Aeolian–fluvial interactions within a fault-controlled basin: Late Cretaceous Chaling Basin, South China

The Upper Cretaceous Daijiaping Formation of the Chaling Basin, southeast China, is a mixed aeolian–fluvial succession accumulated in an erg-margin setting. The roles of climate and tectonics in governing the temporal and spatial arrangement of aeolian and fluvial strata are investigated using lithofacies and architectural-element analyses of outcrops in the eastern part of the basin. Architectural elements of aeolian origin record the preserved expression of dunes, sandsheets, damp and wet interdunes, and sand pods. Architectural elements of alluvial origin record channelized bedload streams and cobble-sand sheetflow units. Distinctive deflation lags and desert pavements are also recognized. The alternating nature of deposition via aeolian and aqueous processes is marked by a series of sand-drift surfaces that form a record of repeated shifts from aeolian to water-lain depositional conditions. Ephemeral water influx to the desert-margin system likely occurred in response to exceptional rainfall caused by monsoonal water discharge and meltwaters from glaciated mountain ranges that bordered the basin. The vertical arrangements of alternating facies associations define stacked wetting-upward cycles, each 0.4–14.2 m thick. Each cycle commences with simple or compound crescentic dune deposits, else with aeolian sandsheet deposits. These are overlain by bedload stream or conglomerate sheetflow deposits. The vertical stacking of these different architectural elements records the contraction and expansion of erg-margin systems in response to climate-controlled variations in the groundwater level, sand availability for aeolian transport, and fluvial and aeolian sediment transport capacity. The stratigraphic evolution was controlled by exceptional rainfall events at the basin margin, consequent floods into the dune-field margin and associated fluctuations in the water-table level. Orogenic uplift, a subtropical high-pressure system, and a variable groundwater level controlled by a monsoon climate and tectonic subsidence resulted in the development of extensive aeolian desert depositional systems in the South China hinterland during the Late Cretaceous.