Abstract:

In this paper, on the basis of “sequence stratigraphy”, the principles of “spatial orderliness of facies sequence” and “temporal synchronism of environmental change” were applied to solving the problems of regional stratigraphic isochronal or quasiisochronal correlation. That the isochronal or quasiisochronal stratigraphic unit was adopted as the compilation unit of lithofacies paleogeographic maps was basically realized. Additionally, the drawbacks of the “distortion” of the lithofacies paleogeographic maps and the concealment of the change of vertical sedimentary environment caused by the nonisochronous lithostratigraphic units, i.e. “formation, member”, used in the traditional compilation, were overcome. The “new compilation method of quasisimultaneous lithofacies paleogeographic map” may be divided into three studying phases, i.e. single profile sequence stratigraphic column, highresolution sequence stratigraphic column correlation diagram and quasisimultaneous lithofacies paleogeographic series maps. In a marine basin, the sea level synchronously lifts; therefore, the corresponding threelevel sequences were isochronous in whole region. Also isochronous were the low water level, transgression, high water level, compulsive regression wedge and other system tracts, which were marked off by sequence boundary, first flooding surface, maximum flooding surface, regressive surface and other physical boundaries. For these reasons, the corresponding physical boundaries mentioned above in the single profile sequence stratigraphic column in the whole region may be linked together to form the isochronal correlation framework diagram of the studying area, to begin with. Then the strata in the isochronal framework would further be compared to form the correlation diagram. Finally, on the basis of the above work, the isochronous stratigraphic units were selected to compile the lithofacies paleogeographic series maps. The authors took as an example the research results of the early Lopingian lithofacies paleogeography of the west segment of the Pingle depression in central Jiangxi for further expounding. Accuracy of the isochronous correlation was improved after using the “new compilation method of quasisimultaneous lithofacies paleogeographic map”. The compiled lithofacies paleogeographic series maps fully reflected not only vertical and horizontal changes of lithofacies paleogeography in this period, but also the control of the sedimentary environment exerted by the combined effect of crustal movement and sea level eustacy. In addition, it shortened the map compilation units to the least possible, thus making the paleogeographic map more accurate, informative and practical.

Key words: Jiangxi Province, Pingle depression, sequence stratigraphy, highresolution sequence stratigraphic correlation, quasisimultaneous lithofacies paleogeographic map