Linear dunes are rarely recognized in the geological record. By integrating sedimentological observations with aeromagnetic, magnetic susceptibility and magnetization datasets, we reconstruct the morphology of an Upper Triassic aeolian dune field from the sedimentary architecture of deposits preserved in the Sambaíba Formation, Parnaíba Basin, from northeast Brazil. This dune field was buried by lavas from the central Atlantic magmatic province. Aeolian architecture records the migration of superimposed crescentic dunes along the flanks of parent linear megadunes. These bedforms were part of a large aeolian dune field (>55,000 km2), comprising megadunes with east-northeast to west-southwest oriented crestlines, up to 167 m in height, and ~2.7 km in crest-to-crest spacing. Mantled by lava, it is the largest and best-preserved instance of a linear megadune field yet documented in the rock record. The dune field developed in response to the coalescence of north-easterly and south-easterly paleowinds driven by a monsoon system operating at low latitudes (~10°S) of Gondwana during the Late Triassic: this validates atmospheric circulation models which had lacked direct geological support. A Late Triassic aeolian megadune field preserved beneath lava flows in northeastern Brazil, identified by sedimentological and magnetic data, preserves extensive linear dunes whose presence validates simulated monsoon wind directions in low-latitude Gondwana.

This study investigates the influence of modeling choices related to the scale of reservoir heterogeneity on the predicted performance of geothermal doublets in fluvial low-enthalpy geothermal reservoirs. Fourteen geocellular grids were created to systematically analyze the impacts of numerical grid resolution, permeability upscaling methodology, and modeled scales of sedimentary architecture, using MODFLOW-2005 and MT3DUSGS to simulate groundwater flow and heat transport for well-doublet operation over a 35-year period. The results reveal complex relationships between these choices and simulated reservoir behavior: the considered factors have significant influence on injection pressures but only a modest effect on production temperatures (with variations within 2 degrees C after 35 years across all models), likely due, at least in part, to a relative dominance by thermal diffusion over heat advection in the considered scenarios. Simplification of geological architecture through omission of fine-scale features may augment the hydraulic impact of larger flow barriers, such as abandoned-channel mud plugs. The highest injection pressures were simulated on grids that embody sedimentary architectural elements but lack internal facies heterogeneity. The permeability upscaling method also has an effect: simulations on grids upscaled using harmonic averaging consistently yield the highest near-injector pressures, followed by those based on geometric averaging and arithmetic averaging. The dynamic behavior of grids upscaled via flow-based upscaling closely approximates that of grids upscaled using arithmetic averaging, suggesting that bulk hydraulic behavior is dominated by the connectivity of high-permeability units. The performance gap between grids following different upscaling methods decreases significantly for higher grid resolution. Simulations of geological models that incorporate increasingly detailed geological features predict cold-water plumes with slightly more complex shapes and tortuous fronts, as documented by values of plume surface-to-volume ratio. The complexity of the cold-water plume shape, as measured by the surface-to-volume ratio, is slightly higher for well doublets oriented at a high angle to the channel-belt axis, but does not increase systematically with the resolution at which fine-scale features are represented.

Machine-learning tools exist for classifying sedimentary units according to objective and verifiable labels (e.g., lithological types), but the role of geologists in interpretive facies analyses is considered irreplaceable. This study presents a machine-learning method for automating interpretations of fluvial sandbodies following an approach that mirrors the application of classic one-dimensional facies models presented as idealized vertical facies sequences. Ensemble decision-tree models were trained on descriptors of facies sequences (sandbody thickness, average facies thickness, facies proportion, and vertical thickness trend), documented in many geological analogues studied by different research groups, reflecting global sedimentological thinking. The data were synthesized in two alternative datasets of contrasting dimensionality (50 vs 26 features). Up to 1222 facies sequences were used for model training and testing, with data splits operated in different ways: (i) using a partition algorithm, with options to exclude data from two-dimensional outcrop panels and to prevent the same sedimentary bodies from occurring in both splits; (ii) by arbitrarily picking sandbodies that are thought to be easily misinterpreted. Four ensemble machine-learning models were applied to perform binary classifications of (i) fluvial sandbody types according to their general channel or overbank origin, and (ii) channel sandbody types according to the interpreted planform style of their formative rivers ('low-sinuosity or braided' vs 'meandering'). Across all training approaches, the models for general sandbody classification yield accuracy values ranging between 0.76 and 0.87: on average only 16% of sandbodies are misclassified. Comparable predictive power (accuracy: 0.75-0.91) is seen for models classifying formative river patterns from channel-body facies sequences, a result that challenges the much-cited notion that interpreting river planforms from vertical profiles of channel deposits is futile. A benchmark comparison against interpretations by eight sedimentologists demonstrates that cases of model misclassification are in line with errors by human geologists. The outcomes support the possibility of automating sedimentological interpretations of borehole observations (e.g., image logs) using models trained on geological analogues.

