Sedimentary Structures Research Articles

Indications of preferential groundwater seepage feeding northern peatland pools

Groundwater seepage from underlying permeable glacial sedimentary structures, such as eskers, has been hypothesized to directly feed pools in northern peat bogs. These hypotheses directly contradict classical peat bog models for ombrogenous systems, wherein meteoric water is the sole water input to these systems. Variations in the underlying mineral sediment in contact with the peat imply that unrecognized hydrogeologic connectivity may exist with pools in northern peat bogs, particularly where high permeability materials are in contact with the peat. Seepage dynamics originating from these structural variations were investigated using a suite of thermal and hydrogeophysical methods deployed around pools in a peat bog of northeastern Maine, USA. Thermal characterization methods mapped anomalies that were confirmed as matrix seepage or preferential flow pathways (PFPs). Geochemical methods were employed at identified thermal anomalies to confirm upwelling of solute-rich groundwater. Conduits around pools were associated with surficial terminations of suspected peat pipes, based on the inference of pathways extending down into the peat, that focus flow through PFPs in the peat matrix. Discharge also occurred through the peat matrix adjacent to suspected pipe structures and matrix seepage rates were quantified using analysis of diurnal temperature signals recorded at multiple depths. Seepage rates, with a maximum of nearly 0.4 m/d, were measured at localized points around pools. Periods of synchronized temperatures paired with highly muted diurnal temperature signals, recorded in diurnal temperature with depth data, were interpreted qualitatively as activation of strong upward discharge rates through suspected peat pipes. These time periods correlated strongly with local precipitation events around the peatland. Ground-penetrating radar surveys revealed discontinuities in the low permeability glacio-marine clay at the mineral sediment-peat interface, interpreted to be regional glacial esker deposits, which were located beneath and around pools. Heat tracing, specific conductance contrasts, seepage rates, and trace metal concentrations all imply groundwater seepage originating from underlying permeable glacial esker deposits and directly sourcing pools. Preferential groundwater inputs into northern peat bogs may play a key role in developing and maintaining pool systems, with enhanced solute transport impacting peatland ecology, water resources, and carbon cycling.

Sedimentary characteristics and model of Cambrian storm in Xuzhou area

The storm deposition types within the Dabeiwang area of Xuzhou City, Jiangsu Province, China, showcase a wide range of diversity and distinctly apparent characteristics. Based on measured sections and thin-section observations, we have studied the typical characteristics of storm deposition in this area, divided the sedimentary sequence, and summarized a comprehensive model of storm deposition. Various rock types such as thick-bedded dolomitic limestone, oolitic limestone, and calcirudite are developed in the study area. The calcirudite exhibits bamboo leaf-like morphology and various distribution forms. Typical storm sedimentary structures such as scour surfaces and mound cross-bedding were identified in the study area. Based on the distance of the gravel layer from the storm center and the depositional environment, the storm sedimentary sequence in the study area can be divided into allopatric-proximal-lagoon facies storm deposit, allopatric-distal-oolitic shoal facies storm deposit, autochthonous-supratidal facies storm deposit, allopatric-distal-interbeach marine storm deposit, sub-allopatric-tide zone facies storm deposit, and autochthonous-tide zone facies storm deposit. We summarize the comprehensive model of Cambrian storm deposition in the Dabeiwang area of Xuzhou, which has enriched the research results of Cambrian storm deposition in Xuzhou and provides support for the construction of a lithofacies paleogeographic pattern.

Influence of sedimentary structure and pore-size distribution on upscaling permeability and flow enhancement due to liquid boundary slip: A pore-scale computational study

