Debris Flow Deposits Research Articles

Characteristics of debris flow development in Daxilada watershed and its hazard analysis on Lexi Expressway

The occurrence of frequent debris flow catastrophes in the mountainous regions of southwest China has necessitated the inclusion of debris flow disaster analysis and prevention as an essential component in the planning and construction of mountainous roadways. Daxilada watershed is located in the south of Mabian Yi Zuzizhixian, Leshan City, Sichuan Province, and the proposed Leshan-Xichang Expressway (Lexi Expressway) will pass through the upper reaches of Daxilada watershed. It is essential to consider that the presence of debris flows within the Daxilada watershed could have detrimental effects on the construction and functionality of the proposed Luoshanxi Bridge. This study examined the Daxilada watershed as a case study and analyzed the factors contributing to debris flow formation in the area. This analysis was based on field investigations, remote sensing interpretation, and experimental analysis. Additionally, the study utilized the Massflow software to simulate debris flow movement. It integrated the simulation results to determine the potential hazards the Daxilada Gully debris flow posed to the line project. This study found that Daxilada Gully meets debris flow formation conditions. The simulation results demonstrated that during the debris flow activity, there would be a maximum deposition depth of 2.1 m in the proposed Engineering Agency, which may lead to siltation and blocking disaster of the line project. Concerning the parameters related to the debris flow with a frequency of one in a hundred years, in conjunction with the outcomes obtained from numerical simulation, it would provide the design basis of the cross-flow cross-section of the proposed bridge. In a quantitative analysis of the blockage situation in the gully, debris flow deposits have the potential to cause damage to the line project. Debris flow deposits block the gully, but the risk of blockage is small. The study results have specific reference values for the debris flow prevention and control project of Lexi Expressway and offer valuable insights for the prevention and mitigation of similar disasters in relative projects.

A Late-Pleistocene confined volcanic debris avalanche promoted by hydrothermal alteration at the Tinguiririca volcano (Andes of Central Chile)

Distinguishing volcanic debris avalanche deposits from other epiclastic breccia could be complex. For more than 60 years, the Tinguiririca deposit (sourced from the homonymous volcano) in the Andes of Central Chile has been described by different authors as glacial moraines, a lahar, a volcanic debris avalanche, and even a debris flow deposit. To decipher its obscured origin and emplacement dynamics, we have carried out a detailed investigation of its distribution, contact relationships, sedimentology, and facies. Our findings unravel that the 57 km-long deposit is 5 to 300 m thick, totalling a reconstructed volume of 3.64 ± 0.05 km3. It is composed of unsorted heterometric breccias formed by clasts and blocks arranged in mixed and matrix facies characterised by distinctive lithological domains. In general, three clasts lithologies are dominant, consisting of black and grey andesites and hydrothermally altered clasts with jigsaw cracks and fractures. The deposit overlies terraced colluvium along the valleys and forms hummocks and ridges. Emplacement velocities estimates range from 39.6 m/s to 108.4 m/s. Therefore, the Tinguiririca deposit should represent a massive volcanic debris avalanche that formed after a lateral collapse that affected the ancient Tinguiririca Volcanic Complex, during the Late Pleistocene (between 45 ± 18 and c. 19.2 ± 1.2 ka). The abundance of hydrothermal minerals within the deposit's matrix and clasts (i.e., illite, phengite, epidote, tridymite, chlorite, hematite, jarosite, and alunite) all represent the volcano's hydrothermal system that likely favoured rock weakness and edifice collapse. Finally, the new interpretation is valuable for evaluating volcanic hazards and requires further mapping and research efforts.

Late Cenozoic mass transport deposits in the offshore Tanzania continental margin

Sediment mass movements and their associated Mass Transport Deposits (MTDs) have been widely studied due to their economic and geohazard potentials. This study combines 2D and 3D seismic reflection data with a seismic facies approach and attribute analysis to reveal the presence and distribution of different MTDs in the southernmost region offshore Tanzania. Results of seismic facies analysis show that the study area contains different Late Cenozoic MTDs. The MTDs have limited petroleum reservoir potential and include slides, slumps, debris flow deposits and occasional turbidites. The formation of these MTDs was caused by tectonic events associated with the development of the East African Rift System. Seismic attribute maps have shown the locations of channels, remnant blocks, headwall scars, and grooves confirming downslope sediment mass mobilization. The seabed attribute maps have shown areas where recent mass mobilizations were initiated. Some of these areas coincide with faults which have dissected the seabed, forming potential future gravity failure sites. Other future gravity failure sites include channel banks and slope edges, which may be present over the whole Tanzania continental margin. Sediment mass movements may be catastrophic, and therefore future infrastructure installations in the area must involve detailed mapping of the seabed to assess geohazard risks and act accordingly.

