The Sequence Stratigraphic And Sedimentary Evolution Of Lower Jurassic-Lower Cretaceous In South Turgay Basin,Kazakhstan

The exploration to lithology and stratigraphy reservoir is a focus in the South Turgay Basin,which is located in the middle part of Kazakhstan.There are higher degree of structure reservoir exploration in this basin.This paper mainly analyzed the sequence stratigraphy and sedimentary features in the lower Jurassic to lower cretaceous in the South Turgay Basin,which can provide significant geological references for subtle reservoir evaluation in this basin.According to the characteristics of seismic reflection and sequence boundary,a systematic stratigraphy classification and correlation was conducted to build the seismic stratigraphy and third-order sequence stratigraphy framework in the study area.Additionally,we analyzed the sedimentary facies within the sequence stratigraphy framework and summarized their evolution features in the vertical and horizontal scales.Based on the research results,we recognized two first-order sequence boundaries,two secondary-order sequence boundaries and seven third-order sequence boundaries associated with 10 sequences(SQ1?SQ10).Sequences SQ3,SQ6,SQ9 were developed largest three transgressive trace systems.And the two primary sequence interfaces is base unconformity surfaces and on behalf of the regional strata denudation of truncated unconformity surface(K/J);Two secondary sequence interface respectively:on behalf of strata Angle unconformity surface of the tectonic environment transformation(J2kr/J2km),on behalf of the regional rivers-cutting action of stratigraphic overlap(toplap/super)unconformity surface(K1nc2).There are five typical sedimentary facies identified,including rivers,delta,braided delta,fan delta and lake in the lower Jurassic to lower cretaceous in the studied basin.The characteristics of these sedimentary facies demonstrated four depositional patterns:fan delta to lake during the rifted time with two-controlling-faults(SQ1-SQ3),fan delta to lake to delta during the rifted time with one-controlling-fault(SQ4-SQ6),delta to lake during the rift to depression transitional time(SQ7-SQ8),and river to delta to lake in the depression time(SQ9-SQ10).