Sedimentary Features Research Articles

Tectonics-Related Geosites: Towards Accurate Nomenclature

Accurate nomenclature of geological heritage sites (geosites) is necessary to facilitate their description and territorial geodiversity evaluation (both important for sustainable development and efficient land-use planning). As suggested by previous geological heritage studies, tectonics-related geosites are termed differently and, chiefly, provisionally (e.g., as tectonic geosites or structural geosites). Moreover, the nomenclature should take into account modern advances in the understanding of some basic tectonic phenomena. We propose abandoning the separation of structural, neotectonic, and seismic types of geosites and replacing with a single tectonic type. This can be further subdivided into subtypes, although one should consider the complexities in the links between tectonic and other geological phenomena (e.g., unique seismic features are essentially tectonic, but these can be expressed via geomorphological or sedimentary features—a geosite retains tectonic and geomorphological/sedimentary types in this case). The development of accurate nomenclature of tectonics-related geosites requires debates by experts in geological heritage.

Microfabric characteristics of potash ore of the Pripyat potash-bearing basin

The requirements of complex subsoil use are increasing in the Pripyat potash-bearing basin: potash ore of new technologic types, with lower contents of useful components, increased concentrations of harmful impurities. Using all complex of quality indicators assessment of natural types of potash ore is undoubtedly prioritized by characteristic of potash deposits. The study of structural and textural features and composition of potash deposits has been given attention since the time of discover of the Starobin deposit. Systematic study of salt rock petrology has been started after the discovery of the Starobin deposit. Until now in the petrology, there is no recognized rational genetic classification of the structures of salt rocks being potash (potassium-magnesium) ore. The name of certain structure is based on the secondary features that are brightly expressed, color or similarity with different objects. The aim of the present work is an element recognition of the primary sedimentary features of rocks, systematization of primary and secondary characteristics and their typification according to petrochemical parameters. In the article the main microfabric types of potash ore that are typical for the deposits of red-colored and mottled hypersaline association of the Pripyat basin.

New evidence of perfect overlapping of Haploops and pockmarks field: Is it a coincidence?

In the shallow waters of the Bay of Concarneau (South Brittany, France), previous studies reported a dense settlement of the species Haploops (tube-dwelling bioengineer amphipod) that perfectly overlaps a field of pockmarks. A possible mechanistic link may therefore exist between the Haploops colonies and the shallow pockmarks. To test this hypothesis, interferometry sonar and sub-bottom profiler chirp data were acquired in two new areas located in the marine estuary of the Loire River, “La Lambarde” and “Le Croisic”. The new sites share the same sedimentary and geological characteristics as those found in the Bay of Concarneau. The three sites are similarly located in shallow and muddy environments above a faulted Middle Eocene formation that is incised by paleo-valleys. Despite different hydrodynamic conditions and estuarine influence, in the two new investigated areas, the Haploops also settle within the pockmarks field limits. To better constrain the association pockmarks/Haploops, we compared the sedimentary features, seismic signatures and total organic carbon (TOC) content of the sediment. Active pockmark chimneys displaying highly reworked profiles and slightly higher TOC contents suggest a local deeper source of organic matter, which might be an important source of nutrient for the Haploops. In Southern Brittany the pockmarks/Haploops spatial overlap is not a simple coincidence and may therefore present a general pattern for identification of settlement preferences of the specie.

Long-lived mega fault-scarps and related breccias at distal rifted margins: insights from present-day and fossil analogues

Thinning of the continental crust during rifting is accommodated by a number of major faults, only a few of which produce long-lived mega fault-scarps. In this paper, we investigate mega fault-scarps and the sedimentary system located at their toe across magma-poor rifted margins. Our approach combines observations from subsurface examples along present-day margins and field analysis of fossil examples exposed in the Alpine Tethys margins. Whereas present-day examples of rifted margins imaged by seismic techniques provide details about the architecture of the top basement and the relationship between faults and sediments, outcrops give access to the sedimentary features of rocks related to mega fault-scarps. Our study shows that (1) mega fault-scarps are preferentially located at rift domain boundaries, implying a topographic escarpment that juxtaposes rift domains of different crustal thickness, and (2) mega fault-scarps are long-lived local sources for syn- and post-tectonic breccia, respectively produced during and after fault activity.