Low-permeability sedimentary formations, such as tight sandstones, exhibit fluid flow and transport phenomena distinct from those in conventional porous systems due to the dominance of micro- to nanometer-sized pores and variable amounts of boundary slip. The widely used traditional no-slip boundary condition often fails to accurately describe fluid behavior in these formations. A knowledge gap exists in understanding how liquid slip influences fluid dynamics in complex, heterogeneous sedimentary structures, as previous studies have primarily focused on simplified, homogeneous pore geometries. In this study, we investigated the impact of boundary slip on low-Reynolds number fluid dynamics within synthetically designed two-dimensional graded and random pore networks with varying pore-size distributions to account for heterogeneity. Our results showed that velocity variance increased with increasing heterogeneity, following a power-law relationship. The power-law exponents decreased with boundary slip, quantifying how boundary slip mitigated the impact of heterogeneity on velocity variance. We developed a theoretical model to predict asymptotic flow enhancement and derived constitutive relations to estimate the coefficient C and maximum flow enhancement (ΔE) based on the pore-to-grain size ratio and porosity. Energy dissipation increased with both heterogeneity and boundary slip, which we identified as the primary mechanism contributing to asymptotic flow enhancement. This relationship was illustrated by a 1:1 linear correlation between maximum energy dissipation and maximum flow enhancement, regardless of heterogeneity, indicating that energy dissipation due to boundary slip entirely controls the emerging fluid dynamics. The presented theoretical model and constitutive equations offer practical applications for optimizing fluid dynamics in heterogeneous formations.

Megaripple stripes in the Qaidam Basin, China: Morphology, grain size and sedimentary characteristics

Megaripple stripes (MRS) are enigmatic aeolian bedform patterns which are composed of crosswind alternating, wind-parallel megaripple corridors (MRCs) and smaller bedform corridors (SBCs). Compared to SBCs, MRCs have taller bedforms, longer wavelengths, and coarser surface sediments. However, their morphology, grain size, and internal structure are poorly understood. Numerous MRS have been identified in the central-southern edge of the Qaidam Basin. Unmanned Aerial Vehicle (UAV) images and 3D cloud point data were used to explore the morphological properties of MRS, and sediment samples were collected for grain size analysis. The sedimentary characteristics were analyzed through sections of MRC, transition zone between MRC and SBC, and SBC. The results show that the downwind and crosswind wavelengths of MRCs, along with the downwind wavelength of SBCs, decrease in the downwind direction. Conversely, the crosswind wavelength of SBCs displays an increasing trend. The crestline of MRS becomes progressively curved along the downwind direction. The average wavelength of MRCs is 8.51 m, with a height of 0.46 m. The average wavelength and height of SBCs are 1.69 m and 0.07 m, respectively. SBCs are smaller and more densely distributed than MRCs. Most values of the Ripple Index (RI) of MRS clustered between 11 and 60. MRCs exhibit a relatively symmetrical cross-sectional profile, while SBCs exhibit comparatively poor symmetry. MRCs are mainly composed of gravel and very fine sand, with accounting for 63.67 % of content in total. In SBCs, the prevalent grain sizes are very coarse sand and fine sand, accounting for 48.42 % of content in total. MRS display poor sorting, presenting a predominantly positive skewness and wide to very wide peaks. The thickness and inclination of laminae in middle layer 1 gradually decrease from MRCs to SBCs. The sedimentary structure of MRS provides insights into the grain migration in downwind and crosswind directions during their formation.

3D ground-penetrating radar data analysis and interpretation using attributes based on the gradient structure tensor

In near-surface geophysics, ground-penetrating radar (GPR) surveys are routinely used in a variety of applications including those from archaeology, civil engineering, hydrology, and soil science. Thanks to recent technical developments in GPR instrumentation and antenna design, 3D surveys comprising several hundred thousand traces can be performed daily. Especially in complex environments such as sedimentary systems, analyzing and interpreting the resulting GPR volumes is a time-consuming and laborious task that is still largely performed manually. In the past few decades, several data attributes have been developed to guide and improve such tasks and assure a higher degree of reproducibility in the resulting interpretations. Many of these attributes have been developed in image processing or computer vision and are routinely used, for example, in reflection seismic data interpretation. Especially in sedimentary systems, variations in the subsurface are accompanied by variations of GPR reflections in terms of the amplitudes, continuity, and geometry in view of the dip angle and direction. A promising tool to analyze such structural features is known as the gradient structure tensor (GST). To date, the application of the GST approach has been limited to a few 2D GPR examples. Thus, we take the basic idea of GST analysis and introduce and evaluate the corresponding attributes to analyze 3D GPR data. We apply our GST approach to one synthetic and two field data sets imaging diverse sedimentary structures. Our results demonstrate that our set of GST-based attributes can be efficiently computed in three dimensions and that these attributes represent versatile measures to address different typical interpretation tasks and, thus, help for an efficient, reproducible, and more objective interpretation of 3D GPR data.

