柴达木盆地西南缘下干柴沟组下段辫状河三角洲沉积特征

柴达木盆地西南缘昆北断阶带下干柴沟组下段沉积了一套辫状河三角洲沉积，具有重要的油气储集意义。利用录井、钻井岩心、地震、测井以及粒度分析等手段，详细研究了辫状三角洲的沉积特征。研究结果表明，昆北断阶带辫状河三角洲分为三角洲平原、三角洲前缘和前三角洲三个亚相类型。辫状河三角洲平原分为辫状河道和洪泛平原两个微相，辫状河三角洲前缘可分为水下分流河道、河口坝/远砂坝、席状砂、水下分流间湾五个微相。纵向上，经历了辫状河三角洲平原-辫状河三角洲前缘-滨浅湖的演化过程，辫状河三角洲平原发育河道多期次叠加，辫状河三角洲前缘河道化作用较弱。平面上，受两大物源体系影响，发育两个主河道，河道化程度横向差异较大。同生期断层是制约辫状河三角洲发育的首要因素，物源供给制约辫状河三角洲砂体分布和物质构成，古地貌制约辫状河三角洲的形态分布。综合各种地质因素，建立了柴西南昆北断阶带辫状河三角洲沉积模式。

Sedimentary characteristics of braided river delta of the lower member of the Lower Ganchaigou Formation in southwestern Qaidam Basin

A braided river delta deposited at the lower member of the Lower Ganchaigou Formation in the Kunbei step-fault zone of southwestern Qaidam basin is considered to be of great importance to the study of oil and gas accumulation in the region.Analyses based on drilling core,logging and seismic data,as well as grain size statistics,were employed to perform a detailed study on the sedimentary characteristics of the delta.Three subfacies were recognized in the delta:braided-river delta plain,braided-river delta front and prodelta.The plain subfacies can be further divided into two micro-facies:braided channels and flood plain.The front subfacies can be subdivided into five micro-facies:under water distributary channel,mouth bar/distal bar,sheet sand and under water distributary bay.Vertically,the delta evolved successively from braided river delta plain,braided delta front to shore-shallow lake. The plain facies experienced superimposition of multiple channels,while the front facies had only a weak influence over the channels.Horizontally,it was controlled by two major provenances and developed two main channels with horizontal heterogeneity.The syngenetic faults were consi-dered as the major controlling factors upon the development of the delta,while the provenance constraints were thought to have affected the distribution and composition of the delta sandbodies and the paleogeomorphology helped forming the present landform of the delta.A sedimentary model was then established for the delta based on comprehensive analyses of all geological factors.