Thermal history of the Jurassic marine sequences in the Qiangtang Basin, northern Tibetan Plateau: implication for the hydrocarbon preservation

Abstract

The Jurassic marine sequences of the Qiangtang Basin in the northern part of the Tibet Plateau have the best petroleum exploration prospect. The prototype basin has undergone multi-stage and complicated tectonic events since the Cretaceous, especially the mid-Cretaceous tectonic event and the Cenozoic uplift of Tibetan Plateau. However, little information about the impact of these tectonic events on petroleum preservation has been done. In this paper, the burial and thermal histories modeling using vitrinite reflectance (Ro) are used to characterize the impact. The results showed that there is a regional falling of palaeotemperature in the Qiangtang Basin during the mid-Cretaceous indicating a regional tectonic event caused by the collision between Lhasa and Qiangtang blocks. However, the Cenozoic tectonic event caused by the uplift of Tibetan Plateau since 30 Ma was only recorded in the Southern Qiangtang Depression and not obvious in the Northern Qiangtang Depression, which indicates that uplift-denudation caused by the mid-Cretaceous tectonic event was extensive in whole Qiangtang Basin and more significant to the hydrocarbon accumulation than those in the Cenozoic. The event could damage the previously formed hydrocarbon traps and caused the leaking of cap-rocks for the dramatically denudation especially in the Southern Qiangtang Depression. We speculated that the Northern Qiangtang Depression has the lower thickness of denudation and barely influenced by the Cenozoic tectonic events and thus is primary exploration target for gas or gas hydrate.