四川盆地及邻区下寒武统龙王庙组颗粒滩沉积特征与空间分布

通过对区域地质调查剖面资料和钻井资料的研究,结合对部分野外剖面与钻井岩心的系统观察和取样分析,发现四川盆地及邻区下寒武统龙王庙组的颗粒滩主要由颗粒石灰岩(白云岩)和晶粒白云岩构成;颗粒滩以未暴露浅滩为主,发育向上变浅和向上变深2类垂向序列。川中古隆起和黔中古隆起北部地区的颗粒滩的横向规模大、层位稳定性和连续性最好,其余地区颗粒滩多表现为点滩且规模较小。研究区龙王庙期总体上为西浅东深,西南缘、西北缘和北缘为古陆环抱,盆内呈"一隆两坳"的古地理格局。颗粒岩在古地貌高地具有广覆式"五线一带"的平面分布样式。川中古隆起、黔中古隆起北部地区是颗粒滩发育最有利的地区,东北部和东南部的水下岛链区是优质颗粒滩带发育的潜在区。古隆起发育演化对颗粒滩和有利储集相带具有明显的控制效应,次一级海平面升降变化影响滩体的垂向叠置样式和横向连续性。

Sedimentary characteristics and distribution of grain shoals in the Lower Cambrian Longwangmiao Formation of Sichuan Basin and its adjacent areas

Based on data from regional outcrops and wells,together with systematical observation and sampling for some outcrops and wells, it was found that grain shoals in the Lower Cambrian Longwangmiao Formation of Sichuan Basin and its adjacent areas are comprised of carbonate grainstone and crystallized carbonate grainstone.The grain shoals are dominated by unexposed shallow shoals, and mainly develop two types of vertical sequences including upward-shallowing and upward-deepening. In terms of the lateral occurrence of the grain shoals, those in the central Sichuan palaeouplift and the north of the central Guizhou palaeouplift are characterized by a large scale and stable and continuous stratigraphic distribution. In contrast, the shoals in other regions are mainly patched shoals with relatively small scales. Based on the reconstruction of the palaeogeographic pattern of the study area during the Longwangmiao Period, the water depth was shallower in the west and deeper in the east, the basin was surrounded by old lands from southwest, northwest and north, and one uplift was divided two depressions inside the basin. With respect to the lateral occurrence, the grainstones in highlands demonstrate a widely covering style of “five lines and one area”.Central Sichuan palaeouplift and the north of Central Guizhou palaeouplift are superior regions for grain shoals developing,and the sub-marine island chain in the northeast and southeast may be the potential locations for high-quality grain shoals. The development of the palaeouplift evidently had the dominating effects on the development of grain shoals and favorable reservoir sedimentary zone. The sub-level eustatic change influenced the vertical superimposed pattern and lateral continuity of the grain shoals.