Литологическая характеристика колганской свиты юго-западной части Восточно-Оренбургского сводового поднятия

Based on the study of core material, the lithological features of the deposits of the Kolgan formation of the Frasnian stage in the southwestern part of the East Orenburg arch uplift are considered. This formation is an important oil and gas play. Since picking, almost nonintermittent prospecting and exploration works have been carried out. A large bulk of heterogeneous material is received and processed, which complement and expand the knowledge of the geological structure and genesis of sediments. The research was carried out by petrographic and lithological methods. As a result, 5 lithotypes were identified according to the ratio of carbonate and terrigenous components and structural and textural features. It was found that the carbonate component prevailed in all the selected lithotypes, which distinguished this formation from other similar sections, where terrigenous rocks predominated. The presence of bioturbation of varying degrees of intensity and the presence of tempestites is characteristic.

Laminae Characteristics and Their Relationship with Mudstone Reservoir Quality in the Qingshankou Formation, Sanzhao Depression, Songliao Basin, Northeast China

Lamination is the predominant and widely developed sedimentary structure in mudstones. Similar to organic pores in shale gas reservoirs, the inorganic pores in the laminae of shale oil reservoirs are equivalently important high-quality reservoir spaces and flow channels. The laminae characteristics are strongly heterogeneous, being controlled by both deposition and diagenesis. However, the origin of this diversity is poorly understood. A detailed examination of cores, thin sections, and scanning electron microscopy analyses were conducted on the lacustrine mudstone of the Qingshankou Formation in the Songliao Basin to study the influence of deposition and diagenesis on laminae characteristics and their relationship to reservoir quality. Three types of laminae are mainly developed, namely thick siliceous laminae, thin siliceous laminae, and thin siliceous and argillaceous mixed laminae. Deposition controls the type and distribution of laminae. The thin siliceous and argillaceous mixed laminae are controlled by climate-driven seasonal flux variations. The thick siliceous laminae and thin siliceous laminae are controlled by bottom current or gravity-driven transport processes due to increased terrestrial input. The thin siliceous laminae have the optimum reservoir properties, followed by the thin siliceous and argillaceous mixed laminae, while the thick siliceous laminae have the worst properties. Diagenesis controls the pore evolution of the laminae. Different laminae have different paths of diagenesis. The thin siliceous laminae are mainly cemented by chlorite, preserving some primary porosity. The clay mineral content of the thin siliceous and argillaceous mixed laminae is high, and the primary pores are mainly destroyed by the strong deformation of the clay minerals during compaction. The thick siliceous laminae are intensely cemented by calcite, losing most of the porosity. The present study enhances the understanding of reservoir characteristics in laminae and provides a reference for shale oil exploration.

A typical point bar with atypical strata in the McMurray Formation, Alberta, Canada: Floods, tides and high suspended sediment concentrations

AbstractStratigraphic positions and the nature of some breccias and mudstones observed in the Lower Cretaceous McMurray Formation type section (Alberta, Canada) challenge the existing fluvial point bar facies models. The currently applied large‐scale, tidally influenced, sandy bedload facies model suggests that point bars fine upward, where breccias and cross‐strata occur at the base of the succession and mud content increases upward. Instead, this study documents that: (i) mudstone clast breccias are not exclusively associated with basal channel‐lag deposits and can occur throughout the point bar; and (ii) stratified mudstones are not limited to the top of the fining‐upward succession and can occur at or near the channel base. This outcrop data, including lithology, sedimentary structures, trace fossils, bed thickness and boundaries, and the nature of stratal packages, further suggests dynamic interplay between fluvial and tidal processes. This article discusses the potential role of high‐magnitude river floods in temporarily elevated suspended sediment concentrations and highlights that fluid mud processes played a crucial role in mud deposition in both tide‐influenced and fluvial parts of the system. Fluid mud processes allowed mud deposition along the channel base and across the point bar accretion surfaces. The breccias predominantly consist of broken pieces of inclined heterolithic strata and mostly occur on accretion sets of point bars, suggesting erosion and collapse of the point bar rather than of the cutbank. This work introduces a novel perspective to the existing models of point bar sedimentation, offering a new end member and concepts for the interpretation of subsurface data. The authors hope that this research encourages further investigations into similar phenomena elsewhere in the world.

