Characteristics of the Upper Paleozoic marker layers and their formation mechanism in the Ordos Basin
Lithology,electrical characteristics,sequence stratigraphic significance and sedimentary environment of Upper Paleozoic marker layers in the Ordos Basin have been researched based on data of drilling,logging and outcrop.There are main marker layers of limestone,sandstone,mudstone and coal bed in the study area.According to characteristics of sequence interfaces,Upper Paleozoic strata in the study area can be divided into 5 second-order sequences and 12 third-order sequences.SQ1-SQ5 fall into marine strati-graphic sequence,and SQ6-SQ12 fall into continental sequence.The Upper Paleozoic in the Ordos Basin has undergone a sedimentary evolution from marine facies to marine-continental transitional facies to continental facies in general.Marker layers are influenced by lateral changes of sedimentary facies,and mainly formed in the deltas,braided fluvial deltas,rivers,lakes,barrier coasts and shallow sea shelf sedimentary systems.In the process of stratigraphic division and correlation,strata can be reasonably and accurately divided with referenece to marker layers,adjacent wells and thickness changes,etc.
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