AN INVESTIGATION INTO THE CHARACTERISTICS OF THE SEDIMENTARY FILLING IN Es_2-3, JIZHONG BASIN

The ancient basin of Paleogene in Jizhong region is of the faulted depression type. In the depression exist fourteen dustpan-like sags and six uplifts. The regional structural characters of the depression are that depressions' being divided into east and west parts and its evolution history determine the features of the fluvial-lacustrine system and herein the sedimentary tilling. The sedimentary filling in Es_2-3 of Jizhong Basin features the fluvial-lacustrine system being divided into two parts: the west part belongs to standard plain type rivers with complete fades sequences; the east is a lake region. The distribution of the system is not mainly controlled by the local dustpan-like sags. In addition to ordinary rivers there are short ancient rivers of mountain-foot type scattering along the periphery of the lake basin. The evolution process of the sags consists of three great cycles and six secondary transgression and regression cycles, which governs the longitudinal distribution of the sand bodies in the lake basin. The application of seismic stratigaphy to the study of sedimentary filling models in the depression offers plenty of geological information. The reservoirs so far discovered in Jizhong Basin all are sand bodies of lake sediment which fall into six types, the formation of which appears to be determined by the ancient river type and topographic features, and the distribution of which seems to be controlled by ancient rivers as well as the communicated waters. Jizhong region can be classified into four groups and six subgroups of sedimentary system tracts, thus characterizing the sedimentary filling in Es_2-3 in the region.