Development characteristics and formation patterns of Ordovician breccia in the Huainan coalfield

Abstract

The mining of lower coal seams in the Huainan coalfield faces significant threats from water bursts from the Ordovician carbonate karst aquifer. Paleokarst breccias constitute significant water storage spaces, and comprehending their developmental characteristics and formational models is paramount for implementing effective prevention and control strategies against water inrush hazards. Through such methods as the field geological survey, core drilling, petrography, and geophysical exploration, the compositions and textures of carbonate breccias had been investigated. The results indicate that the Ordovician paleokarst breccias can be divided into three types. Syngenetic breccias formed during brief sedimentary breaks, consist of different size gravel particles, with poorly sorted and angular fragments. Pores between angular clasts are filled with calcium and mud cementitious materials, which reveal the significant influence of sedimentary and diagenetic processes. Epigenetic karst breccias occur within the interlayer between the Majiagou and Xiaoxian formations, which originated from the collapse and subsidence of tensioned karst caves in the interlayer. Angular clasts are typically subrounded-angular in shape, and poorly sorted, which development processes are influenced by carbonate lithology, tectonic evolution, and paleogeomorphology. Tectonic breccias occurred along major tectonic belts and consist of angular to subangular poorly sorted gravel size fragments, which development processes are primarily controlled by multiphase tectonic movements, particularly Indosinian-Yanshanian tectonic events. The above research results have provided an important foundation for the safety mining of deep coal seams in the Huainan coalfield, and other coalfields with similar geological condition in China.