Fan Deposits Research Articles

Magnetic Characterization of Sediment Source‐To‐Sink Processes in the Bengal Fan Since 45 ka

AbstractThe Bengal Fan is the largest submarine fan on Earth with a complex submarine channel system. Therefore, it is challenging to understand the evolution of Bengal Fan sediment source‐to‐sink processes. Here we present a synthesis of high‐resolution environmental magnetic records of five sediment cores from the central and lower Bengal Fan to reconstruct sedimentation history for the past 45 ka. Rock magnetic measurements and electron microscopic analyses reveal that detrital (titano)magnetites are the dominant magnetic minerals in the central fan sediments, while lower fan deposits exhibit enhanced magnetofossil contribution. During the last three marine isotope stages, glacial periods have increased detrital magnetic mineral concentration and grain size compared with interglacial periods. This increase is primarily attributed to the weakening of the Indian summer monsoon. Spatially, magnetic mineral concentration and grain size show decreasing trends from north to south and from east to west in the Bengal Fan, which may be modulated by submarine channel shifts. Deposition center migration driven by sea level fluctuations and sediment provenance variations were key factors controlling magnetic mineral concentration and grain size. Therefore, magnetic proxies serve as sensitive indicators of sedimentation patterns within the Bengal Fan. The spatiotemporal distribution of magnetic particles provides valuable insights into the source‐to‐sink dynamics and the dominant factors affecting sediment transportation in global submarine fans.

Terminal Fan Deposition and Diagenetic Control in the Lower Paleogene of the Shahejie Formation, Bonan Sag, Bohai Basin, China: Insights into Reservoir Quality

In the Bonan area, the lower fourth member of the Shahejie Formation (Es4x) is buried beneath a sedimentary pile ranging from 2500 to 5000 m. Understanding the impact of diagenetic alterations on these deeply buried reservoirs is crucial for effective hydrocarbon exploration and production. This study employs a terminal fan sedimentation model, encompassing depositional environments such as feeder channels, distributary channels, floodplains, and basinal zones, to provide insights into the spatial distribution of reservoir properties and their influence on the localization of optimal reservoirs within the sag. The analysis integrates diagenetic facies with well log responses, subsurface porosity trends, and permeability variations across the formation. The petrographic analysis indicates that the sandstone is composed primarily of litharenite, feldspathic litharenite, lithic arkose, and minor amounts of arkose. The dominant clay cement is illite, accompanied by mixed-layer smectite/illite, chlorite, and kaolinite. Thin section observations reveal secondary porosity formed through the dissolution of quartz grains, volcanic rock fragments, and feldspar, along with their associated cements. These sandstones exhibit relatively good sorting, with average porosity and air permeability values of 14.01% and 12.73 mD, respectively. Diagenetic alterations are categorized into three processes: porosity destruction, preservation, and generation. Key diagenetic mechanisms include compaction, cementation, replacement, and dissolution, with compaction exerting the most significant control on reservoir porosity reduction. Statistical analysis indicates that the average porosity loss due to compaction is approximately 13.3%, accounting for about 38% of the original porosity. The detrital rock cement predominantly comprises quartz (42%), feldspar (32%), clay minerals (14%), and carbonate (12%). Under the prevailing depositional conditions, porosity is enhanced by dissolution and fracturing, while late-stage diagenetic cementation by clay and carbonate minerals—excluding chlorite—adversely affects reservoir quality. Consequently, the distributary zone is identified as the primary target for exploration.

A 300 kyr record of past hydroclimate change from alluvial fans in the southern Central Andes