Late Paleocene pipe swarm in the Great South – Canterbury Basin (New Zealand)

We have identified a deeply buried fluid escape pipe province in Cretaceous - late Paleocene sediments of the Great South–Canterbury Basin (NZ). The seismic observations and interpretations point to an unusually vast fossil system of pipes. These features are exceptional in number (>2000 edifices) and appear to have formed from a common root zone. The areal extent of the analysed pipe system (2500 km 2 ) is among the largest systems of fluid expulsion features ever observed in three-dimensional seismic data. The unclustered distribution of the pipes suggests no specific link to faults or buried sedimentary features and, at their maximum vertical development, the pipes are equally distributed above depocentres or structural highs. The majority of pipes terminate at two discrete levels in the late Paleocene. Based on the geometrical relationship of the pipe edifices to the overburden, and the basinal setting of the hosting units, we interpret these horizons as representing the seabed at the time of pipe formation. This interpretation allows us to date the timing of pipe formation as prominently late Paleocene. We envisage that the pipes originated during discrete episodes of fluid venting in this time interval, disrupting the typical progressive basinal compaction-driven pore fluid expulsion. The pipes are associated with biogenic gas expulsion. We discuss their triggers, mechanical processes, and global significance for understanding fluid flow processes in sedimentary basins. Creation of the initial overpressure could be related to in situ biogenic gas generation in the stratigraphic interval coincident with the root zone of the pipes. We hypothesise that the main episode of gas release and pipe formation was associated with a sea-level fall during the contemporaneous late Paleocene Carbon Isotope Maximum. This case study shows a unique example of a preserved Paleogene fluid migration system and highlights how the observation and the interpretation of massive fossil systems of fluid-escape features provides invaluable information in terms of overpressure generation and basin fluid expulsion history. • Unusually vast fossil system of fluid escape pipes discovered offshore New Zealand. • The >2000 pipe edifices formed in the late Paleocene and are at present deeply buried. • They are associated to overpressure development linked to biogenic gas generation. • Gas release likely associated with late Paleocene Carbon Isotope Maximum sea-level fall.

Morphological features and associated bottom-current dynamics in the Le Danois Bank region (southern Bay of Biscay, NE Atlantic): A model in a topographically constrained small basin

The present-day morphology of the Le Danois Bank region has been investigated based on bathymetric and high to ultra-high resolution seismic reflection data. The involved bottom-current processes are associated with the Eastern North Atlantic Central Water, the Atlantic Mediterranean Water and the Labrador Sea Water. Sediments originating from various canyon systems along the Cantabrian Margin and the Asturias continental shelf are transported by downslope and alongslope processes towards the Le Danois intraslope basin. The background flow velocities of bottom currents are all below the threshold (8–10 cm/s) of generating plastered and mounded geometries of contourite drifts. However, bottom currents are locally accelerated (up to 25 cm/s) due to the presence of the Le Danois Bank and the Vizco High, creating a furrow and three moats and generating six plastered drifts, three elongated mounded and separated drifts at different depth intervals. The extension and distribution of the drifts are controlled by slope morphology and/or bottom current velocities. Unlike contourite drifts along other continental slopes, a single contourite drift (the Gijón Drift) with a lateral variation in drift geometry and internal structure indicates the interaction of bottom currents with different flow dynamics. Additionally, scouring of active bottom currents and rapid sedimentation rate of contourite drifts may be at the origin of slope instability events. Besides contourite drifts, internal waves may have induced the formation of sediment waves. In the Le Danois intraslope basin, multiple sedimentary processes work together and shape the present-day seafloor. Bottom currents are focused due to deflection on complex topographical obstacles within a relatively small basin setting, and create a wide variety of sedimentary features, including contourite drifts. The resulting sedimentary features thus have more frequent lateral variations, a feature typical for topographically constrained small basins.

Geochemical constraints on the origin of Neoproterozoic cap carbonate in the Helan Mountains, North China: Implications for mid-late Ediacaran glaciation?

