城口-鄂西海槽西侧晚二叠世碳酸盐台地边缘发育新认识

Sedimentological Architecture of the Late Permian Carbonate Platform Margin to the West of Chengkou-Western Hubei Oceanic Trough, Sichuan, China

基于城口-鄂西海槽西侧地区详细的露头调查、钻井资料分析,结合古生物、古生态以及地层对比,对研究区晚二叠世长兴期碳酸盐台地边缘沉积相及其演化进行详细解剖,得出区内台地边缘骨架礁-凝块石灰泥丘生态-沉积演化对碳酸盐台地边缘构筑具有积极作用的认识。研究表明区内长兴期碳酸盐台地边缘礁滩经历了三个演化阶段:第一阶段,碳酸盐台地边缘坡折带尚未形成,台地边缘礁滩欠发育,且台地前缘斜坡坡度较缓;第二阶段,碳酸盐台地镶边开始形成,发育骨架礁及滩相沉积,垂向上构成进积-加积组合序列,台地前缘斜坡变陡;第三阶段,微生物逐渐占据后生造礁生物生态空间,发育台地边缘凝块石灰泥丘,与上覆台地边缘滩构成垂向加积组合序列,促进了台地边缘正向地貌的发育,使区内台地边缘更加陡峭,台地前缘斜坡发育滑塌角砾岩。造礁生物生态演替及相对海平面变化共同影响并控制长兴期碳酸盐台地边缘构筑过程。

A analysis of detailed field observations drilling data, as well as paleontological, paleoecological, and stratigraphiccorrelations were carried out to characterize the sedimentary facies and understand the evolution of the Changhsingian（Late Permian）carbonate platform margin to the west of the Chengkou-Western Hubei Trough. These data demonstrate the constructive effects of thesedimentation and ecology of the marginal skeletal reefs and the thrombolite mud mounded on the architecture of the carbonateplatform. The model of reef and shoal complexes rim carbonate platform in Changhsingian underwent a three-stages evolution：（1） the slope break of the carbonate platform margin had not yet formed. The reefs and shoals were not fully developed, and the foreslope of theplatform was not especially steep;（2） The rim of the carbonate platform began to form. Skeletal reefs and shoal facies were developed invertical progradation-aggradation association sequences. The foreslope of the platform also became steeper;（3） The ecological niche ofmetazoan was occupied by microbe in Late Changhsingian. The thrombolite mud mounds were formed at this time, when a verticalaggradation sequence with the shoals developed on top of them. This fostered the further building up of the positive relief features of themargin. Meanwhile, the platform margin became much steeper and slump breccia developed on the foreslope of the margin. Theecological succession of reef-building organisms, together with changes in relative sea level, influenced and controlled the evolution ofthe carbonate platform margin throughout the Changxingian Stage.