AbstractAlluvial fans are hypothesised to record signals of past hydroclimate changes in their depositional chronologies and slopes. However, direct tests of this hypothesis have been limited due to challenges in precisely dating the responses of alluvial fans to past climate forcing. Here, we present a new chronology of alluvial‐fan deposition at the Sierra de Aconquija in the southern Central Andes (27°S) spanning ~300 kyr and based on 35 cosmogenic 10Be‐derived exposure ages and eight infrared‐stimulated (IRSL) and optically stimulated luminescence (OSL) ages. The ages reveal that fan deposition was phased with past climate changes. Orbitally‐forced weakening and strengthening of the South American Summer Monsoon coincided with fan aggradation during dry episodes and incision during wetter episodes, consistent with predictions from alluvial‐channel models. These results are in precise agreement with independent palaeoclimate constraints spanning timescales of 103 to 105 years. Fan aggradation‐incision cycles record a predominant influence of precession‐induced variations in precipitation, although climate shifts as rapid as 1 kyr also triggered incision, and fan architecture appears to be further modulated by orbital eccentricity cycles. Incision events on the fans coincide with the ages of moraines in the headwater catchments, including those formed during the Younger Dryas and Last Glacial Maximum. Furthermore, the fan chronology indicates dry conditions in the southern Central Andes during Heinrich Stadial 1, suggesting that enhanced precipitation during this episode was limited to more northerly latitudes. Our results demonstrate that climate change exerts a primary control on simple, source‐to‐sink sedimentary systems and show that alluvial fans can, in some cases, be utilised as terrestrial palaeoclimate archives with which the spatio‐temporal variability of past climate changes can be constrained.

Paleo‐Suture Zone Disrupted by Thrusting: Example From East Junggar (NW China), Southern Altaids

AbstractUnderstanding the tectonic evolution of ancient orogens relies on reconstructing the primary architecture of suture zones that may be modified by post‐subduction events. Modifications in East Junggar, southern Altaids, have led to controversial interpretations about the Paleozoic tectonic evolution. To clarify these relationships, we report the Mesozoic thrust horizon in East Junggar that has displaced the Baishanbao Klippe, which contains siltstone, sandstone, conglomerate and biogeographical Tuva‐Mongolia Tuvaella fauna. This klippe is distinct from units in the footwall that contain Ordovician‐Early Devonian accretionary complexes with dismembered basalts, cherts and deep marine tuffaceous siltstones, Carboniferous volcanic rocks and granites, Middle‐Late Jurassic sediments, and Kazakhstan biogeographic Ordovician‐Late Devonian coral‐brachiopod‐ammonoid fauna. The thrust horizon and the aforementioned units are unconformably capped by Late Jurassic‐Early Cretaceous alluvial fan deposits; it constrains the thrust to a Mesozoic age. These two biogeographic domains were separated by the Paleo‐Asian Ocean until the Late Paleozoic, as evidenced by the 478 Ma Kujibai MOR‐type ophiolite that involved into subduction zone in the Carboniferous. This Mesozoic thrust transported the Baishanbao Klippe for over 100 km southwards from its root in the Altay‐Fuyun area and crossed a cryptic suture zone of the Paleo‐Asian Ocean as an allochthonous unit in East Junggar. It extensively disrupted the primary Paleozoic orogenic architecture of East Junggar that leads to misinterpretation of the regional tectonic evolution. A lesson from disruption of this Mesozoic thrusting is that care must be taken in studies of the architecture of paleo‐suture zones.

Landslide Hazard Mitigation for Sustainability Settlement in Maninjau Lake, West Sumatera

Abstract The landslides around the Maninjau Caldera rim, particularly in the south, have posed a significant threat to lives over the years. Settlements nestled between Maninjau Lake, and the caldera wall are highly vulnerable to these hazards, and relocation is not feasible due to the scarcity of suitable land. The aim of study is to identify the safest area based on historical landslide data which is crucial for mitigation works in developing the Ngarai Sianok-Maninjau Geopark. This paper provides the affected delineation from the recent landslide compared to older events by identifying colluvial sediment and its morphological characteristics. The most recent major landslide occurred on July 13, 2023, in the Tanjung Raya District following heavy rainfall. The western and southern sections of the caldera rim, characterized by the steepest slopes, are most prone to landslides. Approximately 43 landslides with debris flow mechanisms along the inner caldera rim cover 3 villages (Nagari), namely Koto Malintang, Tanjung Sani, and Sungai Batang. Landslide debris in the southeast consists mainly of muddy sand, contrasting with the gravel and boulder sediment found elsewhere. All landslides originate in intermittent streams, creating sediment fans up to 50 meters wide downstream. Given this fan-shaped pattern, dispersed residential development is advisable over clustered housing, especially in Jorong (hamlet) Pantas, Nagari (village) Tanjung Sani. The high susceptibility of all drainage channels to landslides makes the main road vulnerable to disruption. Water transportation is strongly recommended as an alternative to prevent residents from becoming isolated if the main road is blocked.

