Rift Basin-Fill Architecture of Fluvial-Lacustrine Lower Permian Lucaogou and Hongyanchi Low-Order Cycles, NW China

Abstract

Rapid lateral facies change, autogenic processes, and irregular topography of continental rift basins challenge the reconstruction of basin-fill architecture. A process-based approach, using interpreted climatic and tectonic controlling processes on sedimentation in addition to observable attributes, may be useful to correlate sedimentary cycles. This hypothesis is tested for Lower Permian Lucaogou and Hongyanchi low-order cycles (LCs) in the Tarlong-Taodonggou half-graben, using outcrop and petrographic data. The fluvial-lacustrine graben fill covers 88 km2. Depositional environments and controlling sedimentary processes were interpreted on 5 measured sections, 0.2-5 km apart. Lucaogou LC has a transgressive base over underlying alluvial-fan deposits of the Daheyan LC. The Lucaogou LC is composed of deepwater deposits interspersed with deltaic deposits. The top of Lucaogou is an erosional unconformity overlain by fluvial deposits of basal Hongyanchi LC, followed upward by deepwater deposits. It is capped by a graben-wide fluvial erosional unconformity overlain by paleosols and fluvial deposits of the Quanzijie LC.