How and when did Paleozoic Maizuru back-arc basin close? Implications on the East Asian continental margin tectonics

The paleo-continental reconstruction of Asia during the Permian–Triassic boundary indicates major tectonic readjustments between multiple continental blocks in the north of North China Craton (NCC) due to complex plate subduction system(s). One of the major consequences was the closure of the Paleo-Asian Ocean. In a similar time frame, Proto-Japan was also evolving through plate-subduction with the opening of the Maizuru back-arc basin. The spectacular linear near-continuous belt of the Maizuru Terrain in the Inner Zone of Southwest Japan holds the rock record of the opening of the back-arc basin, sediment-fill in this basin culminating into closure-related pulsative debris flow deposits (i.e. the Tonoshiki Formation). However, the exact deformation mechanism(s), paleo-stress regime, their mesoscopic to microscopic rock record, and exact timing hold the keys to connecting the closure event of the Maizuru back-arc basin and the possible tectonics, in particular the closure of the PAO in Asia. With this aim, we report here the micro- to meso-structural geological records of rock units of the Maizuru Terrane which indicate evidence of (1) pre-depositional hydrofracturing, (2) extensive syn-lithification fracture-vein formation due to (3) broad WNW-ESE to E-W compressional paleostress regime using the fracture-vein analysis, (4) deformational e-twin development with the dominance of Type II twin indicating a maximum temperature of 300 °C with no evidence of overprinting. This brittle deformation affected all the lithounits of the Maizuru back-arc basin but not the overlying units deposited after the basin closure. New U-Pb detrital zircon age data of the rocks belonging to the Maizuru Group and also the overlying Fukumoto Formation fixes the age of the above-mentioned deformation event at ∼ 250 Ma. All these data help to assess the possible paleo-position of Proto-Japan and a clear tectonic scenario between the NCC, the Central Asian Orogenic Belt, and the Khanka-Jiamusi Massif in East Asia.

Potential for Events Similar to the Deadly West Salt Creek Landslide, Grand Mesa Area, Colorado

ABSTRACT The deadly West Salt Creek Landslide of 2014, one of the largest landslides to occur in the United States in historical time, was surprising in its suddenness and length of runout. Its source area, the edge of Grand Mesa in western Colorado, was potentially the source of other similar landslides in the past, based on previous mapping in the region. The purpose of this research was to evaluate the potential for similar events by detailed mapping of several canyons flanking West Salt Creek, using aerial imagery and age-dating techniques not available to previous mappers. We conclude that, while the West Salt Creek Landslide has the potential to reactivate in a similar manner to the 2014 movement, the potential for a similar event in the flanking canyons is low. Mapping and semi-quantitative geomorphic methods suggest that the deposits present in several canyons on either side of West Salt Creek are glacial or stream deposits, with one canyon containing debris-flow deposits. Our interpretations are based on the morphology of deposits in the canyons, the presence of specific landform features, measurements of mobility index and longitudinal profiles, and comparison with regional analogs. Furthermore, other mass movements in the region that are of similar magnitude had either slower movement or much shorter runout. The large block at the head of West Salt Creek and the earlier block that shattered and mobilized in 2014 are also unique features locally, distinguishing this setting from others, but also indicating the potential for a future similar event.

