Abstract:

 In this article，based on the principle of sequence stratigraphy, the sequences in Lower Cretaceous of Tanan depression in Tamtsag Basin,Mongolia are discriminated and correlated according to well logging and seismic data, and four third-order sequences（SQ1-SQ4）are identified. On the basis of these results, the characteristics of sequence structures are studied and the types of sequences are classified through analysis of the tectonic evolution features: SQ1 and SQ2 are sequences of initial rift lacustrine basin，SQ3 is a sequence of maximum rift lacustrine basin, and SQ4 is a sequence of post rift lacustrine basin. The sequence structures are mainly controlled by tectonic subsidence patterns, because the tectonic subsidence patterns are different in the evolution time of Tanan depression, three types of sequence models are formed, which are simple half graben shaped slope model, differential subsidence and tectonic rollback model, and depression sequence model. The development and distribution of stratigraphic and lithologic traps are distinct in different sequence models.

Key words: Tanan depression, sequence structure, controlling factor, sequence model