Sedimentary Geology最新文献

The Crato Konservat-Lagerstätte is one of the main Mesozoic fossil sites from Gondwana, recording a wide diversity of terrestrial and non-marine aquatic fossils of great paleobiological and evolutionary significance. This conservation deposit is recorded in a 9 m-thick interval of laminite, microbialite, and grainstone deposited in a lake system with variable water level, alternating moments of hypersaline and freshwater conditions. Despite numerous studies describing new species of plants, arthropods, fish, pterosaurs, birds, and many others, there remains a significant gap in our understanding of the most common and archetypal fossils, which are the rod-shaped macrofossils found on bedding surfaces in distinct stratigraphic intervals of the Crato Konservat-Lagerstätte. The rod-shaped macrofossils are up to 1.6 cm-long and 0.1 cm-wide, straight to curved compressions that preserve pyritized microfossils. Here we interpret the rod-shaped macrofossils as macroscopic organic aggregates that sank into the lakebed in a process called lake snow. During high organic productivity periods in the epilimnion, planktonic organisms thrived and produced exopolymers responsible for aggregation. Their concentrations in the limestone bedding planes reflect intensity of lake snow and environmental seasonality. Aggregates are prolate particles that are commonly oriented, suggesting their transport as bedload for short distances, which was facilitated by biostabilization by microbes and their exopolymers. Finally, pyritization was mediated by microbial communities living in the lakebed.

On the basis of a combination of heavy mineral data, provenance-sensitive heavy mineral indices, garnet major element chemistry, rutile trace element chemistry and zircon U–Pb geochronology, six major changes in sandstone provenance during Carboniferous deposition in the northern Pennine Basin, UK, have been recognised. These changes are a manifestation of both tectonic and climatic factors. The earliest Tournaisian sediment was supplied from the local Southern Uplands High, but the increasingly humid climate led to the establishment of the Pennine River system, which introduced northerly-derived sediment from farther afield in the mid Tournaisian. This system was operative until the mid Bolsovian, but shows stratigraphic variations due to changes in input from different parts of the Pennine River hinterland (East Greenland, northern Scotland, western Norway). These variations are believed to be at least partly related to tectonism, since the maximum supply from high-grade metamorphic sources in East Greenland in the Namurian was concurrent with a tectonically-driven change in drainage direction in this part of the northern sourcelands. In addition, at the base of the Visean, there was a temporary influx of mature sediment coincident with a climatically-driven regression and, at the base of the Duckmantian, sediment was briefly introduced from the west as a far-field manifestation of Alleghanian tectonism. Finally, continued uplift of the Variscan mountain belt to the south of the UK led to establishment of northward-directed transport systems that reached the northern Pennine Basin in the mid-Bolsovian, leading totermination of supply from the Pennine River.

An integrated approach combining petrography, photogrammetry, geochronology, SEM, and geochemical data was utilized to analyze lithofacies, stacking patterns, and lateral facies variations, and to interpret environmental dynamics during the deposition of carbonates from ‘La Barre du Cengle’ in the Early Paleogene. Located in the SE of France, the elliptical Cengle Plateau stretches 7 km from east to west and is 2 km wide, featuring cliffs ranging in thickness from 20 to 35 m. These cliffs showcase grayish, beige, and pinkish limestones dominated by palustrine facies, forming part of the ‘Calcaire de Saint Marc’ Formation of the Arc Basin. Sedimentary deposits within this interval were repeatedly subjected to subaerial exposure due to fluctuations in lake levels driven by climate, resulting in the organization of elementary sequences at decimetric to metric scales, which stack up into small-scale sequences at the decametric order. Deposition occurred under mainly subarid climatic conditions, with paleogeographic variations in the basin corresponding to changes in lake base levels over time and space. At least four frequencies of base level variation are present: very high and seasonal frequency, responsible for the formation of palustrine facies; high frequency, which generates the elementary sequences; medium frequency, which leads to the formation of the small-scale sequences; and low frequency which corresponds to the deposition of the entire set of limestones that form the Cengle cliff. The transition between lacustrine, palustrine, and pedogenic environments consistently occurs from west to east over time. In the more distal regions, the proportion of lacustrine facies tends to increase, and the thicknesses of the preserved sedimentary record tend to be greater. Conversely, palustrine and pedogenic facies predominate in the more proximal areas, typically resulting in decreased thickness.

