Litho-tectonic cycles and petroleum signification of Miocene sediment of Phú Khanh basin

Tran Thi Dung, Tran Nghi, Nguyen Thi Phuong Thao, Dinh Xuan Thanh, Tran Thi Thanh Nhan,
Nguyen The Hung, Luong Hong Huoc, Nguyen Thi Huyen Trang

Integrating the relationship between sedimentary characteristics and tectonic movements can classificate the Miocene sediments of Phu Khanh basin into 3 litho-tectonic cycles: early Miocene cycle, middle Miocene cycle and late Miocene cycle. This is a dialectic relationship with causal relation and function-variables. In which the cause is the tectonic movement and the result is the sedimentary feature. If according to mathematics, sediment is a function and tectonic motion is a variable: TT = f (KT). Each litho-tectonic cycle consists of 2 phases: (1) the subsidence phase consists of 3 successive processes: the syngenesis process, the diagenesis process and the catagenesis process (change of rock). At the end of the subsidence phase, the sedimentary rock has not been deformed, the lying position of the rock is still horizontal; (2) the uplifting phase corresponds to the hypergenesis process. In this process sedimentary rocks are deformed such as fold, fault, compression and sagging. The three litho-tectonic cycles have repetition but the following cycle reaches a higher level than the previous cycle according to the rules of evolution as follows: (1) early Miocene litho-tectonic cycle with polymictic terrigenous composition, sedimentary basins in the form of inland trenches with strong subsidence; (2) middle Miocene litho-tectonic cycle has 2 types of sedimentary complexes, which are oligomictic terrigenous and coral reef carbonate, filled with oval-shape basin, stable tectonic; (3) late Miocene litho-tectonic cycle has 3 types of sedimentary complex: oligomictic terrigenous, containing bioclastic terrigenous sediment and coral reef carbonate fill the shallow, expansive basin, stabilizing tectonic. The boundary between the litho-tectonic cycles is the angular unconformable boundary, represented by the eroded surface of river channel in the continental environment.

Keywords: litho-tectonic cycle, lithofacies complex, polymictic, oligomictic, terrigenous, coral reef.