Sedimentary characteristics and geological significance of a mixed-process delta for petroleum exploration in the Zhuhai formation of the Baiyun Depression, Pearl River Mouth Basin, China

The Zhuhai Formation in the Baiyun Depression of the Pearl River Mouth Basin in the northern South China Sea is a marine delta influenced by multiple hydrodynamic forces, including rivers, waves, and tides, resulting in a mixed-process delta. As a result of the combined effects of these forces, the distribution patterns and reservoir structures in the sandstone formations of the Zhuhai Formation are extremely complex. This paper provides a detailed description of the coring section of the Zhuhai Formation drilled in the Baiyun Depression, focusing on the lithology, sedimentary structure, special containers, and depositional dynamics of the coring section. It also summarizes the characteristics of a hybrid power delta controlled by rivers, waves, and tides, and explores the geological significance of this mixed-process delta for oil and gas exploration. The study reveals that sedimentation controlled by rivers primarily consists of medium-to-fine sandstones with interbedded cross-bedding and parallel bedding. Scour-fill structures and a bell or box-shaped natural gamma ray logging curve (GR) are also observed. Seismic reflection exhibits strong amplitude and high continuity. Wave-controlled sedimentation, on the other hand, predominantly consists of silt and fine sandstones with scouring, wave-formed cross-bedding, abundant bioturbation, and a serrated and funnel-shaped GR curve. Seismic reflection shows medium amplitude and high continuity. Tidally-controlled deposits are characterized by thin interbeds of mudstone, siltstone, and fine sandstone, as well as vein laminations, undulating composite laminations, lenticular laminations, and biclastic layers. The GR curves for tidally-controlled deposits are sharp or jagged with funnel shapes, and seismic reflections exhibit medium amplitude and continuity. The hydrodynamic features controlling sedimentation during the depositional period of the Zhuhai Formation in the Baiyun Depression exhibit evident zonation on a planar scale, influenced by sedimentary paleogeography and sea-level changes. River control is predominant in the northern Zhuhai Formation, with local wave influence and minimal tidal influence. In the southern part, tidal action becomes increasingly important. In terms of reservoir properties, wave-controlled reservoirs display significantly better porosity and permeability compared to tidally-controlled and river-controlled reservoirs. Tidally-controlled reservoirs exhibit high heterogeneity with a wide range of porosity and permeability values. The varying influences of different hydrodynamic drivers in different locations have led to significant variations in the size, morphology, and physical properties of sand bodies within the marine delta sediments of the Zhuhai Formation in the Baiyun Depression. Thus, the type and intensity of sedimentary hydrodynamics become the primary controlling factors for the development of high-quality reservoirs.

The effects of beach energy on sediment entrainment within the nearshore ice complex

Shore ice forms along beaches in cold climates and during its formation is capable of entraining sediment from the nearshore. Upon breakup, entrained sediment within the ice can be rafted to deeper waters, melt out and lost to the nearshore sediment budget. Previous studies have hypothesized that this sediment rafting could be a principal source of sediment loss from the nearshore sediment budget. However, fundamental questions remain about the primary mechanisms for entraining sediment within the ice, particularly differences between high and low energy beaches. In this study we collected a series of sixty-four ice cores from five different beaches along the Laurentian Great Lakes that spanned low to high energy regimes. These ice cores were analyzed for ice structure, sediment structure and entrained sediment mass. We found that low energy beaches primarily entrained sediment within the icefoot as the ice directly adhered sediments to its base. Conversely high energy beaches primarily entrained sediment when sediment laden water was washed atop the ice through wave action and subsequently incorporated into the ice structure. Overall, for a range of high energy beaches we find that in floating ice, sediment makes up approximately 1% of the total weight, which is nearly an order of magnitude greater than in low energy beaches (e.g., 0.1%). These findings provide a general description of the most important processes for sediment entrainment within nearshore ice for both high and low energy beaches, motivating a 1% approximation for estimating sediment budgets associated with shore ice.