Feedback mechanism between gully landforms and sediment trapping efficiency in a check dam

Check dams have been used worldwide for a variety of purposes. With increasing age, check dams gradually lose their sediment trapping function via the continuous deposition of material carried by debris flows and flash floods, and eventually, check dams become unable to perform the designed mitigation function. In this paper, the sediment deposit evolution in a dam with multiple debris flow surges and its influence on the sediment trapping effect were investigated. The results showed that the debris flow deposition process can be divided into three phases: the backwater-controlled deposition phase, landform-controlled deposition phase, and quasi-equilibrium phase. The sediment trapping ratio of the check dam gradually decreased as the deposit volume increased and was linearly negatively correlated with the sediment deposition rate. Moreover, a mathematical model describing the negative feedback between deposit volume and sediment trapping ratio was established, and the physical meanings of the coefficients in the model and their empirical values were clarified. Furthermore, the deposit distribution, which satisfied the Weibull distribution in the longitudinal direction, was revealed. In the cross-sectional direction, the distribution of deposition gradually became uneven with increasing sediment filling rate.

Organic geochemistry, sedimentology and palaeontology of the Khatyspyt Formation, Arctic Siberia: Towards an integrated view of Ediacaran biofacies

The terminal Ediacaran Khatyspyt Lagerstätte (ca. 550–544 Ma) of Arctic Siberia has been a prime target for geobiological research. Previous evidence suggested that Ediacaran macroscopic soft-bodied organisms could be highly sensitive to sedimentary processes and various environmental factors such as water column stratification and seawater redox-conditions. By integrating organic geochemistry, sedimentology, and palaeontology of the Khatyspyt Formation, we identified three biofacies. The most proximal Longifuniculum biofacies consists of outer- to mid-ramp debris flow deposits and is characterised by a high taxonomic diversity and biomarker proxies pointing to a non-stratified non-euxinic water column. The most distal Aspidella biofacies comprises outer-ramp thin-bedded calcareous turbidites and is also marked by a high taxonomic diversity, although the associated biomarker proxies provide evidence for a stratified euxinic environment. Transient between those is the Nenoxites biofacies, consisting of outer- to mid-ramp debris flow deposits and characterised by a low taxonomic diversity, with biomarker proxies indicating redox instability. This systematic pattern suggests that the distribution of Ediacaran organisms was influenced by a heterogenous redox landscape. More specifically, the highest diversity of benthic soft-bodied organisms, including the iconic Charnia masoni, appears in stratified euxinic environments, while the highest diversity of macroalgae is found in non-stratified settings. The occurrence of a complex Ediacaran community in a stratified euxinic environment suggests that anoxia might have driven ecological differentiation of organisms, and that heterogeneous and dynamic redox landscapes were far more significant in early animal evolution than hitherto appreciated.

Formation mechanism of high-quality Palaeogene “compositional mixing” reservoirs in lacustrine rift basins: A case from the offshore Bohai Bay Basin, China

Mixed siliciclastic-carbonate reservoirs are currently considered a unique type of reservoir for hydrocarbon exploration. However, to date, research on “compositional mixing”, an important type of mixed sediment, remains relatively scarce. In recent years, significant breakthroughs in hydrocarbon exploration have been achieved in compositional mixing deposits, which are found within a lacustrine setting of the offshore Bohai Bay Basin in China. Despite the lack of systematic studies on their formation mechanisms, these discoveries are insightful case for understanding compositional mixing reservoirs (CMRs). In this study, an interdisciplinary approach that integrates petrographic analysis, cathodoluminescence analysis, reservoir characterization, and high-pressure mercury injection tests from drilled wells, cores, and thin sections, is employed to elucidate the characteristics of CMRs and the factors controlling reservoir modifications. Our findings reveal that compositional mixing deposits predominantly occurred with fan delta systems adjacent to uplifts. Two distinct reservoir types, namely, mixed slide deposits and mixed sandy debris flow deposits, were formed by coexistence of fan delta front siliciclastics with shallow-water biota (carbonate components). A comparative analysis of reservoir properties suggests that CMRs are of equivalent or superior quality to fan delta systems, challenging existing paradigms. This superiority is attributed to two primary factors: (1) the unique internal texture of compositional variations significantly influences subsequent diagenesis, leading to the extensive development of selective dissolution porosity and a reduction of clay cementation; and (2) distinctive early diagenetic events, including micrite envelopes and early dolomitization, markedly enhance the reservoirs’ resistance to compaction. In contrast, fan delta deposits lacking carbonate components do not undergo selective dissolution and their siliciclastic composition facilitates clay cementation. This study offers novel insights and a model for understanding the formation mechanism of CMRs, providing implications for future global petroleum exploration in mixed sediment reservoirs.

