PRELIMINARY OBSERVATIONS ON VESTIGES OF GLACIATION FOUND AT THE BASE OF MIDDLE CARBONIFEROUS ROCKS IN THE SOUTHERN PART OF JILIN PROVINCE
Dctachment No. 3, Specialized Comprehensire Prospecting Brigade directly under Geological Bureau of Jilin Province
Vestiges of late Paleozoic glaciation were first found (September, 1973) in the vieinity of the Jinkeng Ridge, Tonghua, Jilin province——loeated roughly at longitudes 126°10'—127°45'E and latitudes 41°50'—42°10'N. It is here called "Jinkeng Ridge tillite". The Jinkeng Ridge tillite and related rocks occurring at the base of the middle Carboniferous overlies unconformably the middle Ordovician limestones, and is separated above from the middle Carboniferous sandstones by a depositional break. The geological ages for both the underlying and overlying strata are based on index fossils. As the regional geology shows that there is a complete lack of Silurian, Devonian and lower Carboniferous strata, the Jinkeng Ridge tillite should be assigned to the early middle Carboniferous or slightly earlier. The lower part of the tillite beds is made up of varved claystones and gravelly claystones; the middle part, "conglomerates" cemented by argillaceous matter; and the upper part, "conglomerates" cemented by arenaceous matter. They refleet in ascending order the features of glacial varve, till and glaciofluvial deposits respectively. The tillite contains fairly large amounts of glacially striated pebbles and a variety of plastically deformed fragments, which wiry widely in size and are chaotically oriented. They are composed chiefly of quartzites, or quartz sandstones, and small amounts of limestones. Although they had been subjected to diagenesis and structural disturbances, the tillite concerned has still preserved fundamentally its glacial features.