东昆仑早—中二叠世生物礁建造特征

Reef-building Mechanism in the Early-Middle Permian, the East Kunlun

本文从造礁群落演替、层序地层和海平面升降等方面,结合大地构造引起基底沉降的证据,论述了东昆仑早—中二叠世生物礁的建造特征。东昆仑生物礁中包含6种造礁群落,各群落生物组成和结构与环境因素密切相关,4个生物礁发育阶段中群落演替关系显著。礁相地层中可识别SB_1层序界面1个和SB_2界面4个,可划分出5个三级层序。层序的沉积相序显示清晰,按曲线形态将海平面升降归为4个周期。据区域地层和相分布资料反映的古地理环境变迁,推论出石炭纪至早—中二叠世造礁期柴达木地块与羌塘地块间聚合离散的4个构造期。东昆仑生物礁的生长发育与造礁群落的演化阶段、海平面升降周期和大地构造期彼此吻合,证明生物礁建造与各控制因素间具密切制约关系。海西中—晚期柴达木地块与羌塘地块的开—合转换,为生物大规模造礁创造了长期稳定的环境。

Reef-building was controlled by the community succession, sea-level elevation and basement changes caused by tectonics. Six kinds of reef-building communities have been sorted out, which possessed different compositions and occupied respective ecological sets. Types and thrivingness of communities were distinctive and replaced one after another in the four stages of reef development. Sedimentary cyclothems are clearly discernible in the reef-facies strata, which could divide into five sequences and fourteen types of parasequences. These se-quences represent varied degrees of rising-falling cycles of the sea-level, which limited community distributions and reef-building velocities. Based on the analysis of community succession, sea-level elevation and paleo-geographic variation in the working area, four stages of tectonic evolution in the Hercynian can be distin-guished , which made up two open-closing cycles between the Qaidam plate and the Qiangtang plate. The reefs were built in the open-closing transitional period of the mid-late Hercynian, while southern margin of the Qaidam plate kept a stable condition continuously.