北部湾盆地涠西南凹陷涠11区流一段扇三角洲沉积特征及控制因素

Sedimentary Characteristics of Fan Deltas and the Dominated Factors in W11 Area of 1st Member of Liushagang Formation in Weixinan Depression,Beibuwan Basin

北部湾盆地涠洲11区流一段发育缓坡型和陡坡型两种类型的扇三角洲。结合岩电震资料,分析了这两类扇三角洲的异同,并探讨了造成这两类扇三角洲沉积特征异同的主控因素。其中陡坡型扇三角洲主要分布于研究区北部陡坡带的流一段中亚段,粒度较粗,以重力流成因的厚层砂砾岩体为主,沉积厚度大,平面展布小;而缓坡型扇三角洲主要分布于研究区南部的涠西南低凸起缓坡带附近的流一段下亚段,粒度相对偏细,牵引流与重力流沉积构造均较发育,沉积厚度相对较小,平面延伸范围广。两类扇三角洲形成与分布特征的不同主要受控于构造格局、古地形的差异以及基准面变化等。

Fan deltas of the abrupt slope and the gentle slope areas,were developed in the W11 area of 1st Member of the Liushagang Formation in Southwestern Weizhou Depression,Beibuwan Basin. Based on the lithology,logging and seismic data,the different characteristics between these two kinds of fan deltas were analyzed and the main controlling factors of the fan delta were discussed. The fan deltas at abrupt slope area,which were mainly distributed at the steep slope zone of the middle part of 1st Member of the Liushagang Formation in the northern of the study area,were comparatively coarse grain-sized and were mainly thick-layer sandstone rock deposited from the gravity flow,with large depositional thickness and small scale planar distribution. However, the fan deltas at gentle slope,which were widely distributed in the lower part of 1st Member of the Liushagang Formation at Southwestern Weizhou Salient in the southern of the study area,had a mixed gravity flow and tractive current with relatively fine grain-sized,a small depositional thickness and a wide range of planar extension. The development and distribution of these two kinds of fan deltas were mainly controlled by structural framework,paleotopography and basal level change.