowered sea level, as a prograding continental shelf onto the Challenger Plateau at the southern end of Lord Howe Rise. The plateau subsided below sea level during early Eocene time, an event accompanied by slow upbuilding of the plateau. Major outbuilding appeared only in early to middle Miocene time, following a rerouting of major surface currents from the area.
A study of the Alpine fault zone and the Fiordland region of the South Island of New Zealand from February through April 1972 indicates high but diffuse microearthquake activity. Composite focal mechanism solutions show that a regional northwest-southeast compression dominates the tectonic pattern. This direction is nearly normal to the Alpine fault, indicating that the Alpine fault is now undergoing a large component of thrust faulting. This agrees with geologic data for uplift of the Southern Alps along the Alpine fault beginning in mid-Miocene time and accelerating in the Pliocene, the time of the Kaikoura orogeny. Before the Kaikoura orogeny, the Alpine fault apparently was a transcurrent fault. This major change in the New Zealand tectonic pattern could have been produced by a relatively minor migration of the nearby Indian-Pacific pole of rotation. Incipient underthrusting of the Tasman Sea appears to be occurring off the Fiordland coast, terminating at the point where the Lord Howe Rise intersects the coast. To the north is a zone of oblique continental convergence, with the Southern Alps being rapidly uplifted along the Alpine fault. North of the Alps, much of the motion is transferred to several faults that have more easterly strike; these formed in the Kaikoura orogeny and constitute a new transform fault system.
In the northern South Island of New Zealand, displacement at the Pacific-Indian plate boundary is accommodated by the ENE-striking, right-lateral strike-slip Marlborough fault system. The southernmost Marlborough Fault is the Hope Fault; the late Pleistocene-Holocene horizontal slip rate on this fault is 20-25 mm/yr, about half of the rate of Pacific-Australian plate motion. Near the eastern end of the Hope Fault, most displacement is transferred to the north-northeast-striking Jordan Thrust, but the average dip-slip rate at the surface trace of this thrust is less than 4 mm/yr. It is proposed that most slip takes place on a blind thrust, expressed at the surface by the fault-propagation folding of the Seaward Kaikoura Range, and that the rate of uplift of this range is as high as that of the Southern Alps, 6 to 10 mm/yr. -from Authors
A deep seismic-reflection profile shot across the South Taranaki basin,
New Zealand, indicates up to 10 km of crustal thickening beneath the
Taranaki boundary fault at the eastern margin of the basin. The seismic
data also show a broad flexure of the entire crust, the locus of the
flexure-producing load appearing to be in the vicinity of the Taranaki
boundary fault. Such crustal thickening and flexure suggest a
compressional, foreland-basin style of late Cenozoic development rather
than the rift-graben origin previously assumed. This change in
interpretation for the South Taranaki basin has implications for
evaluating the thermal history of the basin and its possibilities for
hydrocarbon prospects. The study therefore demonstrates the value of
deep seismic exploration of a hydrocarbon-bearing basin in its early
stage of exploration.
The Cape Egmont Fault Zone (CEFZ) is a major structural boundary within the predominantly offshore Taranaki Basin. The northeast‐southwest‐striking principal fault within this zone, the Cape Egmont Fault (CEF), represents the westernmost zone of active deformation associated with the Hikurangi subduction system, and is characterised by normal separation and pronounced surface expression across the Taranaki continental shelf. It has a 53 km long, 1–5 m high seafloor scarp, located 6 km to the east of the Maui‐A production platform, and comprises four segments, each characterised by differences in fault geometry and behaviour. Average slip rates on the CEF for the last 225 000 years range from 0 to 0.8 mm/yr, suggesting concomitant extension rates of 0.1–1.8 mm/yr that are comparable with the deformation rates calculated for onshore active faults in the Taranaki‐Wanganui region. The presence of a seafloor scarp and historic seismicity associated with the CEFZ are considered to be indicative of the recently active nature of the CEF. Analyses of high‐resolution seismic reflection profiles and piston core samples suggest that the most recent movement on the CEF was at least post‐10–11 ka ago. During the late Pliocene‐Quaternary, it is unlikely that the CEFZ has accommodated significant amounts of strike‐slip, as proposed by previous workers. Movement over the last 2–3 Ma is inferred to have been predominantly normal, possibly with an element of dextral oblique‐slip.
