Sequence Stratigraphy And Tectonic Control On Depositional Systems Of The Palacogene In Qikou Depression, Bohai Bay Basin

Qikou depression in Bohai Bay basin is a Cenozonic nonmarine faulted basin whichdeveloped since Pateogene Period. It's an oil-rich basin composing one of the majorpotential prospecting area, and plays an important role in state exploration strategies. Thewealth of research concerning tectonic control on deposition in tectonic active basin hasprovided a rich vein of scientific publishing over the recent years. Research on tectonicframework and tectonic active controls on the sand disperse system and depositionalsystem in syndepositional-faulted basin therefore has great significance in research andapplication.Based on the criteria of sequences boundaries, the Paleogene section in QikouDepression can be divided into 2 second-order sequences, 8 third-order sequences andseveral fouth-order sequences. Four genetic types of sequence boundary and stratigraphycharacter were gained. Recognition of six facies associationa is based on mapping andfacies analysis included log, core and seismic facies. The study concluded that four beltsof depositional system were existed in depression, which were controlled by arrangementand activity of syndepositional tectonics.Palaeotectonic framework determined the division of tectonic sub-units whichaffected sequence frame and distribution of sedimentary facies. Three deposit sourcesexisted in the depression and controlled four sand disperse systems which depocenterswere located at southwest slope-break zone, center of south edge of depression, the joint ofHaiyi faults and northeast bordering faults, and the joint of central lobe bordering faultsand northeast bordering faults.Extensional growth faults and syndepositional slope-break zones are shown to controlthe formation of depositional sequences. This paper develped two tectono-strtigraphicmodels for the evolution of sedimentary sequence in syndepositional slope-breaks. Onemodel is formed on gentle step-slope-break zones, which slope-breaks limited depositsboundry;anther model is formed on steep faults, which formed the aggradation sequenceswhen as margin faults, and formed progradation sequences when moving basinvvard.From the base of reservior, we concluded that slope-break zones in QikouDepression had good reasons to form potential lithologic and stratigraphic hydrocarbonreservoirs. We suggested two locations as exploration target.