Late Cenozoic sedimentary records of the uplift of the Karlik Mountain and aridification of the Hami Basin, central Asia

The Karlik Mountain, at the extreme easternmost Tianshan, marks the terminus of the modern Central Asian Orogenic Belt and serves as a natural laboratory for exploring how strain spreads from the margins of the Eurasian plate to its interior. This study investigates Cenozoic strata, including Oligocene-Miocene Taoshuyuanzi Formation and Pliocene Putaogou Formation, in the Hami Basin through detailed facies analysis, detrital zircon U-Pb geochronology, and magnetic susceptibility to reconstruct the Cenozoic mountain-building history and climate variation of the easternmost Tianshan. Provenance analysis indicates that the Cenozoic sediments were derived from the north and can thus be used to reflect the mountain-building processes of the Karlik Mountain. Facies analysis shows that the Taoshuyuanzi Formation began with fan delta deposits at the lake margin, followed by lacustrine deposits, while the Putaogou Formation is dominated by alluvial fan deposits. The synchronization with intense aridification, as revealed by sedimentary features, allows us to propose that the coarse-grained alluvial deposition in the Putaogou Formation of the Hami Basin marks the Pliocene uplift of the Karlik Mountain. The magnetic susceptibility increased dramatically in the Pliocene, with the trend correlating well with that of the lithology coarsening. The tectonic uplift of easternmost Tianshan, along with the subsequent extreme aridity associated with the global cooling and orogenic barrier, facilitated the preservation of magnetite, leading to the accumulation of alluvial deposits with increased magnetic susceptibility during the Pliocene.

Beyond boundaries: Depositional environment controls on erodibility, process, and form in rivers incising sedimentary bedrock

Abstract Bedrock rivers adjust to the properties of the rock into which they incise, imprinting the geologic past on Earth's surface. We compared rock properties and channel form along the Dry Fork in the Allegheny Mountains, West Virginia, as it crosses between Mississippian sandstone and carbonate rock units, to investigate how the depositional history of channel-margin bedrock influences modern channel form. We used thin-section petrography to interpret site-specific depositional environments. We quantified rock strength with point-load testing, discontinuity spacing by measuring bed and fracture spacing, and channel form through cross-section surveys. Petrography indicates that the sandstone was likely deposited in an alluvial fan, while the carbonate formed in a shallow-marine environment. The sandstone has modestly higher point-load strength than the carbonate, but the units differ more dramatically in their discontinuity spacing. The sandstone is thinly (3–10 cm) bedded and densely (50–100 cm) fractured; the carbonate has thicker (45 cm) beds and sparser (180–300 cm) fractures. Sandstone channel cross sections are wider, shallower, and rougher, whereas carbonate cross sections are narrower, deeper, and smoother. Results suggest that a transition from plucking-dominated erosion in the discontinuity-rich sandstone to abrasion- and/or dissolution-dominated erosion in the discontinuity-poor carbonate, rather than differences in rock strength, drives observed morphologic differences. Differences in discontinuity spacing might arise from differential bed thickness between the two units, both because bed boundaries are discontinuities and because thinner beds lead to more densely spaced fractures. We hypothesize that depositional dynamics—the unsteady deposition of an alluvial fan resulting in thin beds versus steady, shallow-marine deposition that deposited thicker beds—explain the observed differences in bed thickness, discontinuity spacing, and modern erosion process dominance and channel form, emphasizing how modern Earth-surface processes are contingent on the geologic past.