Geochemistry of carbonate microbialites through time and space: Insights from the microbialite collection of the Muséum National d'Histoire Naturelle (MNHN), France

Microbialites are microbial sedimentary structures that constitute some of the oldest traces of life on Earth. By their deposition in a wide range of sedimentary environments and their presence throughout most of geological time, the sedimentological and geochemical signatures they preserve represent important paleoenvironmental archives for understanding Earth's biological and geochemical co-evolution. Here we present a large microbialite collection containing >1370 curated specimens, covering all continents except Antarctica and spanning >3.5 Ga of Earth history, that is accessible to the international scientific community for examination and sampling at the Muséum National d'Histoire Naturelle (MNHN) in Paris, France. After cataloguing and evaluating the samples for their lithology, biogenicity, and inferred depositional environments, we characterized the collection for selected geochemical parameters, notably carbonate stable carbon and oxygen isotope ratios, as well as major, trace, and rare earth element compositions. Finally, we explore the different geochemical proxies analyzed with regards to their utility for reconstructing evolving Earth surface environments and/or microbial metabolisms via comparison of geochemical data from the MNHN Microbialite Collection to a compilation of similar proxy data for carbonates worldwide. We demonstrate that certain temporal trends previously recognized in carbonates worldwide (e.g., with respect to variations in C and O stable isotope compositions and redox sensitive trace element enrichments) are well reflected in this collection. Our findings highlight the utility of the MNHN Microbialite Collection and microbialites more generally for reconstructing the conditions associated with habitable environments in deep time and for tracing the response of microbial communities to the geochemical evolution of Earth's surface.

Trace metal and organic biosignatures in digitate stromatolites from terrestrial siliceous hot spring deposits: Implications for the exploration of martian life

Novel biosignatures of laminated, microbial, digitate sedimentary structures – stromatolites – from modern geothermal fields of the Taupō Volcanic Zone, New Zealand, and from El Tatio, Chile, provide an opportunity to investigate evidence of extremophile life preserved in siliceous hot spring deposits, or sinters, interpreted as analogs for early life on Earth and possibly Mars. Synchrotron-μXRF, electron microprobe analysis, Raman spectroscopy, and optical microscopy are used in a coordinated approach to identify corroborating textural and chemical (organic, inorganic) evidence of life in these modern, opaline (amorphous) siliceous materials. Fluid mobile elements, such as As and Sr, track the growth history of the digitate structures. Trace element enrichments of Ca, Al, Ga, +/− Fe, Mn, As, Rb, Cs, and Sr, are identified in silicified sheaths of microbial filaments embedded within the sinter. In contrast, silicified diatoms in some sinter samples show no trace element enrichment. Gallium enrichments have also been observed in other 16 ka and Jurassic (150 Ma) microbial palisade sinter textures, suggesting the potential for preservation through geologic time, even after recrystallization to quartz. Raman analysis reveals spectra of organics, consistent with pigments for UV protection in cyanobacteria, in silicified sheaths around microbial filaments and are co-located with trace metal enrichments in digitate structures. Due to spectral bands, the location of these molecules (i.e., in the sheaths), and the sampling locations, we ascribe the spectra to scytonemin and carotenoid class molecules. The combined analytical approach outlined here provides a robust means to assess the validity of novel biosignatures, with application to the exploration of Mars, where preservation of opaline silica in >3.6 Ga deposits has the potential to preserve a range of microbial biosignatures.

Deep learning algorithm-enabled sediment characterization techniques to determination of water saturation for tight gas carbonate reservoirs in Bohai Bay Basin, China

Understanding water saturation levels in tight gas carbonate reservoirs is vital for optimizing hydrocarbon production and mitigating challenges such as reduced permeability due to water saturation (Sw) and pore throat blockages, given its critical role in managing capillary pressure in water drive mechanisms reservoirs. Traditional sediment characterization methods such as core analysis, are often costly, invasive, and lack comprehensive spatial information. In recent years, several classical machine learning models have been developed to address these shortcomings. Traditional machine learning methods utilized in reservoir characterization encounter various challenges, including the ability to capture intricate relationships, potential overfitting, and handling extensive, multi-dimensional datasets. Moreover, these methods often face difficulties in dealing with temporal dependencies and subtle patterns within geological formations, particularly evident in heterogeneous carbonate reservoirs. Consequently, despite technological advancements, enhancing the reliability, interpretability, and applicability of predictive models remains imperative for effectively characterizing tight gas carbonate reservoirs. This study employs a novel data-driven strategy to prediction of water saturation in tight gas reservoir powered by three recurrent neural network type deep/shallow learning algorithms—Gated Recurrent Unit (GRU), Recurrent Neural Networks (RNN), Long Short-Term Memory (LSTM), Support Vector Machine (SVM), K-nearest neighbor (KNN) and Decision tree (DT)—customized to accurately forecast sequential sedimentary structure data. These models, optimized using Adam's optimizer algorithm, demonstrated impressive performance in predicting water saturation levels using conventional petrophysical data. Particularly, the GRU model stood out, achieving remarkable accuracy (an R-squared value of 0.9973) with minimal errors (RMSE of 0.0198) compared to LSTM, RNN, SVM, KNN and, DT algorithms, thus showcasing its proficiency in processing extensive datasets and effectively identifying patterns. By achieving unprecedented accuracy levels, this study not only enhances the understanding of sediment properties and fluid saturation dynamics but also offers practical implications for reservoir management and hydrocarbon exploration in complex geological settings. These insights pave the way for more reliable and efficient decision-making processes, thereby advancing the forefront of reservoir engineering and petroleum geoscience.

