白云凹陷北坡珠江组下段陆架边缘三角洲特征及其主控因素

Characteristics and main controlling factors of the shelf-edge delta of the lower member of Zhujiang Formation in the northern Baiyun Depression

  • 摘要: 为了明确白云凹陷北坡珠江组下段陆架边缘三角洲的形成演化阶段及其主要控制因素,采用地震沉积学、层序地层学的相关理论和方法,结合钻测井数据、地震反射结构特征和均方根振幅属性等资料,在前人研究的基础上对该陆架边缘三角洲的识别特征、演化模式和控制因素进行了重新认识和探讨分析。结果表明:陆架边缘三角洲在顺物源方向具有高角度斜交型前积反射,缺乏顶积层的海岸平原相,其前端发育盆底扇沉积;垂向沉积序列以多期反旋回的前三角洲、席状砂、河口沙坝和水下分流河道的叠置为特征,发育陆坡区常见的生物扰动、泥质条带变形和滑塌、滑动现象;珠江组下段陆架边缘三角洲形成于强制海退体系域时期,并伴随着盆底扇的发育,而低位体系域时期主要发育斜坡扇和低位楔状体;构造活动促使白云凹陷北坡在珠江组下段时期形成稳定分布的陆架坡折带,珠江组下段时期古珠江携带的充沛物源和该时期强烈的海平面下降使碎屑沉积物能够进积至陆架边缘,甚至陆坡地区形成陆架边缘三角洲沉积。

     

    Abstract: In order to reveal the evolutionary history and controlling factors of the shelf-edge delta discovered in the Lower Member of Zhujiang Formation in the northern Baiyun Depression, seismic sedimentology and sequence stratigraphy are applied with the support of drilling data, logging data, seismic reflection configuration and root mean square amplitude attributes. Seismic reflection characteristics suggest a high angle oblique progradational body in parallel to the direction of sediment movement. Topset deposits are missing. Instead there are fan deposits in front of the delta laid on the bottom of the basin. The vertical sequence of the delta is characterized by the multiple reverse cycles changing from prodelta, sheet sand, mouth bar to underwater distributary channel upwards. There are abundant bioturbated structures, shale strip deformation and sliding features usually found on continental slope. The shelf-edge delta in the Lower Member of the Zhujiang Formation was formed in forced regressive systems tract periods, and accompanied by basin floor fans. However, in the lowstand system tract period there were mainly developed slope fans and low wedgelike sand bodies. A stable distribution of shelf break zone was formed in the period while the Lower Member of Zhujiang Formation was deposited under the control of tectonic movement. Shelf-edge delta occurred in the shelf margin and slope area by the huge amount of sediment discharge from the paleo-Pearl River and the strong sea-level falling then.

     

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