Clinoforms, as fundamental components in sedimentary basin fills, represent the preserved stratal expression of slope systems that link shallow-water and deep-water environments in carbonate depositional systems. Although large-scale carbonate clinoforms developed extensively in the Tarim Basin during the early Cambrian, their geometry, sedimentary evolution, and controlling factors have not yet been systematically studied. This research integrates 3-D seismic, drilling and well-logging data to perform a quantitative and systematic analysis of the seismic facies, geometrical characteristics, and depositional evolution of the Cambrian (Stage 3) Xiaoerbulake Formation clinoforms. A high-resolution sequence stratigraphic framework is constructed using the Integrated Prediction Error Filter Analysis (INPEFA) method. Seven distinctive seismic facies (SF1-SF7) are identified in the study area; these correspond to seven facies belts distributed in three depositional environments: mixed tidal flats, inner ramp and middle ramp. The analysis recognizes five higher-order composite clinothems (CC1-CC5) and seventeen subordinate clinoforms (C1-C17). Collectively, these record an overall progradation from southwest to northeast. Clinoform-edge trajectory patterns initially exhibit an aggradational trend that progressively transitions to a predominantly progradational trend. Two 3rd-order sequences (SQ1 and SQ2) are distinguished within Stage 3, each containing multiple 4th- and 5th-order sequences. SQ1 comprises CC1-CC3 (C1-C10), whereas SQ2 comprises CC4-CC5 (C11-C17). The early depositional system is characterized by a gently inclined carbonate ramp system, whereas the later stage evolves into a distally-steepening ramp. The development of these clinoforms was controlled by the interplay of several factors. Relative sea-level fluctuations directly controlled available accommodation and the resultant geometry of developed clinoforms. The spatial variability of paleogeomorphological features, such as a central depression surrounded by elevated margins, governed accommodation and controlled clinoform trajectory, progradation distance, and aggradation thickness. Moreover, paleoclimate and paleoceanographic conditions indirectly influenced clinoform development by modulating carbonate production and hydrodynamic energy. This study addresses the knowledge gap concerning the sequence-stratigraphic evolution of carbonate clinoforms on a ramp and clarifies the main controlling factors on clinoform growth. These findings provide valuable insights into the evolution of ancient carbonate ramps and contribute to a more comprehensive understanding of global carbonate clinoform systems.

Deeply buried (>7000 m) Middle Cambrian (Miaolingian) carbonate rocks in the northern Tarim Basin, China, represent a highly promising target for resource exploration. Their reservoir quality is governed by complex diagenetic processes, including multiple stages of dolomitization and subsequent dedolomitization. This study presents an integrated analysis using petrology, stable isotopes, trace elements, fluid inclusion microthermometry, and in situ U–Pb dating from seven wells. We systematically interpret the complex diagenetic history and fluid evolution of the Miaolingian carbonates. Results reveal a complete paragenetic sequence from near-surface to deep-burial diagenetic realms. Early diagenesis was dominated by marine-derived fluids in near-surface to shallow-burial realms, where supratidal and seepage–reflux dolomitization led to the formation of early dolomicrite (Md1) and grainy/microbial dolomite (Md2), along with the precipitation of dogtooth/fibrous cements (Cd1). With increasing burial depth, normal seawater influenced by geothermal circulation formed very fine- to fine-crystalline dolomite (Md3) and associated granular cements (Cd2). In the intermediate- to deep-burial realm, the diagenetic system was dominated by basinal fluids. The fabric of early dolomites was destroyed under elevated temperatures (∼110 °C) to form fine- to medium-crystalline dolomite (Md4). This was followed by cementation of euhedral (Cd3) and blocky (Cd4) dolomite cements. Late-stage diagenesis was tightly coupled with regional tectonic activity. Saddle dolomite (Sd) precipitated from high-temperature (∼139 °C), high-salinity (∼22 wt.%) tectonic–hydrothermal fluids, and some Md4 may have been altered by these fluids. U–Pb dating of early calcite cements (Cc-Ⅰ) yields an age of 459.1 ± 3.3 Ma, constraining the initial episode of the middle Caledonian Orogeny. Fluid inclusions within these cements have high temperatures (110.2–125.2 °C) and exhibit seawater-like rare earth elements and yttrium (REY) patterns, indicating a record of buried formation water. Subsequently, episodes II and III of the middle Caledonian Orogeny induced fluid mixing between Ca2+-rich formation water and meteoric water in the intermediate burial realm, causing localized dedolomitization that formed matrix calcite (Mc) and late-stage calcite cements (Cc-Ⅱ), characterized by lower homogenization temperature (Th) values (∼90–110 °C). Integration of diagenetic phases with reservoir quality reveals contrasting porosity evolution. Seepage–reflux and seawater dolomitization were the constructive processes, while supratidal, burial and hydrothermal dolomitization, and dedolomitization were predominantly destructive, occluding pore space and deteriorating reservoir quality.

