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Deconvolving Signals of Tectonic and Climatic Controls From Continental Basins: An Example From the Late Paleozoic Cumberland Basin, Atlantic Canada
Abstract
The internal architecture and external form of fluvial channel bodies is governed by both intrinsic and extrinsic controls. Extrinsic controls such as climate, eustasy, and tectonism are believed to have modest effects on channel-body types and geometries in high-subsidence settings. The effects of climate are particularly cryptic in high-accommodation settings and have proven extremely difficult to separate from other extrinsic controls such as tectonics and eustasy. The thick successions preserved in such basins have the potential to be relatively stratigraphically complete and are, therefore, valuable for interpreting basin evolution. This study documents the external geometry and internal architectural styles of fluvial channel bodies in a spectacularly exposed, 7-km-thick, Mississippian–Permian section from the Cumberland Basin, Atlantic Canada. Four fluvial styles are recognized: perennial, strongly seasonal, ephemeral, and fixed. Fluvial styles are not randomly distributed throughout the stratigraphic succession; instead discrete stratigraphic intervals consist of predominantly one type of fluvial style. Four stratigraphic intervals (E1–E4) in which strongly seasonal fluvial styles are predominant are recognized and alternate with intervals that are characterized by either perennial or ephemeral deposits. This suggests that a coherent record of climate change as manifested by changes in precipitation and runoff regime is recorded in the internal architecture of sandbodies.
... In non-marine strata, parasequences, parasequence sets and key surfaces are not easy to identify. Nevertheless, sequences and systems tracts in non-marine strata can be identified according to changes in facies associations, architectural styles and the geometries of depositional channels that are in response to variations in the rate of accommodation creation and fluvial discharge (Allen et al., 2013;Currie, 1997;Martinsen et al., 1999). Non-marine depositional sequences can be subdivided internally into three systems tracts (lowstand, transgressive and highstand; Catuneanu, 2006;Shanley & McCabe, 1994), which are analogous to those of marine successions (Catuneanu, 2006). ...
... Overall, tectonism, specifically the rapid uplift of the footwall and propagation of the normal faults, creates the accommodation in the hanging wall and more generally affects the gradients and river patterns that control hinterland transport capacity (for example, Gulf of Corinth: Gawthorpe et al., 2018). Climate fluctuations in the drainage basin lead to changes in sediment + water supply and transport capacity (Allen et al., 2013) and the climate at the lake affects evaporation. ...
Upper Palaeozoic lacustrine basin deposits not only record local tectonism but are also an archive to evaluate global palaeoclimate changes linked to the Late Palaeozoic Gondwanan ice age. The Tournaisian Horton Group of Nova Scotia, south‐east Canada, accumulated in rift basins following the final accretion of peri‐Gondwanan terranes to the Appalachians. Sedimentology, mineralogy and geochemistry of the well‐exposed sandstones and shales at the classic Blue Beach section ( ca 353.5 to 352 Ma) reveal the interplay of local tectonism and global climatic controls on lacustrine sedimentation. The lacustrine depositional environment gradually transitioned from deep water offshore at the base of the section to wave‐dominated and fluvial‐dominated nearshore at the top. Multiple small transgressive‐regressive sedimentation cycles have an average 21 ka duration, likely related to Milankovitch cyclicity. Unusually abundant soft‐sediment deformation structures (SSDS) and landslides are the sedimentary responses to frequent earthquakes during the most active phase of rift subsidence. The overall succession shows changes from a shallowing‐up balanced‐filled to an overfilled lacustrine basin. The chemical weathering intensity index and the Th/K ratio show a longer‐term trend from dry and cool conditions low in the section to humid and warm conditions near the top, with rapid change in the transition period. The section records the peak of the global mid‐Tournaisian carbon isotope excursion and the corresponding cooling event (354 Ma to approximately 351 Ma). The sedimentary succession is a response to long‐ and short‐term climatic cycles influencing lake level and sediment supply during the time of maximum rift basin subsidence recorded by the soft‐sediment deformation structures.
