Sedimentary environments of the Neogene basins associated with the Cao Bang – Tien Yen Fault, NE Vietnam

Abstract

The Na Duong, That Khe and Cao Bang sedimentary basins associated with the Cao Bang – TienYen Fault (northern Vietnam) developed in the zone subparallel (distance ca. 150 km NW) to the major strike-slip Red River Fault Zone that separates the South China and the Indochina terranes. These fault-controlled basins are filled with thick series of Neogene terrestrial deposits. Thirteen sedimentary lithofacies were distinguished and grouped into facies associations to represent seven depositional environments, as follows: alluvial fans, gravel-dominated fluvial channels, sand-dominated fluvial channels, flood plains, lake margins and/or river mouths, lakes, and swamps. The facies association pattern, different in each of the investigated basins, is interpreted as a coal-bearing fluvial to lacustrine environment for the Na Duong Basin, and a fluvial environment for the That Khe Basin. The most complex pattern is displayed by the Cao Bang Basin and interpreted as an alluvial-fan to lacustrine environment. The origin of theses basins may be correlated with a sinistral transtensional regime which occurred in the Early to Middle Miocene. Besides tectonic activity, the evolution of particular basinswas also controlled by the climate,which caused a change in the rate of sediment supply and weathering conditions. The present-day shape of these basins does not correspond to their original plan, having resulted from the post-sedimentary uplift and erosion.