In the exposed, western approaches to Cook Strait, westerly storms are considered to have generated southeastward-moving, coast-parallel currents which have been responsible for the formation and maintenance of stable ridges of black, mafic sand and ephemeral ribbons of light, felsic sand. These bedforms are examined using side-scan sonographs.The black sand ridges probably formed 12,000 to 9000 years ago as “shoreface connected shoals”. Since inundation by rising sea level, their form has been perpetuated by occasional storm-generated currents, the only strong currents in the area. Formation ceased about 9000 years ago when rock promontories to the west began to act as natural barriers to the rapid longshore supply of black sand.The light sand ribbons represent the feather edge of a seaward-migrating prism of fine, mobile, river-derived, sand. During prolonged storms, wind drift and storm surge currents drive the sand in ribbons along the rippled, shell-and-black-sand-floored troughs between ridges.
The declinations of the primary magnetization of sedimentary rocks in
the northern part of the New Zealand plate-boundary zone, after thermal
or alternating field cleaning, have been used to determine tectonic
rotations about vertical axes of rigid crustal blocks. The pattern of
rotations during the last 4 Ma, combined with structural style and
continuity, defines seven structural domains each ca 100 × 100-200
km across, which contain crustal blocks up to 100 km across and 20 km
thick. Large crustal blocks (tens of km across) in two of these domains
have rotated clockwise more than 20° relative to one of the margins
of the plate-boundary zone in the last 4 Ma. Their behaviour appears to
be controlled by the nature of the plate boundaries, such as the
presence of an underlying subducted slab and the strength of the crust
at the back of the overlying crustal wedge. Small crustal blocks (<
10 km across) may have rotated clockwise through angles greater than
20° during the last 4 Ma, floating on an underlying zone of more
distributed deformation. The tectonic rotations of the large crustal
blocks, and the nature of the deformation at their boundaries, combined
with an interpolation of the relative plate positions, can be used to
reconstruct the plate-boundary zone at ca 4 Ma.
As the deep seismic zones are associated with subducted oceanic crust, it is important to establish the extent and continuity of each of these zones, using consistent earthquake locations. Then the former oceanic crust can be restored to the surface of the Earth by unfolding the seismic zone about the trench. This unfolded crust should be used in plate reconstructions. This process has been carried out for the deep seismic zone in the Kermadec-New Zealand region, where the deep seismic zone is defined by a careful selection of I.S.C. hypocenters and the former oceanic crust is established by unfolding. Plate reconstructions using two sets of rotation poles show that the deepest parts of the observed seismic zone along its length were not subducted at the same time. Further the currently observable zone is not directly associated with earlier volcanism in northwest New Zealand between 6 and 20 Ma ago.
The subduction zone under the east coast of the North Island of New Zealand comprises, from east to west, a frontal wedge, a fore-arc basin, uplifted basement forming the arc and the Central Volcanic Region. Reconstructions of the plate boundary zone for the Cainozoic from seafloor spreading data require the fore-arc basin to have rotated through 60 degrees in the last 20 Ma which is confirmed by palaeomagnetic declination studies. Estimates of shear strain from geodetic data show that the fore-arc basin is rotating today and that it is under extension in the direction normal to the trend of the plate boundary zone. The extension is apparently achieved by normal faulting. Estimates of the amount of sediments accreted to the subduction zone exceed the volume of the frontal wedge: underplating by the excess sediments is suggested to be the cause of late Quaternary uplift of the fore-arc basin. Low-temperature--high-pressure metamorphism may therefore be occurring at depth on the east coast and high-temperature--low-pressure metamorphism is probable in the Central Volcanic Region. The North Island of New Zealand is therefore a likely setting for a paired metamorphic belt in the making.