Indication of Deep-Water Gravity Flow Types by Shelf-Edge Trajectory Migration Patterns: A Case Study of the Quaternary Qiongdongnan Basin, South China Sea

The shelf-edge trajectory is comprehensively controlled by tectonics, sediment supply, sea level, and climate fluctuations; its migration and evolution have a strong influence on what happens in the deep-water depositional system during the Quaternary. The shelf-edge trajectory pattern, sediment-budget partitioning into deep-water areas, and reservoir evaluations are focused topics in international geosciences. In this paper, the Qiongdongnan Basin (QDNB) in the northern South China Sea is taken as an example to study how shelf-edge trajectory migration patterns can influence the types of deep-water gravity flow which are triggered there. Through quantitatively delineating the Quaternary shelf-edge trajectory in the QDNB, four types of shelf-edge trajectory are identified, including low angle slow rising type, medium angle rising type, high angle sharp rising type, and retrogradation-slump type. A new sequence stratigraphic framework based on the migration pattern of shelf-edge trajectory is established. There are four (third-order) sequences in the Quaternary, and several systems tracts named lowstand systems tract (LST), transgressive systems tract (TST), and highstand system tract (HST) are identified. This study indicates that the type of deep-water gravity flow can be dominated by the shelf-edge trajectory migration patterns. When the shelf-edge trajectory angle (α) ranged between 0° and 4°, the continental canyons were mostly small-scaled and shallowly incised, with multiple large-scale sandy submarine fan deposits with few MTDs found in the deep-water area. When the angle (α) ranged from 4° < α < 35°, the size and incision depth of the continental slope canyons increased, relating to frequently interbedded sandy submarine fan deposits and MTDs. When angle (α) ranged from 35° < α < 90°, only a few deeply-incised canyons were present in the continental slope; in this condition, large-scaled and long-distance MTDs frequently developed, with fewer submarine fans deposits. When angle (α) ranged from 90° < α < 150°, the valley in the slope area was virtually undeveloped, sediments in the deep-sea plain area consisted mainly of large mass transport deposits, and submarine fan development was minimal. Since the Quaternary, the temperature has been decreasing, the sea level has shown a downward trend, and the East Asian winter monsoon has significantly enhanced, resulting in an overall increase in sediment supply in the study area. However, due to the numerous rivers and rich provenance systems in the west of Hainan Island, a growing continental shelf-edge slope has developed. In the eastern part of Hainan Island, due to fewer rivers, weak provenance sources, strong tectonic activity, and the subsidence center, a type of destructive shelf-edge slope has developed. The above results have certain theoretical significance for the study of shelf-edge systems and the prediction of deep-water gravity flow deposition type.

Hydrologically sensitive carbonates: Tectonic and groundwater controls on synrift sedimentation in the Late Jurassic–Early Cretaceous of the western Cameros Basin, Northern Spain

AbstractBasin hydrology and subcrop are key controls on carbonate sedimentation in continental basins. Hydrologically sensitive carbonates can record groundwater fluctuations within an aquifer in deep time. Late Jurassic extension, footwall uplift, erosion and karstification of marine Jurassic carbonates in the western Cameros Basin (Spain) saw deposition of ?Upper Kimmeridgian‐Tithonian syntectonic alluvial fan deposits (Señora de Brezales Formation). Biogenic laminar calcretes and phreatophytic rhizocretions record roots exploiting capillary fringe groundwater. Progressive infill of rift topography and footwall erosion lowered sedimentary gradients and clastic supply during deposition of the ?Tithonian–Berriasian Rupelo Formation. Distal alluvial marls (Las Viñas Member) contain charophytes, with 2 m thick carbonate lenses at the top reflecting intermittent rise of groundwater in ponds on the basin floor. Stacked palustrine limestones with rare charophytes and laminar calcretes (Ladera Member) record overstep of seasonal carbonate wetlands onto basin margins and footwall highs with intense pedogenetic modification during lengthy seasonal exposure. Overlying Berriasian charophyte‐ostracod wackestones, displaying microkarst cavities and interbedded intraclastic conglomerates, with vivianite sauropod bones, footprints and polygonal desiccation cracks at the top (Mambrillas de Lara Member) record open lacustrine conditions with limited subaerial exposure and high water tables. Desiccation‐cracked limestones and marls with correlatable evaporite horizons (Rio Cabrera Member) contain marginal marine foraminifera and dasycladaceae at the top. Lagoonal conditions reflected transgression to seaward and intermittent marine connection via the Basco‐Cantabrian Basin. The distribution and thicknesses of hydrologically sensitive carbonates reflected onlap onto a faulted and karstified marine Jurassic carbonate pediment and the subtle influence on hydroperiod of fault (and potentially localised Triassic salt) controlled differential subsidence and transgressive groundwater rise. Hydrological facies evolution reflects progressive basin infilling and eustasy beyond. Transitions in this continental succession from clastic to carbonate facies and from closed to open hydrology record hydrological change over time rather than contemporaneous deposition under Walther's Law.