A Hydrodynamic‐Based Physical Unified Modeling for Simulating Shallow Landslide Local Failures, Mass Release and Debris Flow Run‐Out Extent Behavior

AbstractAccurate prediction of shallow landslide occurrence and the subsequent motion range after transformation into debris flows is crucial for reducing disaster‐induced losses. The use of Cellular Automata‐based (CA) hydrodynamic models has seen increasing application in predicting landslides, debris flows, and other related hazards. However, previous CA‐based models have primarily focused on the motion and evolution process of debris flows, lacking detailed description about the dynamic instability associated with shallow landslides. In this study, we propose a comprehensive CA‐based model that is based on existing theories and improved models for simulating hydrological processes, sliding surface identification algorithms, threshold‐based mechanical interactions, material entrainment, and deposition. The model was applied to the Yindongzi (YDZ) landslides in Sichuan, China. The accuracy of the model was validated through comparisons with field investigation results and calculations based on shallow water equations. This model enables efficient and rapid prediction of shallow landslide occurrence time, volume, spatial distribution, and runout distance. Evaluation of the model’s predictive performance reveals an error range of −23.12% to +44.26% for YDZ landslides. Moreover, the influence of different shallow landslide failure patterns on the deposition and erosion of debris flows was analyzed. The results indicate that the failure patterns of shallow landslides significantly affect the deposition and entrainment capacity of debris flows. This study provides a novel approach for predicting the occurrence of shallow landslides and the subsequent motion, entrainment, and deposition after transformation into debris flows.

Hyper KANAKO System을 활용한 토석류 피해 저감을 위한 계통적 사방대책의 평가

Understanding the local and regional topography and land use of an area is crucial to prevent debris flow recurrence sites caused by heavy rainfall. Scientific techniques, such as numerical modeling, are available for effective planning of management measures and predicting potential debris flow deposition sites from future rainfall events because they consider topography and land use. Quantitative evaluation results were produced by determining the arrangement, size, and type of check dams and modeling debris flow mitigation in the Hyper KANAKO system. The results revealed the original catchment had an increased vulnerability to soil erosion, transport, and deposition compared to the catchment with check dams. Furthermore, the systemic arrangement of check dams proved to be effective in reducing debris flow deposits when compared to a standalone arrangement. Future research is necessary to improve the erosion control planning, maintenance, and evaluation processes. The numerical model and resulting data from this study will be effectively utilized in decision-making by stakeholders to reduce the risk of future sediment-related disasters.

Tectonic geomorphology and Quaternary slip history of the Fuyun fault, southwestern Altai Mountains, central Asia

The northwest-trending Altai Mountains of central Asia expose a complex network of thrust and strike-slip faults that are key features accommodating intracontinental crustal shortening related to the Cenozoic India-Asia collision. In this study, we investigated the Quaternary slip history of the Fuyun fault, a right-lateral strike-slip fault bounding the southwestern margin of the Altai Mountains, through geologic mapping, geomorphic surveying, and optically stimulated luminescence (OSL) geochronology. At the Kuoyibagaer site, the Fuyun fault displaces three generations of Pleistocene–Holocene fill-cut river terraces (i.e., T3, T2, and T1) containing landslide and debris-flow deposits. The right-lateral offsets are magnified by erosion of terrace risers, suggesting that river course migration has been faster than slip along the Fuyun fault. The highest Tp2 terrace was abandoned in the middle Pleistocene (150.4 ± 8.1 ka uppermost OSL age) and was displaced 145.5 +45.6/–12.1 m along the Fuyun fault, yielding a slip rate of 1.0 +0.4/–0.1 mm/yr since the middle Pleistocene. The lower Tp1 terrace was abandoned in the late Pleistocene and aggraded by landslides and debris flows in the latest Pleistocene–Holocene (36.7 ± 1.6 ka uppermost OSL age). Tp1 was displaced 67.5 +14.2/–6.1 m along the Fuyun fault, yielding a slip rate of 1.8 +0.5/–0.2 mm/yr since the late Pleistocene. Our preferred minimum slip rate of ~1 mm/yr suggests the Fuyun fault accommodates ~16% of the average geodetic velocity of ~6 mm/yr across the Altai Mountains. Integration of our new Fuyun slip rate with other published fault slip rates accounts for ~4.2 mm/yr of convergence across the Chinese Altai, or ~70% of the geodetic velocity field.

