DEEP-DERIVED CLASTICS IN FINE-GRAINED SEDIMENTARY ROCKS IN PERMIAN LUCAOGOU FORMATION IN SANTANGHU BASIN, XINJIANG, NW CHINA

The NW-SE trending Santanghu basin is located in Xinjiang, NW China, between Tianshan Mountains and Altai Mountains. Santanghu basin was in intraplate rift evolution stage, under regional extension geological background in late Carboniferous. During early-mid Permian the basin was a starved, deep lacustrine intracontinental rift basin.

Fine-grained sediments have become a focus for geologists nowadays since oil demand continue increasing. However, it is hard to conduct detailed petrology and mineralogy study constrained by their extremely fine grain size and current experimental conditions. Therefore these dark fine-grained rocks have long been considered as mixed deposits of terrigenous clasts and chemical precipitates. This work studies black fine-grained rocks in Permian Lucaogou Formation of Santanghu Basin. The rocks present laminated and people used to think it mainly composed of mudstone, dolomicrite, micrite tuff and tuffite. By means of cores, thin sections and electronic probe observation, combined geochemistry data results, evidence of volcanic and hydrothermal activities has been found and some clastics carrying deep source information are observed. Furthermore, these rocks turn out to dominantly compose of unstable minerals and a few metastable minerals with low grade of texture maturity. As a result, this paper prefers to consider the rock series as laminated fine-grained rocks which composed of deep-derived, magmatic-hydrothermal exhalative-related clastics. And the deep-derived clastics may derive from magmatic - hydrothermal material or fluids in variety depth of interior earth, rather than weathered source rocks or hydrothermal precipitation.