Tectonic-sedimentary Evolution Of The Kongdian Period In The Dongying Sag,Bohai Bay Basin

The study area,the Dongying Sag,is located in the southeast part of the Jiyang Depression,Bohai Bay Basin.The target formation,the Ek,is mainly characterized with a set of continental clastic-lacustrine mudstone deposits developed in Paleogene.Given that considerable petroleum resources have already been discoveried,these formations have been regarded as significant petroleum reservoirs and conducted lots of researches.Therefore,on the basis of previous studies,here,we takes the Kongdian Formation stratum in Dongying Sag as the research object,after observing and identifying sedimentary facies markers,analyzing the profile characteristics of main active faults,and calculating the average activity rate of each fault in the core,the deposits developed in the Kongdian period in the study area Analysis of the facies type,sedimentary distribution status,and identification,tectonic pattern,and evolution characteristics of the seismic interface,completed the study of the sedimentary system tectonic pattern of the Cenozoic Paleogene Kongdian Formation in the Dongying Sag,Bohai Bay Basin During the period,the controlling effect of fault activity on the stratum was discussed,and conclusions presented in this report can be summarized as follows:(1)The sedimentary facies of the Kongdian Formation are analyzed,and it is believed that there are two different sedimentary facies combinations in the depositional period of the first member of the Kongdian Formation,namely,alluvial fan-flood flood lake-dry salt lake sedimentary combination and periodic lake-inshore water in the wet period The lower fan sedimentary combination,the former includes alluvial fans,braided rivers,flooded lakes and dry lakes and other sedimentary facies types,the latter includes lakes,near-shore underwater fans and storm facies.During the deposition period of the second member of Kong,the study area mainly developed nearshore subaqueous fans and lakes of the same sedimentary facies type.The lake facies can be divided into sedimentary subfacies such as beach shallow dam,semi-deep lake and deep lake.(2)The plane distribution characteristics of sedimentary facies are analyzed,and it is considered that during the first period of the hole,the alluvial fan deposits are at the edge of the basin,and the flooded lake deposits transition to the interior of the basin,and they evolve into dry salt lake deposits in the northern depression zone of the basin;During the deposition period,the southern slope belt mainly developed beach shallow lake and bar deposits,and it evolved into a semi-deep lake-deep lake deposition in the northern Lijin-Minfeng depression,and the nearshore underwater fan body was developed in the gully part of the steep slope belt in the north of the basin.(3)Within the study area,mainly synthesizing seismic,logging and other data,on the basis of structural stratigraphic division,first of all,the residual stratum thickness of different stratigraphic units is clarified,and then combined with the fault development characteristics of the study area and the results of balance profile analysis to determine The paleo-tectonic pattern of the target stratum is known.In the second phase of Kongkong,the northwest-trending fault system still controlled the paleo-tectonic pattern of the entire study area.The Dongying sag appeared as a faulted basin with the northeast faulted boundary and the southwest over-lapped to the Luxi uplift.In the first period of Kong,the Tanlu fault zone changed from an early left-handed strike-slip feature to a right-handed strike-slip feature.The activity intensity of the early northwestern fault system gradually weakened.Gradually controlling the paleo-tectonic pattern of the entire study area,the Dongying Sag as a faulted basin with the north faulted boundary and the south over-lapped to the Luxi uplift.