The Synthesis Study Of The Sedimentation Environment About The Pleistocene Gravel Stratum In Mingshan-Danleng

As regarded the most representative area in the southern of China and the Yangtze river valley, the Quaternary sediment wide-spreads in the front of the Long -Men mountain and on the western plain of Sichuan. Especially in the lower terrace along the river and the platform on the Chengdu plain of the front of Long-Men mountain, the Quaternary sediment overlay the large acreage. The different geological age of the Pleistocene gravel bed was overlaid by the latter sequentially. Its uniqueness was expressed by its huge thickness and kept undamaged. In this paper, the study of Pleistocene series would supply very important scientific basis for the Tibet's lifting, the features of neo-tectonic movement in Long-Men mountain , the evolution of Chengdu basin and the climate change of the Quaternary.Combining the related materials with the regional geology mapping, the author studied on the paleogeography, the source of sediment, the paleoclimate environment though several techniques, such as remote sensing, digital elevation model, the features of the sedimentation, the analysis of geologic climate and so on. In this paper, the author summarized the following conclusions:(1) According to the geographical location, the deposit environment, the sediment and the surface of the Pleistocene gravel stratum, the author divided the Pleistocene series in this area into four catalogues: the "DaYi" pebble-bed, the "MingShan-QiongLai" pebble-bed, the "DanLeng-SiMeng" pebble-bed and the "Ya'an" pebble-bed.(2) The four sections of the Pleistocene series not only correlated on the space-site, but also had inheritance in the deposit epoch. Based on the above features of the pebble-bed, the author generalized the deposit epoch of the Pleistocene series. The "DaYi" pebble-bed was deposited in last stage of the Pliocene-the early stage of the early Pleistocene, the "MingShan-QiongLai" pebble-bed conglomerated between the last stage of the early Pleistocene-the middle Pleistocene, the "DanLeng-SiMeng" pebble-bed was deposited between the middle-last stage of the middle Pleistocene and the "Ya'an" pebble-bed was deposited in the late Pleistocene.(3) With the comprehensive discussion in the space-spreading, the constitution of the section,the pebble structural fabrics and the geologic climate of the Pleistocene series in this area, the study indicated that the Pleistocene series was carried by the cross river out from Long-Men mountain. It was deposited in different time on the foreland basin under the temperature-dry heat climate.(4) Through the general study on the Pleistocene series, the author inversed the rule for the change of QingYi-river in the foreland basin in different epoch.