SE Cambodia and SW Vietnam Geology, Burial and Uplift History

Abstract

The geology of SE Cambodia and neighboring SW Vietnam is only superficially known. Based on extensive fieldwork, seismic investigation and laboratory analysis we present a first account on the outline and geological history of the region important for understanding its petroleum potential and the potential of the pre-Cenozoic in the nearby Gulf of Thailand. The geology of SE Cambodia and SW Vietnam is characterized by three N–S-trending structural belts continuing offshore into the Gulf of Thailand to the south. The eastern belt located in Vietnam and westernmost Cambodia is composed by mid- to Late Cretaceous, subduction-related granitic and volcanic rocks dated by U/Pb-zircon analysis. These magmatic rocks were intruded into and overlying Paleozoic, Triassic and Jurassic strata. Jurassic granites also occur in the area probably testifying to a protracted period of paleo-Pacific subduction underneath the region during Mesozoic time. The central belt is a highly complex fold and thrust belt croping out in SW Vietnam and in SE Cambodia but continues offshore into the Gulf of Thailand to the south. The belt is composed by strongly deformed Paleozoic and Mesozoic rocks. Cambrian–Devonian clastics are intruded by subduction-related Early Permian Granites and overlain by their associated extrusives documented by U/Pb-zircon dating. These Lower Permian rocks are in turn overlain by mid- to Upper Permian carbonates and Triassic sand and mudstones. The westernmost belt is composed by an up to ~4 km thick Lower and mid-Cretaceous continental sand- and mudstone succession closely resembling the Korat Group of Thailand. A few shallow-marine interludes suggest a setting closer to a Cretaceous seaway compared to the Thailand Khorat Group. Apatite and zircon fission track analysis suggest that the three belts were rapidly uplifted during Paleocene and Eocene time, which is corroborated by seismic stratigraphic analysis and vitrinite reflectance data. Early Cenozoic uplift occurred subsequent to the termination of Cretaceous magmatism and was associated with massive compression along the central thrust and fold belt and more moderate deformation of the Cretaceous basin located within the western belt.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015