松辽盆地盆西斜坡白垩系姚家组下切谷充填结构

白垩纪青山口组沉积末期至姚家组沉积初期,松辽盆地发生了湖平面大幅度下降,湖区大规模萎缩,形成了SSQq-qn和SSQy-n之间的二级层序界面.这一时期,西部斜坡普遍暴露,缺失了三级层序SQqn4和SQy1地层,并在齐齐哈尔古水系的作用下在西部斜坡的北部形成了下切谷.下切谷长约70km,宽约20km,呈NW-SE延伸.在SQy23层序水进域,下切谷逐渐被充填.下切谷发育区SQy23水进域的地层厚度明显高于相邻区域,在沉积走向上的高地层厚度梯度带反映了下切谷的边界.下切谷充填序列具有多期旋回性特征,一个完整的短期充填旋回的底界为侵蚀面,侵蚀面之上依次发育泥砾岩、具交错层理含陆源砾石和泥砾中-细粒砂岩、具波纹层理粉砂质泥岩和泥岩.充填下切谷的不同短期旋回的砂体在空间上具有叠瓦状结构.在倾向剖面上,砂体沿下切谷底界面逐层叠置超覆,向盆地方向分叉并尖灭在泥岩中,反映了河-湖共同作用.在横剖面上,砂体呈透镜状错叠.早期的砂体主要发育于相对深谷部位,相对高部位以泥质充填为主,后期的砂体不受原始深谷限制.在SQy23最大湖泛期,下切谷内以泥质充填为主.

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.