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K-Ar geochronology of weathered basement K-Ar ages (Ma) versus grain size (µm) for the analysed samples from the highly weathered basement of offshore wells 6408/12-U-01 and 6814/04-U-01, as well as Andøya borehole BH3 onshore. K-Ar age errors (bars) are within 1σ uncertainties (see Table S3).
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Following the latest Permian extinction ∼252 million years ago, normal marine and terrestrial ecosystems did not recover for another 5-9 million years. The driver(s) for the Early Triassic biotic crisis, marked by high atmospheric CO2 concentration, extreme ocean warming, and marine anoxia, remains unclear. Here we constrain the timing of authigeni...
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The Spiti region, renowned as the Museum of Indian Geology, is a world-famous sedimentary succession containing well-exposed sequences from Neoproterozoic to Cretaceous age. In this study, Triassic siliciclastic sedi-mentary rocks of the Lilang Supergroup were chosen to understand weathering history, provenance, paleoclimate, and depositional condi...
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... The K-Ar method was selected to date fine-grained clay minerals within the extensively altered Kolga granite, aiming to pinpoint the timing of weathering (e.g., Fredin et al., 2017;Knies et al., 2022). Both the mineralogical composition of bulk material and different grain size fractions derived from the U1565A and U1566A rock samples were studied with X-ray diffraction following protocols outlined by Tartaglia et al. (2020). ...
Three boreholes drilled during the International Ocean Discovery Program (IODP) Expedition 396 have yielded unexpected findings of altered granitic rocks covered by basalt flows, interbedded sediments and glacial mud near the continent‐ocean transition of the mid‐Norwegian margin. U‐Pb and K‐Ar geochronological analyses were conducted on both protolithic and authigenically formed K‐bearing minerals to determine the age of granite crystallisation and subsequent alteration episodes. The granite's crystallisation age based on 104 zircons is 56.3 ± 0.2 Ma, and subsequent exhumation along with alteration/weathering events took place between 54.7 ± 1 and 37.1 ± 1 Ma. This intrusion represents the youngest granite discovered in Norway and intruded at an extremely shallow crustal level before a rapid rift‐to‐drift transition. The shallow emplacement of granitic rock and its fast exhumation before and during the onset of volcanism holds significant implications for the syn‐ and post‐breakup tectonic evolution of volcanic margins.
... Chert deposition in the PCE was affected by the end-Permian mass extinction (Beauchamp and Baud, 2002;Yang et al., 2022b). The loss of siliceous organisms coincided with a decline in primary productivity (e. g., Grasby et al., 2016Grasby et al., , 2020Knies et al., 2022) and development of oceanic anoxia (e.g., Grasby et al., 2021;Yang et al., 2022b), which led to the collapse of Permian chert deposition. Marked warming of seawater caused by the eruption of the Siberian LIP and arc-related volcanic activity (Sun et al., 2012;Chen and Xu, 2019) further decreased the silica preservation potential and promoted the disappearance of chert deposits (Yang et al., 2022b). ...
... A long δ 15 N profile from the Sverdrup Basin of the northwestern Pangean margin documented the persistence of nutrient-N stress in the aftermath of the PTME until the Ladinian Stage of the late Middle Triassic (Knies et al., 2013(Knies et al., , 2022Grasby et al., 2016). This record implies that the recovery of the nutrient N reservoir considerably post-dated stabilization of other oceanic systems (e.g., carbon cycle, temperature and redox), which largely occurred around the Early-Middle Triassic boundary. ...
... The full re-establishment of an aerobic N cycle may have occurred asynchronously in the global ocean. This event took place unambiguously around the ALB at Guandao, but it may have occurred somewhat later in the Sverdrup Basin, where evidence of anaerobic N cycling is found well into the Ladinian (Figs. 5 and 7; Knies et al., 2022). Such spatial asynchronicity may have been influenced by the small size of the oceanic nitrate pool in the Middle Triassic ocean, as in some Mesoproterozoic basins (Stüeken, 2013;Koehler et al., 2017). ...
... Uniform productivity suggests an end to the stress linked to nutrient-N deficiency that had existed since the PTME. Concurrent increases of δ 13 C carb and δ 13 C org during the Ladinian-Carnian are observed globally and thought to have been related to the full recovery of terrestrial ecosystem productivity during that interval (e.g., Dal The δ 15 N profile for northwestern Pangea is from Knies et al. (2013Knies et al. ( , 2022 and Grasby et al. (2016), and that of the Northern Deepwater Basin is from Du et al. (2021). LOESS smoothing was applied to curves to highlight long-term changes. ...