... In non-marine strata, parasequences, parasequence sets and key surfaces are not easy to identify. Nevertheless, sequences and systems tracts in non-marine strata can be identified according to changes in facies associations, architectural styles and the geometries of depositional channels that are in response to variations in the rate of accommodation creation and fluvial discharge (Allen et al., 2013;Currie, 1997;Martinsen et al., 1999). Non-marine depositional sequences can be subdivided internally into three systems tracts (lowstand, transgressive and highstand; Catuneanu, 2006;Shanley & McCabe, 1994), which are analogous to those of marine successions (Catuneanu, 2006). ...
This study aims to interpret and document the depositional architecture styles and sequence stratigraphic framework of the Ash Shumaysi Formation in the Jeddah‐Makkah region, the west‐central part of Saudi Arabia, and presents an example of rarely discussed, local‐scale sub‐basins (half grabens). It also shows the relationships between synchronous sedimentary processes and pre, syn and post‐rift conditions. The described lithofacies and their facies associations indicate the presence of seven architectural depositional styles: proximal‐distal braided fluvial, meandering fluvial (point bar), crevasse splay, floodplain, estuarine and lacustrine. A proposed depositional model for the Ash Shumaysi Formation is drawn. The Ash Shumaysi Formation forms a second order depositional sequence, which is organised into two third order depositional sequences (sequences I and II) bounded by three sequence boundaries. Each third‐order sequence encloses the low accommodation systems tract and high accommodation systems tract. The low accommodation systems tract represents the coarse‐grained, braided‐distal fluvial facies developed during low accommodation space associated with high sediment supply (high discharge). The high accommodation systems tract encloses the fine‐grained deposits of point bar, estuarine and lacustrine facies that reflect the creation of significant accommodation space and low sediment supply (low discharge). Vertical and lateral variations of the inferred depositional architectural styles, sequences and systems tracts reflect that tectonic forces and climate are the main controlling factors during deposition of the Ash Shumaysi Formation, although base‐level changes in response to sea‐level changes cannot be ruled out.
The Antigonish sub-basin lies within the late Paleozoic Maritimes Basin of Atlantic Canada. Late Devonian to early Carboniferous basin development resulted in a basin-and-range topography, within which the clastic Horton Group was deposited in grabens and half-grabens. The overlying Visean Windsor Group contains substantial evaporite units; later basin development was accompanied by expulsion of these evaporites. In the Antigonish sub-basin a significant stratigraphic omission surface initially described as a thrust was subsequently reinterpreted as the extensional Ainslie Detachment. This surface can be examined in drill-core, where the halite-bearing interval is reduced to 3.8 m of halite-cemented breccia of sedimentary rock fragments. The halite cement is sub-horizontally foliated and lineated. At Lakevale an outcrop section of the Windsor Group is reduced in thickness to tens of metres. Above a basal limestone unit containing pseudomorphs of gypsum, most of the Windsor Group is represented by sedimentary-clast breccias which resemble those seen in core, but with the halite removed by solution in the near-surface environment. The stratigraphic record within the sub-basin implies that expulsion of lower Windsor salt was initially toward the edges of the basin where rising diapirs blocked the deposition of Middle Windsor group, but in the basin centre a second salt unit was deposited. Subsequently, during contractional inversion of basin-bounding faults, the middle Windsor salt was expelled into diapirs near the centre of the basin. The Ainslie Detachment is reinterpreted as a primary salt weld: a boundary between units formerly above and below expelled lower Windsor evaporites. The resulting stratigraphic omissions and structures match those seen above expelled evaporite layers on continental margins.