The separation of Gondwana was controlled by preexisting Proterozoic structures and by the development of rift aborted basins, of which the Araripe Basin (NE Brazil) is one of the best examples. Previous studies have focused on the presence and provenance of Aptian–Albian shallow-marine incursions in the Araripe Basin but to date, little attention has been given to its paleodrainage evolution during sedimentation stages. Understanding the paleodrainage evolution is crucial for determining sediment sources and how topographic changes relate to the geodynamic development of the northern part of South America during the fragmentation of Gondwana, and this study investigates the provenance of Mesozoic rift and post-rift sedimentary rocks in the Araripe Basin using a multi-proxy dataset comprising major and trace element concentrations, Sm–Nd isotopic composition, and detrital zircon U–Pb ages. The low Eu/Eu* ratios (0.3–0.9) and high Th/Sc ratios (>0.64) in the most of analyzed samples suggest a felsic and silicic source. The εNd(0) values (−12.3 to −23.7) and T_DM ages (1.68 to 2.55 Ga) of analyzed samples suggest overall ancient crustal sources. The presence of oval and elongated zircon grains suggests a major contribution of first-cycle transport sediments. The presence of 2.3–1.8 Ga and 0.63–0.58 Ga U–Pb zircon ages further indicates the dominant contribution of the Borborema Province influenced by the Brasiliano cycle (650–520 Ma). The low contribution of Tonian (∼940 Ma) zircons to the U–Pb zircon age distribution of the rift-beginning stage sample associated with published paleocurrent direction suggests sources located in the northern and northwestern terranes of the Borborema Province. The increase of Tonian (0.9–1.0 Ga) zircon grains during the rift stage suggests a provenance change with a dominant source in the eastern terranes during the rift stage. During the post-rift I stage, the decrease of 1.2–0.72 Ga zircon ages suggests a change in the source areas, with the paleodrainage coming from northern Borborema Province, similar to that of the rift-beginning stage. The samples of the post-rift II stage exhibit dominant contributions of Paleoproterozoic and Neoproterozoic U–Pb ages related to the Albian to Cenomanian uplift of the Borborema plateau during the opening of Equatorial Atlantic Ocean. Together with previous published studies, these findings highlight the significant role played by the post-rift continental uplift to the paleodrainage of the northern part of South America.

Debris avalanche deposits are developed on slopes in various environments, including submarine volcanoes, continental volcanoes, continental slopes, and mountain ranges. In contrast, research is relatively scarce on the coarse-grained subaqueous debris avalanche deposits formed by the collapse of steep basin margins in continental small rift basins, which are controlled by tectonics. Through the interpretation of satellite imagery, field investigations, and the study of the morphological characteristics and internal structures of sediments, a massive debris avalanche event during the Early Cretaceous, Xiguayuan Formation of the Luanping Basin at the northern edge of the Yanshan tectonic belt on the North China Block, named the Wangying Debris Avalanche Deposit (WYDAD), has been identified and analyzed for its kinematics, dynamics, and long-runout mechanisms. The study reveals that based on sedimentology, internal structures, and basal characteristics, five different types of sedimentary morphologies can be identified from the source zone to the distal zone: convergent ridges and grooves (longitudinal expansion and lateral compression), transverse ridges and grooves (compression), longitudinal ridges and grooves (shearing and stretching), arcuate ridges and grooves (compression), and mixed sediments (radial extension). The grain size of coarse-grained debris avalanche deposits decreases with increasing transport distance and fragmentation due to jigsaw cracking, while matrix content increases. Additionally, the entrainment of fine-grained substrate and the mixing of lake waters during the transport of debris avalanches often evolve into secondary debris flows or high-density turbidity currents. Debris avalanches are likely primarily controlled by regional tectonic activity and volcanic action. Compared to subaerial debris avalanche deposits, the subaqueous WYDAD exhibits characteristics such as low fragmentation, smooth underwater terrain due to water resistance and buoyancy, and higher fluidity. The mechanism for the long-distance, high-speed transport of the WYDAD is explained by “hydroplaning” and high pore pressure generated by non-draining shear. This study provides insights into the transport processes of coarse-grained subaqueous debris avalanche deposits in continental rift basins. It verifies whether such sediments can serve as a primary sedimentary system for CCUS or potential resource storage.