Two-phase approach to modeling the grain-fluid flows with deposition and entrainment over rugged topography

We present a grain-fluid mixture for debris flows moving on a rugged (non-trivial) topography, where entrainment and deposition may take place. The model equations are derived with respect to a terrain-following coordinate system, which is constructed based on the topographic surface. The coordinates are fixed in space, and a “sub-topography” is added on the coordinate surface to account for the variation in the local topography when entrainment or deposition takes place. Numerical implementation is made based on a GPU-accelerated simulation tool, into which the entrainment-deposition mechanism is integrated accordingly. Two numerical examples are assigned to investigate the key features of the proposed model. One is on a horizontal plane, on which a finite mass of grain-fluid mixture is released from the state of rest. In this example, debris flow deposits significantly impact the post-event morphology and the associated flow behaviors. The other concerns a moving mass down an inclined chute merging into a horizontal deposition plane, where the levee formation is reproduced. At the end, the model is validated against grain-water experiments and applied to a large-scale historical event to evaluate its applicability.

Debris-flow avulsion tendency estimated from boreholes or channel cuts

Debris fans are an important landform for human habitation and development in mountainous regions. While much research in debris flow runout has focused on quantifying recurrence intervals and volume predictions, less research has focused on predicting their paths, which is important to reduce hazards to life and property. This project uses a quantitative stratigraphy tool, the compensation index, to evaluate the likelihood of debris path alteration by avulsion. The compensation index is a quantitative measure of the strength of compensational stacking, which measures the tendency of flow events to preferentially fill topographic lows. A significant constraint on the use of the compensation index for debris-flow hazard analysis is the need for large natural exposures of fan stratigraphy and the difficulty of mapping flow boundaries. Therefore, a more readily available proxy for estimating the compensation index of debris fans is needed, such as vertical stratigraphic sections from borehole data or natural channel incisions. Data from four previous studies was used to correlate trends in unit thickness to the compensation index calculated using data generated from simulated boreholes along the measured cross-sections. It was found that the central tendency and coefficient of variation of unit thickness had moderate correlation to the compensation index, and therefore predictive capacity, in both submarine and subaerial debris fans. By contrast, the same data for fluvial channelized floodplains revealed no correlation to compensation index. Therefore, a limited number of vertical stratigraphic sections could provide a reasonable estimate of the compensation index, and therefore avulsion tendency, of a debris-flow deposit.

CFD-DEM numerical investigation of the effects of water content and inclination angle on interactions between debris flows and slit dam

Debris flows, composed of sediment–water mixtures, can pose significant risks to downstream populations and infrastructure in mountainous regions. Slit dams have been demonstrated as being effective measures for decreasing the destructivity of debris flows. Reliable evaluations of the interactions between debris flows and slit dams are challenging if the complicated component characteristics of debris flows, such as the water content, are not considered. Here, a multi-scale study of debris flows impacting a slit dam is conducted via computational fluid dynamics and discrete element method (CFD-DEM) simulations to understand the influences of the water content (controlled by solid volume fraction in this study) and the channel inclination angle on flow–slit dam interactions. The results indicate that both the initial solid volume fraction and the channel inclination angle have significant effects on the impact kinematics of flow–slit dam interactions and regulation functions of the slit dam: (i) For gentle slopes, the deposition of debris flows is primarily influenced by flume basal friction, and the normalized peak total impact forces have little difference for a given inclination angle, whereas for steep slopes, an overtopping can occur, further result in the increasing of the normalized peak total impact forces with the increase of solid volume fraction. (ii) The run-up height and retention efficiency are also analyzed to provide a scientific reference for optimizing the design of slit dams.

