Explore the vast range of titles available.

River channels shape landscapes through gradual migration and abrupt avulsion. Measuring the motion of braided rivers, which have multiple channel threads, is particularly challenging, limiting predictions for landscape evolution and fluvial architecture. To address this challenge, we extended the capabilities of image‐based particle image velocimetry (PIV)—a technique for tracking channel threads in images of the surface—by adapting it to analyze topographic change. We applied this method in a laboratory experiment where a straight channel set in non‐cohesive sediment evolved into a braided channel under constant water and sediment fluxes. Topography‐based PIV successfully tracked the motion of channel threads if displacements between observations were less than the channel‐thread width, consistent with earlier results from image‐based PIV. We filtered spurious migration vectors with magnitudes less than the elevation grid spacing, or with high uncertainties in magnitude and/or direction. During braided channel initiation, migration rates varied with the channel planform development, showing an increase as incipient meanders developed, a decrease during the transitional braiding phase, and consistently low values during the established braiding phase. In this experimental setup, migration rates varied quasi‐periodically along stream at the half scale of initial meander bends. Lateral migration with respect to the mean flow direction was much more pronounced than streamwise migration, accounting for approximately 80% of all detected motion. Results demonstrate that topography‐based PIV has the potential to advance predictions for bank erosion and landscape evolution in natural braided rivers as well as bar preservation and stratigraphic architecture in geological records. Plain Language Summary Rivers naturally move across the landscape through gradual migration and abrupt shifts, with direct consequences for riparian ecosystems, fluvial sedimentology, and riverside communities. Current knowledge of river mobility is especially limited for braided rivers, which are composed of multiple interwoven sub‐channels (called channel threads) that can move independently. To address this knowledge gap, we expanded techniques that track channel thread motion from photos by applying them to elevation data. We find that for a laboratory experiment where a braided river is initiated from a straight channel, migration rates first accelerate and then slow down. These rates fluctuate regularly along the river, particularly around incipient meander bends. Channel banks and bars tend to migrate laterally rather than downstream, although this tendency diminishes over time. Findings from this study can help better understand past environments from sedimentary rocks and assess erosion and flood risk from shifting rivers. Key Points Topography‐based particle image velocimetry effectively tracks the migration of braided channel threads in a laboratory experiment During the initiation of a braided channel, channel threads migrate quickly as incipient meanders form and slow down as braiding develops Similar to channel belt growth, migration rates vary quasi‐periodically along stream, at the half scale of initial meander bends

The Surface Water and Ocean Topography (SWOT) satellite can simultaneously observe river elevation, width, and slope with high spatio‐temporal coverage and resolution (Fu et al., 2024, https://doi.org/10.1029/2023gl107652). The River Single‐Pass (RiverSP) product from SWOT provides geolocated river surface water dynamics with global coverage, but it utilizes simplified river centerlines that do not properly represent braided rivers. We present a method for integrating high‐resolution pixel cloud SWOT data with Sentinel‐2 multispectral imagery for multi‐channel river analysis, with a case study over the Brahmaputra River. We generate dynamic river centerlines from multispectral river masks and apply SWOT observations to the generated centerlines. We find that refined centerline knowledge allows for improved estimates of river surface water dynamics in braided channels when compared to RiverSP. For the Brahmaputra, we find that water surface elevation can vary by 0.5 m and slope can vary by 2 cm/km between parallel channels of the braided river.

The transition to continental collision c. 650 Ma induced the bimodal hypsometry of the Arabian-Nubian Shield (ANS), and triggered the formation of voluminous post-amalgamation basins. The intermontane Kareim Basin is a voluminous post-amalgamation depocenter within the ANS. It comprises a thick siliciclastic fill (~ 7 km thick) that accumulated over tens of millions of years during late Neoproterozoic East African orogeny related to the amalgamation of West and East Gondwana. The basin fill consists of four main facies associations (FA1 to FA4) associated with 11 siliciclastic lithofacies and one volcaniclastic lithofacies, which are interpreted as alluvial fan to lacustrine deposits that accumulated under humid to semi-arid conditions. A conglomerate-dominated lithofacies characterizes proximal alluvial fan deposits (FA1), whereas mid to distal alluvial fan strata are represented by braided stream sandstone-dominated lithofacies and conglomerate (FA2–3). Distal fan deposits are composed mainly of sandstone and fine-grained lacustrine sediments (FA4). Tectonically-induced unconformities separate three depositional stages in the Kareim Basin. The lower stage comprises three sandstone-dominant cycles, locally separated by unconformities. The middle stage of the basin represents a stage of syn-depositional tectonic inversion, consistent with the presence of recycled basal boulders derived from the lower stage, and a divergence in the dominant paleo-current directions. Furthermore, thrust faults, tilted and overturned older strata, and the first occurrence of material derived locally from Pan-African volcanic rocks (the Dokhan Volcanic Suite) and basement gneiss domes are additional clues for the syn-depositional tectonic inversion. The upper stage comprises conglomerate-dominant cycles, and represents the transition to post-collisional extension and rapid subsidence. Detrital zircon U–Pb ages constrain the syn-depositional inversion of the basin to later than c. 635 Ma, likely coinciding with the onset of collision between West with East Gondwana.