Documenting coeval sedimentary processes across continental to marine systems is challenging, especially in cases with poor preservation, uncertain correlations, and limited data. Outcrops of the Carboniferous Millstone Grit Group in Nidderdale, North Yorkshire, England, record mechanisms of sediment transport and deposition, and associated facies changes, across an ancient coastal plain to submarine ramp. The aim is to document controls on sedimentation from fluvial to deep-water systems via ramp-hosted deltas, and to determine why and how sediment is stored in each palaeoenvironment. Twenty-seven sedimentary logs (totalling ca. 470 m) were recorded from two correlated quarries and adjacent outcrops exposing a vertical rock unit of similar to 160 m. Nineteen facies were identified and assigned to ten facies associations; integration with photo panels allowed interpretation of architectural elements and construction of depositional models. The following depositional environments were recognised: (i) mudstone-dominated offshore marine ramps intercalated with turbidites, (ii) heterolithic delta lobes, (iii) lower delta plains with distributary channels, (iv) upper delta plains, (v) alluvial plains with fluvial channel belts. The recognised architectural elements record relationships between coevally active and neighbouring depositional environments. Results demonstrate mechanisms of sediment transport across a sand-prone fluvial coastal plain, via a river-dominated delta, to a submarine ramp with turbidites. This model of sediment transport from continental to marine realms provides a predictive framework applicable to subsurface analogues to help predict the distribution of sedimentary facies, bounding surfaces, architectural changes, and stratigraphic evolution of depositional environments across a linked fluvio-deltaic to submarine systems in deltaic ramp settings.

Calculating the strike-slip component of fault displacement is challenging, making quantitative determination of the kinematic properties of a fault zone difficult. This study introduces a novel fault zone model to offer improved opportunities to reconstruct the history of fault evolution. We provide a new quantitative calculation method of fault geometry that can identify piercing points where branch faults are offset by a master fault. This method is based on the geometric relationships between the attitude of a master fault and its branch faults. From these observations, it is possible to quantitatively calculate the displacement components and kinematic properties of a fault zone. Additionally, the existing stereographic projection method is adapted by considering the attitude of fault planes to provide an alternative approach to solve the problem of fault kinematics. This method can be used to derive the pitch angle of a fault with the new model by analyzing the intersection attitudes of a master fault and its branch faults through intersecting planes. Applied to 3D seismic data with well control from the Jiyang Depression, results show higher strike-slip intensity near principal displacement zones adjacent to the Tan-Lu and Lan-Liao fault zones, whereas extensional deformation dominates the central sector. Moreover, both methods yield consistent results in reconstructing the structural history of fault zones. This demonstrates the practical application of the new model and demonstrates that methods employed for the model can be used in the kinematic analysis of fault zones more generally, which has previously been challenging in subsurface studies.