The late Neoproterozoic Era was characterized by dramatic transitions in climate, including Snowball Earth glaciation, and in the increasing oxygenation state of the atmosphere and oceans. However, late Neoproterozoic glacial deposits are poorly documented in North China. To better understand the Neoproterozoic glacial events in North China, we investigated five sections along a north-south transect across the Helan Mountains capturing a transition from shelf margin to intrashelf basin. This effort revealed an excellent exposure of Neoproterozoic diamictite and associated carbonate succession (Zhengmuguan Formation) on the western shelf margin of North China. Sedimentary features in the diamictite indicate that it might be a glacial sequence partially influenced by sediment gravity flows, with values for the Chemical Index of Alternation (CIA) consistent with cold, arid depositional environment. The overlying carbonate succession is sporadic, with exposures confined mostly to southern areas that disappear to the north. Identification of the Zhengmuguan sequence as a cap carbonate is based on the occurrence of distinctive attributes that are widely found in typical Neoproterozoic cap carbonates around the world. The ∼1.6-m-thick cap carbonate consists of a lower thinly laminated dolomite and an upper thick-bedded dolomite, directly overlying the top of the Zhengmuguan glacial diamictite. Based on field and petrographic observations and high-resolution geochemical analyses of major, trace, and rare earth elements; organic carbon isotopes (δ13Corg); and total organic carbon (TOC), we are able to interpret the depositional environments and the possible origin of the cap carbonate. The occurrence of late Ediacaran fossils in the overlying Tuerkeng Formation imply that the Zhengmuguan Formation is mid-late Ediacaran and thus may represent a mid-late Ediacaran glaciation. Our petrographic and geochemical results suggest the Zhengmuguan cap carbonate was initially deposited via glacial meltwater with significant inputs from continental weathering subsequently overprinted by upwelling anoxic deep seawaters along a continental margin. In summary, our data from a poorly known mid-late Ediacaran cap carbonate capture a high-resolution record of shifting climatic and oceanographic conditions of at least regional importance. The uncertainties of these interpretations are high, but the potential importance of these findings justifies the need to publish the data and our conclusions—along with the unavoidable caveats that come with any poorly dated frontier section.

Proportional relationship between the flux of catchment-fluvial segment and their sedimentary response to diverse bedrock types in subtropical lacustrine rift basins

Abstract Sedimentary features of a source-to-sink (S2S) system produce distinct responses to diverse bedrock types (i.e., silicate and carbonate rocks) in the catchment; these majorly influence the sediment flux, volume, and grain size in the sink area. By comparing a modern S2S system of Holocene Erhai Lake Basin (ELB) (in southwestern China) and an ancient S2S of Eocene western Offshore Bohai Bay Basin (OBBB) (in eastern China), we investigated the differences and proportional ranges among sandy sediment flux (Qf) and sediment discharge (Qs) from catchment associated with diverse bedrock types in a humid and subtropical lacustrine rift basin by combining with the Google-topographic-map, BQART-model, and seismic-geomorphology analysis. Based on geomorphological and 3D visualization analysis, we identified the differences among multiscale catchment-fluvial segments and their sedimentary responses in S2S systems, and then extracted parameters of catchment-unit area (A), catchment relief (R), and total sediment discharge (Qs, calculated by BQART model). Furthermore, we analyzed sediment-dispersal patterns and sandy sediment fluxes in the nearshore (Qf) using regional geologic data, outcrops and the Google Earth database in the Holocene ELB, and using seismic geomorphology in the Eocene western OBBB. Finally, quantitative analysis of the modern and ancient S2S segments was used to investigate the total sandy sediment flux (Qf), which is supplied by >60% of the entire sediment discharge (Qs) for catchments with silicate bedrocks (e.g., metamorphic rock and granite), while the ratio Qf/Qs corresponding to carbonate bedrocks is less than 30%. Additionally, the ratio Qf/Qs for catchments with mixed silicate carbonate bedrocks ranges between 30% and 60%. These results not only provide a new perspective for investigating sandy sediments in a subtropical lacustrine rift basin, but also yield implications for better understanding of continental S2S system theory for diverse bedrock types.