The Ordos Basin’s Hangjinqi Shiligahan west zone Xiashihezi Formation 1 Member gas reservoir exhibits significant exploration and development potential. However, its sedimentation and reservoir characteristics are poorly understood. To address this, geological, seismic, macroscopic, and microscopic methods are combined. The available data includes core observation, thin sections, physical property analysis, mercury injection curve interpretation, seismic attribute predictions, and so on. The results show that the target stratum lithology and sedimentary structure are complex and diverse. They are dominated by gravelly coarse sandstone facies with strong hydrodynamic conditions, intercalated with thin mudstone and siltstone. The vertical meter-scale cycle sedimentation characteristics are distinct, representing a typical shallow braided river deposition. Through the mutual calibration and verification of lithology, logging, and seismic facies, the braided channel and its internal microfacies boundaries were accurately delineated. The reservoir primarily consists of gravel-bearing coarse sandstone, featuring intergranular and intragranular dissolved pores as the primary types of reservoir space. The pore types are predominantly mesopores and small pores, with pore-throat combinations favoring mesopores and medium throats, as well as medium to small pores and fine throats. The reservoirs average porosity and permibility are 7.6% and 0.53mD, respectively. This defines a typical reservoir with low to ultra-low porosity and low to ultra-low permeability. The sedimentary microfacies and their associated hydrodynamic conditions are crucial for the development of the reservoir in the Xiashihezi Formation 1 Member. This leads to variations in reservoir properties and pore structures. Thus, the reservoirs are predominantly located in the channel bar microfacies, clearly demonstrating characteristics of facies-controlled reservoir development.

In the setting of the increasing density of exploration wells, and the decreasing scale and increasing difficulty of discovering Jurassic paleogeomorphology reservoirs, it is urgent to deepen the fine depiction of pre-Jurassic paleogeomorphology features and to analyze their controlling effect on reservoirs. Based on abundant logging data combined with indoor microscopic observation and experimental testing, the paper applies the theory of reservoir configuration analysis for the first time to the single-channel period division of the pre-Jurassic Meng-Shaan paleochannel which deposited with the braided channel sand bodies. Meanwhile, it reveals the controlling effect of hydrocarbon accumulation and the distribution characteristics of the Yan 10 1 reservoir as ' paleogeomorphology and sedimentary facies combination' to determine the type, 'migration channel' to determine the distributing range, and 'low-amplitude structure' to determine the trap in the study area, and also the reservoir accumulation modes in different channel ranges have established. In conclusion, the single-channel boundary of the Meng-Shaan paleochannel in different periods controls the path of oil and gas migration, thus controlling the distribution range and reservoir type of the Yan 10 reservoir. Moreover, depending on the production data we derived that it should prefer the composite trap reservoir of the Fuxian period and the Yan 10 2 period, as well as the structural reservoir on the periphery of the Yan 10 2 period single-channel for the further exploration of the Yan 10 paleogeomorphology reservoirs within the development range of the Meng-Shaan ancient river. In particular, the lithologic trap reservoirs within the Fuxian period channel and the Meng-Shaan main channel, such as the reservoirs of the 'Source' of the secondary channel type and the paleochannel type, which could as a replacement accumulation model for increasing reserves and production.

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.

The causes of the severest crisis in the history of life around the Permian-Triassic boundary (PTB) remain controversial. Here we report that the latest Permian alluvial plains in Shanxi, North China, went through a rapid transition from meandering rivers to braided rivers and aeolian systems. Soil carbonate carbon isotope (δ 13 C), oxygen isotope (δ 18 O), and geochemical signatures of weathering intensity reveal a consistent pattern of deteriorating environments (cool, arid, and anoxic conditions) and climate fluctuations across the PTB. The synchronous ecological collapse is confirmed by a dramatic reduction or disappearance of dominant plants, tetrapods and invertebrates and a bloom of microbially-induced sedimentary structures. A similar rapid switch in fluvial style is seen worldwide (e.g. Karoo Basin, Russia, Australia) in terrestrial boundary sequences, all of which may be considered against a background of global marine regression. The synchronous global expansion of alluvial fans and high-energy braided streams is a response to abrupt climate change associated with aridity, hypoxia, acid rain, and mass wasting. Where neighbouring uplands were not uplifting or basins subsiding, alluvial fans are absent, but in these areas the climate change is evidenced by the disruption of pedogenesis.

