Tanan Depression is one of the most important oil and gas exploration areas in Hailaer-Talmud Zagat Basin. Various data including cores

logs and 3D seismic data were integrated to study in detail the sequence stratigraphic framework and sedimentary system characteristics of K 1 n1（ the 1st member of Nantun Fm） in Tanan Sag

Haita Basin. Three unconformites and two lake flooding surfaces were identified in K 1 n1

according to which K 1 n1was divided into three thirdorder sequences. The types of sedimentary facies and distribution characteristics of sedimentary system were analyzed on the basis of isochronous stratigraphic framework. Three sedimentary systems namely fan delta

sublacustrine fan and lake were identified in the K 1 n1. Fan delta sedimentary system under the control of provenance on the western gentle slope dominated in the study area during the deposition of the middle-lower part of K 1 n1due to the influences of oscillatory subsidence of"flood basin"during passive rifting. In contrast

lake deposition system was predominant in the study area during the deposition of the upper part of K 1 n1due to the rapid subsidence in the process of active rifting. At the same time

the secondary depression-controlling faults experienced NW-SE extension and tilted

forming large-scale reverse normal faults. Efficient hydrocarbon expulsion characteristics of interbeded source rock and reservoir combination

high porosity and permeability of distributary channel sands of fan delta front facies and structural high in the upthrown block of fault jointly determined the footwall of antithetic fault in the western subsag to be the main location of oil accumulation.