When Deserts Feed Lakes: Aeolian Sand Supply to Lacustrine Systems in the Triassic Yanchang Formation, Ordos Basin, China

This study documents， for the first time， aeolian deposits within the Triassic Yanchang Formation， one of China’s most important oil-bearing units. The analyzed succession， exposed along the Yanhe River， includes a nearly 10 m-thick interval accumulated under underfilled lacustrine conditions. These deposits consist of well-sorted fine-grained sandstones displaying low-angle asymptotic cross-bedding， climbing translatent strata， pin-stripe lamination， and granule ripples， all indicative of aeolian deposition. The deposits are interpreted as grainfall dunes formed where grainfall processes dominated over tractional crest migration. Interbedded wet interdune deposits composed of mudstones， hyper concentrated-flow conglomerates， and massive sandstones record episodic flooding by ephemeral fluvial systems linked to seasonal and high-frequency climatic fluctuations. Their stratigraphic position indicates that extensive marginal sectors of the Yanchang Lake became subaerially exposed during low lake-level stages， favoring temporary storage and textural maturation of sand-sized sediments in peripheral desert systems. During subsequent wetter intervals and transgressive stages， these aeolian sands were remobilized basin ward by fluvial and hyperpycnal flows， contributing to lacustrine sandy depositional systems. The recognition of aeolian systems in the Yanchang Formation provides a new depositional framework for understanding the abundance of well-sorted sandstones in the Ordos Basin and highlights the key role of climatic forcing in aeolian-lacustrine interactions.