Tectonic controls on lacustrine source rock occurrence in the Huizhou Sag, Pearl River Mouth Basin, China

Abstract

ABSTRACTStudy of the factors controlling lacustrine source rock deposition is critical to predict potential source rocks and discover hydrocarbon reserves. Tectonic controls on source rock deposition have been a major research focus in recent decades. In this study, we integrated geochemical, geophysical, and microfossil data to investigate the effect of tectonic movements on lacustrine source rock deposition of the Wenchang Formation in Huizhou Sag, Pearl River Mouth Basin, southern China. Geochemical, geophysical, and microfossil analyses suggest that the lacustrine source rocks are characterized by high total organic carbon (TOC) contents, type I and type II1–2 kerogen, which primarily originated from aquatic organic matter (OM), and a peak oil-generation thermal maturity stage. Rift-related faults controlled the formation and distribution of two types of half-grabens in the Wenchang Formation. Synsedimentary faults created a large amount of accommodation space, making the half-grabens under-filled. Under warm and humid climatic conditions, plankton were abundant and organic matter supply was sufficient in the half-grabens of Huizhou Sag during the deposition of Wenchang Formation. Maximum flooding surfaces (mfs) created high accommodation spaces and strongly reducing conditions, which are favourable for organic-rich lacustrine source rock preservation. Source rocks close to the depocentre and slope of the half-grabens have high TOC contents. The depositional environment (i.e. the stable highly reducing conditions) of the lacustrine source rock was largely controlled by tectonics, therefore faulting activities were considered as the most important factor controlling the occurrence of lacustrine source rock. Models of lacustrine source rock deposition were established for the Wenchang Formation in the half-grabens using a multiple analysis model. This model is also suitable for investigating the deposition of other lacustrine source rocks in half-grabens with tectonic and climatic conditions similar to those of the South China Sea Basin.