Influence of sedimentary processes and fault tectonics on the evolution of submarine canyons in the East Andaman Basin: Insights from high-resolution seismic data analysis

The Andaman Sea Basin, a well-known back-arc spreading centre and a mature petroliferous basin, presents a unique and complex scenario for understanding the interplay of sedimentary processes and fault tectonics on seafloor geomorphology evolution, particularly in the eastern shelf region. This study, using high-resolution 3D seismic data and published exploratory well-seismic interpretation results, aims to establish a comprehensive stratigraphic framework for the Tanintharyi region, spanning the Lower Miocene, Middle Miocene, Upper Miocene, Pliocene, and Quaternary. A submarine canyon system was identified and investigated along the Tanintharyi continental slope within the East Andaman Basin, comprising thirteen slope-confined canyons arranged predominantly in an east-west vertical slope orientation. By analysing seismic reflection features, five distinct seismic facies have been identified, including basal lag (BL), slump and debris-flow deposits (SDFDs), canyon confined sheets (CCSs), laterally inclined packages (LIPs), and channel-levees (CLs). The evolution of this canyon system, a vital focus of this study, can be categorised into three phases based on the morphology and sedimentary structures observed: canyon initiation, canyon extension, and erosion-sedimentation. The findings of this study highlight the critical controlling role of faults in canyon evolution, with the intensity of fault activity displaying a negative correlation with canyon size, indicating the direct impact of faults on geomorphological changes. In addition, the geomorphological changes induced by fault activity have resulted in changes in sediment supply, dispersal, and sedimentation rates, thus significantly impacting the spatial distribution and dimensions of slope-confined canyons within the East Andaman Basin, with far-reaching implications.

Fluvial deposits of the Patlanoaya Group in southern Mexico: the stratigraphic record of an Early Mississippian supradetachment basin formed along the margin of Gondwana during the closure of the Rheic Ocean

ABSTRACT The Rheic Ocean closure stratigraphic record in southern Mexico is largely exposed in the Paleozoic Acatlán Complex. One of the most distinctive characteristics of the Acatlán Complex is the presence of high-pressure rocks, interpreted as remnants of the Rheic Ocean and the adjacent continental margin of Gondwana, which were subducted and then exhumed to the surface. Despite its importance in reconstructing the dynamics of the westernmost Rheic Ocean closure, the timing and mechanisms of exhumation of these high-pressure rocks remain debated. Some authors have tentatively interpreted the late Paleozoic, fluvial to marine succession of the Patlanoaya Group in southern Mexico as the sedimentary response to the exhumation of high-pressure rocks of the Acatlán Complex. Therefore, these sedimentary rocks may be particularly helpful in understanding the timing and evolution of high-pressure rocks exhumation during the Rheic Ocean closure. In this work, the tectono-sedimentary evolution of the continental deposits of the Patlanoaya Group was reconstructed, integrating sedimentologic, petrographic, and U-Pb detrital geochronological data to test the different scenarios proposed for the exhumation of the Acatlán Complex high-pressure rocks. Our data suggest that the lower Patlanoaya Group was deposited in an Early Mississippian basin with a two-stage evolution: a phase characterized by debris flow deposits derived from small-scale reliefs composed of low-grade metamorphic rocks and a subsequent phase marked by an NNE-trending fluvial system deposits sourced from low-metamorphic grade rocks of a mylonitic zone. Therefore, the lower Patlanoaya Group deposition was controlled by a major NNE-trending mylonitic shear zone associated with the development of a supradetachment basin linked to the progressive exhumation of high-pressure rocks during an Early Mississippian major extensional event. This work highlights the importance of sedimentary deposits in reconstructing the late Paleozoic history of the Acatlán Complex during the Rheic Ocean closure and the final stage of the Pangea assembly.

Sedimentary characteristics of mixed source fine-grained gravity-flow and its significance for shale oil exploration in a lacustrine depression basin: A case study of the Chang 73 Sub-member of the Triassic Yanchang Formation in Ordos Basin, NW China

