Biostratigraphy and palaeoenvironment of the dinosaur-bearing sediments inLower Cretaceous of Mazongshan area, Gansu Province, China

This paper discusses the lithostratigraphy of the Xinminbao Group in the Ma zongshan area of Gansu Province, northwestern China, and the correlation of its biota. The Xinminbao Group was deposited in a fluviolacustrine setting in Mesozoic graben basins under a semi-arid, subtropical climate. The foss il sites concentrated in the lower part of the group have yielded dinosaurs , mammals and other vertebrates that are comparable to the Aptian-Albian ve rtebrate assemblages that have been found in Mongolia and Siberia. Based on their invertebrate and vertebrate fossils, sediments of the lower part of the Xinminbao Group are considered to be Late Barremian-Aptian in age, alth ough the middle and upper parts could be as young as Albian. The megafossil plants and conchostracans are comparable to those of the Yixian and Jiufuo tang Formations in eastern China (Barremian-Aptian). The palynoflora is als o comparable to that of the upper Lower Cretaceous elsewhere in northern Ch ina, although the presence of two angiosperm taxa, Asteropollis and Tricolp ites, suggests that the main fossil sites are Albian. These biostratigraphi c data for the Mazongshan area provide a new temporal calibration for the t errestrial biotas of the Lower Cretaceous of central Asia, where most of th e known dinosaur-bearing sediments lack precise palynological, radiometric and magnetostratigraphic dating. (C) 2001 Academic Press.