Cross-examining Earth’s oldest stromatolites: Seeing through the effects of heterogeneous deformation, metamorphism and metasomatism affecting Isua (Greenland) ∼3700 Ma sedimentary rocks

The ∼3700 Ma and 3800 Ma meta-volcanic and -sedimentary rocks in the Isua supracrustal belt (Greenland) were affected by heterogeneous ductile deformation under amphibolite facies conditions (∼500–650 °C), and variably modified by secondary silica and carbonate mineralisation deposited from diagenetic and metasomatic fluids. Rare low-deformation areas preserve original volcanic features – submarine basaltic pillows and sedimentary features – including bedding. These are best-preserved in two dimensions on flat- to moderately-inclined outcrop surfaces, but invariably are tectonically-stretched along a steeply-plunging third dimension, through stretching in the direction of fold axes; a style of deformation found throughout Earth’s history.There is a debate about whether rare relicts of ∼3700 Ma stromatolites preserved in metadolomites that formed in a shallow marine setting (Nutman et al., 2016) represent bona fide biogenic primary structures fortuitously preserved in low deformation, or whether these structures are manifestations of deformation combined with non-biogenic deposition of secondary carbonate (Allwood et al., 2018). Here, we critically test the primary nature of the sedimentary rocks hosting the proposed stromatolites and also the veracity of the proposed stromatolites, by addressing the following questions: (i) Are the rocks an in situ outcrop of known age, or displaced blocks of unknown age or origin?; (ii) How much of the carbonate is of an originally sedimentary versus a secondary (i.e., metasomatic – introduced) origin?; (iii) Is the seawater-like REE + Y (rare earth element and yttrium) trace element signature carried definitely by carbonate minerals and therefore diagnostic of a cool, surficial sedimentary system?; (iv) Are the proposed stromatolites consistent with biogenicity in terms of their geometry and fine-scale layering, or could they be the product of soft sediment or structural deformation (compression in folding)? The answers to these questions, which combine diverse observations from geologic context, geochemistry and stromatolite morphology show that the weight of evidence is consistent with a biogenic origin for the stromatolites formed in a shallow water setting and are inconsistent with formation entirely through inorganic processes.

Minjiwarra: archaeological evidence of human occupation of Australia’s northern Kimberley by 50,000 BP

Recent archaeological research in Australia’s north-eastern Kimberley has luminescence dated a large red sedimentary feature, known as Minjiwarra, with artefacts in stratified contexts from the late Holocene to ∼50,000 years ago. This site is located on the Drysdale River, with preliminary excavations undertaken as part of an ARC Linkage Project. Deeply stratified sites in association with rockshelters are uncommon across the NE Kimberley and basal dates at open cultural deposits vary greatly. Most of them are mid-Holocene in age. However, Minjiwarra appears to cover the entire span of potential human occupation in this region, with associated lithic technology, reported on here.

Early Cretaceous sedimentary evolution of the northern Lhasa terrane and the timing of initial Lhasa-Qiangtang collision

Lower Cretaceous strata in the Baingoin basin of the northern Lhasa terrane record initial collision between the Lhasa and Qiangtang blocks, followed by the early uplift of central Tibet. North-south traverses across the Baingoin basin highlight major differences between the Duba Formation in the north and the quasi-coeval Duoni Formation in the south. The Duba Formation documents upward transition from shallow shelf and deltaic environments to coarse-grained siliciclastic fluvial sedimentation. Abundance of detrital zircons yielding Jurassic-Cretaceous ages with εHf(t) values mainly between −2 and +10, occurrence of chert, Cr-spinel, and pyroxene grains, together with southward paleocurrent directions indicate that the Duba Formation was sourced from the southern Qiangtang terrane and Bangong-Nujiang suture zone to the north. The Duoni Formation in the south was deposited in shelfal to fan-delta and fluvial environments. Abundant volcanic clasts, detrital zircons yielding Cretaceous ages with mainly negative εHf(t) values, and northward paleocurrents indicate an active volcanic source located in the central Lhasa terrane to the south, with minor input from the northern Lhasa terrane. Only the northern part of the Baingoin basin was directly controlled by the Lhasa-Qiangtang collision and may thus be considered a peripheral foreland basin, whereas the southern part was mainly influenced by tectonic processes related to the northward subduction of Neotethyan lithosphere, and may thus be comparable to a retroarc foreland basin. But these sedimentary features and the 139–79 Ma Baingoin plutonic intrusion do not fit well with classical foreland-basin models. Zircon chronostratigraphy constrains the final consumption of Bangong-Nujiang oceanic lithosphere and initial collision between the Lhasa and Qiangtang microcontinents to have taken place by 122 Ma, which has major implications for paleotectonic reconstructions of the Tibetan Plateau.

