Tectono-stratigraphy characteristics of the Lower Cretaceous Saihantala Sag in the Erlian Basin, China: Normal faulting and controls on the depositional variability

Abstract

Tectonism is one of the most important factors controlling the formation of sedimentary stratigraphy in lacustrine rift basins, but the controlling effects need to be further clarified. Based on 2D and 3D seismic data, well logs, logging data, and core data from the Saihantala Sag, our study aimed to analyse the fault system of the sag, determine its tectonic evolution process, establish the faulting pattern of the sag, recognise its depositional systems, and finally discuss the relationships between the tectonic factors and the basin evolution and sediment filling process.Four types of depositional systems including fan-delta, braided-delta, near-shore subaqueous fan and lacustrine deposits were recognized in the Saihantala Sag based on an integrated analysis of the well logs, cores and seismic data. The results indicated that 1) The Xilin fault is the eastern boundary fault of the Saihantala Sag, and its subsections and connections controlled the stratigraphic pattern of the sag. 2) tectonic evolution controlled the evolution of the lake basin and depositional systems in the Saihantala Sag, especially the deposition of near-shore subaqueous fan and the connection and retrogradation of braided-delta and fan-delta systems. 3) The tectonic evolution also controlled the filling pattern of the Saihantala Sag, which features two sets of braided-delta deposits in its gentle slope belt and one set of fan-delta deposits and two sets of near-shore sub-lacustrine fan deposits in its steep slope belt. 4) All three tectonic belts (Zhabu, Yihe and Saisi) mainly experienced a middle-late activated single-cycle faulting pattern, which controlled the distribution of braided-delta front deposits and lenticular sandy bodies.