During the Carboniferous, western Gondwana was affected by numerous transgressions resulting from fluctuations in the ice sheet throughout the Late Paleozoic Ice Age. These sea level rises are well documented in western Argentina basins: Paganzo, Río Blanco, San Rafael, and Calingasta–Uspallata. Three transgressive events are recognized: The first corresponds to the post-glacial transgression of early Bashkirian age, which flooded the basins of western Argentina. The second transgression, the Pennsylvanian Transgression 1, is limited to the San Rafael, Río Blanco, western Paganzo, and Calingasta–Uspallata basins. This transgression facilitated the deposition of carbonaceous shales and thin coal beds in transitional estuarine-type environments. This stratigraphic interval is accompanied by megaflora of Nothorhacopteris–Botrychiopsis–Ginkgophyllum, microflora of Raistrickia densa–Convolutispora muriornata Subzone b, and an association of marine invertebrates that constitute the Marginovatia–Maemia Fauna. Finally, Pennsylvanian Transgression 2 or “Stephanian” transgression is more extensive and is associated with a Moscovian age invertebrate fauna. This contribution focuses on a sedimentological and paleontological analysis of the Pituil Formation. This unit comprises five facies associations: I, offshore; II, shoreface; III, deltaic systems; IV, barrier islands; and V, coastal lagoon. These sedimentological data and the fossil content of the Pituil Formation allow us to characterize the Pennsylvanian Transgression 1 in the Calingasta–Uspallata Basin and correlate it with other basins in western Gondwana.

Deciphering the facies and architecture of alluvial successions provides invaluable insights into the interplay of tectonics, climate, eustasy, and autogenic processes affecting terrestrial sedimentary systems. The stratigraphic response of fluvial systems to variations in discharge and sediment-supply regimes is now well-understood and is tied to changes in climate, precipitation patterns, or sediment sources. The uraniferous Chu-Sarysu Basin in south Kazakhstan occupies the tectonically stable Turan Platform on the eastern margin of the Peri-Tethys, and the study of its Palaeocene–Eocene sedimentary fill offers an opportunity to unravel eustatic and climatic controls that drove the architecture of reservoirs hosting economically important deposits. The stratigraphic succession comprises two multistorey, laterally extensive, sheet-like sandstone bodies floored by prominent erosion surfaces and interpreted as the deposits of channel belts. These packages are interstratified with floodplain, coastal-wetland, and marine-embayment complexes reflecting major extra-channel belt avulsions and marginal-marine incursions on the low-gradient alluvial plain. The stratal architecture was controlled by changes in accommodation likely induced by well-documented sea-level changes in the Peri-Tethys during the Palaeogene, which permitted the development of a chronostratigraphic framework. Eustatic variations culminated in the widespread flooding of the Turan Platform in the middle Eocene, reflected by transgressive lags above a wave ravinement surface capping terrestrial and marginal-marine deposits. Marked changes in fluvial facies, floodplain styles, and inferred channel planforms between Palaeocene and Eocene strata suggest a climatic overprint on river discharge and sedimentation. Upper Palaeocene meandering channel deposits encased in well-drained floodplain strata are indicative of perennial discharge under a semi-arid climate, whereas lower Eocene low-sinuosity channel fills, displaying evidence for transcritical flows and abundant in-situ vegetation, point to intermittent runoff patterns consistent with a humid and seasonal climate. An evolution in atmospheric moisture at the Palaeocene–Eocene boundary from arid to humid conditions has been reported across the Tethys region, and linked to global climatic perturbations of the Palaeocene–Eocene Thermal Maximum.

