Study On The Paleogeography Of Upper Jurassic And Cretaceous In Northern Sichuan Basin

Based on the theories and methods of sedimentology, sequence stratigraphy, the detail survey on the field outcrop, and the analysis of drillhole information. The author made the stratigraphic division, studied in detail paleogeographical characteristics and evolution of the Upper Jurassic and Cretaceous in the northern Sichuan basin, then, compiled the lithofacies paleogeographical map.By using the method of sedimentology, this paper divided the sedimentary system of Upper Jurassic and Cretaceous in northern Sichuan basin into 4 types of sedimentary systems. The Upper Jurassic were built of fluvial - lacustrine and alluvial fan - fan delta - delta clastic sedimentary system, the Lower Cretaceous were fluvial - lacustrine and alluvial fan - fan delta - delta clastic sedimentary systems, and the Upper Cretaceous was fluvial - lacustrine clastic sedimentary system, and then it discussed the characteristics and distribution of sedimentary system, and basin-filling evolution.With the research findings of the group, combined with palaeostructure analysis, stratigraphy and palaeocurrent research. It also determined 3 tectonic sequence, 10 third - order sequence and compiled the lithofacies paleogeographical map of Upper Jurassic and Cretaceous which adopted tectonic sequence as basic mapping unit.The map had medium-scale and rightly delivered the paleogeographical characteristics of the study area.Finally, the paleogeographical characteristics and evolution in different tectonic sequence was demonstrated in details and comparison with Mid– Yangtze area. Then it concluded that, with compressive stress, the paleogeographical patterns of northern Sichuan basin gradually shrunk to southwestern Sichuan basin. After the Early Cretaceous, there is different paleogeographical evolution between Sichuan basin and Mid– Yangtze area.