This study investigates the transport and evolution of fine-grained gravity-flow deposits in lacustrine basins, focusing on the relationship between fine-grained deposits and their respective source–reservoir combinations. Such knowledge is vital for the exploration and development of unconventional oil and gas resources within the source-rock series of continental lake basins in China. We investigated the fine-grained gravity-flow deposits of the Late Triassic Chang73 Sub-member within the Yanchang Formation in the Ordos Basin. Our approach combined core observations, field outcrop evaluations, thin section analysis, scanning electron microscopy, geochemical data, and laboratory measurements. The sedimentary facies, characteristics, controlling factors, and sedimentary model of the fine-grained gravity-flow deposits are investigated. The primary sources of fine-grained sediments are terrestrial clastic and volcanic–hydrothermal fine-grained sediments. These sediments are mainly developed in warm, humid environments with abundant precipitation, favoring a highly reducible hypoxic terrestrial brackish–freshwater environment. Ten lithofacies and eight bed types of fine-grained gravity-flow deposits are categorized. Bed types represent deposits of muddy slide deposits, muddy slump deposits, muddy debris flow deposits, muddy flow deposits, hybrid event beds, fine-grained transitional flow deposits, surge-like turbidity flow deposits, and fine-grained hyperpycnal flow deposits. As a result of paleo-seismicity, volcanic events, and paleogeomorphology, instability and subsequent collapse of the delta front sediments led to the formation of gravity-flow deposits. These deposits formed the “channel–lobe complex” and “sublacustrine fan” sedimentary systems in both the southwestern and northeastern parts of the basin, respectively. Meanwhile, extraordinary flood events formed during the Carnian Pluvial Episode (CPE) played a significant role. It prompted increased fluvial drainage that drove fine-grained hyperpycnal flows through pre-existing valley systems, resulting in the establishment of the “channel–lobe complex” sedimentary system. The Chang 73 Sub-member contains high-quality hydrocarbon source rocks, laying the foundation for shale oil. The introduction of volcanic ash and the influence of hydrothermal activities amplify the enrichment of organic matter within the lacustrine basin. Fine-grained gravity-flow deposits yield siltstone-rich sweet intervals, primarily seen in surge-like turbidity and hyperpycnal flows. The interbedding of sandy and muddy sediments, influenced by hybrid event beds and fine-grained transitional flows, establishes a stratigraphic arrangement in which the upper layer nourishes the underlying reservoir. This structure is particularly beneficial for the development of shale oil and gas sweet intervals.

Exploring debris flow deposit morphology in river valleys: Insights from physical modeling experiments

A comprehensive understanding of the deposit morphodynamics of debris flows in river valleys is crucial for disaster prevention and mitigation in mountainous areas. However, debris flows in river valleys are complex and variable, and the influence of the composition and terrain on deposit mechanisms and morphology remains unclear. In this study, a series of laboratory experiments were conducted to investigate the impact of the water content, slope, and grain size distribution on the deposit morphology of debris flows in river valleys. In the experiments, debris flows form narrow and elongated shuttle-shaped deposits upon entering river valleys. Increased water content and slope enhance the mobility of debris flows, resulting in wider deposit widths, gentler deposit slopes, and larger deposit areas. An increase in the gravel fraction partially facilitates the movement and deposition of debris flows. However, a large number of coarse particles may increase internal friction within the debris flow, hindering the spread of deposits and resulting in a relatively concentrated deposit with a steeper morphology. Furthermore, the debris flow regime shifts from friction to collision as the water content, slope, and gravel fraction increase. Debris flows dominated by collision forces exhibit higher mobility and a wider impact area, potentially leading to more severe disaster consequences. Compared with unconfined debris flows, the deposit area of debris flows in the river valley is smaller, and the deposit width to height ratio is larger. There is a power function relationship between deposition area and Savage number in river valleys. Additionally, particle sorting and flow regime transformation during the movement and deposition of debris flows can significantly impact the morphology and internal structure of the deposits in river valleys and then affect the development of debris flow dam breaching. In summary, this study utilized experiments to simulate natural debris flows, offering fresh insights into the depositional behavior of debris flows in river valleys.