Sedimentological analysis of the outcropping Sherwood Sandstone Group, northern Cheshire Basin, UK, documents the preserved stratigraphic expression of water table-controlled aeolian-dominated erg-margin successions (Wilmslow Sandstone Formation and lower Helsby Sandstone Formation), overlain by dryland fluvial deposits (middle Helsby Sandstone Formation). A quantitative assessment of sedimentary architectures and a comparison with analogous depositional systems reveals that strata of the Sherwood Sandstone Group are similar to other aeolian-dominated successions that also accumulated in rift basins, in erg-margin settings and where the water table interacted with the sediment surface. In stratal successions of erg-margin origin in the Wilmslow Sandstone Formation and Helsby Sandstone Formation, the dominant facies associations comprise: (i) thin cross-bedded dune sets characterized by foreset-toeset grainflow strata; and (ii) lenticular bodies of dry and damp-to-wet interdune strata. Together, these associations record accumulation of small, rapidly migrating transverse or oblique dunes, and intervening isolated interdune depressions. Two types of interdune deposits are observed: (i) near-horizontal wind-ripple laminated sandstone; and (ii) irregular to wavy-laminated sandstone with adhesion strata. These deposits indicate dry and damp-wet surface conditions, respectively. Dune climbing is demonstrated by the interfingering between dune toesets and interdune strata; this was enabled by accommodation generation driven by fault-related subsidence and associated relative water-table rise. Accumulation via climbing at very low angle but net positive, else by non-climbing mechanisms, is demonstrated by erosional, sharp dune-interdune bounding surfaces, which likely developed during slowdowns in subsidence rate. Episodic absolute water-table rise may have occurred during wet seasons or due to intense precipitation events, potentially in a monsoon climate. Water-table fluctuations may have also occurred in response to longer-term climatic perturbations following the Permian-Triassic mass extinction event. This study helps to constrain the factors controlling the accumulation of Triassic aeolian and mixed aeolian-fluvial successions, and their long-term preservation. Quantitative models are proposed to explain aeolian dune-interdune facies architectures. These can be used to guide predictions of three-dimensional sedimentary heterogeneity in the subsurface.

Determining the provenance history of Jurassic sediments in the southwestern Tarim Basin is crucial for deciphering the tectonic evolution of the Western Kunlun-Pamir Paleo-Tethys Realm, which forms the northwesternmost segment of the Himalayan-Tibetan Plateau. Yet, the detailed spatial provenance variation of these strata is poorly constrained. This study integrates field observations from three outcropping sections (cumulative thickness of similar to 6800 m) and three wells (similar to 3600 m) from four distinct regions: Qimgan, Oytag, Toyunduk-Kyzyltau, and Fusha. Samples were collected for analysis of sandstone petrology (n = 54), heavy mineral assemblages (n = 18), and detrital zircon U-Pb geochronology (n = 10) to delineate the spatial differences in Jurassic provenance. The results indicate that the southwestern Tarim Basin can be demarcated into two tectonic domains: (1) Detrital zircons in the Qimgan and Oytag regions were predominantly derived from nearby Triassic backarc volcanic rocks. Additionally, late Paleozoic subpopulations were sourced from a volcanic sequence exposed in the northeastern part of North Pamir Terrane, induced by Carboniferous-Permian Paleo-Tethys subduction. North Pamir Terrane served as the main elevated source area, with negligible contributions from Central and/or South Pamir terranes. (2) The detrital zircons of early Paleozoic and Neoproterozoic ages from the Toyunduk-Kyzyltau and Fusha regions predominantly originated from the North Kunlun and South Kunlun terranes in response to Triassic collisional orogeny that induced significant uplift, effectively disconnecting the more distant provenance areas of the Tianshuihai and/or Songpan-Ganzi terranes. Insights from provenance analysis permit the delineation of a refined geodynamic model for the tectonic evolution of the closure of the Western Kunlun-Pamir Paleo-Tethys Realm. This study demonstrates Triassic backarc volcanism in the northeastern Chinese Pamir region, which supports a previously proposed hypothesis. These findings not only deepen our insights into the tectonic evolution of the Western Kunlun-Pamir Paleo-Tethys Realm but also significantly enhance our understanding of the dynamics of sedimentary basins, crustal development, and resource prospecting within convergent orogenic settings.

