Search

Understanding the evolution of river systems in southern Africa is fundamental to constrain the evolution of landscape and sediment dispersal patterns. It is widely considered that the upper Zambezi River was connected with the Limpopo River during the Cretaceous, forming what was then the largest river in Africa. Crustal flexure during the Paleogene severed the upper Zambezi drainage from the Limpopo, setting the framework of the modern Zambezi and Limpopo River systems. We present first evidence—based on heavy‐mineral assemblages from cores drilled offshore of the Limpopo River mouth and samples collected in different reaches of the modern Limpopo River, integrated with magnetic susceptibility, detrital‐zircon geochronology, and geomorphological analysis—suggesting that the current Limpopo River formed recently in the Plio‐Quaternary. Plio‐Quaternary climate change is envisaged to have controlled the recent dynamics of river drainage and consequent distribution of sediment loads, as observed in many other transcontinental rivers worldwide. Plain Language Summary: Landscape evolution, sediment dispersal patterns, and the accumulation of hydrocarbon and mineral resources in southern Africa, were largely determined by the evolution of the vast Zambezi‐Limpopo River system. It is widely believed that this river system attained its current configuration during the late Paleogene as a consequence of mantle‐driven dynamic uplift. Based on heavy‐mineral assemblages from river sediments and an International Ocean Discovery Program ocean core, we argue here instead for a Plio‐Pleistocene age for the formation of the modern characteristics of the Limpopo River (i.e., tens of millions of years younger than previously thought). This challenges the current paradigm on both formation modality and driving mechanisms of this vast river system. Plio‐Pleistocene climate change is envisaged to have controlled the dynamics of river drainage and consequent distribution of sediment loads, as observed in several other transcontinental rivers worldwide, underscoring the importance of these climate changes in driving river evolution world‐wide. Key Points: The modern Limpopo River of South Africa formed in the Plio‐PleistocenePlio‐Pleistocene drainage reorganization was driven by climate changeFormation age and driving mechanisms of South African rivers are revisited [ABSTRACT FROM AUTHOR]

Jiudong Sandy Land in the western Hexi Corridor is one of the dust source regions of the Chinese Loess Plateau and is highly sensitive to climate change. Determination of when this sandy land formed would help resolve major questions about the desertification history of inland Asia; however, until now, this has been hindered by the lack of depositional records. Here, we report the results of optically stimulated luminescence (OSL) dating, grain size and grain surface analyses from a new drill core obtained from Jiudong Sandy Land. Our aims are to constrain its age of formation. Analysis of sedimentary facies reveals that the sediments in the lower part of the core (35.2–16.7 m) were deposited by fluvial processes, but that the sediments in the upper part consist primarily of aeolian sand. The OSL dating results indicate that the transition from fluvial to aeolian facies occurred at ∼89.8 ± 7.6 ka. Combined with various loess-based environmental proxies from Jiudong Basin, the new litho- and chronostratigraphic evidence reported in this study indicates that the age of ∼89.8 ± 7.6 ka represents the formation age of the Jiudong Sandy Land. [ABSTRACT FROM AUTHOR]

Fluvial response to allogenic and autogenic controls concerns the understanding of landform evolution related to the interaction between tectonic movements, climate, surface process and human activity. Paleo-channels, as part of geomorphic archives, have been widely employed to study this issue during recent decades. Previous work has however concentrated on the mechanisms driving river migration. A new approach, in which multiple elements are considered, is employed here in the examination of paleo-channel formation in the Jiudong Basin, located at the northeastern margin of the Tibetan Plateau and characterized by active tectonic deformation, a dry climate and ancient human activity. Based on geomorphic and sedimentary analysis, eight paleo-channels formed by the Taolai and Hongshuiba rivers (two tributaries of the Beida River catchment) have been identified. AMS14C dating of the overlying lacustrine sediments defined their respective abandonment at ca. 22.2, 20.9, 15.3, 18.8, 13.9, 11.9, 3.5 and 1.1 cal. Ka BP. The migration histories of the two rivers have been reconstructed, and then well correlated with reference to archives of tectonic, climatic and human influence. Our results suggest that these controlling factors seem to be coupled and have a competitive relationship in driving river migration. In the northeastern margin of the Tibetan Plateau, channel migration can therefore be regarded as a result of fluvial response to the interaction between rapid tectonic activity, climatic fluctuation and human influence. • 8 paleo-channels have been identified in the northeastern margin of the Tibetan Plateau. • These paleo-channels have been constrained by AMS14C dating in the last glacial period. • These paleo-channels are coupled record of climate, tectonics and human influence. [ABSTRACT FROM AUTHOR]

