Stratigraphic division and age of Upper Carboniferous - Lower Permian Baoligaomiao Formation in Qagan Obo area, Sonid Left Banner, Inner Mongolia

Abstract: During the 1:50 000 regional geological survey in Qagan Obo area, the authors found that the sequence of Baoligaomiao Formation exposed in Qagan Obo area is complete, and the strata have abundant plant fossils and clear division marks. Baoligaomiao Formation was reclassified during route survey and profile measurement into four lithologic members according to the lithological and biological appearance. The first member is lacustrine and gray, grayish green clastic rocks with a little mild volcanic rock, and there are a large number of Angela plant fossils in the siltstones; the second member is alkaline-acidic brick red rock intercalated with purple volcanics with sand (gravel) rock, and the U-Pb dating of zircon from the trachyte and rhyodacite yielded ages of (297.0±1.2)Ma and (323.0±1.4)Ma; the third member is gray and purple gray andesitic volcanics with clastic rock; the fourth member is gray rhyolitic volcanic rocks with sandstone and marl, and the sandstone also has a large number of Angela plant fossils. Based on the results of the identification of plants fossils and isotopic data, the authors hold that the formation age of the Baoligaomiao Formation is Late Carboniferous - Early Permian .