Effects of polypropylene films and leached dissolved organic matters on bacterial community structure in mangrove sediments

Over the past decades, the accumulation of plastics in mangrove ecosystems has emerged as a significant environmental concern, primarily due to anthropogenic activities. Polypropylene (PP) films, one of the plastic types with the highest detection rate, tend to undergo intricate aging processes in mangrove ecosystems, leading to the release of dissolved organic matter (DOM) that may further influence the local bacterial communities. Yet, the specific effects of new and weathered (aged) plastic films and the associated leached DOM on bacterial consortia in mangrove sediments remain poorly understood. In this study, an incubation experiment was conducted to elucidate the immediate effects and mechanisms of the new and relatively short-term (45 or 90 days) aged PP films, as well as their leached DOM (PDOM), on characteristics of DOM and the bacterial community structure in mangrove sediments under different tidal conditions. Surface morphology and functional group analyses showed that both new and aged PP films exhibited comparable degradation profiles under different tidal conditions over the incubation period. As compared to the new PP film treatments, the introduction of the short-term aged PP films significantly affected the content of humic-like compounds in sediments, and such effects were partially ascribed to the release of PDOM during the incubation. Although the addition of PP films and PDOM showed minor effects on the overall diversity and composition of bacterial communities in the sediments, the abundance of some dominant phyla exhibited a growth or reduction tendency, possibly changing their ecological functions. This study was an effective attempt to investigate the relationship among plastic surface characteristics, sedimentary physicochemical properties, and bacterial communities in mangrove sediments. It revealed the ecological ramifications of new and short-term plastic pollution and its leachates in mangrove seedtimes, enhancing our understating of their potential impacts on the health of mangrove ecosystems.

Constraints on a long-lived Paleoproterozoic metamorphic process in a middle- to lower-grade metamorphic complex, Songshan area, southern North China craton: Evidence from minor- and trace-element thermometry and geochronology

The Dengfeng Complex and Songshan Group comprise a middle- to lower-grade metamorphic complex with abundant lithological associations in the Songshan area (central Henan, China), representing an excellent opportunity to investigate the thermal history of the North China craton. The polymetamorphic Dengfeng Complex is a typical granite-greenstone belt that records a late Paleoproterozoic metamorphic event (ca. 1.95−1.80 Ga) overprinting on a late Neoarchean metamorphic event (ca. 2.51−2.41 Ga). In contrast, the Songshan Group preserves well-developed stratigraphic sequences and sedimentary structures with greenschist-facies metamorphism. Numerous studies have focused on the late Neoarchean metamorphic event from the Dengfeng Complex, whereas the thermal evolution of ca. 1.95−1.80 Ga units from the Dengfeng Complex and Songshan Group has been largely overlooked. Quartzite of the Songshan Group unconformably overlies schists of the Dengfeng Group, and they show coherent NNE-SSW−striking schistosity structures with dip angles of ∼50°−65°. Here, the metamorphic temperatures from the Dengfeng Group were constrained to be ∼510−550 °C by the Ti-in-biotite geothermometer. The Ti-in-quartz and Zr-in-rutile geothermometers record metamorphic temperatures of ∼480−550 °C or 520−555 °C for the Songshan Group, respectively. Laser ablation−inductively coupled plasma−mass spectrometry U-Pb dating of monazite and rutile constrains the timing of metamorphism of the Songshan Group to be ca. 1.94−1.83 Ga, while zircon constrains the timing of metamorphism of the Dengfeng Complex to be ca. 2.53 Ga and ca. 1.95−1.87 Ga. By integrating geochronologic data from the Dengfeng Complex and Songshan Group, the ca. 2.53 Ga metamorphic age of amphibolite may be connected with Neoarchean subduction-accretion processes, whereas the consistent temperature obtained in this study ca. 1.95−1.83 Ga indicates that the Songshan area may have experienced a long-lived metamorphic event, which could have resulted from the final collision between the Western and Eastern blocks of the North China craton in the late Paleoproterozoic. The persistence of a Paleoproterozoic hot orogen for millions of years was probably the norm in the North China craton, which provides new insights into the tectonic-thermal evolution in the southern North China craton.