Diagenetic History and Biosignature Preservation Potential of Fine‐Grained Rocks at Hogwallow Flats, Jezero Crater, Mars

AbstractThe Mars 2020 Perseverance rover discovered fine‐grained clastic sedimentary rocks in the “Hogwallow Flats” member of the “Shenandoah” formation at Jezero crater, Mars. The Hogwallow Flats member shows evidence of multiple phases of diagenesis including Fe/Mg‐sulfate‐rich (20–30 wt. %) outcrop transitioning downward into red‐purple‐gray mottled outcrop, Fe/Mg clay minerals and oxides, putative concretions, occasional Ca sulfate‐filled fractures, and variable redox state over small (cm) spatial scales. This work uses Mastcam‐Z and SuperCam instrument data to characterize and interpret the sedimentary facies, mineralogy and diagenetic features of the Hogwallow Flats member. The lateral continuity of bedrock similar in tone and morphology to Hogwallow Flats that occurs over several km within the western Jezero sedimentary fan suggests widespread deposition in a lacustrine or alluvial floodplain setting. Following deposition, sediments interacted with multiple fluids of variable redox state and salinity under habitable conditions. Three drilled sample cores were collected from this interval of the Shenandoah formation as part of the Mars Sample Return campaign. These samples have very high potential to preserve organic compounds and biosignatures. Drill cores may partially include dark‐toned mottled outcrop that lies directly below light‐toned, sulfate‐cemented outcrop. This facies may represent some of the least oxidized material observed at this interval of the Shenandoah formation. This work reconstructs the diagenetic history of the Hogwallow Flats member and discusses implications for biosignature preservation in rock samples for possible return to Earth.

Distinguishing fault offset from climatically modulated channel deflections: Insights from the Pearblossom slip-rate site, Mojave section of the San Andreas fault, California, USA

Abstract Fault slip histories are essential for understanding seismic hazard and regional fault system development but fundamentally depend on identifying, dating, and reconstructing displaced markers. Here, we use a case study of the Pearblossom site along the Mojave section of the San Andreas fault in California (USA) to show how pulses of sediment aggradation during wet periods can complicate such reconstructions by producing “imposter offsets”—landforms that develop with an initial deflection that is easily misread as tectonic displacement caused by fault slip. Specifically, we document two channels on the downstream side of the fault: a subtle one that we interpret to have been beheaded and displaced 24–49 m from a source channel on the upstream side of the fault, and a second and more prominent one that we interpret as an imposter offset of 36–88 m. Using optically stimulated luminescence dating, we determine that the source channel incised between 1.44 ± 0.43 ka and 1.27 ± 0.18 ka with a subsequent phase of alluvial fan aggradation at ~0.6 ka, when the channel with the imposter offset formed. Because the pulse of fan deposition coincides temporally with a wet period in Southern California precipitation records, we attribute formation of the imposter offset and the alluvial fan into which it incised to climatically modulated deposition at the site. Comparing precipitation records with charcoal ages compiled from multiple Mojave Desert region locations suggests that other slip-rate sites may be similarly affected. Although climatic effects can complicate slip-rate studies, we show that the morphology and upstream position of the deflected channel can indicate whether a site likely records useful information about fault slip.

Thousands of shallow, relict gullies indicate thermo-erosion on the sandy uplands of northern Lower Michigan during the Late Pleistocene

Thousands of shallow, relict gullies indicate thermo-erosion on the sandy uplands of northern Lower Michigan during the Late Pleistocene

Spectral decomposition predicts the distribution of steep slope fans in the rift basin of eastern China

Spectral decomposition predicts the distribution of steep slope fans in the rift basin of eastern China

Syntectonic Late Devonian terrestrial sedimentation in the southern Bonaparte Basin, Western Australia

