During the past 20 years,based on the investigation of the Cenozoic strata and mammalian fossils along the Ulungur and IrtyshRiver basins in Xinjiang,the Cenozoic strata and their ages on the northern margin of the Junggar Basin have become increasingly clear.Our study reveals that the Cenozoic deposits are nearly continuously deposited from the Late Eocene to Late Miocene,with abundant mammalian fossils in several horizons,providing a rare opportunity to explore mammalian evolution and palaeoenvironmental changes in the area.Particularly,on the western edge of the Duolebuljin terrace on the south bank of the Ulungur River,the Suosuoquan,Halamagai,and Kekemaideng formations records the transition from aeolian deposits dominated by red mudstone and silt to shallow grey-green lacustrine deposits,and finally to fluvial deposits dominated by yellow-brown conglomerate.The corresponding fossil assemblages in the six fossil layers are comparable to the mammalian fauna of the upper Shanwangian,lower Tunggurian,and middle Tunggurian,indicating a transition from dry and cold,to relatively warm and humid,and again back change to drying and colding.The magnetic polarity can be will correlated to C5Cr～?C5AAn,equivalent to 16.8～?13.5 Ma.Mammalian fossil assemblage of Tunggurian begins at the bottom of the Halamagai Formation,corelating to C5Cr(16.726～17.277 Ma),with an approximate age of 16.8 Ma,which roughly coincides with the lower boundary of the optimum climate period of the Middle Miocene.Considering that the animal assemblage is controlled by the climate background,We suggested considering 17 Ma should as the beginning of the Tunggurian period,and recommend the Duolebuljin section in Xinjiang as a candidate stratotype section for the Tunggur stage.In addition,we also discussed the issues of climate change related to the stratigraphy involved in the study.
万方数据
维普