The sedimentary architecture of carbonate platforms is determined by distinct paleobiological, tectonics, climatic, oceanic and environmental conditions. During the Cambrian period, a rimmed carbonate platform system developed over an area of similar to 28 x 10(4) km(2) in the Tarim Basin. However, the evolution mechanism and its predominant controlling factors remain poorly understood. The investigation utilized integrated analysis of cores, thin sections, 3-D seismic, well logging and geochemical data to explain the sequence stratigraphic framework, depositional architecture and main controlling factors. Sixteen distinct microfacies (MF1-MF16) are identified based on thin-section analysis of the five lithofacies, which could be further grouped into fourteen microfacies associations (MA1-MA14). These fourteen microfacies associations respectively represent fourteen facies belts of the five facies of the shelf, outer ramp, middle ramp, platform margin and restricted platform. Microfacies and seismic characteristics have provided the basis for establishing a sequence-stratigraphic framework. Two regionally extensive second-order sequences (CS1-CS2) are developed in the Lower-Middle Cambrian succession; CS1 incorporates five third-order sequences (Sq1-Sq5); CS2 incorporates three third-order sequences (Sq6-Sq8). The lateral migration and vertical arrangement of depositional facies resulted in a unique depositional architecture. The overall carbonate platform architecture is interpreted from 3D seismic data, integrated with the depositional facies interpretations to document the evolution of the depositional setting over time from a broad shelf (Sq1-Sq2), to a distally steepening ramp (Sq3-Sq4), to a weekly rimmed platform (Sq5), and finally to a strongly rimmed platform (Sq6-Sq8). Relative sea-level (RSL) curves were reconstructed through an integrated analysis of Fischer plots from three wells. The determined RSL curve matches closely with reconstructed paleo-water depths indicated by the distribution of microfacies types. The inferred paleo-water depths changes comprise two long-term shallow-deep-shallow trends, upon which eight intermediate-term cycles are superimposed. Microfacies also have been applied to explain the evolution of the platform in response to RSL change and other environmental factors. A major transgression occurred in the lower parts of CS1. Results demonstrate that RSL and paleo-water depth changes in the Lower-Middle Cambrian are consistent with known global sea-level changes indicated by geochemical elements. The architectural and sequence-stratigraphic evolution of the progradational rimmed carbonate platform was controlled principally by eustasy. This study is important due to the limited information on Cambrian rimmed platforms.

The Upper Cretaceous Daijiaping Formation of the Chaling Basin, southeast China, is a mixed aeolian-fluvial succession accumulated in an erg-margin setting. The roles of climate and tectonics in governing the temporal and spatial arrangement of aeolian and fluvial strata are investigated using lithofacies and architectural-element analyses of outcrops in the eastern part of the basin. Architectural elements of aeolian origin record the preserved expression of dunes, sandsheets, damp and wet interdunes, and sand pods. Architectural elements of alluvial origin record channelized bedload streams and cobble-sand sheetflow units. Distinctive deflation lags and desert pavements are also recognized. The alternating nature of deposition via aeolian and aqueous processes is marked by a series of sand-drift surfaces that form a record of repeated shifts from aeolian to water-lain depositional conditions. Ephemeral water influx to the desert-margin system likely occurred in response to exceptional rainfall caused by monsoonal water discharge and meltwaters from glaciated mountain ranges that bordered the basin. The vertical arrangements of alternating facies associations define stacked wetting-upward cycles, each 0.4-14.2 m thick. Each cycle commences with simple or compound crescentic dune deposits, else with aeolian sandsheet deposits. These are overlain by bedload stream or conglomerate sheetflow deposits. The vertical stacking of these different architectural elements records the contraction and expansion of erg-margin systems in response to climate-controlled variations in the groundwater level, sand availability for aeolian transport, and fluvial and aeolian sediment transport capacity. The stratigraphic evolution was controlled by exceptional rainfall events at the basin margin, consequent floods into the dune-field margin and associated fluctuations in the water-table level. Orogenic uplift, a subtropical high-pressure system, and a variable groundwater level controlled by a monsoon climate and tectonic subsidence resulted in the development of extensive aeolian desert depositional systems in the South China hinterland during the Late Cretaceous.

