Tectonic and Climatic Influences on Architecture of Sequences and Sedimentary Systems in a Post-Rift Basin: Insight from Late Cretaceous Northern Songliao Basin
The influence of basin tectonics and climate change on source and sink system,sedimentary system and sequence construction of post-rift basin still need to be studied.Songliang Basin (SB) is a Late Cretaceous large petroliferous post-rift basin. Based on tectonicsequence analysis method,using log curves,observations of cores,3D seismic data and logging data,two second-order sequences (SS) and seven third-order sequences are identified in the fourth member of Quantou Formation to seconder member of Nenjiang Formation in this study. Low accommodation sequences in the lower part of a SS and in dry climate,and high accommodation sequences (HAS) in middle to upper part of a SS and in humid to semi-humid climate,are identified in the seven sequences. It is found that the HASs can be divided into a sequence architecture in gentle slope and a sequence architecture controlled by in flexural slope break on the basis of paleorelief. The architecture of sequences in SSs was responses to tectonic movement. A thermal subsidence episode started at a subsidence after uplifting of basin basement of basin uplifting,which resulted in dry to semihumid climate,erosion and unconformity,then the subsidence of basement of basin resulted in sequences deposited in a low accommodation space,while higher rate of subsidence and lower rate of supply resulted in quick increase of accommodation,humid to semihumid climate,and lake level rising,and a HAS characterized by thick TSTs and HSTs. Stratigraphic traps near surfaces of SSs,and sand bodies of gravity current deposits influenced by Paleo relief, flooding events associated with paleoclimate,shoreline trajectory associated with sediments supply,developed in TSTs and early HSTs of high accommodation sequences are dominant lithologic traps. A lot of gravity current deposits were developed in sequences Sqqn1 and Sqn1,corresponding to two maxim lake transgressive events of two second-order sequences respectively. The sand bodied of gravity flow deposits were deposited predominantly at downward slopes of flexural slope break zones.