Sedimentary characteristics and storm origin of the sandy debris flow deposits from the Yanchang Formation in the Xunyi region, Ordos Basin: An approach

The Chang-8 to Chang-6 oil reservoirs from the Yanchang Formation in the southern part of the Ordos Basin belong to the meandering delta-bathyal to abyssal lake deposits with developed gravity flow deposits. These gravity flow deposits were once reported as the turbidity current deposits and sandy debris flow deposits. The latter are supported by the authors on the basis of cores and well logs for the Yanchang Formation in the Xunyi region. These sandy debris flow deposits are originated from the storm processes, and characterized by the storm deposits such as erossional structures, sole casts, wave ripple laminations, wave marks and biological escape traces. The idealized depositional units of storm deposits in the study area consist of the intervals of massive beddings (A), lag deposits (B), parallel beddings (C), hummochy cross-beddings and/or wave ripple laminations (D), and argillutite (E), which are involved into three vertical depositional sequences. The approach to the sandy debris flow deposits and storm processes herein is significant to the study of palaeogeography and palaeoclimates and petroleum exploration in the study area.