The response of bedrock channels to differential rock uplift in eastern Qilian Mountain significantly dictates the topographic evolution of the northeastern margin of the Tibetan Plateau. Our ability to extract tectonic information directly from channel profiles mainly depends on the calibration of incision processes laws. Here we assess the degree and nature of channels response to differential rock uplift in eastern Qilian Mountain base on an empirical calibration of the shear-stress incision model utilizing field survey data (lithologic resistance, sediment flux, discharge and channel width). Parameters calibration indicates that channels developed in the high mountain zone (HMZ) show an approximate 1.1–1.3 times increase in erosion coefficient K than in the low mountain zone (LMZ), mainly attributing to the adjustments of channel width and discharge. Moreover, profiles analysis reveals a systematic geographic distribution of steepness indices and concavity in this area. The regions of high and low steepness indices are spatially associated with the higher (high rock uplift rates) and lower (low rock uplift rates) parts of landscape, respectively, suggesting that the spatial distribution pattern of channel steepness mainly reflects the differential rock uplift. Channels with abnormal high concavity values apparently associate with the major thrust faults, suggesting that the differential rock uplift is controlled by the thrusting of major active faults. Combining parameters calibration with profile analysis between the two zones, the possible increase in rock uplift rates is 2–4 times in the HMZ than in the LMZ indeed. [ABSTRACT FROM AUTHOR]

Despite decades of study, the factors that controlled the formation and evolution of the upper reaches of the Yellow River, including uplift of the northeastern Tibetan Plateau, Pliocene-Pleistocene climate change, and autogenetic processes are still poorly constrained. The stratigraphic record of such paleogeographic evolution is recorded in the sequence of nine terraces formed during progressive incision of the Yellow River in the last 1.7 Ma. This article investigates in detail for sediment provenance in terraces of the Lanzhou area, based on heavy-mineral and geochemical (REE) signatures. Two main provenance changes are identified, pointing each to a major paleogeographic reorganization coupled with expansion of the upper Yellow River catchment and enhanced sediment fluxes. The first change took place between the deposition of terrace T9 (formed around 1.7 Ma) and terrace T8 (formed around 1.5 Ma), when rapid fluvial incision point to tectonic control and active uplift of northeastern Tibetan Plateau. The second change took place between deposition of terrace T4 (formed around 0.86 Ma) and terrace T3 (formed around 0.14 Ma), during a period of low incision rates and notably enhanced sediment fluxes as a response to enhanced East Asian Summer Monsoon and consequently increased precipitations, pointing instead chiefly to climatic control. [ABSTRACT FROM AUTHOR]

Knowledge of the composition of modern fluvial sediments is important for understanding the combined effect of lithology and climatic factors on the erosion and sedimentation within drainage basins, However, this information is incomplete in arid and semiarid environments. In this study, 37 modern fluvial sediment samples were collected from the Heihe River and its major tributaries, in the NE Tibetan Plateau, and for analyses of heavy minerals, trace and rare earth elements (REEs) and grain size. The main aim was to explore the influence of erosion, transport and deposition processes on sediment composition, and to define appropriate provenance indicators specific to these rivers. Along the Heihe River, the amount of unstable minerals is abundant and not changing, these result suggests that chemical weathering plays only a minor role. The composition of six sediment samples obtained from the upper-middle reaches of Heihe River are influenced by hydrodynamic sorting processes, which resulted in enrichment of heavy minerals. In addition, the mineralogical and geochemical compositions lead to different conclusions regarding the contributions from tributaries to the sediments in the middle-lower reaches of the Heihe River. This may reflect the occurrence of contrasting hydrodynamic conditions in Heihe River and its tributaries which result in the transport of different size fractions. Moreover, the <63 μm fraction of the sediments from the Heihe River basin has been affected by inputs of eolian dust, which means that this fraction is less influenced by the rock types within the sediment source areas than is the case for the other size fractions. Therefore, we conclude that the sand fraction is more suitable for source to sink analysis of fluvial sediments within this and comparable environments. In the upper areas of the Fengle River basin, the combination of low temperature, sparse vegetation coverage and high precipitation have resulted in intense erosion. This case reminds us to note the effect of the climatic zonation on the provenance analysis in arid regions. [ABSTRACT FROM AUTHOR]