Aptian–early Albian sedimentation in the Essaouira-Agadir basin, Western Morocco

Aptian to early Albian times were marked by various geodynamic and paleoenvironmental events such as large igneous province volcanism, perturbations of climate and the carbon cycle, and sea-level changes. The Essaouira-Agadir basin (EAB), located on the Atlantic passive margin of Morocco, offers good and fossiliferous exposures of the Aptian–Albian sedimentary series. A detailed analysis of this succession made it possible to establish a biostratigraphic framework. The identification of discontinuities allowed to define eight depositional sequences. As most of them are correlatable with depositional sequences of other Tethyan areas, they suggest that eustacy was the main parameter controlling sedimentation. The analysis of sedimentary facies and nannofossil assemblages provides information on paleoenvironmental changes.Sedimentation in the EAB evolved from a very low energy, carbonate ramp in the early Aptian to a low energy, slightly deeper, mixed carbonate-clastic ramp in the early Albian. This change occurred along with an increase of clastic input, a change from oligotrophic to mesotrophic faunal assemblages, and a decrease of sea-surface temperatures. The occurrence of current sedimentary features, sporadic dysaerobic deposits and local phosphatic and glauconitic crusts suggests that upwelling currents were significant during this period.Paleogeographic and isopach maps support a transgressive trend in the late Aptian and early Albian, and unravel subsidence anomalies suggesting mild halokinetic movements during Aptian‒early Albian times.

Analysis of the tectonic and sedimentary features of the southern margin of the Krzeszowice Graben in Southern Poland based on an integrated geoelectrical and geological studies

In this paper, geophysical technique ERT (Electrical Resistivity Tomography) supported by geological methods (macroscopic and microscopic observations) have been used to study shallow structure of the southern margin of the Krzeszowice Graben in the vicinity of Nawojowa Góra (southern Poland). The fieldwork was focus on the characterizing facies of the Upper Jurassic sediments that crops out in the selected quarry. Special attention was also paid on its microfacies development in order to broadly characterise these sediments. Geological studies of the exposed sediments have revealed that in this site calciturbidites and debris-flow deposits are present. The 2D ERT survey has been developed over the quarry exposure and within adjacent area, with the aim of identifying the 2D subsurface geology. Separate ERT survey lines have been performed and in the case of each profile, combined array configuration has been applied. In all obtained 2D ERT cross-sections, gradient analysis (showing the distribution of the maximum vertical and horizontal gradients of the interpreted resistivity) was carried out. These data provides additional information about spatial distributions of the various geoelectrical/geological layers. Beyond the Upper Jurassic sediments, which prevail in the research area, several lithological units were outlined on the ERT profiles that contain both the Upper Cretaceous sediments, Oligocene-Miocene karst deposits as well as Quaternary deposits. The use of the both geological and geophysical methods has allowed also delineating the zones which could be interpreted as fault zones. Geological interpretation has been considerably enhanced by forward 2D ERT modeling, by which it was possible to resolve some of the hypothesis derived from the interpretation of the field data. The distribution of the gravity flow deposits of different types in the marginal southern part of the Krzeszowice Graben reflects Late Jurassic fault activity. All obtained data have ultimately lead to a better understanding of the sediment distributions and the presence of tectonics in the geological context of the southern margin of the Krzeszowice Graben, supplying relevant information to its geological interpretation.