Late Devonian sedimentation in the southern Bonaparte Basin was controlled by, and provides a record of, contemporaneous fault movements in the Halls Creek Orogen. An important episode of Late Devonian faulting caused uplift and southward tilting of the Carr Boyd Ranges block and uplift and northward tilting of the O’Donnell Ranges block forming the Galloping Creek and Ragged Ranges sub-basins, respectively. Uplift of the Carr Boyd Ranges provided the eastern source of the Ragged Range Conglomerate, while the south-dipping Carr Boyd Ranges and the uplifted O’Donnell Ranges and Bow River blocks formed the northern and western sources of the Galloping Creek Formation. Conglomeratic facies on both the northern and southwestern margins of the Galloping Creek Sub-basin record interaction with a fault-controlled topography. The apparent lack of unconformities within the northern Galloping Creek Formation and the progressive increase in siltstone content towards the centre of the sub-basin suggest that faulting was no longer an active driver for sedimentation. While alluvial fan deposition infilled the southwestern part of the sub-basin, the remainder of the Galloping Creek Formation was deposited by fluvial systems that changed from an initial proximal braided stream character to a later distal character with more extensive floodplain deposition. Post-depositional folding and faulting of the Galloping Creek Sub-basin were confined to movement on the Halls Creek and Glenhill faults with a probable 10+ km of sinistral offset and uplift of the western block along at least the latter.

Safety Factor Analysis on the Stability of the Retaining Wall Structure in Cimahi City, Indonesia

Retaining wall is a construction built to hold the ground on the slopes. Retaining wall can be said to be safe if its safety factors have been taken into account.In this study will be calculated the security factor based on SNI 8640:2017 on the location to be built retaining wall located in the area of Cimahi City, West Java using the help of software with two-dimensional finite element method.Based on the soil type map, the majority of the Cimahi City area consist of Tuffaceous Clay and Sandy Clay soils, which are alluvial fan deposits of volcanic origin, with soil thickness ranging from 1 m to 5 m. Retaining wall structures using cyclopean concrete appear to be slimmer compared to those using stone masonry. The use of dolken wood piles as additional reinforcement in locations using cyclopean concrete can strengthen the structure on the sliding plane, thus preventing overturning. Based on the modeling, the use of this structure resulted in a safety factor value greater than 1.5, with a displacement of 20 cm.

New evidence of glacier advances during Lateglacial Interstadial deciphered from facies evolution in proglacial lacustrine basins of the Maurienne Valley, French Alps

New evidence of glacier advances during Lateglacial Interstadial deciphered from facies evolution in proglacial lacustrine basins of the Maurienne Valley, French Alps

A new example of polyphase basin formation in western Anatolia: Plio-Quaternary Tavşanlı Graben, Kütahya

ABSTRACT The southwestern part of Turkey is called the ‘western Anatolia Extensional Province‘. Today, there is an approximately N-S-oriented extension in this area. The seismically active region is characterized by E-W and N-S-trending grabens. The tectonism and evolution of Tavşanlı Graben, one of these grabens, during the Plio-Quaternary period are the main subjects of this study. The Tavşanlı Graben, about which there is no information in the literature, has been defined for the first time in this study, and the geometrical and kinematic properties, relative ages, and interrelationships of some Neogene-aged faults, especially Quaternary-aged faults, have been presented in the manuscript. The data obtained indicate strike-slip faulting in the late Pliocene in the region. These E-W striking faults and the basin they formed are the first in western Anatolia with these features. In the Quaternary, E-W-oriented normal faults were formed in the region. The asymmetric topography of the graben area is consistent with the other E-W-oriented grabens in western Anatolia. Late Cretaceous basement rocks and Miocene-aged units are observed at the margins of the graben, which are fragmented by faults. The fill of the graben is Quaternary-aged fan deposits and alluvium. In this study, it was determined that the Tavşanlı Basin, which started to form with a transtensional mechanism at the end of the Pliocene, was transformed into the Tavşanlı Graben in the Pleistocene. The basin formation, which started with directional faulting in the late Pliocene, evolved into a graben in the Quaternary, and reached its present form by completing its development in two phases, supports the views that adopt the multi-stage deformation of western Anatolia in the late Cenozoic. In addition to contributing to the literature on this subject, the article will also serve as a basis for future paleoseismological studies.