Characteristics and long-runout mechanisms of the coarse-grained debris avalanche deposit in the ancient continental rift basin

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.

Imprints of washover sediments by tropical storm Pabuk 2019 along the coast of the Gulf of Thailand; insight into coastal geomorphological response to storm surge

Tropical storm Pabuk (4th January 2019) struck southern Thailand, causing damage to the low-lying coastal area. The combination of waves, storm surge, and high tide resulted overwash and inundation of regions on the West coast of the Gulf of Thailand (GOT) side. After the event, we conducted a field survey from January 7–10 and 15–20, 2019 to investigate the effect of storm surges and the degree of damage from the site under the eye of storm affected area up to the north 500 km from the landfall sites. This paper investigates how variations in coastal geomorphological features respond to the storm surge generated by tropical storm Pabuk at a regional scale. Coastal damage was observed along the beach from the presence of the scour, beach scarp, knocked down trees, and destroyed buildings and infrastructure. The most damaged area was at Nakhon Si Thammarat (NST), where the tropical storm made landfall with maximum wind speeds of almost 100 km/h and a storm surge height of 5 m. At NST site, the washover deposits extended as far as 80 m from the coastline with a maximum inundation of 330 m. From this study, two types of washover deposits including perched fan and washover terrace were identified. The thickest washover sediment, 60 cm thick, was discovered in a relatively low-lying area adjacent to a small estuary. Mud rip-up clasts, planar stratification, cross stratification, foreset bedding, scouring at base, and sharp and erosional contact are characteristics of sedimentary structures found in storm sediments. Bedform surfaces, such as current ripples with indicated storm surge direction, were well-preserved at several sites. We suggest that the local geomorphological controlling factors, especially coastal elevation have played important roles in the difference of coastal geomorphological responses as well as the type of washover deposits.

Barite-bearing “septarian concretions” (upper Cretaceous – Paleocene) from the Biban area (north Algeria)

The "septarian barite concretions" have garnered significant interest worldwide. This study presents the first detailed investigation of these sedimentary structures in Algeria, with a primary focus on elucidating their genesis through petrography, SEM-EDS, major and trace elements (including REEs), and sulfur isotope analysis. The sampled concretions occur in Upper Cretaceous-Paleocene marl layers from the Biban area, primarily in two main sectors (Koudiat Djebassa and Sidi Ziane), situated within the Southern Tellian Atlas in Northern Algeria (Maghrebides). While these barite concretions exhibit diverse morphologies, our analysis focuses specifically on oblate ellipsoidal concretions. The flattened shape of these concretions may stem from compressed echinoid tests or small, oblate septarian cracked concretions representing the flattened cores. Notably, these concretions feature an outer cortex of radial fibrous barite crystals, measuring centimeters in thickness. Petrographic examination coupled with SEM-EDS analysis suggests that concretion growth occurred from porewaters in unconsolidated, soft sediments at shallow burial depths beneath the sediment-water interface, manifesting in three growth episodes: (i) an initial stage characterized by primarily thin lamellar barite crystals intertwining to form rosette-like structures in concretion cores, (ii) a later stage marked by radial-fibrous barite crystal growth in concretion margins, and (iii) the filling of septarian cracks by barite. The presence of terrigenous sediment, particularly abundant in rosette-like barite crystals, indicates growth within highly porous sediment. Conversely, the radial fibrous outer cortex is related to an effective displacive growth mode. The δ34S values of the barite concretions (ranging from 16 ‰ to 24.4 ‰), consistent with seawater values, which document that seawater was the primary sulfur source. Furthermore, REE geochemistry further supports the seawater origin of diagenetic fluids rather than a hydrothermal one. Concretions are suggested to have formed in organic-rich, fine-grained sediments at shallow depth below the sea floor, in sedimentation halts, and as a result of microbial degradation of organic matter. Barium was supplied to porewaters within the methanogenic zone, precipitating as barite when, migrating upwards, reached the boundary with the overlying sulfidic zone.