• Detailed source-to-sink analysis between the Qilian Shan and the Jiudong Basin. • Provenance analysis reveals two changes of drainage pattern since 7.0 Ma. • Drainage evolution was closely linked to both tectonic uplift and climate change. • Climatic cooling at ∼2.75 Ma promoted river capture. In tectonically active regions, surface uplift is generally considered to be an important cause of drainage evolution, but the effect of climate change on this process has not been fully evaluated. In this study, we conducted a provenance analysis of Minghai (MH) drill-core sediments from the foreland basin (i.e., the Jiudong Basin) of the Zoulang Nan Shan (the central part of the northern Qilian Shan). We aimed to reconstruct the fluvial evolution of the basin and to determine the role of tectonic activity and climate change in the evolutionary process. Provenance analyses indicate the existence of two changes in drainage pattern since 7.0 Ma that are closely linked to the thrusting process of the North Qilian Shan fault system. During the first (∼4.5 Ma) change, the in-sequence thrusting induced rapid uplift of the Yumu Shan in the frontal area of the Zoulang Nan Shan, which caused diversion of the rivers flowing through the Yumu Shan. During the second change (∼2.75 Ma), the thrusting of the North Qilian Shan fault caused intense uplift of the Zoulang Nan Shan, resulting in the capture by transverse rivers in its northern slope of rivers within the mountain range. Additionally, aridification at ∼4.5 Ma and climatic cooling at ∼2.75 Ma affected the evolution of the rivers. The aridification at ∼4.5 Ma resulted in reduced runoff, erosion, and fluvial incision rate, and facilitated the first change in the drainage pattern. The climatic cooling at ∼2.75 Ma induced rapid erosion in the upper reaches of the rivers and enlarged the erosion rate contrast between the south and north side of the Zoulang Nan Shan, both of which facilitated the second change in the drainage pattern. Overall, our study reflects the combined effects of tectonic uplift and climate change on the drainage evolution process. [ABSTRACT FROM AUTHOR]

Continental-scale drainage reorganization is generally understood to result from landform evolution forced by the coupling between tectonic activity and climate change, attracting worldwide attention. Planation surfaces and river terraces constitute the most direct geomorphological archives for integrating the history of river systems and for reconstructing processes of drainage reorganization based on provenance analysis of the fluvial sediments. The Middle Yellow River has incised into the Ordos Block, which was previously levelled by a planation surface, creating the Jinshaan Gorge and linking the Hetao Basin to the north and the Fenwei Basin to the south. Multiple lines of evidence, from terraces correlation, sedimentary characteristics, and fluvial provenance, suggest that the Middle Yellow River catchment was occupied by fluvio-lacustrine systems before drainage integration, accumulating a sedimentary sequence derived from surrounding Red Clay and bedrocks during the period between 8.3 and 3.7 Ma. The planation surface was uplifted subsequently, forcing reorganization of the fluvio-lacustrine systems. Their integration resulted in the formation of the Jinshaan Gorge prior to 1.2 Ma. Numerous terraces were created during incision by the Middle Yellow River from north to south along the gorge. Our data, obtained from zircon U Pb dating and lithological composition of fluvial gravels, further points to a remarkable discrepancy in provenance between the fluvio-lacustrine systems overlying the planation surface and the terraces sequence formed by the integrated Middle Yellow River, confirming the drainage reorganization process constrained by the geomorphic records. • Fluvio-lacustrine systems occupied the Middle Yellow River before integration. • Yellow River terraces are different from fluvio-lacustrine systems in provenance. • The Middle Yellow River has been excavated and integrated during Plio–Pleistocene. [ABSTRACT FROM AUTHOR]

Strategic studies of gravel deposits, in particular using heavy-mineral analyses, have thrown light on the important unresolved question as to the timing of the initiation of the Yellow River drainage through the Sanmen Gorge, which linked the headwaters of that system in the Fenwei Basin and further upstream with the North China Plain and the Pacific Ocean in the east. Survey of the Sanmen Gorge reach revealed previously unrecognized gravel levels: a higher fifth terrace (T5) and a gravel that formed on a high-level planation surface that is preserved on the flanks of the gorge, below the Xiaoshan upland. This high-level gravel differs markedly from the Yellow River terraces, with a lack of material from the upstream catchment, and would appear to represent a small fluvial catchment that developed in the area during the formation of the planation surface, before the Sanmen Gorge was excavated. Comparison was also made with basin-fill gravels from the endorheic fluvio-lacustrine system that existed immediately upstream of the gorge, and was captured by the Yellow River when the latter was cut, and with the modern bedload gravel of the Yellow River in this reach. The former contains significant quantities of unstable hornblende, which implies more local derivation for the endorheic system, whereas the modern bedload resembles the terrace gravels in showing compositional maturity and long-distance transport from upstream within the catchment. The work reinforces a minimum age of 1.2 Ma for the formation of the Sanmen Gorge. • The gravel layer accumulated on the planation surface along the eastern front of the Xiaoshan represents a local river. • The local river sediments are different from the typical Yellow River gravels and the upper Sanmen Formation. • The Sanmen paleolake within the Fenwei basin was finally disrupted by the westward capture of this local river. • The Sanmen Gorge was excavated by the local river through the Xiaoshan separating the Fenwei basin and North China Plain. • The Yellow River integration may be attributed to the remarkable climatic fluctuation starting in the Mid-Pleistocene. [ABSTRACT FROM AUTHOR]

