The Incised Valley Filling Architecture of Cretaceous Yaojia Formation in the Western Clinoform of Songliao Basin

To ascertain the period of shaping and filling of the incised valley,and the incised valley filling architecture in the western Clinoform of Songliao basin,we made use of the data of core and of more than 300 boreholes,and adopted the theories and methods of sequence stratigraphy and sedimentology to make an in-depth study on the incised valley filled by Cretaceous Yaojia Formation in the western Clinoform of Songliao basin. The incised valley in the western Clinoform of Songliao basin formed during the end of the deposition period of Qingshankou Formation and the early deposition period of Yaojia Formation in Cretaceous. It was about 70 km long and 20 km wide,extending NW-SE,and was filled gradually in the time of the transgressive system tract of SQy23 sequence (TSTy23).The filling succession of the incised valley is characterized by its multi-cycle.The bottom boundary of a perfect short-term filling cycle is the erosion surface,above which successively develop gompholite,medium-fine sandstone contained terrigenous gravels and mud pebble with the cross bedding,silty mudstone with ripple stratification and mudstone.The architecture of sand bodies with different short-term cycles that filled the incised valley presents imbricate arrangement in space.In the dip-profile,the sand body overlaps bed by bed along the bottom surface of the valley,splits toward the basin and pinches out into mudstone,reflecting the joint influence of stream and lake.In the strike profile,the sand bodies present lenticular staggered arrangement.The early sand body was developed at the relatively deeper place of the valley,while the higher place of the valley was dominated by the mudstone.The later sand body was not limited by the former deep valley.In the period when the lake-level of SQy23 reached maximum,the incised valley was filled mainly by the muddy sediment.