Study On Sequence Lithofacies Paleogeography Of Xixiangchi Formation Of Cambrian In Sichuan Basin

The Dolomites of the Cambrian Xixiangchi Formation in the Sichuan Basin are very developed.The sedimentary palaeogeographic pattern of the previous strata,the genetic mechanism of dolomite,and the characteristics of the reservoir are rich in research results.The author found in the research of the predecessors.The understanding of the set of rock sedimentary environment is quite different,and there are many viewpoints,which brings many confusions for the subsequent related scientific research.Based on this,the paper takes the Cambrian Xixiangchi Formation in the Sichuan Basin as the research object,and carries out the study of the sequence facies paleogeography of the Xixiangchi Formation.Based on the theory of sedimentology,sequence stratigraphy and seismic stratigraphy,the thesis combines drilling core observation,logging data,seismic data,drilling data and related test analysis data system on the basis of field geological section survey and sample collection.Carry out sequence stratigraphy study of the Xixiangchi Formation in the Sichuan Basin,establish a sequence stratigraphic framework,and reveal the distribution characteristics of the Xixiangchi Formation in the isochronous stratigraphic framework;focus on the geological outcrops in the field,combined with drilling and seismic data.To carry out research on the types and characteristics of sedimentary facies;comprehensive sequence stratigraphy and sedimentary facies studies,using the third-order or third-order sequence system as the mapping unit,systematically compiling the Cambrian wash basin in the Sichuan Basin Pre-facial facies paleogeographic map reveals the temporal and spatial distribution characteristics and differences of different facies.The rock types of Xixiangchi Formation in Sichuan Basin are mainly carbonate rocks,next is clastic rocks and metamorphic rocks.The carbonate rocks are mainly dolomite,with a small amount of limestone deposits in some sections and mixed rocks in the southwestern part of the basin.Two supersequences and 11 third-order sequences were identified,and the isochronal stratigraphic framework of the third-order sequence stratigraphy of the whole basin was established.The sequence pattern of "two kinds of sequences,one kind of structure and low-level absence" was revealed,and the spatial distribution characteristics of strata under the control of paleo-uplift were clarified.Four sedimentary systems,including mixed tidal flat,carbonate platform and platform margin slope-basin,were identified.The spatial distribution and evolution of sedimentary facies were revealed,and the existence of early gypsum strata in Xixiangchi Formation was clarified.The lithofacies and palaeogeography features of the Sichuan Basin during the Xixiangchi Period are systematically revealed by using the third-order sequence system tract or the third-order sequence system tract as the mapping unit.During SQ1 period,Sichuan Basin turned into a large-scale regression cycle on the basis of the continuous progressive cycle of Gaotai Formation.Evaporative lagoon deposits were developed in many parts of the basin,and other areas were characterized by the deposition from the limited platform cloud tidal flat to the platform beach.During the SQ2 period,there was a transition from regression cycle to progressive cycle,and platform interior began to develop more inner platform deposits.In SQ3,the inner Beach was well developed,and there were many beach facies aggregation zones in the basin.In the middle of Sichuan Basin,the development of the beach in the western margin of the paleo-uplift is parallel to that of the paleo-uplift.During the SQ4 period,the sandy debris beaches developed around the central Sichuan paleouplift showed inherited growth.During SQ5 period,it showed continuous accretive growth.By the SQ6 period,the acceleration of regressive cycle resulted in the drowning of most of the beaches in the basin,and only the local highs still had the inner beaches.During the SQ7 period,the basin as a whole showed thin-bedded limited platform deposits.