Morphodynamic interactions of continental shelf, beach and dunes: the Cabopino dune system in southern Mediterranean Spain

AbstractThe complex morphodynamic interactions between nearshore, shoreface and dune systems are usually simplified by studying these zones and their associated processes in isolation. However, the established relationships between each of them suggests that an integrated approach is required to examine the genesis, evolution and adaptation of the entire morphodynamic system. The Cabopino dune system in the southern Spanish Mediterranean Sea provides a clear example of a linked morphodynamic system in which a relatively large dune system has been generated and grown through the supply of sediments from an adjacent littoral supply environment. Here, we present a conceptual model of how the nearshore has provided suitable conditions for beach and dune development. We purport that synchronization of sediment activation in the marine and aeolian sections of the system have played a major role in this microtidal setting in which temporal aspects are not only tied to storm action, but to large sedimentary features moving alongshore. © 2019 John Wiley & Sons, Ltd.

Evaluating emplacement temperature of a 1000-year sequence of mass flows using paleomagnetism of their deposits at Mt. Taranaki, New Zealand

Temperature can be an important characteristic used to distinguish primary pyroclastic density currents or block-and-ash flows from other collapses not primarily related to an eruption, and also governs the type and level of hazard presented by these mass flows. We examined several mass-flow deposits within the AD1000-1800 Maero Formation at Mt. Taranaki, New Zealand, for field characteristics of hot emplacement - such as the presence of charcoal, baking of soils, or gas-elutriation piping - and conducted a paleomagnetic study of their thermoremanent magnetization (TRM) to determine emplacement temperatures. Results show that the majority of the deposits result from block-and-ash flows emplaced over ~500°C. Some of these deposits were indistinguishable in the field from a re-worked or low-temperature emplaced lahar or landslide deposit, indicating that sedimentary features are not a clear determinant of high emplacement temperature. The high emplacement temperatures suggest that the time between dome emplacement and collapse during this period was usually brief (<30 years), with some events consisting of rapid and repeated growth and collapse of lava domes, possibly within the same prolonged lava effusion episode.

Field Survey of the 2018 Sulawesi Tsunami Deposits

On 28 September 2018, a Mw 7.5 earthquake struck Sulawesi Island, soon followed by a destructive tsunami. This study provides a case history of tsunami deposition where submarine landslides or coastal collapses have contributed to and intensified tsunami generation. The sedimentary features resulting from this complex tsunami mechanism are not yet well understood. We surveyed tsunami deposits at six locations along the coastline of Palu Bay, in addition to measuring tsunami flow depth, run-up height, and inundation distance at each site. In general, the tsunami height was less than 8 m with a maximum inundation distance of 310 m. The tsunami deposits are thin with simple sedimentary structures such as fining upward sequences. These sedimentary characteristics are typical of tsunami deposits elsewhere around the world. This work is a preliminary study, in that numerical modeling including sediment transport has not been performed. Further work is needed to distinguish tsunamis with different source mechanisms.

Lithological typing, depositional environment, and reservoir quality characterization of the \u201cM-Field,\u201d offshore Douala Basin, Cameroon

Sedimentary features such as channel sands and submarine fan sequences are important hydrocarbon reservoirs throughout the world and may be interpreted from bed thickness trends and log motifs. The log motifs of four well logs were employed during this study to delineate reservoir architectural depositional features and environment, determine their lithological attributes, and evaluate reservoir properties. Gamma ray log signatures were utilized to infer depositional features, discriminate litho-units, and define depositional environment; resistivity log was employed to identify reservoir zones and formation fluids, while the combined density and neutron logs aided in the estimation of reservoir porosity and lithological typing. Results of analysis show seven laterally discontinuous reservoirs: one in Well X (X2), three in Well Y (Y1, Y2, Y3), and three in Well W (W1, W2, and W3) with thicknesses of 6.2 m, 19.2 m, 7.6 m, 78.7 m, 100.9 m, 38.1 m, and 41.6 m, respectively. Reservoirs architecture reveal distributary channel sands, submarine fan lobes, and deep tidal channel-fills deposited within the deep marine mud-rich N’kapa Formation. Average porosity, water saturation, and hydrocarbon saturation values of Well X and Well Y reservoirs are 20.8%, 30.8%, 69.2%, and 40.2%, 18.3%, 81.7%, respectively, indicating moderate-to-good reservoir quality. Also, the permeability values are moderate to good (74.89–12,584 md), except for Y3 and Well W reservoirs whose well log-derived permeabilities were unreliable due to their non-irreducible nature. Density-neutron crossplots indicate heterogeneous reservoir lithologies comprising of limestone, dolomite, and sandstones, with predominant calcite and subordinate dolomite as mineral matrix. Crossplot of water saturation and porosity revealed grain-size variation ranging from fine-grained to silty sediments with bulk volume water values suggesting Well X and Y reservoirs to be homogeneous and will produce water-free hydrocarbons, while Well W reservoirs are heterogeneous water-prone reservoirs.