Six wave stations were occupied for 2$\frac{1}{2}$ months along a great circle between New Zealand and Alaska. Twice-daily wave records were analysed to yield energy spectra E$\_{i}$(f, t) for station i as functions of frequency and time. Events from major storms appear as slanting ridges in the E$\_{i}$(f, t) field; the ridge lines f$\_{i}$ = (g/4$\pi $) (t - t$\_{0}$)/$\Delta \_{i}$ determine source time, t$\_{0}$, and source distance, $\Delta \_{i}$; rough estimates of direction $\theta \_{i}$(f) were made at two stations. Twelve major events, including several from antipodal storms ($\Delta \approx $ 180 degrees) in the Indian Ocean, could be clearly tracked from station to station. Source parameters are found to be mutually consistent, and usually in accord with weather information. Cuts in E$_{i}$(f, t) along the ridges give spectra from which the effect of dispersion is removed. These were corrected for geometric spreading and island shadowing. Comparison of the corrected ridge spectra between stations indicate negligible attenuation for frequencies below 70 mc/s (less than 0$\cdot $02 dB/deg between New Zealand and Alaska), and 0$\cdot $15 dB/deg at 80 mc/s, with a considerable scatter from event to event. At higher frequencies the events disappear into a background spectrum which is remarkably uniform over the Pacific, and presumably the result of global high winds along the entire storm belt of the South Pacific. The attenuation in the near zone of the storm (within a distance comparable to the storm diameter) is estimated at 0$\cdot $2 dB/deg at 70 mc/s and 0$\cdot $4 dB/deg at 80 mc/s. Wave-wave interactions have been derived from a perturbation expansion of the Navier-Stokes equations. The computed attenuation due to interaction between wave groups from a storm is not inconsistent with observations in both the near and far zones. The observed super-exponential decay is attributed to the decrease in interaction efficiency with diminishing wave energy along the path and dispersive narrowing of the spectral peak. Interaction with background (such as the trade wind sea) is unimportant. The conclusion is that the observed propagation could be accounted for by the effects of Stokes interaction (section b, c, figure 38) between wave groups from a single storm.
A method using marker stakes and rings has been developed to measure the disturbance of beach sediments. Results of a study using this method in Palliser Bay reveal marked differences between the head of the bay, which is fully exposed to the prevailing southerly waves, and the eastern side of the bay, which is in a more sheltered position. At the head of the bay, wave conditions dominantly control diurnal variations in beach disturbance, but on the eastern side of the bay, the effect of rhythmic tidal translation of the breakpoint is more important. This is because of the wave-energy filtering effect of wave refraction and a subtidal rock and boulder reef.At the head of the bay, diurnal fluctuations in the height of water tables within the beach are also dominantly controlled by the prevailing wave conditions. Water table levels were not studied on the eastern side of the bay, but it is expected that tidal fluctuations are dominant here.At all 3 sites studied, disturbed sediment is predominantly of granule size, and disturbance on the lower part of the beach averages around 0.2 m. The maximum disturbance observed was 1.65 m.
3.5 kHz seismic profiles are used to characterise the seabed in Cook Strait. The various acoustical responses have been classified into nine groups or echo‐types which, together with sediment samples, photographs, and side‐scan sonography, provide an insight into modern erosional and depositional processes operating in the strait.Much of northern Cook Strait is underlain by semi‐consolidated, late Pleistocene sediments that are eroded by strong, tide‐dominated currents even at depths >200 m. Locally, erosion of these deposits is impeded by a lag gravel pavement that occupies much of the 150–350 m deep central strait. The same strong currents effectively transport bedload along the Wellington continental shelf, which is a rocky platform with a patchy veneer of mobile sand and gravel. Outside the main tidal stream, within semiprotected embayments, deposition is manifest by prominent sediment bodies of mud and sand prograding across the inner‐middle shelf. Seaward of the shelf, in southern Cook Strait, the seafloor is dissected by a complex of submarine canyons that appear to syphon off tidally transported sand to the nearby Hikurangi Trough. However, in at least one place, transport is impeded by a slide blocking the canyon axis. Outside submarine canyons, products of gravitational mass movement are not conspicuous, even though Cook Strait lies across a zone of high seismicity. This scarcity of evidence is, in part, attributed to current modification of any such deposits.
Boreholes and offshore seismic profile surveys in southern Evans Bay, WelIington Harbour, indicate that a drowned river valley has been partly infilled with sediments during two glacial interglacial cycles. The original valley was probably eroded along the shatter zone of a late Pliocene fault situated on the eastern side of the bay. The infilling sediments include two assemblages: (I) interglacial age (including Holocene) shelly marine sands and muds, which have a palynoflora from flourishing rimu-podocarp forest, and (2) g1acial age gravelly and carbonaceous terrestrial deposits, wh ich have a palynoflora dominated by grasses or, in slightly milder times, by beech and manuka. Postdepositional deformation of early Holocene sediments may indicate either further faulting along the shatter zone of the Pliocene fault or an effect of sediment compaction during earthquake stress. Deformation of late Holocene sediments is interpreted as differential compaction and slumping being a secondary effect of earthquake shaking.