As the threat of unstable braided river geomorphology to the resilience of local communities grows, a better understanding of the morphological changes in a river subject to climate is essential. However, little research has focused on the long-term planform change of the braided reaches and its response to hydrological changes. The reach around Majuli Island (Majuli Reach), the first and typical braided reach of the Brahmaputra River emerging from the gorge, experiences intense geomorphological change of the channels and loss of riparian area every year due to the seasonal hydrological variability. Therefore, focusing on the Majuli Reach, we quantitatively investigate changes in its planform morphology from 1990 to 2020 using remote sensing images from the Landsat dataset and analyze the influence of discharge in previous years on channel braiding. The study shows that the Majuli Reach is characterized by a high braiding degree with an average Modified Plan Form Index (MPFI) of 4.39, an average reach width of 5.58 km, and the development of densely migrating bars and active braided channels. Analysis shows a control point near Borboka Pathar with little morphological change, and the braided channel shows contrasting morphological changes in the braiding degree, bars, and main channel between the reach upstream and downstream of it. The area of the riparian zone of the Majuli Reach decreased by more than 50 km2 during the study period due to migration of the main channel toward the island. The braiding degree of Majuli Reach is positively correlated with the discharge in previous years, with the delayed response time of the MPFI to discharge being just 3–4 years, indicating the unstable feature of the Majuli Reach with varied hydrology conditions.

The Abu Gabra and Bentiu formations are widely distributed within the interior Muglad Basin. Recently, much attention has been paid to study, evaluate and characterize the Abu Gabra Formation as a proven reservoir in Muglad Basin. However, few studies have been documented on the Bentiu Formation which is the main oil/gas reservoir within the basin. Therefore, 33 core samples of the Great Moga and Keyi oilfields (NE Muglad Basin) were selected to characterize the Bentiu Formation reservoir using sedimentological and petrophysical analyses. The aim of the study is to de-risk exploration activities and improve success rate. Compositional and textural analyses revealed two main facies groups: coarse to-medium grained sandstone (braided channel deposits) and fine grained sandstone (floodplain and crevasse splay channel deposits). The coarse to-medium grained sandstone has porosity and permeability values within the range of 19.6% to 32.0% and 1825.6 mD to 8358.0 mD respectively. On the other hand, the fine grained clay-rich facies displays poor reservoir quality as indicated by porosity and permeability ranging from 1.0 to 6.0% and 2.5 to 10.0 mD respectively. A number of varied processes were identified controlling the reservoir quality of the studies samples. Porosity and permeability were enhanced by the dissolution of feldspars and micas, while presence of detrital clays, kaolinite precipitation, iron oxides precipitation, siderite, quartz overgrowths and pyrite cement played negative role on the reservoir quality. Intensity of the observed quartz overgrowth increases with burial depth. At great depths, a variability in grain contact types are recorded suggesting conditions of moderate to-high compactions. Furthermore, scanning electron microscopy revealed presence of micropores which have the tendency of affecting the fluid flow properties in the Bentiu Formation sandstone. These evidences indicate that the Bentiu Formation petroleum reservoir quality is primarily inhibited by grain size, total clay content, compaction and cementation. Thus, special attention should be paid to these inhibiting factors to reduce risk in petroleum exploration within the area.

The tight gas reserves in the Hangjinqi area are estimated at 700 × 109 m3. Since the exploration of the Hangjinqi, numerous wells are already drilled. However, the Hangjinqi remains an exploration area and has yet to become a gas field. Identifying a paleo-depositional framework such as braided channels is beneficial for exploration and production companies. Further, braided channels pose drilling risks and must be properly identified prior to drilling. Henceforth, based on the significance of paleochannels, this study is focused on addressing the depositional framework and sedimentary facies of the first member (P2x1) of the lower Shihezi formation (LSF) for reservoir quality prediction. Geological modeling, seismic attributes, and petrophysical modeling using cores, logs, interval velocities, and 3D seismic data are employed. Geological modeling is conducted through structural maps, thickness map, and sand-ratio map, which show that the northeastern region is uplifted compared to northwestern and southern regions. The sand-ratio map showed that sand is accumulated in most of the regions within member-1. Interval velocities are incorporated to calibrate the acoustic impedance differences of mudstone and sandstone lithologies, suggesting that amplitude reflection is reliable and amplitude-dependent seismic attributes can be employed. The Root Mean Square (RMS) attribute confirmed the presence of thick-bedded braided channels. The results of cores and logging also confirmed the presence of braided channels and channel-bars. The test results of wells J34 and J72 shows that the reservoir quality within member-1 of LSF is favorable for gas production within the Hangjinqi area.