Research On Sequence Stratigraphy And Sedimentary Facies Of Lower Cretaceous In West Area Of Baiyinchagan Sag

The subject formation is devided into three third grade sequences by the unconformity surfaces which are recognized by drilling data,log data and seismic data by combining method of classic sequence stratigraphy and High resolution sequence stratigraphy : sequenceâ… , sequenceâ…¡and sequenceâ…¢. It is further divided into six fourth grade sequences by subordinated unconformity surfaces which are recognized by precise interpretation: sequenceâ… 1,sequenceâ… 2,sequenceâ…¡1,sequenceâ…¡2,sequenceâ…¢1 and sequenceâ…¢2.Based on the fourth grade sequence framework, the short-term base-level cycles are recognized by High resolution sequence stratigraphic method.There are fan delta facies,braided river delta facies,turbidite fan facies and lakes faciess which are recognized by petrology sedimentary facies marks and physical geography sedimentary facies marks.Four sedimentery sources are recognized in the study area by petrology distribution and seismic reflaction characters:the NE dicretion source near by Xi19,the NW dicretion source near by Da30,the NNW dicretion source near by Xi6 and the NNW dicretion source near by Xi10.The horizontal distribution of the faciess is devided by the horizontal distribution of sand-ground ratio,the horizontal distribution of electrofacies,the horizontal distribution of seismic facies and the horizontal distribution of seismic attribute. The fan delta facies is mainly distribute in sequenceâ…¢in the southwest, southeast northeast of the study area.The braided river delta facies is mainly distribute in sequenceâ… 1 to sequenceâ…¡2 in the southwest, south and east of the study area.Delta facies distribution iscontroled by the slope break,fault and channel.The fan delta facies and braided river delta facies deposite up the slope break,and the turbidite fan facies deposite down the slope break.