The geoseismic character of the rift and fault-subsident continental basins of eastern Mongolia

The geoseismic interpretation of seismic lines from the East Govi, Tamtsag, and Choibalsan basins of eastern Mongolia illustrates basin development from typical rift geometry through fault subsidence, to a phase of wrench structuration and fault-block inversion. These eastern Mongolian basins are located in an accretion zone to the south of the Siberian craton. They are close to a number of similar Chinese intraplate basins. In particular, the geology of the Songliao basin is well documented and the Mongolian basins appear to have a similar geological history. The good-quality seismic response allows identification of the following features characteristic of different phases of the evolution of the basins: (1) rift fill sequences with typical chaotic to divergent seismic configuration on the edges of V-shaped grabens, (2) the oblique and sigmoidal internal seismic configuration of a prograding delta system, (3) parallel seismic reflectors in the center of the subsiding basins (By analogy with the adjacent Chinese basins these sediments are thought to consist of low-energy lacustrine sediments. In the Songliao basin these deposits are important source beds and it is likely that they represent the source of oils known in the East Govi basin), (4) deep fossil river erosion and subsequent infill, (5)more » wrench-type fault patterns, associated intrusions, and inversion of fault blocks, and (6) limited Neogene subsidence as a result of uplift due to interplate collision.« less