Sedimentary evolution and source provenance of the First Member of Lower Cretaceous Duhongmu Formation in Sanghe area,Baiyinchagan sag

Sanghe area is an important oil-bearing zone in the Baiyinchagan Sag.Oil exploration in the Baiyinchagan Sag has been carried out for many years,but fundamental geological data of Sanghe area remain insufficient.Based on a comprehensive analysis of core and logging data,regional geological setting,sedimentary facies types of the 1st Member of Lower Cretaceous Duhongmu Formation in Sanghe area of Baiyinchagan Sag, the authors made a systematical study of their distribution and evolution characteristics.The results show that three types of sedimentary facies are developed in this area,namely fan delta,lacustrine fan and slump turbidite fan facies.From the margin to the center,the granularity of sediments becomes finer and the facies are gradually developed from fan deltas or shore-shallow lake to semi-deep lake.The same evolution regularity is observed from the bottom to the top.Based on an analysis of clastic particle types and heavy minerals of the sandstone,the authors hold that the sediments of the 1st Member of Duhongmu Formation in Sanghe area must have come from Bayinbaolige swell situated in the north of the Baiyinchagan Sag,with the characteristics of multiphase, spasm and being adjacent to the source rocks.The results also suggest that the source rocks are mainly sedimentary rocks and subordinately igneous rocks as well as small amounts of metamorphic rocks.