The Research On Sedimentary System Of Chang6-chang2, Yanchang Formation, Fuxian Area, Ordos Basin

The research on Sedimentary system of chang6—chang2, upper Triassic, Fuxian area, Ordos basinFuxian area is located in the southeast of Ordos basin, including the Fuxian area of SINOPEC and its circum areas. Chang6—Chang2 of Yanchang formation is the object of this paper. Based on the study of sedimentary characteristic and all kinds of symbols in facies, determined the types of facies and microfacies, the development condition of the facies and its spread in plane surface. Then according to the analyzing of boron element, restoring the paleosalinity, characteristic of paleogeography and the evolvement in plane surface of the paleogeography. Drawing the lithofacies paleogeographic map in different periods.According to the comprehensive analysis of the outcrops, cores, facies in well logging, combined to all kinds of symbols in facies, the types of facies in Chang6—Chang2 is lake delta facies, lake facies and turbidites facies in lakes. The development characteristic of these facies are Analyzed. The sedimentary system of delta is dominated by delta front microfacies and it contains in every formation. The microfacies of delta plain can be found only in the Chang4+5—Chang 2 periods and the extent of this microfacies is limited. Turbidite facies is located in the southwest of the studying area in Chang 6 period. In Chang 6 period, the southwest of the studying area is deep lake environment. The turbidite in low density comes from the end collapse of braided river delta front with steep slope.The paleogeography characteristic and its evolution in the studying area are studied. The lithofacies paleogeographic maps in different periods are drawed. It is concluded that the sedimentary pattern of lake delta in Chang6—Chang2 periods is aggradation delta. The sedimentary sequence is a big inverse cycle from the bottom to the top. In Chang6 stage, the microfacies in the Fuxian area is delta front. Sedimentary facies of delta is development in large areas in Chang4+5 periods, and the lake strandline is located in the well line of Zhongfu 30 and Zhongfu 32. Progradation is obvious in Chang3 period and the sedimentary facies in the full studying area is delta. The lake strandline is located in the well line of Fu 32, Fu11 and Zhongfu 21 in that period. In Chang2 period the delta moved to the south continuly, and the lake strandline is located in the well line of Niuxi 5 and Fugu6. South to this line, the sedimentary microfacies is delta front.