Facies architecture and depositional evolution of Palaeocene–Eocene, Subathu Formation, Garhwal Himalaya, Uttarakhand, India

The Late Palaeocene–Middle Eocene marine sedimentary sequence of the Himalayan foreland basin, represented by the rocks of Subathu Formation, is enriched with the presence of foraminifera, bryozoa, corals, gastropods, bivalves and so on within both carbonate and clastic dominant lithologies. The carbonate and the shale consist mainly of larger benthic foraminifera (LBF) and the assemblage is composed of Nummulites and Assilina along with the other skeletal and non-skeletal components. The presence of a palaeosol at the base of Subathu indicates a gap in sedimentation. The lithological and biotic assemblages along with the bed form, bed geometry and primary sedimentary features helped us to establish four facies associations, A, B, C and D, and have been corroborated with the shoreline migration (transgression/regression) history. The facies association-A, representing the basal horizons of Subathu Formation, indicates the onset of transgression and deposition in lagoonal condition with carbonaceous shale and oolitic ironstone, followed by the facies association-B and -C deposited in shallow marine shoreface. The uppermost unit, i.e., the medium- to coarse-grained sandstone (facies association-D) of Subathu Formation, represents a fall in relative sea level (progradational stacking pattern), whereas the underlying contact between the facies association-B and -C is represented by an aggradational stacking pattern between the siltstone and the shale, but certainly without exposing the shelf. Petrographic studies based on characteristic features such as framework constituent, the percentage of matrix and grains, nature of cementing material, textural features and fossil content help to deduce a distinct change in depositional setting from an open marine (shelf) to shoal, a lagoon that gradually grades to foreshore/beach environment. The study reveals that the basin has gone through a transgressive (facies association-A and -B), regressive (facies association-C) as well as distinct forced regressive (facies association-D) phase of shoreline migration history.

Wind in Jezero Crater, Mars

AbstractWind generates erosional and depositional morphologies across Mars, including in Jezero crater, the planned landing site for the Mars 2020 rover. Known for subaqueously formed sedimentary features, Jezero crater also hosts wind‐formed features that provide insights about the local wind regime. We combine interpretations from dunes, wind streaks, transverse aeolian ridges, and yardangs to holistically understand the recent history of wind in Jezero crater. Together, these features describe modern easterly winds trending toward 263° ± 8° and older southwesterly winds that formed small yardangs. Previous research has suggested that aeolian processes eroded the delta deposit in Jezero crater. We propose early southwesterly winds removed the majority of material, exposing the more lithified units seen today. Modern easterly winds continue to cause erosion, but lithologic heterogeneities remain the dominant control on delta deposit evolution. Aeolian erosion has accentuated existing sedimentary structures, leaving the striking delta remnant seen today.

Non-seismic soft-sediment deformation structures from Late Pleistocene lacustrine deposits of Lake Van (Eastern Turkey): Storm and overloading effect

Soft-sediment deformation structures of different types and sizes are frequently observed in the lacustrine deposits of Lake Van. According to sedimentary features and regional factors, these structures are categorized as non-seismic originated and seismically-induced, soft-sediment deformation structures. Well-preserved non-seismic originated, soft-sediment deformation structures were observed in fine-grained sandy and silty deposits at three locations (Çatakdibi, Yumrutepe, and Yukarıışıklı), and occur at different stratigraphic horizons, exhibiting morphological variability as they consist of load, flame, and slump structures. The formation mechanisms of these structures are determined by the characteristics of their sedimentary facies and environmental conditions. Overloading, caused by rapid coarse sediment deposition or underwater landslides, and storm waves are identified as triggering mechanisms, while rapid sediment accumulation and underwater mass movements caused by volcanogenic shakes are the conditions responsible for the formation of non-seismic soft-sediment deformation structures, in terms of regional geodynamics.