Water discharge and sediment flux variations are important parameters controlling the morphodynamic behaviour of rivers. Although quantitative estimates for water discharge and sediment flux variability are well-constrained for modern rivers, far fewer assessments of flow and sediment flux intermittency in ancient fluvial systems from the rock record are available. In this study, a relationship between water discharge, sediment flux variability and patterns of changing flu-vial stratigraphic architecture in the Middle Eocene Escanilla Formation, Spain, is explored. Water discharge intermittency factor (I WF), calculated as a ratio of the total water discharge (over the averaging time period) to the instantaneous channel-forming water discharge if sustained for the same period, ranges from 0.03 to 0.11 in the high amalgamation intervals and from 0.10 to 0.32 in the low amalgamation intervals. Similarly, the sediment flux intermittency factor (I SF) is estimated to be in the range of 0.008 to 0.01 in the high amalgamation intervals and of 0.01 to 0.03 in the low amalgamation intervals. Consequently, high amalgamation intervals were most probably deposited under more intermittent and short-lived intense precipitation events while low amalgamation intervals were the result of less intermittent flows spread throughout the year. Overall, these estimates are consistent with values from modern ephemeral rivers typically found in arid to semi-arid climate and is in agreement with available proxy data for the Middle Eocene climatic context of the studied alluvial system. This highlights an important connection between hydroclimate, river morphodynamics and landscape evolution, and has implications to predict river flow and sediment transport across the Earth's surface in the geological past. K E Y W O R D S discharge intermittency, Escanilla Formation, flux intermittency, Middle Eocene, palaeohydraulics
One of the goals of sequence stratigraphy is to model the conditions that generate stratigraphic architecture at outcrop to basin scales. Accommodation and sedimentation are the principal variables included in sequence-stratigraphic models that describe facies architecture in marine successions. Similar models exist to describe wholly nonmarine architecture. Distinct models are commonly applied to basins containing predominantly lacustrine or predominantly fluvial facies, which can make it difficult to apply models to the entire history of a basin that may include both lacustrine-dominated or fluvial-dominated phases, depending on climatic and tectonic conditions. To account for these changing conditions over the history of nonmarine basins, we present a conceptual three-dimensional model that describes the potential architectural patterns under specific combinations of accommodation, sediment flux, and water balance. Sectors of the model delineate where basins are underfilled or overfilled with respect to accommodation and limited with respect to sediment and water, creating eight zones with different implications for the development of facies architecture. Different types of basins (e.g., foreland, extensional, pull-apart, intracratonic) show broadly different trends in architecture through time. Subtle changes in accommodation, sedimentation, and water balance in the model correspond to shifts in facies architecture between lithostratigraphic units, but architectural transitions within individual basins are more important indicators of evolving basin conditions than comparisons among all basins. This model may serve as a guide for comparing the influence of distinct drivers of architecture among different types of basins as well as identifying important intervals of change during the history of basin filling. The availability of commensurate data on the history of accommodation, sedimentation, and water balance is, however, an ongoing challenge to reconstructing complete basin histories. Future analyses will test how well predicted facies stacking patterns compare to observed nonmarine stratigraphic successions resulting from the combination of accommodation, sediment flux, and water balance during the history of basin filling.
The Himalayan foreland basin originated through the India–Asia continent–continent collision driven by downward flexing of the Indian plate. It forms an ideal assemblage to delineate the role of process-controlled sedimentary fill in basin evolution. This paper provides the first comprehensive account of the lithofacies associations and architecture of the Middle Siwalik succession of the Himalayan foreland basin in the south-central Himachal
Pradesh sector, India through detailed sedimentological analysis. Eight lithofacies form three distinct sand, gravel, and silt-mudstone lithofacies associations pertaining to specific depositional environments. Architectural elements have been defined together with bounding surfaces separating them.
Sedimentological investigations reveal that the Middle Siwalik sequence represents a flash flood dominated piedmont fan and proximal to middle megafan. The fan expansion cycles indicate tectono-climatically controlled sedimentation in the Middle Siwalik foreland basin. Frequent flooding and a high sedimentation rate were influenced by the tectonic uplift along the reactivated thrusts in the hinterland coupled with phases of
monsoonal intensification.