Fluvial fan sedimentary characteristics of distributive fluvial system

The characteristics of fan sediment in the distributive fluvial system are evaluated based on a thorough analysis of modern silt in the Guertu river distributive fluvial system, as well as data obtained from UAV aerial photography and satellite remote sensing. The Guertu River Distributive Fluvial System (DFS) is classified into three stages, namely "proximal," "middle," and "distal," based on the examination of river morphology, sediment variations, sedimentary attributes, and other relevant aspects throughout different sections of its tributaries, from the source to the mouth. At the upstream section of the downstream fining sequence, the slope is the steepest and the hydrodynamic conditions are intense, resulting in the formation of a predominantly big gravel braided river. The river bed section has a morphology resembling a combination of a "V" and a "U" shape. It is characterized by a narrow and deep configuration, with a relatively short breadth. The sediment primarily consists of medium to large-sized gravel with minimal sand content. The gravel exhibits good roundness and displays a considerable degree of orientation. The primary microfacies present are braided channel and flood plain. The slope of the central area is decreased in comparison to the nearby end, primarily due to the presence of extensive braided rivers. The river bed has a greater width, with minor eolian dunes visible in the river channel. The gravel particles are predominantly fine to medium in size, and there is an increased amount of sand present. The predominant microfacies are braided channels, floodplains, and eolian dunes. At the distal end, the slope is minimal, the landscape is level, the braided river transitions into a meandering river, the sediment consists primarily of sand, and the signs of bioturbation are clearly visible. The primary microfacies consist of braided channels, meandering channels, floodplains, eolian dunes, lakes, and swamps.

Climate variability in a 3.8 Ma old sedimentary record from the hyperarid Atacama Desert

Climate variability in a 3.8 Ma old sedimentary record from the hyperarid Atacama Desert

Source-to-sink processes and genetic mechanism of progradational and lateral accretion submarine fans in the Qiongdongnan Basin, South China Sea

Submarine fan reservoirs are important accumulation zones for oil, gas, and natural gas hydrates, offering significant potential for hydrocarbon exploration. During the deposition period of the Sanya Formation in the southern part of the Changchang Sag of the Qiongdongnan Basin, a large submarine fan developed. However, the internal structure, source-sink system, and formation mechanism of this fan remain poorly understood, posing significant challenges to exploration in this area. This paper examines the source-to-sink sedimentary processes and deposition of submarine fans, using the Changchang Sag, in the Qiongdongnan Basin in the Northern South China Sea, as an example, which will provide valuable general guidance for deep water oil and gas exploration. Based on the theories of seismic stratigraphy and seismic sedimentology, this paper utilizes techniques such as seismic facies analysis, seismic attribute optimization, paleogeomorphology reconstruction, and source-to-sink sedimentary system analysis to analyze the 3D seismic data of the study area. Research indicates that the Sanya Formation in the Changchang Sag of the Qiongdongnan Basin comprises three depositional units: submarine fan, feeder channel, and Semi-deep marine to deep marine mudstone. The submarine fan is a fan formed by the coupling and convergence of submarine fans sourced from the southwest and southeast. Internally, it is divided into three sub-facies: the proximal fan of the sand-rich submarine fan, the main body of the sand-rich submarine fan lobes, and the distal lobes of the sand-rich submarine fan. The submarine fan sourced from the southwest extends nearly north-south and is primarily fed by sediment transported through three large, banded ancient valleys. The sedimentary filling is characterized by three-phase progradation. The submarine fan sourced from the southeast extends nearly east-west and is primarily fed by sediment transported through a single large, banded ancient valley. The sedimentary filling is characterized by two-phase lateral accumulation. During the deposition period of the Sanya Formation, certain areas of the southern uplift belt were exposed for extended periods and subjected to weathering and erosion. Sediments are transported to large ancient valleys through small supply channels. A large number of sediments were transported to the southern slope of the Changchang sag through the provenance channel system such as large ancient valleys and slope belts and deposited in the center of the sag. These make up a complete system of large ancient uplifts and submarine fan source-to-sink sedimentary systems.The sedimentary model is a lobed submarine fan controlled by semi-restricted ancient valleys and expansive basins.