江汉盆地潜江凹陷潜三段古地貌与砂体成因分析

Palaeogeomorphology and origin of sandbodies of the Member 3 of Qianjiang Formation in Qianjiang Sag,Jianghan Basin

蚌湖洼陷是潜江凹陷潜江组的沉积、沉降中心,其两侧砂体的成因与分布是一个有争议的问题。通过岩心观察、水动力条件及碎屑锆石定年分析,明确了蚌湖洼陷两侧砂体的成因联系;进一步通过连续地层单元内的沉积古地貌恢复,明确了古地貌与砂体分布的关系。研究认为潜江凹陷潜三段沉积时期北部发育荆门地堑与汉水地堑两大物源体系,中部发育蚌湖—王场洼陷,西部发育丫角—新沟低凸起及斜坡带,东部为斜坡带,南部则为缓坡带。潜三段沉积时期,蚌湖洼陷南部的砂体既不是前人认为的"盐湖密度流"越过蚌湖洼陷的沉积产物,也不是牵引流横穿蚌湖洼陷搬运而来,而是牵引流经西部斜坡上的古沟谷搬运沉积下来的。

The Banghu Sub-Sag is the depositional and subsidence center of the Qianjiang Formation in Qianjiang Sag. Origins of sandbodies along its two sides and their distribution have been a controversial topic. Their origins have been distinguished by core observation, hydrodynamic analyses and clastic zircon dating analysis. Further more, the relationship between palaeogeomorpbology and sandbody distribution was identified. The research indicates that during the deposition of the Member 3 of the Qianjiang Formation, two provenances-Jingmen and Hanshui were developed in the north, the Banghu-Wangehang Sub- Sag was developed in the central area, a ＂Y＂ shaped low uplift and a slope was present in the west, a slope belt was developed in the east and expansive gypsum-bearing mudstones of shore-shallow lacustrine origin were deposited in the south slope belt. New research results show that during the deposition of the Member 3 of Qianjiang Formation, the sandbodies along the south side of the Banghu Sub-Sag were neither deposits of salt density fluid flowing through the Banghu Sub-Sag, nor transported by traction, but transported and deposited along the ditch-trough or west slope by traction.