Gravity measurements suggest that the earth’s crust has a thickness of about 20 km beneath the south-eastern margin of the New Caledonia Basin. From a point 50 km within the edge of the New Zealand continental shelf the crust thickens to a maximum value of about 36 km near the Marlborough Sounds. Residual gravity and magnetic anomalies indicate that a broad belt of dense, magnetic rocks underlies the South Taranaki Bight but does not appear to extend beneath Taranaki Province. These rocks may be either Paleozoic intrusives similar to those found in the South Island, Or Pleistocene volcanics similar to Egmont Andesite.
The Wanganui Basin, western North Island, New Zealand, contains a thick (up to 5 km) sequence of Cenozoic sediments unconformably overlying Mesozoic and Paleozoic greywacke basement rocks.Gravity anomalies suggest that along the western edge of the basin, north of Moeroa, a trough in the basement extends northwards as far as Waitaanga where it splits into two branches; one continuing NNE to Aria, the other NE to Waimiha. Between the Te Ahi-Ohura Fault and the Nukumaru-Hauhungaroa Fault, the basement forms a broad, gently sloping shelf. On the eastern side of the basin, a smaller trough extends NE from Taihape to Erewhon. Known basement uplifts at Mt Stewart, Marton, and Santoft do not have any significant gravity expression. The anomalies do not support the idea that the basin contains two sub-basins separated by a basement high.Magnetic measurements indicate that no large amounts of strongly magnetised volcanic rock are likely within the Cenozoic sediments.
Seismic reflection data reveal that the major dextral transcurrent faults of the North and South Islands, with the possible exception of the Wairau Fault, do not link directly across Cook Strait. Off Marlborough, the extension of the Wairau Fault is a series of northeast-trending fractures, one of which runs west of Kapiti Island towards the mouth of the Rangitikei River. En route, the Wairau Fault defines the western margins of the prominent Wairau and Narrows sedimentary basins. The southeastern edge of the Wairau Basin is the Awatere Fault which bends sharply to the east to merge with the steep topography of Cook S trait Canyon. The neighbouring Hog Swamp Fault follows a similar trend. The Clarence Fault has not been identified offshore whereas the Kekerengu and Hope Faults can be traced only a few kilometres beyond the coast.On the Wellington side of Cook Strait, the offshore extensions of the Ohariu and Wellington Faults terminate in the thick sedimentary pile of the Wairau Basin. Further along the coast, the West Wairarapa Fault extends to Cook Strait Canyon where it appears to be offset dextrally, the southerly continuation extending to the Marlborough continental shelf.Faults from both islands terminate in the central strait along an apparent dextral offset. This is attributed to the clockwise rotation and dislocation of the fault belt in response to differential movement between the Indo-Australian and Pacific plates in late Cenozoic times.
Analysis of sediments recorded in a piston core, located east of southern North Island, New Zealand, gives a detailed record of climate change at the end of the last glacial. Accumulation rates1 of both detrital (quartz) and biological (carbonate and biogenic silica) components of the sediment are much higher during glacial than post-glacial time and they all show a synchronous, rapid decline at 14,700 yr BP. We attribute this to a decline in intensity of the strong glacial westerly winds in the New Zealand region as the polar winds contracted to their present latitudes2–6. The greatest rate of quartz accumulation occurs between 16,200 and 14,700 yr BP and is not matched by any change in carbonate or silica accumulation. We believe this reflects accelerated fluvial transport of detritus out of the mountain ranges and consequently increased aeolian dust transport before the decline of the polar westerlies.
Seismic reflection profiles recorded across southern North Island, New Zealand, define the structural details of a convergent plate boundary. The eastern profile delineates the thrust wedges and back-tilted basins of the accretionary prism which overlies a detachment zone marking the top of the subducted Pacific plate. Most of the younger part of this wedge is isolated from the landward part of the sequence by an oceanward dipping detachment zone. The western profile defines a broad crustal downwarp in the “back-arc” region of the plate boundary overlying the 20–50 km deep subduction zone. The crustal section farther to the west comprises a generally transparent middle crustal layer and a reflective lower crust. Dipping reflective zones in the middle crust may delineate low-angle normal faulting associated with a Cretaceous extensional episode. Detailed Seismological data demonstrate the close association of the top of a zone of high Seismicity, inferred to mark the subducted Pacific plate, with the base of the reflective sequence identified as the base of the overriding Australian plate.