How did rivers in the wet tropics (NE Queensland, Australia) respond to climate changes over the past 30 000 years?
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ABSTRACT The nature and timing of fluvial response and coincident changes in climate as inferred from multiple, independent proxies are examined in the wet tropics of north‐eastern Australia. Chronostratigraphic data provide evidence for regionally synchronous fluvial aggradation at 30–13 ka, 8–5 ka and again from 1 ka. Terrace incision and removal occurred at 13–8 ka and 5–1 ka. A new synthesis of regional palaeoenvironmental proxy records spanning the last 30 ka highlights key periods of environmental change. Comparison of the records of fluvial and environmental change reveals the relationship is complex with no clear relationship between river aggradation/incision and wetter/drier conditions. The nature and timing of fluvial response in the wet tropics also shows broad similarities with coastal valleys in south‐eastern New South Wales, suggesting continental‐scale controls on fluvial response to changing climate during the Late Quaternary in Australia. Copyright © 2017 John Wiley & Sons, Ltd.Keywords:
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The variability of Late Holocene fluvial dynamics in the Swiss Alps is traced from fan delta deposits using a multi-proxy approach. The spatial coexistence of wetland, alluvial and fluvial environments on the low-gradient Lutschine fan delta provides a high-resolution fluvial record. The sedimentary record shows seven major aggradation pulses from 3600 cal year BP to the present. Furthermore, 19 minor burial episodes occur between 3600 and 1050 cal year BP at intervals of between 100 and 130 years, suggesting that aggradation during the period of interest was triggered by centennial flood events. Nine coarse-grained flood layers, deposited at a recurrence interval of between 200 and 600 years, coincide with positive radiocarbon anomalies and cold phases in the Alps. The solar influence on the regional hydrological regime is proposed as the main factor triggering the flooding events.
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Tufas are constructional landforms composed of calcium carbonate. They are common in karst terrains, and are known worldwide as useful archives of palaeoenvironmental information. In the case of fluvial tufas, these carbonate deposits experience net aggradation when environmental conditions are stable, whilst incision through the deposits occurs when conditions become wetter. In this study, the first of its type in temperate Australia, we used geomorphological and sedimentological evidence preserved in fossil tufas and alluvial terraces to investigate the fluvial history of Davys Creek (NSW, Australia). The nature and timing of fluvial changes along two quasi-independent reaches of the creek were synchronous, suggesting the operation of externally driven processes rather than local internal fluvial adjustments. Following a period of sustained aggradation, rapid incision occurred along the creek between 1500 and 1600 years before present ( bp ) in response to a shift to a moister climate. This was succeeded by a second major aggradation event (1500 years bp to 150 years bp ), then subsequent incision following the arrival of Europeans at 150 years bp.
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Since the establishment of the classic Theory of Alpine Glacial Cycles, a close relationship between glacial activities and fluvial terrace development has been observed. However, problems such as the extent and mechanisms through which glacier advances influence downstream fluvial aggradation, are not fully understood. The Aba Basin, located on the eastern Tibetan Plateau, features well-developed river terraces. In conjunction with this, the upstream Nianbaoyeze Mountains have undergone intense glacial activities during glacial periods. The integration of these features make this source-to-sink system an ideal site to study these problems. In this work, we utilized Luminescence and Radiocarbon dating methods to reconstruct terrace sequences in the Aba Basin. Furthermore, geochemical analyses were undertaken to delineate trends in provenance variation during terrace aggradation periods, and subsequently to assess the impact of sediment supply from the Nianbaoyeze Mountains. Integrating our analysis of fluvial evolution in the Aba Basin with glacier activities from the Nianbaoyeze region and correlating them with regional and global paleoclimate data, we present detailed insights into how glacial activities have driven terrace formation in the Tibetan Plateau since the late Pleistocene. Our research offers new perspectives on the fluvial processes in periglacial regions, enhancing the understanding of the interplays between fluvial landform dynamics and glacial-interglacial cycles.
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Abstract Accurate dating is necessary to get insight in the temporal variations in sediment deposition in floodplains. The interpretation of such dates is however dependent on the fluvial architecture of the floodplain. In this study we discuss the fluvial architecture of three contrasting Belgian catchments (Dijle, Geul and Amblève catchment) and how this influences the dating possibilities of net floodplain sediment storage. Although vertical aggradation occurred in all three floodplains during the last part of the Holocene, they differ in the importance of lateral accretion and vertical aggradation during the entire Holocene. Holocene floodplain aggradation is the dominant process in the Dijle catchment. Lateral reworking of the floodplain sediments by river meandering was limited to a part of the floodplain, resulting in stacked point bar deposits. The fluvial architecture allows identifying vertical aggradation without erosional hiatuses. Results show that trends in vertical floodplain aggradation in the Dijle catchment are mainly related to land use changes. In the other two catchments, lateral reworking was the dominant process, and channel lag and point bar deposits occur over the entire floodplain width. Here, tracers were used to date the sediment dynamics: lead from metal mining in the Geul and iron slag from ironworks in the Amblève catchment. These methods allow the identification of two or three discrete periods, but their spatial extent and variations is identified in a continuous way. The fluvial architecture and the limitation in dating with tracers hampered the identification of dominant environmental changes for sediment dynamics in both catchments. Dating methods which provide only discrete point information, like radiocarbon or OSL dating, are best suited for fluvial systems which contain continuous aggradation profiles. Spatially more continuous dating methods, e.g. through the use of tracers, allow to reconstruct past surfaces and allow to reconstruct reworked parts of the floodplain. As such they allow a better reconstruction of past sedimentation rates in systems with important lateral reworking.
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The fluvial process of establishing new equilibrium in river section upstream of Aojiang River estuary due to constructed reservoir is studied by means of 1-D tidal flow-sediment mathematical model coupling with 2-D model.The characteristics of hydrology,sediment transport and fluvial process are analyzed.The calculation condition, the techniques for solving some key problems and verification of computation results are presented.The flow and fluvial process are predicted.It is found that the aggradation develops rapidly in the early stage after construction of reservoirs and it tends to degrade afterward until a new equilibrium is established.The aggradation process develops from upstream to downstream and the thickness of deposition at the river bend is smaller than the transition section between two bends.The water depth of navigation at the port will be affected by the sediment deposition.
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ABSTRACT The nature and timing of fluvial response and coincident changes in climate as inferred from multiple, independent proxies are examined in the wet tropics of north‐eastern Australia. Chronostratigraphic data provide evidence for regionally synchronous fluvial aggradation at 30–13 ka, 8–5 ka and again from 1 ka. Terrace incision and removal occurred at 13–8 ka and 5–1 ka. A new synthesis of regional palaeoenvironmental proxy records spanning the last 30 ka highlights key periods of environmental change. Comparison of the records of fluvial and environmental change reveals the relationship is complex with no clear relationship between river aggradation/incision and wetter/drier conditions. The nature and timing of fluvial response in the wet tropics also shows broad similarities with coastal valleys in south‐eastern New South Wales, suggesting continental‐scale controls on fluvial response to changing climate during the Late Quaternary in Australia. Copyright © 2017 John Wiley & Sons, Ltd.
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