Tectonically-controlled sedimentation of Cenozoic deposits from selected basins along the Vietnamese segment of the Red River Fault Zone

Abstract

Small, narrow sedimentary basins occur along the main faults in the Vietnamese segment of the Red River Fault Zone (RRFZ), which is the major discontinuity separating the South China and Indochina microplates. The sedimentary basins of the RRFZ are grouped into three main sections: along the Red River Valley, the Chay River Valley and the Lo River Valley. The sedimentary basins are filled with thick series of Palaeogene and Neogene clastic deposits that differ in type and origin. In the lower part of the basin fill, coarse-grained deposits predominate. In the upper part, different types of sandstones, siltstones and brown coal occur. There are no sediments of Late Pliocene age. Quaternary deposits are represented by sands and gravels. Biostratigraphical data are very poor, therefore only lithostratigraphical subdivision is applied. Thus, it is possible that deposits from adjacent basins associated with the RRFZ represent strata of different ages. The investigations were focused on the Lo River Basin (associated with the Chay River fault), Yen Bai Basin (associated with the Red River fault) and Co Tiet Basin (associated with the southwesternmost branch of the Red River fault). Thirteen sedimentary facies were recognised in deposits filling the investigated basins. The facies were grouped into five facies associations representing five distinct depositional environments. These comprise alluvial fan, gravel-dominated fluvial channel, sand-dominated fluvial channel, alluvial plain and lacustrine environments. In addition, the basin fills show features characteristic of strike-slip basins.