Interaction of fluvial and eolian sedimentation processes, and response to climate change since the last glacial in a semiarid environment along the Yellow River

Abstract

Interactions of fluvial and eolian processes are prominent in dryland environments and can significantly change Earth surface morphology. Here, we report on sediment records of eolian and fluvial interactions since the last glacial period, in the semiarid area of northwest China, at the limit of the Southeast Asian monsoon. Sediment sequences of last glacial and Holocene terraces of the Yellow River are composed of channel gravels, overlain by flood sands, eolian dunes, and flood loams. These sequences, dated by optically stimulated luminescence, record interlinks between fluvial and eolian processes and their response to climate change. Sedimentologic structures and grain-size analysis show flood loams, consisting of windblown sediment, deposited from floodwater suspended sediment. The gravel and sand were deposited during cold periods. During transitions from cold to warm phases, the river incised, and dunes were formed by deflation of channel and floodplain deposits (>70 and 21–16 ka). Dunes also formed at ~0.8 ka, probably after human intervention. After dune formation, flood loam covered dunes without erosion during peak discharges at the beginning of the subsequent warm period. The fluctuations of the Southeast Asian monsoon as a moisture-transporting agent have perhaps been the driving force for interactions between fluvial and eolian processes in this semiarid environment.

Specifying the External Impact on Fluvial Lowland Evolution: the Last Glacial Tis(Z)a Catchment In Hungary and Serbia

“…The upper flood sediments generally contain a fraction with mode around 40 µm (the red (top sediment) curve in the left diagram of Figure 4), which is the typical mode for loess deposits B abandoned-meander fill Pointbar sediments in this region [67,68], thus easily interpreted as reworked (alluvial) loess deposits [69]. In addition, the flood sediment often contains also a sand fraction (most obvious in the right panel of Figure 4) indicating some flow on top of the previous floodplain [69,70]. The channel fill shows a clear bimodality (Figure 4, right panel): one fraction is a fine silt (c. 19 µm that corresponds with the fine component in the regional loess cover [67,68] and is preferentially settled in the standing water of the abandoned meander, in contrast to the coarser-grained silt (40 µm) which is dominating in the flood sediments; the second fraction is a clay (c. 2 µm) which can only be deposited by settling in standing water ('lacustro-aeolian loess' [69].…”

Specifying the External Impact on Fluvial Lowland Evolution: The Last Glacial Tisza (Tisa) Catchment in Hungary and Serbia

“…The upper flood sediments generally contain a fraction with a mode around 40 µm (the red (top sediment) curve in the left diagram of Figure 4), which is the typical mode for loess deposits in this region [67,68], thus easily interpreted as reworked (alluvial) loess deposits [69]. In addition, the flood sediment often also contains a sand fraction (most obvious in the right panel of Figure 4) indicating some flow on top of the previous floodplain [69,70]. The channel fill shows a clear bimodality (Figure 4, right panel): one fraction is a fine silt of c. 19 µm, corresponding with the fine component in the regional loess cover [67,68] and preferentially settled in the standing water of the abandoned meander, in contrast to the coarser-grained silt (40 µm) which is dominant in the flood sediments; the second fraction is a clay (c. 2 µm) which can only be deposited by settling in standing water ('lacustro-aeolian loess' [69]).…”

Episodic Sedimentary Evolution of an Alluvial Fan (Huangshui Catchment, NE Tibetan Plateau)

“…The material (about 20 g) was first dried and then ground to powder to determine concentrations of U, Th, and K using neutron activation analysis (NAA). The water content varied during the long-term burial period, so we assumed 50% of the saturated water content as the average value during historical time according to previous work [16,26], with an absolute uncertainty of 7% of this value to allow for possible fluctuations on the basis of the local climatic characteristics. Based on applying conversion factors from Guérin [63] and beta attenuation factors from Mejdahl [64], the external beta and gamma dose rate was calculated using the radionuclide concentration.…”

“…The intricacy of fluvial response, including aggradation/incision rhythms and terrace formation, to late Quaternary climate change, has been studied for several decades [16,[18][19][20][21]. In addition, the interactions between fluvial and aeolian processes and their response to climate change in semi-arid areas have also been reported elsewhere in China and around the world [22][23][24][25][26]. Alluvial sequences allow process inference, which then can be used to infer environments, at the depositional site, as well as environmental change and related controls in the catchment area [17].…”