Lithofacies types and cycle patterns of shale layers of Qingshankou Formation in Gulong Sag,Songliao Basin
Based on core observation,thin section identification,geochemical test and Markov chain analy-sis,the lithofacies types and cycle patterns of shale layers of Qingshankou Formation in Gulong Sag are discussed.According to the classification standard of"organic matter abundance-sedimentary structure-mineral composition-lamination density-lithology",the shale layers of Qingshankou Formation in Gulong Sag are divided into 7 lithofa-cies,including high TOC-high density laminae-clay shales(A),high TOC-high density laminae-felsic shales(B),medium TOC-low density laminae-felsic shales(C),low TOC-low density laminae-felsic shales(D),low TOC-layered-siltstones(E),low TOC-layered-ostracoid limestonse(F)and low TOC-layered-dolomites(G).Based on lithofacies combination patterns and their distribution characteristics,three cycle patterns are divided:① the static water cycle pattern(A-B-C-A)is mainly developed in the highstand system tract;② the turbidite cycle pattern(A-B-C/D/E/F-A)is mainly developed in the transgressive system tract and the regressive system tract;③ the dolomite cycle pattern(A-B-C-D/G-A)is developed in all three system tracts.The west of Gulong Sag mainly developed turbidite cycle,the center of Gulong Sag mainly developed static water cycle,and the Sanzhao Sag on east side mainly developed static water-dolomite cycle.The distribution of cycle models is mainly affected by provenance,paleoclimate and paleosalinity.
shale layerslithofaciescycle patternQingshankou FormationGulong Sag
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