Sequence Stratigraphy of Lower Cretaceous in Suhongtu -Yingen Basin

Key words: 
• Suhongtu-Yingen basin /
• lower cretaceous /
• sequence stratigraphy sequence /
• system tracts /
• source-reservoir-cap rocks /
• assemblages /

Abstract: Based on sedimentary, palaeontological and seismic data, the sequence stratigraphy of the LowerCretaceous in the Suhongtu-Yingen basin has been studied. The Lower Cretaceous is divided into 1 se-quence and lowstand system tract, transgressive system tract as well as highstand system tract. Accord-ing to incumbent style of parasequence, parasequence sets are divided into transgressive style, retrogres-sive style and accretion style. In this region, the lower Cretaceous in divided into 9 parasequence sets, andretrogression parasequence style is developed much better among them. Early period of the Early Creta-ceous has experienced great changes in the Suhongtu-Yingen basin. From Early Cretaceous to Later Cre-taceous, allavial fan, fan delta, shallow lake and deep-lake are developed and turbidity current and debrisflow that belong to lake transgressive stratigraphic sequence of retrogressive style exist in deep-lakemelane mudstone. In late of Early Cretaceous shore-shllow lake has changed into shore-lake swamp andriver that belong to lake retrogressive stratigraphic sequence of transgressive style. In the region, shal-low-deep lake melane mudstone and shale of transgressive system tract that its depth is thick and its or-ganic content is rich and style is good, showing which is important hydrocarbon source rocks. Among fandelta stratigraphic sequence of lowstand system tract, accretion style is more characteristic. In otherwords,its lower part belongs to fan delta plain,its middle belongs to fan delta front and its upper belongsto profan delta. The characteristics reflect that the region might be in the margin of active basin,in whichlake changes from shallow to deep, fan delta retreats with it and rate of subsidence is more rapid thanrate of sedimentation. Reservoir ability of fan delta front is good among them, shore-shallow lake beachsandbody is important gas-oil reservoir body and deep-lake mudstone and shale of transgressive systemtract and shore-lake swampy mudstone of highstand system tract are good cover rock. They have consti-tuted favoruable source-reservoir- cap rocks assemblages.