The Stratigraphic Sequences And Depositional Environments Of The Haifanggou Formation In The Longhuitou Basin Of Xingcheng City

The present thesis is on the research of the stratigraphic sequences、the geological ageand the depositional environments of the Haifanggou Formation in the Longhuitou Basinof Xingcheng City by lithostratigraphic correlation, grain size analysis of sandstone andanalysis of fossil pollen.This study contains the following aspects:(1) Field works on three sections. The section1(PⅠ) is in the Sidaogou ofLonghuitou; the section2(PⅡ) is in the westside of coastal way; the section3(P Ⅲ) is inthe northern beach of Longhuitou. The result of data analyzing and lithologicalassociation correlation indicate that the Haifanggou Formation in the Longhuitou Basin iscomposed of yellow-green-brown medium-coarse, poorly sorted, subangular toroundedpolymictic conglomerates, foldering several layers of purple fine-grained greywacke,yellow-green shale and carbonaceous mudstone.(2) The stratigraphic sequences of the Haifanggou Formation in the LonghuitouBasin are correlated to other typical area in western Liaoning. Their rock typesare basically similar and with same lithological associations, thus they could be correlatedwith each other. The differences between the Haifanggou Formations in several basins areexplained from their different tectonic positions and evolutionary levels of basin.(3) Terrestrial plant fossils and pollen fossils were found in the HaifanggouFormation of the Longhuitou Basin. The Podozamitaceae gen. indet. in the LonghuitouBasin belongs to the Coniopteris-Phoenicopsis flora of western Liaoning; Thepollen fossils in the Longhuitou Basin is named as Osmundacidites–Asseretosporaassociation. The Osmundacidites–Asseretospora are similar with the Cyathidites-Piceaepollenites in the Yan’an Formation of the Erdos Basin-Dongsheng area and theCyathidites-Classopollis in the Haifanggou Formation of Nanpiao area, indicating that theHaifanggou Formation in the Longhuitou Basin was formed in the Middle Jurassic. (4) The results of the conglomerate particle size and composition statistics and thesand particle size analysis from the Haifanggou Formation in the Longhuitou Basin showthat: this stratum is the piedmont depression alluvial fan face with the characteristics ofthe channel deposits and overflow deposition; the gravel of sedimentary conglomerate arefrom the underlain geological bodies (stratum) of surrounding areas and withoutlong-distance handling; This stratum is further divided to flowing sub-facies as root-fan,middle-fan and end-fan based on the characteristics of the lithology combination cycle.(5) The Longhuitou Basin is considered to be a piedmont sag basin by discussing theMesozoic tectonic setting and structural characteristics of this basin.