Origin Analysis on Breccia of the Lower Mantou Fromation of Cambrian System in Reservoir Area in Hekou Village

摘要

Mantou Fromation of Cambrian System is one of the major strata developed in the reservoir and dam area. It belongs to Mantou Fromation of Cambrian System, which is closely related to the engineering geology and leakage feature of the reservoir, and the breccia is found to distribute in many places in the lower part Mantou Fromation. Geological body and lithological features of breccias are described in significant detail in this paper. The breccia of the lower Mantou Fromation can be classified into 2 types. Origin of the two types of the breccia was analyzed on basis of the result of the sedimentary environment study and mineral chemical composition testing. One type of the breccia was formed in the lower incompetent rock layers of Mantou Fromation, formed by weathering and unloading at the offshore slopes; the other type was developed in the brittle rocks in the lower portion of Mantou Fromation as a result of tectonic movements. This origin analysis offers a basis for the assessment on engineering geological issues and reservoir leakage in the reservoir areas.