Tectono-sedimentary analysis of the Lower Cretaceous succession in the sags of the Ondor Sum uplift, Southern Erlian Basin, NE China

Abstract

The tectonics of continental rift basins and the accompanying deposition processes are areas of increasing research interest. The Ondor Sum uplift is located in the southern Erlian Basin, NE China. It is a promising site for petroleum exploration. In this study, we used 2D and 3D seismic, well-log and core data to conduct a tectono-sedimentary analysis of the sags of the Ondor Sum uplift.Three types of depositional systems were identified, including fan-delta, braided-delta and lake depositional systems. Of these, the fan-delta and lake deposits are highly developed, while the distribution of braided-delta deposits is limited. The rift sags in the area consist of a SE-faulting and NW-overlapping type, a NW-faulting and SE-overlapping single-faulted dustpan-like rift sag and a double-faulted rift sag. The tectonic evolution models of the area were of two types: an inheritably-developed type, applicable to the single-faulted dustpan-like rift sag and double-faulted rift sag, and a structurally migrated type.The early-to medium-term-activated as well as the long-term-activated faults controlled both the sediment filling of the Wulanhua and Chazhong sags and the distribution of their sand bodies. Both differential and balanced uplifting during the Late Yanshanian period determined the stratigraphic development and configuration of the sags. Given the similarities the sags of the Ondor Sum uplift shares with the petroliferous sags of the inner Erlian Basin, combining with the petroleum discovery in the Wulanhua and the Chazhong sags and relatively shallow burial depth of the target layers, the sags in this area are likely to contain hydrocarbons and should thus be explored for their resource potential.