The hanging-wall ramps of rift basins are prone to the accumulation of large sedimentary bodies and are potential areas for the presence of large subsurface geological reservoir volumes. This paper comprehensively utilizes data from sedimentology, seismic reflection, geochemistry, and palynology to study the paleotopography, water conditions, paleoclimate, and sediment supply of the fourth member (Mbr 4) of the Shahejie Formation in the Raoyang Sag of the Bohai Bay Basin, China. The sedimentary characteristics, evolution, and preserved stratigraphic architectures of shallow-water deltaic successions are analyzed. Multiple indicators—such as sporopollen, ostracoda, fossil algae, major elements, and trace elements—suggest that when Mbr 4 was deposited, the climate became progressively more humid, and the lake underwent deepening followed by shallowing. During rift expansion, the lake level began to rise with supplied sediment progressively filling available accommodation; sand delivery to the inner delta front was higher than in other parts of the delta, and highly active distributary channels formed a reticular drainage network on the delta plain, which was conducive to the formation of sandstone up-dip pinch-out traps. In the post-rift period, the lake water level dropped, and the rate and volume of sediment supply decreased, leading to the formation of a stable dendritic network of distributary channels. At channel mouths, sediments were easily reworked into sandsheets. The distribution of sandstone and mudstone volumes is characterized by up-dip pinch-out traps and sandstone lens traps. The network of channel body elements of the shallow-water deltaic successions is expected to act as an effective carbon dioxide storage reservoir. This study reveals the influence of multiple factors on the sedimentary characteristics, evolution, and internal network of shallow-water deltas at different stages of rift basin evolution. This knowledge helps improve resource utilization and the sustainable development of comparable subsurface successions.

Geogenic arsenic in soils and aquifers is a threat to public health, which can be mitigated by improving our understanding of arsenic distribution in natural environments. In alluvial plains traversed by meandering rivers, solid- and aqueous-phase arsenic concentrations tend to vary across sedimentary deposits accumulated by different processes linked to river morphodynamics: mud-prone and commonly organic-rich abandoned-channel fills arising from meander cut-off act as local sources of arsenic, which can be transferred to adjacent point-bar deposits related to meander growth. Meanwhile, spatial variability in arsenic contamination may also arise from variations in sediment provenance across a fluvial landscape, and from inherent downstream changes in a fluvial system. Yet, the relative importance of facies and provenance as controls on arsenic concentrations in fluvial sediments still needs to be assessed. Through integrated analyses of geomorphological, sedimentological and geochemical data, this study examines the spatial variability in arsenic distribution from deposits of the late Holocene channel belt of the Po River, Italy. Three study areas were investigated along a >100 km stretch of channel belt to evaluate the possible roles of downstream changes in river behaviour and sediment supply from variably arsenic-rich catchments. Sedimentological controls on solid-phase arsenic concentrations are recognized at the scales of both elementary lithologies (facies) and depositional sub-environments, highlighting the roles of morphologically recognizable abandoned-channel fills as sources of arsenic that can be mobilized via groundwater flow and become trapped in point-bar elements. Although solid-phase arsenic concentrations are dominantly related to the presence of organic matter and clay, local arsenic enrichment may be related to arsenic advection across meander-belt sediments, a process that is itself controlled by petrophysical heterogeneity. No evident relationship is seen between arsenic concentrations and point-bar facies distributions related to styles of meander morphodynamic evolution. Yet, limited variability across the study areas suggests that the facies control remains dominant over a potential provenance control related to catchment integration. The results help elucidate the role of sedimentary heterogeneity in the distribution of arsenic in sediments, soils and aquifers, in the Po Valley and other analogous fluvial environments.

Palaeosols are common in sedimentary successions of continental origin, and notably they comprise the majority of the thickness of some accumulated successions of fluvial origin. Yet, detailed investigation of palaeosols and evaluation of their palaeoenvironmental significance are not routinely undertaken in detail in many sedimentological studies. A careful analysis of palaeosols may, however, reveal that sedimentary units, which appear similar if based solely on the facies analysis, indeed show strongly distinct palaeoenvironmental and depositional characteristics. This is the case of the upper portion of the Bauru Group, a 100-190 m-thick Maastrichtian red sandstone unit of fluvial origin, present over an area of c. 180,000 km2 in south-eastern Brazil. In this study, the palaeosols of this unit, which constitute 25-92 % of the succession by thickness, are used to decipher palaeoenvironmental climate conditions, sediment source areas, and relationships between pedogenic and depositional processes. Through the combined study of macroscopic, micromorphological, and geochemical aspects of the palaeosols and of facies analysis of the deposits, the upper portion of the Bauru Group succession is separated into three sectors: north -western, north-eastern, and south-eastern. Although these three areas are all characterised by similar lithology types and lithofacies, indicative of deposition in alluvial systems, the palaeosol analysis highlights that they were each characterised by different climate, different clastic source areas and different dynamics and interaction of the pedogenic and sedimentary processes. This research reveals the critical significance of the palaeosols for discriminating otherwise apparently similar depositional units. (c) 2024 Elsevier B.V. All rights reserved.