Scree conglomerate and its derivatives in the Upper Cretaceous Kallankurichchi Limestone, Ariyalur Group, Cauvery Basin, South India

The repetitive influx of coarse clastics of mixed composition, siliciclastics and carbonates, locally common in the lower part of the Upper Cretaceous marine Kallankurichchi Limestone specifies a resurgence of tectonic unrest in the Cauvery rift basin, India. The basin-margin scree and its derivatives elicit diverse modes of emplacement and differ in many ways from denoting it only as basal conglomerate. The study meticulously reveals the depositional history of these basin-margin coarse clastics. The scree conglomerate bodies are wedge-shaped in appearance and often have flat, eroded tops. At places, their surfaces, tops and flanks, are encrusted with Inoceramus although internally, they are mostly unfossiliferous. They are clast-supported and extremely poorly sorted, having interstitial spaces filled by sand-sized grains at the basal part. The clasts can be traced into the underlying Sillakuddi Sandstone and the granitic basement. The clasts derived from the sandstone are angular and measure up to 60 cm in length, while the basement-derived clasts dominate the smaller (maximum diameter measured 5 cm) and more rounded population. The elongated clasts are chaotically arranged, even oriented sub-vertically, reclining on other clasts. The lowermost scree conglomerate has a sharp base, and the pebbles sunk into the underlying sandstone, although no discernible impact laminae wrapping their bottom were ever observed. Evidently, the scree fans were initiated under the sea, which permitted the slow sinking of assorted rock fragments dropped from above. The sporadic occurrence of marine fossils further corroborates this contention. The scree conglomerates at different stratigraphic levels transitioned laterally into conglomerates of mass flow origin and then to massive calcarenite, together forming wedge-shaped bodies. The initial alignment of clasts parallel to bedding transforms to a chaotic alignment representing the transition from internally sheared flow to debris flow and associated shapes. Matrix-supported fabric grades into massive calcarenite, suggesting gravity-driven transformation. Further down the wedge, the massive calcarenite turns into cross-stratified facies, making it evident that laminar flow turned turbulent in the course of body transformation of the sediment-driving flows. It can be presumed that these flows were triggered by subsidence, which resulted from renewed gaps in formation and led to the collapse of scree cones. Facies variability suggests scree deposits giving way downslope to debris flow and related deposits. Eventually, all the scree products pass laterally into the carbonate formation basinwards.

Significance of a Mesoproterozoic tide-reworked fan delta – tidal flat transition: A transgressive-regressive model

Records of tide-reworked fan delta facies models are rare in literature, attributed to their lower abundances due to complex sediment distribution pattern by two exclusive end-member flows, viz., a seaward directed subaerial to subaqueous debris flow, and dominant tidal current system interfering with and reworking the debris flow. Lack of appropriate analogues of tide-reworked fan deltas makes the ancient examples more significant. The analysis of such rare tide-reworked fan deltas from deep-time, e.g., Mesoproterozoic, turns out to be unique due to the gap in clear understanding of the alluvial-fluvial vs marine processes in non-vegetated land parts. The lower part of the Mesoproterozoic Rajgarh Formation, Lalsot Basin, North Delhi Fold Belt, Aravalli Craton in NW India, provides a rare record of a tide-reworked fan delta depositional system. Sedimentary facies analysis reveals eleven lithofacies grouped under three major facies associations, viz., (i) gravel-rich conglomerate facies association, characterized by stacked debris flow deposits forming a subaerial alluvial fan, representing the delta topset component, followed downslope by (ii) pebbly, cross-stratifed sandstone facies association, characterized by reworking of the subaqueously emplaced debris flows by ebb-tidal currents, to produce the mouth bar and the delta front depositional systems, and finally, (iii) sandstone-mudstone heterolithic facies association, characterized by abundant tidal signatures in pebble-free thin-bedded sandstone-mudstone heteroliths with tidal bundles, herringbone cross-strata and wave ripples, characterizing a stable platformal subtidal-intertidal flat depositional system. The lower-middle part of the succession records an aggradational stratal stacking pattern of the subaerial alluvial fan changing to progradational stratal stacking of the laterally accreted debris-rich tide-led clinoforms producing the delta topset – mouth bar – delta front transiton of a tide-reworked fan-delta under successive regressive conditions, representing syn-rift deposition near the basin margin. A retrogradational stratal stacking pattern overlies the fan-delta succession, and signifies a transgression by landward encroaching tidal flat system over the fan-delta system during post-rift phase in a stable platformal setup, where debris supply is ceased. A regressive-transgressive model characterizing the transition from a fan-delta to tidal flat depositional systems portrays fluctuations in the accommodation conditons in response to complex interplay of basin tectonics and relative sea level changes in the Mesoproterozoic riftogenic Lalsot Basin.