Depositional systems, sequence stratigraphy and basin filling evolution of Erlian fault lacustrine basin, Northeast China

摘要

Mian fault basin, including more than 40 grubens and half grabens, is one of the major oil prospecting and producing areas in North China. The basin was formed by extension during the Jurassic to Early Cretaceous period, and was filled with more than 3000m of alluvial/fluvial and lacustrine deposits. Five 2nd order (sequence set) and nine to twelve 3rd order sequences have been identified by recognition of unconformities in the basin fills based on the integrated analysis of seismic profiles, logging and cores. Parasequence sets and parasequences can be classified by major lacustrine Hooding surfaces. The depositional systems formed in the basin include alluvial fan, fan delta, braided stream delta, sublaeuslrine fan and lacustrine turbidite deposits. Three types of lacustrine sequences have been identified in term of I'acies associations : (1) deep lacustrine basin sequences, mainly consisting of (hick lacustrine nuidstones. sublaeustrine fan and deep water fan delta systems; (2)shallow lacustrine basin sequences, predominately composed of fan delta and braided stream delta systems; and, (3)shallow lacustrine and fluvial basin sequences. It is still controversial whether the formation of sequence boundaries was related to climate change or tectonism, but it seems to be clear that the origin of the major unconformities confining 2nd order sequences is likely related to or enhanced by variation in the tectonic subsidence rate or inversion caused by episodic tectonism. The deltaic sandy bodies and incised channel fills formed along the hinged and axial margins are the economically important reservoir sandstones that are found in the basin. The sublacustrine fan sandstones formed in the central basin constitute a second potential reservoir type. The fan delta deposits along the escarpment margin may also form a major potential for reservoir facies.