In the present study, different geocellular models of meander-belt stratigraphic architectures were produced that are representative of the sedimentary products of sand-bed meandering rivers and their petrophysical heterogeneity. The static models were created by combining a rule-based stratigraphic modelling approach with geostatistical modelling, and were applied in groundwater-flow and heat-transport simulations using MODFLOW-2005 and MT3D-USGS software. Overall, histories of injected cold-water plume propagation were examined considering: (i) three architectural frameworks as representative of different river morphodynamics; (ii) four scenarios of facies architecture; and (iii) alternative well layouts. The presence, size and spatial distribution of sedimentary heterogeneities related to river hydrodynamics, channel-form abandonment or modes of meander-transformation are seen to control the shape of the thermal plume, thereby affecting well-doublet performance. The considered scenarios of facies make-up for point-bar deposits have a modest influence on the temperature decline near the abstraction well. The presence of sandstone beds in the lower heterolithic parts of abandoned-channel fill does not facilitate significant thermal-plume expansion beyond the mud-plug. The effect of basal lags made of open-framework conglomerates on heat advection depends on their geometry but is effectively negligible when it makes up less than 1% of the deposits. Relatively thin mud drapes lying on point-bar accretion surfaces are seen to act as baffles to flow but their impact is minimal in view of their small number. The study provides useful and novel insights into the potential impact of sedimentary heterogeneity in fluvial reservoirs, which can be applied to the design of well doublets and to highlight areas that deserve further investigations.

The Precambrian was characterized by unique palaeoenvironmental conditions in the Earth's atmosphere, biosphere and geosphere. This study presents a global quantitative analysis of Precambrian sedimentary successions of aeolian, alluvial, fluvial, lacustrine and glacigenic origins, examined in the broader context of Earth evolution. In the Precambrian, an apparent scarcity of aeolian successions is observed. This may be linked to: (1) differences in atmospheric density, which controlled wind erosion and sedimentation; (2) different astronomical configurations, which may have influenced tides and atmospheric circulation, thereby affecting sand availability and the width of subtropical zones; (3) potentially hotter and more humid climates, restricting dry-sand availability; (4) a lack of vascular vegetation that could prevent reworking of aeolian deposits; (5) poor preservation potential; (6) misinterpretation of the Precambrian record. Mixed aeolian-alluvial strata are more abundant, perhaps because their preservation in the geological record was favoured by water tables sustained by incursions of alluvial systems into otherwise aeolian dominated environments. Aeolian deposits were preferentially accumulated during phases of supercontinental breakup, where rapidly subsiding rift basins provided accommodation suitable for preservation. Other than in the Neoproterozoic record, where glacigenic deposits dominate, alluvial strata are the most common and thickest type of continental deposit in the Precambrian. Precambrian braided alluvial systems were more widespread than in the Phanerozoic. Major alluvial systems formed preferentially during phases of supercontinent assembly, whereby alluvial systems drained major orogens, and long drainage pathways developed from supercontinent interiors to coastlines. In the Paleoproterozoic, ephemeral, saline to partly arid lakes developed extensively in the desertic interior of Columbia. Glacial deposits preferentially formed in the breakup phase of supercontinental cycles; this supports theories invoking enhanced chemical weathering of uplifted rift shoulders as a driver of carbon dioxide sequestration, global cooling, and glaciation. Overall, the number of identified continental successions increases towards the Precambrian-Phanerozoic boundary. This may be an artefact of an increasingly more complete stratigraphic record as time progresses. However, the abundance of continental successions varies on a quasi-periodic cycle of 500 - 700 Myr, with peaks coinciding with the tenure and breakup of Precambrian supercontinents.