Global warming, widespread oceanic anoxia and stagnation, and large perturbations of the global carbon cycle characterized the end-Permian to Middle Triassic interval. Nitrogen isotopes of marine sediments (δ15Nbulk) decreased through the Permian–Triassic transition, implying development of nitrate-limited and ammonium-dominated conditions (i.e., anaerobic marine N cycle) in Early Triassic oceans, which may have contributed to the delay in marine biotic recovery following the end-Permian mass extinction. However, the temporal evolution of the nitrogen cycle and the role of nutrient supply in marine ecosystem recovery during this interval remain poorly understand. Here, we present a new high-resolution Permian–Triassic nitrogen isotope curve from the Nanpanjiang Basin of South China. Low δ15N (−2‰ to +2‰) during the Griesbachian-to-Smithian substages (i.e., first ∼2 Myr of Early Triassic) reflects enhanced nitrogen fixation concurrently with climatic hyperwarming and expansion of oceanic anoxia. A large rise in δ15N (to +8‰) followed by a decline (to −2‰) reflects an aborted recovery of the marine N cycle during the Spathian substage of the Early Triassic. During the Middle Triassic, δ15N fluctuations between +1‰ and +4‰ during the Anisian Stage, followed by stabilization around +4‰ in the Ladinian Stage, suggest a slow stepwise re-establishment of the aerobic marine N cycle. Although both South China and northwestern Pangea experienced a transition to anaerobic N cycling during the Early Triassic, South China experienced an earlier and more rapid onset of this event as well as larger N-cycle fluctuations during the recovery interval than northwestern Pangea. Overall, N cycle changes coincided with those in paleotemperature and ocean-redox state, demonstrating an integrated response of the marine system to the extreme environmental perturbations of the Early Triassic. In summary, our results support persistence of nutrient-N-limited conditions and strong microbial N-fixation throughout the Early Triassic, with a full return to the aerobic N cycle only after stabilization of oceanic environmental conditions during the Middle Triassic.
... The Permian-Triassic mass extinction (PTME) is the largest known biological catastrophe of the Phanerozoic (Erwin, 1994;Shen et al., 2011;Song et al., 2013a;Dal Corso et al., 2022). The recovery of marine ecosystems from the PTME was very long (~5 Ma) (Lehrmann et al., 2006;Tong et al., 2007a;Chen and Benton, 2012;Brayard et al., 2017), and a number of studies have demonstrated that stressed oceanic conditions-including oceanic anoxia (Bond and Wignall, 2010;Song et al., 2012;Grasby et al., 2013;Lau et al., 2016;Zhang et al., 2018), high temperatures Sun et al., 2012;Romano et al., 2013;Trotter et al., 2015;Chen et al., 2016), large perturbed marine carbon and sulfur cycles (Payne et al., 2004;Tong et al., 2007b;Horacek et al., 2007aHoracek et al., , 2007bClarkson et al., 2013;Song et al., 2013bSong et al., , 2014bStebbins et al., 2019), enhanced weathering (Huang et al., 2008;Algeo and Twitchett, 2010;Song et al., 2015;Chen et al., 2020;Knies et al., 2022), and volcanic eruptions (Payne and Kump, 2007;Xie et al., 2010;Zhang et al., 2021b;Boscaini et al., 2022)-not only happened during the PTME, but also persisted until the late Early Triassic or early Middle Triassic (Algeo et al., 2011;Chen and Benton, 2012;Song et al., 2014a;Wei et al., 2015). ...
The Early Triassic records the largest inorganic carbon isotope excursions of the Phanerozoic. The causes of these enormous δ¹³C shifts remain unclear. Here, we present a new high-resolution marine carbonates δ¹³C record from the Yashan section in the northeastern Yangtze Platform of South China. The δ¹³C profile shows two significant positive excursions (with maximum δ¹³C values of ∼ +6‰ and ∼ +9‰, respectively) at the Induan–Olenekian boundary and Smithian–Spathian boundary, which is similar to what is recorded in the shallow platform in Nanpanjiang Basin and in the upper Yangtze Platform area. Negative δ¹³C excursions during the Griesbachian–early Dienerian, Smithian and middle Spathian, are coincident with warming intervals and accounted for by coeval peaks of volcanic activity (e.g., the release of CO2 from the Siberian Traps and arc volcanism). Enhanced marine primary productivity, as a final effect of massive carbon release, could account for the two positive δ¹³C excursions, with minor influence of local effects on the magnitude of the shifts. Although the age of volcanism after the Permian–Triassic mass extinction is still not constrained, more lines of evidence support a volcanism-temperature-weathering-productivity mechanism of δ¹³C perturbations during the Early Triassic.