• Aeolian sand deposited in riverbed rather than floodplain sedimentary environment. • Low weathering intensity during the late Holocene between 3.3 and 1.0 ka. • Rapid aeolian sand accumulation after climate-driven hydrological events. Investigating fluvial-aeolian interactions is important for understanding Earth surface processes in arid regions. In this study, we conducted detailed grain size, geochemical, and heavy-mineral analyses of the 21.25-m-long HDZ core to determine the provenance of Holocene aeolian deposits in Inner Mongolia and their relationships with the Yellow River and surrounding desert areas. Significant differences in grain-size parameters and concentration of geochemical elements with stratigraphic depth were highlighted. Compositional data and heavy-mineral assemblages indicate that aeolian sediments blown into the Yellow River channel were largely derived from the Ulan Buh Desert or Kubq Desert and supplied by the Ten Tributaries during the rainy season. Chemical indices depicta particularly low weathering intensity during the late Holocene between 3.3 and 1.0 ka, when the dry-cool climate led to desert expansion in the Inner Mongolia region of the Yellow River. Starting from ∼2000 BP during the Han Dinasty, large-scale immigration, extensive agricultural activities, and intensified animal grazing compromised the stability of surface soil, leading to desertification and enhanced aeolian-sand transport across the Inner Mongolia region. Our research helps understand the extreme sensitivity of vulnerable dry environments to climate change at different time scales and provide a reference for provenance identificationin a region of extensive fluvial-aeolian interactions. [ABSTRACT FROM AUTHOR]

The fluvial archives in the upper-reach Yellow River basins provide important information about drainage history of the northeastern Tibetan Plateau (TP) associated with geomorphologic evolution and climate change. However, the Pliocene fluvial strata within this region have not been studied in detail, hence limiting the understanding of the late Cenozoic development of regional fluvial systems. In this paper, we present the results of a study of the geochronology, sedimentology, and provenance of the fluvial sequence of the Wuquan Formation in the Lanzhou Basin in the northeastern TP. Magnetostratigraphic and cosmogenic nuclide burial ages indicate that the Wuquan Formation was deposited during 3.6–2.2 Ma. Furthermore, sedimentary facies, gravel composition, paleocurrent data, and detrital zircon U Pb age spectra reveal that the fluvial sequence resembles the terraces of the Yellow River in terms of source area, flow direction, and depositional environment. Our results indicate that a paleo-drainage system flowing out of the northeastern TP was established by ca. 3.6 Ma and that the upstream parts of the Yellow River must have developed subsequently from this paleo-drainage system. The late Pliocene drainage system fits well with the dramatic uplift of the northeastern TP, an intensified Asian summer monsoon, and global increase in erosion rates, which may reflect interactions between geomorphic evolution, tectonic deformation, and climate change. [ABSTRACT FROM AUTHOR]

• Nine river terraces have been identified and dated along the lower Taohe River. • The development of the modern river valley in this area began at 1.4–1.14 Ma. • Tectonic uplift and climate change were the main controlling factors. A flight of nine river terraces has been well developed and preserved along the course of the lower Taohe River. Based on optically stimulated luminescence (OSL), electron spin resonance (ESR), paleomagnetic and loess-paleosol stratigraphic analyses, we found that the accumulation ages of the gravel layers of terraces T9–T1 correspond to the loess layers L13, L9, L8, L6, L5, L4, L3-L2, L1-4 and L1-1, respectively. The chronologic results indicate that the formation and development of the modern river valley in this area occurred between 1.4 and 1.14 Ma. The topographic fluctuation caused by the Kunhuang Movement appears to have been the main reason for the reorganization of the river system and valley development in the area. In the context of this tectonic uplift, fluvial processes were coupled with the regional climate on a geomorphic equilibrium scale; i.e., over a glacial-interglacial cycle. That is, river aggradation appears principally to have occurred during glacial periods, while a graded state existed during interglacial periods. In addition, rapid river downcutting in response to climate change occurred during the transition periods from glacial to interglacial climates. [ABSTRACT FROM AUTHOR]