ABSTRACTStrata produced by fluvial dunes can provide insight into the hydrological regime of ancient rivers. Recent experiments indicate that conditions of disequilibrium between bedforms and formative flows may be inferred from the coefficient of variation of preserved dune cross‐set thickness, suggesting that this quantity may act as a proxy for the flashiness of river floods relative to the time required for full bedform translation. To assess whether this idea is applicable to interpretations of the stratigraphic record, this study examines published data relating to more than 2600 cross‐sets from 53 sedimentary units of 19 river systems. The presented analyses must not be over‐interpreted, because the considered rivers span different environmental settings, the data sources are heterogeneous in terms of type and dimensionality, and some variables were established by applying empirical relationships. Yet, significant findings are revealed. Larger rivers exhibit discharge and bedform characteristics that are more conducive to disequilibrium; however, a modest increase in the coefficient of variation of cross‐set thickness, CV(Dst), as opposed to the expected decrease, is seen as a function of river size. Crucially, smaller CV(Dst) values are not systematically associated with conditions that should favour dune disequilibrium. Meanwhile, only ca 25% of the studied examples demonstrate cross‐set thickness statistics compatible with quantitative formulations of the autogenic control by variable dune topography – the notion of ‘variability‐dominated’ preservation. These findings indicate that the variability in cross‐set thickness may be a poor predictor of discharge variability, perhaps because of the multiplicity of factors controlling dune preservation, such as bedform hierarchy, transport stage and depth‐dependent variations in dune disequilibrium. To improve interpretations of cross‐stratified deposits, further research is needed: (i) to establish the value of process‐to‐product models for reverse product‐to‐process interpretations; and (ii) to define representative samples for preserved dune deposits accounting for temporal and spatial variability in preservation potential.

Within aeolian systems, complex dune morphologies can develop due to the interplay of a variety of allogenic and autogenic controls. As a result, the preserved sedimentary record of aeolian dune deposits is highly varied, exhibiting an array of sedimentary architectures and facies heterogeneities. However, reconstructions of such aeolian sedimentary architectures are usually based on limited information from one-dimensional borehole data or two-dimensional outcropping successions; as such, it is challenging to predict three-dimensional architectures and the distribution of small-scale facies heterogeneities of aeolian sedimentary successions. To address this, a novel rule-based forward stratigraphic model, the Dune Architecture and Sediment Heterogeneity model (DASH), has been developed to reproduce three-dimensional sedimentary bodies, bounding surfaces and associated facies distributions formed by a wide range of dune morphologies and morphodynamic behaviours. The model generates architectural frameworks produced by dune and interdune migration and aggradation, based on a long-established modelling approach; it then applies a series of rules that reflect geological understanding or observations from geological analogues to populate the three-dimensional space with facies domains. The model has been applied to simulate the stratal architectures and facies organization of (i) three idealized examples of successions produced by different dune morphologies, and (ii) a real-world case example from the Triassic Helsby Sandstone Formation, Cheshire Basin, UK. The results demonstrate how the model can be used to predict likely facies distributions in three dimensions, which themselves can be used to constrain models of petrophysical properties constructed with geostatistical techniques. The model can therefore be applied to assist reconstructions of subsurface architectures and petrophysical heterogeneity.

Nearshore incised valleys are important conduits for the transport of sediment, nutrients, pollutants and organic carbon from the continents to the sea. Therefore, it is essential to understand the autogenic evolution of deltas confined within incised valleys and how such evolution is affected by relative sea-level rise. To date, limited research has focused on how deltas constrained by incised valleys or other forms of antecedent topography respond to rising sea level. An existing theory of autostratigraphy envisages scenarios in which two-dimensional or unconfined three-dimensional fan deltas can experience three evolutionary stages under constant rates of relative sea-level rise and sediment supply: progradation, autoretreat and post-autobreak transgression. In this work, an integrated study of geometric numerical models and physical experiments is undertaken to investigate autostratigraphic delta evolution for a variety of incised-valley geometries, under conditions of constant rates of relative sea-level rise and sediment supply. Results indicate that interplays of antecedent topography (valley geometries) and sediment mass balance expressed in resultant deltaic geometries can result in autogenic changes in shoreline dynamics and river avulsion frequency on deltas. The following primary findings arise. (i) Compared to valleys with rectangular and trapezoidal cross-sectional profiles, valleys with triangular cross-sections tend to contain deltas that experience faster rates of progradation, autoretreat and post-autobreak transgression under rising sea level, and exhibit a more prominent convex-seaward shoreline trajectory. (ii) The shoreline trajectory is also related to delta topset geometry, becoming more convex-seaward under decreasing topset slopes. (iii) River avulsion frequency on deltas with rising sea level varies markedly across valleys with different geometries, even under the same rate of relative sea-level rise; this is attributed to the difference in temporal evolution of shoreline migration for different valley geometries and the resultant difference in the delta topset aggradation. This study highlights complexities in responses of sedimentary systems under the confinement of different topographic configurations that have hitherto largely been overlooked in sequence-stratigraphic models. The findings provide insight into future shoreline behaviour and river avulsion hazard on confined deltas, and for decoding the stratigraphic record.