The Cumberland Basin is a key area in the regional nomenclature because it contains the type sections of the Cumberland and Pictou groups, and well exposed sections of strata traditionally assigned to the Riversdale group (abandoned) and Canso group (abandoned and replaced by the Mabou Group). The constitutent formations of the Cumberland and Pictou groups examined by this study include in ascending order: Cumberland Group, 1. Claremont and 2. Boss Point, (both formerly assigned to the Riversdale group, now abandoned); 3. Polly Brook (new); 4. Joggins (redefined); 5. Springhill Mines (new); 6. Ragged Reef (new); 7. Malagash (new); and Pictou Group, 8. Balfron (new); 9. Tatamogouche (new); and 10. Cape John (redefined. The revised Pictou Group; includes all of the redbed dominated, non coal-bearing strata above the Cumberland Group. -from Authors
The Boss Point Formation of Maritime Canada comprises alternating successions of braidplain sandstone, lacustrine mudstone, and lacustrine fluvio-deltaic sandstone and mudstone. These rocks were deposited within an active strike-slip basin during the early Pennsylvanian (Westphalian A), at a palaeolatitude of 8°S. Palaesols comprise a small but distinct proportion of the formation, and typically occur at the tops of fining upward sandstone–siltstone cycles. Spherulitic siderites from the Boss Point Formation occur within sandy and silty palaeosols. They occur as ‘large’ (> 200 µm) and ‘small’ (< 200 µm) diameter spherulitic nodules within calcrete, and show either a radially arranged ferroan calcite and siderite spar morphology, or contain a core of ferroan calcite, surrounded by a later formed sheath of siderite. Analytical data indicate that with respect to CaMgMn, wide compositional variation occurs within the siderites. The Boss Point Formation siderites are similar to, but contain less Ca for a given Mg/Mn ratio, than previously published siderite compositional data. Published data, together with the results from the Boss Point Formation, indicate that a continuum exists in freshwater siderites, between the relatively Mn-depleted and the Mg-enriched analytical fields that were previously reported. The relatively low Ca values determined in the Boss Point Formation samples reflect the general lack of calcium in the sedimentary basin during sedimentation. Both chlorite and smectite clays may have been important sources of iron. It is concluded that the spherulitic siderites are eogenetic, and formed within small anoxic ponds rich in organic matter, under reducing and low dissolved sulphate conditions. With time these pools dried up, ferroan calcite precipitating as calcrete nodules around the earlier formed siderite spherulites.
The continental sediments that accumulated in Provence during the Upper Cretaceous/Palaeocene are organized in several similar sequences that evolve from fluvial to lacustrine facies. A first attempt to analyse the parameters governing such a sequential arrangement persisting during some 30–40 m.y. is based on a detailed analysis of the two best preserved sequences (Rognacian–Vitrollian). The horizons of detrital sediments (quartz sand channel bodies, bars or sand sheet) developed in a braided system network which spread on a silty floodplain. Sediment supply was dominantly fine grained and water stage fluctuations were common. Sand bodies are the result of cumulative deposits of flood episodes; high stages are characterized by channel fill deposits, and low stage by build-up of sand bars and development of algal mats or oncolites. The lacustrine carbonate muds precipitated in shallow water depth lakes. Base level fluctuations controlled the sequential arrangement, and the carbonate muds were often subjected to subaerial exposure. Sediment supply was probably low as testified by the long periods of non-deposition, the intense bioturbation of the sediments, and the low detrital content of the lacustrine deposits. The basin palaeogeography is governed by two fault systems: an E–W oriented one that defined the drainage pattern, and a NNE–SSW one that controlled the lateral variations of facies. The braided system was, from time to time, bound by locally derived conglomerates which accumulated along the E–W oriented fault system and are evidence of tectonic pulses. The subsidence rate was fairly low (some 300 m over approximately 15 m.y.) and suggests at least a local compressional deformation. Based on the lithofacies arrangement, a model involving thrust and strike-slip displacement along the E–W trending system may be suggested. From the two analysed sequences, the lithofacies assemblages are governed by a combination of climatic influence controlling base level fluctuations as well as extensive pedogenesis, and of tectonic activity influencing sediment influxes as well as the evolution of depositional environments. Periods of tectonic quiescence and an average low rate of sediment influx allowed climatic influences on sediment to develop and be preserved. Such a balance, between braided fluvial and shallow lacustrine environments, was maintained over such a long period because the low rate of sediment influx roughly matched the subsidence rate. In this context, the environmental fluctuations linked with climatic or tectonic changes were only of limited amplitude.
Clastic deposits can be subdivided into microforms, mesoforms, and macroforms [using Jackson’s (1975) terminology], reflecting a range of physical scales of deposit and the time scale during which they form. A formal three-dimensional subdivision of some types of deposit, which clarifies these physical and temporal scales, can now be attempted using the concept of a hierarchy of internal bounding surfaces. Brookfield’s (1977) three-fold classification of eolian bounding surfaces is widely accepted. Allen’s (1983) comparable attempt to classify fluvial bounding surfaces is also useful but, it is suggested here, should be expanded to a six-fold hierarchy, mainly to facilitate the definition of macroforms.