A Quaternary mass transport complex (MTC), formed by debris flows on a slope with numerous elliptical depressions in the Qiongdongnan Basin, is identified using three-dimensional seismic data. 25 % (5.7 km³) of the total volume of the MTC was deposited on the Upper and Middle slopes, mainly owing to the elliptical depressions capturing the bypassed debris flows. The megascour with slot-like geometry on the base of the MTC trends north–north-east on the Upper and Middle slopes, implying debris flows flowed downslope toward the north–north–east. The steep slope is responsible for the bypassing of the main body of debris flows. Moreover, the steep slope probably accelerated the debris flows, and thus the debris flow plowed, eroded and incorporated the substrate sediments to form the megascour. As a result, 75 % (17.3 km³) of the total volume of the MTC occurs on the Lower slope, mainly consisting of the lobe-like accumulation zones 1 and 2. Trends of the pressure ridges in the lobe-like accumulation zone 1 suggest debris flows spread in an unconfined manner due to the relatively gentle Lower slope, until it reached the topographic barrier to the north. As a result of the blocking of the topographic high, only a portion of the debris flows continues to flow northeastward evidenced by the small-scale megascour with slot-like geometry on the base of the MTC resulting from the relatively steeper slope. It is clear that the topography of the pre-existing slope plays a significant role in the depositional process and dispersal of the MTC. Topography of the pre-existing slope mainly resulted from tectonic movements and sedimentary infilling processes. It was also complicated by the elliptical depressions that were formed by the normal-drag along the arcuate normal-faults, which are attributed to sediment load that favors the downward slip on the walls of the erosional troughs within the substrate of the MTC. The steep slope and high sedimentation rates probably are important triggers for the occurrence of the MTC. This study is helping to improve current knowledge of the interaction between debris flows and the topography of the pre-existing slope.

Reef islands, elevated only a few meters above sea-level and restricted in area, are not only confronted with rising sea-levels, but the surrounding reef ecosystems, which are the only source of sediment maintaining those islands, are threatened by global (e.g. ocean warming and acidification) and local anthropogenic (e.g. pollution and destructive fishing methods) stressors affecting many tropical coastal areas. These stressors can increase coral mortality and lead to shifts from coral- to macroalgal-domination, likewise altering the production of skeletal carbonate sediment and ultimately endanger the physical persistence of reef islands. Here we study the evolution of an Indonesian reef island that has been inhabited since the 20th century. By analyzing the sedimentary record covering the last 5800 years from sediment cores taken on the island, we study the formation processes during the Holocene. For understanding the spatial dynamics, we compare the sediment record of the past decades with observations from satellite imagery data. Two shifts in the sedimentological composition over time point to alterations in the sediment-supplying reef ecosystems. The first sedimentological shift occurred from 3900 years BP on, shortly before the initial formation of the island, when the skeletal composition was diversified, presumably reflecting the modification of the reef ecosystem following a sea-level drop. A second sedimentological shift in the youngest sediments is marked by increased proportions of the calcifying green algae Halimeda, indicating that the reef ecosystem has shifted toward algal-domination, presumably reflecting increasing anthropogenic pressure. Of significance, shoreline change analysis reveals that the island is in an accreting state and has grown by 13 % in surface area over the past 24 years. Our findings suggest that the compositional alterations in sediment supply did not destabilize the reef island, and underline the adaptive potential of these landforms.

Our study investigates organic matter (OM) enrichment at the peripheries of marine basins, contrasting with prior research focused on central regions. We analyze three shale formations at three distinct deposition sites: the Marcellus (M) shale near an orogenic belt, and the Wufeng-Longmaxi (WL) shale, the Ohio (O) shale adjacent to a forebulge uplift. By examining factors such as redox conditions, clastic input, paleoproductivity, sedimentary facies and geological activities, we identify that the OM enrichment in shale (M shale) near the orogen resulted from significant inputs of river detritus and semi-deep shelf environment. Additionally, local enrichment is primarily influenced by volcanic ash sedimentation. The shale (O shale) at the distal end of the forebulge shows high OM concentration due to its stable deep-water shelf environment. Local enrichment in this area is caused by sediment re-sedimentation and glaciation. Similarly, the shale (WL shale) at the proximal end also exhibits a high OM concentration due to its stable deep-water shelf environment. In this case, volcanic ash deposition and transgression are responsible for the local enrichment. Our findings reveal how paleogeography and geological activities impact OM enrichment in basin peripheries, while also offering insights into evaluating shale gas reservoirs.