Biogeochemical traces and microbe-mineral interactions in the hyperarid core of the Atacama Desert

Life found various ways to thrive in hostile desert environments. Common adaptation mechanisms are protection against desiccation and UV radiation in biofilms and biocrusts as well as the hypolithic and endolithic colonization of rocks. One of those hostile regions is the Atacama Desert in Northern Chile with its hyperarid core, counted among the most arid places on Earth. Besides the aridity, life faces severe restrictions in these surroundings, e.g. extremely high UV radiation, scarce nutrient supply, and immense salt concentrations. Still, microbial communities and soil organic matter are crucial for the stability of soils and surface sediments in arid ecosystems. Combining molecular mass spectrometry for lipid biomarkers, scanning electron microscopy, and nuclear magnetic resonance spectroscopy, we individually investigated two factors that are of particular importance for the stability of dryland landscapes now and in the future: 1) We studied biogeochemical traces (organic remnants) in surface sediments along an aridity gradient with regard to possible decomposition and/or sequestration of organic compounds. 2) We investigated the interaction of lithobiontic and endolithic microbial communities with the mineral surface with special regard to the stability of soil and surface sediment structures in different areas of the Atacama Desert: in the region of the Salar Grande, Pisagua, and the Quebrada da Aroma. We analyzed halite- and calcium sulfate-dominated evaporitic crusts with and without visible microbial colonization. Organic traces were present in all investigated samples. Following an aridity gradient along the Quebrada de Aroma from an annual precipitation of about 20 mm to the hyperarid core with approx. 2 mm, we found a decrease in functionalized molecular compounds and plant-derived biomarkers (long-chain fatty acids, sterols) as well as an increase in aromatic hydrocarbons, indicating strongly decomposed remnants of plants and microorganisms. The investigation of halite- and calcium sulfate-dominated evaporitic crusts from the Salar Grande, Pisagua, and Aroma region revealed tight interactions of microorganisms with the mineral substrate. Indications of recent bacterial activity were ubiquitous (e.g. short-chain membrane fatty acids, carbohydrates of extracellular polymeric substances (EPS)). Scanning electron microscopy revealed that especially the microbial EPS within evaporites seems to biochemically stabilize mineral aggregates by agglutination. Moreover, fungal biomarkers showed that fungi and fungal parts of lichen were not only present at the surface of physical soil crusts but form widespread networks in the crusts and thereby contribute significantly to the physical stabilization of soils and surface sediments and erosion protection.

Centimeter-scale sedimentary structures in a lacustrine delta front, northern China: Ripples or Froude supercritical-flow bedforms?

Sedimentary strata are a significant record of the Earth and planetary history, and accurate recognition of sedimentary structures and their link to environmental conditions is a key component in deciphering past surface processes. Centimeter-scale sedimentary structures are commonly acknowledged as ripple cross-laminations, but here we document ambiguous centimeter-scale structures from a lacustrine delta front in northern China, that at careful look do not seem to fit with the known ripple cross-lamination criteria. The here documented sedimentary structures range from scour-and-fill, irregular lenses with structureless or low- and high-angle, up- and downstream dipping, concave and convex laminations. These centimeter-scale sedimentary structures thus considerably differ from ripple cross-laminations in their outer shape, internal organization, and morphometric parameters. Detailed comparison of these centimeter-scale structures with Froude supercritical-flow structures suggests that they were likely produced by Froude supercritical flows. Such centimeter-scale supercritical structures are not unique in the Bantanzi delta, as they have been also documented in a variety of settings ranging from rivers to deepwater turbidites. In light of this finding, we expand the Froude supercritical-flow sedimentary structures to centimeter scale, and advocate caution in interpreting centimeter-scale sedimentary structures axiomatically as ripple laminations.