The Early Triassic Smithian and Spathian time intervals are characterized by perturbations in the global carbon cycle, fluctuations in sea surface temperature, high turnover rates of marine nekton, and a change in terrestrial vegetation. Despite the importance of this time interval, comprehensive multiproxy investigations from Early Triassic high and middle latitude regions remain scarce due to the difficulty in accessing sections. The objective of this study is to increase our understanding of regional and local palaeoenvironmental and carbon cycle perturbations from a middle Smithian to late Spathian middle latitude section from Central Spitsbergen. Geochemical analyses show an increase in phosphorus and nitrogen just at and above the Smithian–Spathian boundary (SSB). High primary productivity led to increasingly anoxic conditions in bottom waters during the middle and late Spathian, enhancing the preservation of organic matter in the sediments. Anoxic conditions restrain phosphorus remineralization, allowing it to be recycled within the water column. This increase in anoxia is consistent with observations in other Arctic basins, demonstrating larger regional similarities in palaeoenvironmental conditions. The fluctuations in isostatic and eustatic sea levels affected organic carbon sequestration by regulating organic matter mineral interactions via the control of grain size within the sediment. This study demonstrates that local organic carbon sequestration in the Barents Sea shelf during the Spathian was influenced by a multitude of factors, including sedimentology, redox conditions, nutrient availability, and primary productivity.
Smøla island, situated within the mid-Norwegian passive margin, contains crystalline-basement-hosted intricate fracture and fault arrays formed during a polyphase brittle tectonic evolution. Its detailed study may strengthen correlation attempts between the well-exposed onshore domain and the inaccessible offshore domain, further the understanding of the passive margin evolution, and provide useful constraints on petrophysical properties of fractured basement blocks. A combination of geophysical and remote sensing lineament analysis, field mapping, high-resolution drill hole logging, 3D modelling, petrographic and microstructural studies, and fault gouge K–Ar geochronology made it possible to define five deformation episodes (D1 to D5). These episodes occurred between the post-Caledonian evolution of the regional-scale Møre–Trøndelag Fault Complex (MTFC) and the Late Cretaceous and younger crustal extension preceding the final stages of Greenland–Norway break-up. Each reconstructed deformation stage is associated with different structural features, fault and fracture geometries, and kinematic patterns. Synkinematic mineralisations evolved progressively from epidote–prehnite, sericite–chlorite–calcite, chlorite–hematite, hematite–zeolite–calcite, to quartz–calcite. K–Ar geochronology constrains brittle deformation to discrete localisation events spanning from the Carboniferous to the Late Cretaceous. Multiscalar geometrical modelling at scales of 100, 10, and 1 m helps constrain the extent and size of the deformation zones of each deformation episode, with D2 structures exhibiting the greatest strike continuity and D1 features the most localised. Overall, the approach highlighted here is of great utility for unravelling complex brittle tectonic histories within basement volumes. It is also a prerequisite to constrain the dynamic evolution of the petrophysical properties of basement blocks.
The age and formation of the Scandinavian mountains and the Norwegian strandflat have long been the subject of dispute. Some researchers argue that the present-day mountains are remains of the Caledonian orogen while others claim that the Caledonian nappes after erosion were buried by Mesozoic sediments and subsequently exhumed. In order to clarify these issues, we have studied remains of chemically weathered rocks (saprolites) from the coast to the interior of central Norway. The multidisciplinary study includes digital topography, electrical resistivity tomography (ERT), XRD, XRF, palynological analyses and K–Ar dating of samples from outcrops, trenches and core drilling. The coastal areas are dominated by an outer strandflat and an inner joint-valley landscape, while the interior is characterised by smoother landscapes referred to as palaeo-surfaces. Remnants of pre–Tertiary weathering occur in the joint valley landscape as well as on the palaeo-surfaces. The saprolites are found within fault- and fracture-zones and at depths exceeding 50 m in drillholes. It is suggested that the old saprolites were strongly eroded along the coast and in the fjords and valleys such as in Orkdalen and Sunndalen. K–Ar dating of mainland clay alteration most frequently yielded Jurassic ages along a profile extending from the coast to the Dovrefjell mountains (c. 1400 m a.s.l.). The formation age of the smectite- and kaolinite-containing saprolites seems to be almost contemporaneous along this profile implying that the entire area was subject to weathering in a warm and humid climate, such as prevailed during the Late Triassic and Jurassic. Palynological residues containing thermally altered Triassic and Jurassic pollen and spores in the clay-infected bedrock lend support to the saprolite interpretation. The Mesozoic landscape in central Norway was consequently shaped by uplift and deep weathering in the Jurassic. The entire Trøndelag county was most likely covered by Mesozoic sedimentary rocks until Cenozoic exhumation. The landscape was modified by Cenozoic tectonic uplift and erosion, and finally reworked by Pleistocene glacial erosion. We therefore conclude that both the observed saprolites and the shape of the present-day landscape in central Norway give a strong impression of the original Jurassic weathering surface.
