玛湖凹陷百口泉组扇三角洲砾岩岩相及成因模式

Conglomerate Lithofacies and Origin Models of Fan Deltas of Baikouquan Formation in Mahu Sag,Junggar Basin

玛湖凹陷斜坡带下三叠统百口泉组复杂砾岩为近源粗粒扇三角洲成因,根据砾岩的沉积特征,可细分为扇三角洲平原、扇三角洲前缘及前扇三角洲,其中扇三角洲前缘又细分为前缘外带和前缘内带。根据沉积构造、颗粒形状、排列方式、支撑形式、胶结类型等特点精细划分了9种砾岩岩相,并总结了6种岩相组合序列,它们分别反映碎屑水道、辫状水道、辫状分支水道、辫流坝、水下分流河道和水下碎屑朵体等不同沉积微相环境。对比了夏子街、黄羊泉、克拉玛依扇三角洲的砾岩颜色、粒度、颗粒接触关系、结构与成分成熟度以及主要发育的砾岩岩相,进而理清了该区扇三角洲发育的控制因素、扇三角洲发育部位、物源供给强度、地形坡度与坡降规律;最终建立了西环带扇三角洲成因模式:夏子街扇三角洲为长轴持续供给型碎屑流主控的帚状扇三角洲,黄羊泉扇三角洲为山间供给充足型碎屑流与牵引流共同作用的朵状扇三角洲,克拉玛依扇三角洲为山前供给略少型牵引流作用控制的扇状扇三角洲。

On the basis of observation and description of cores,combining with the logging and seismic reflection characteristics,the complex conglomerates of the Baikouquan formation in Mahu sag of Junggar basin were studies.The Baikouquan conglomerates is proximal coarse fan delta genesis and can be subdivided into fan delta plain,fan delta front and pro-fan delta,according to the sedimentary characteristics of the conglomerates,and the front can be subdivided into inner front and outer front.In view of the sedimentary structure,particle shape,arrangement and support forms and cementation type,etc,the nine kinds of conglomerate lithofacies and the six lithofacies associations were described,which reflect different sedimentary microfacies environments,respectively：debris channel,braided channel,braided distributary channel,braided channel bar,underwater distributary channel and lobate body.The color,grain size,particle contact relationship,sedimentary structure,compositional and textural maturity of the conglomerates were compared among Xiazijie,Huangyangquan and Karamay fan deltas.And then the control factors,developed positions,source of supply and gradient of slope of the development of the fan delta were cleared.Finally,the origin models for the proximal coarse fan deltas were established：Xiazijie fan delta is a long axis and brush-like one controlled by continual supply of debris flow; Huangyangquan fan delta is a lobate one controlled by intermont enough supply of debris flow and tractive current,and Karamay fan delta is a fan-like one controlled by piedmont partial supply of tractive current.