贵阳花溪地区早-中三叠世碳酸盐岩角砾岩楔沉积特征

Sedimentary features of carbonate breccia wedges of the Early-Middle Triassic in Huaxi area,Guiyang City

早—中三叠世贵阳花溪地区位于浅水碳酸盐岩台地向深水盆地过渡的斜坡带,各沉积体系域特征明显,特别是低水位期碳酸盐岩角砾岩楔发育。野外调查发现研究区共发育4期低水位期碳酸盐岩角砾岩楔,说明该区在早—中三叠世至少经历了4次明显的海平面变化。碳酸盐岩角砾岩楔的位置迁移反映了台地边缘位置的迁移和海平面相对变化幅度的大小,其中谷立角砾岩舌相对于其他角砾岩楔向台地方向延伸距离最远,代表了台地边缘位置向台地方向迁移的距离最大,张家湾角砾岩楔代表了安尼初期的海平面快速下降。根据碳酸盐岩角砾岩楔的沉积特征和各岩石地层单元的几何接触关系,判断出该区碳酸盐台地前缘演化过程为:缓斜坡型台缘→沉积型台缘→礁镶跌积型台缘。

The Huaxi area of Guiyang was located in the slope of transitional belt from shallow-water carbonate platform to deep-water basin during the Early - Middle Triassic, and each sedimentary systems tract has its own characteristics, especially the carbonate breccia wedge of lowstand systems tract （LST）. The field investigation indicates that there are four phases of development of carbonate breccia wedge of LST, which reflects that this area experienced at least four times of significant sea level changes in the Early- Middle Triassic. The migration of carbonate breccia wedge also reflects the shifting of the platform margin and the relative sea level changes. Among them, the Guli breccia wedge extended the furthermost distance to the platform, which represents that the platform margin shifted to the platform for the furthermost distance. The Zhangjiawan breccia wedge represents a rapid sea level falling in the Early Anisian. In addition, this study reconstructed the evolution of carbonate platform margin based on the analyses of the depositional characteristics of the breccia wedges and the geometric connecting relationships of each lithostratigraphic unit： ramp platform margin to depositional platform margin to reef by-pass margin.