Kaolinite clayrocks of the Koogah Formation, New South Wales

Abstract

Abstract The Koogah Formation, which is the equivalent of the Greta Coal Measures of the lower Hunter Valley, is restricted in outcrop to the area lying immediately to the northeast of Wingen. The unit increases in thickness from 30 to 230 m in an easterly direction and consists for the most part of kaolinite clayrocks that range in texture from fine-grained to coarsely conglomeratic. Residual volcanic textures are characteristic of most of the kaolinite clasts and there seems little doubt that the detritus was derived from weathered zones developed on the Werrie Basalts, and accumulated in an alluvial fan environment. Nevertheless, in parts of the Koogah Formation lithic-quartz sediments that presumably represent fluvial material transported from a geosynclinal source which lay some distance to the north or west are abundant, and in the cores of two boreholes these sediments predominate to the virtual exclusion of the kaolinite clayrocks.