Evolution of the Tamtsag Basin / NE-Mongolia — part I: basin fill

Abstract

The Tamtsag Basin in NE Mongolia is part of a widespread basin system which formed during Late Jurassic and Cretaceous times (Graham et al. 2001, Qing-Ren et al. 2003). It is filled with continental sediments and volcanics which can reach up to 4 km in thickness. Rifting and subsequent basin inversion led to a complex basin geometry characterized by several horst and graben structures. The geodynamic causes for regional basin formation are discussed controversially and several hypothesis ranging from orogenic collaps via subduction rollback to collision-induced rifting have been put forward. Scientific research on the Mesozoic basins in Mongolia has so far concentrated on the East Gobi Basin to the south (Graham et al 2001, Prost 2004, Johnson 2004) and some work has also been published on the Hailar Basin (Qing-Ren et al. 2003), the northeastward continuation of the Tamtsag Basin into China. Fundamental data on the fill and tectonics of the Tamtsag Basin in between is still missing. This is partly due to poor exposure as most of the basin fill is covered by Cenozoic sediments and only locally, near the bordering faults, rocks are accessible for surface investigations. However, recent discoveries of oil in the Tamtsag and Hailar Basins have resulted in intense exploration activity and a strong interest in the area. This contribution describes the results of a field campaign in fall 2005 focusing on the basin fill while a companion paper (Davaa et al. this volume) deals with the basin structure and hydrocarbon potential of the Tamtsag Basin.