Marine To Lacustrine Deltaic Evolution And The Deltaic System Of Shan 2 Member To He 8 Member,Southeastern Ordos Basin

Ordos Basin is one of the most petroliferous basins in China.Shan 2 Member-He 8 Member in southeast Ordos Basin shows a great exploration potential.Because most work regarding Shan2 Member-He 8 Member focused on reservoir,sedimentary facies,sedimentary environments,sandstone types,and oil formation conditions,few studies have been conducted related to geochronologic stratigraphic framework.As the sequence division scheme is inconsistency and numerous,the sequence stratigraphic framework is required to be reconstruct in the study area.Furthermore,Shan 2 Member-He 8 Member still requires a systematic research regarding deltaic materials and its evolution considering its chronology,the targeted formation should be studied by using sedimentology and sequence stratigraphy.In order to solve this scientific problem,based on much core description,stable isotope analysis,thin section and scanning electronic microscope observation,deltaic development geologic background,marine to lacustrine evolution,deltaic materials,deltaic 3-D distribution are conducted to research deltaic formation,development,and origin.The deltaic materials can be classified into 15 lithofacies,6 lithofacies association and 6 sedimentary sequences.The deltaic sedimentary models are erected.A sequence stratigraphic framework is constructed based on geochronologic stratigraphy.The deltaic 3-D distribution is also researched.Main achievements and innovative points are as follows.1.The stable subsidence of North China Craton provides an accomadation space for the deltaic formation and development.Yin Mountain in the north and paleo Qinling Ocean arcs and uplifts in the south sustained a continued sediment supply.A gentle slope of the study area is good for a large area deltaic development.2.Based on a statistical data,the sediment supply of He 8 Member>Shan 1 Member>Shan2 Member.The paleoclimate in He 8 Stage is cold and dry compared with Shanxi Formation based on stable isotope analysis.It underwent a not obvious sea regression from Shan 2 Stage to He 8 Stage.He 8 Member is featured by a transgression influenced lacustrine basin based on a B,Ga,and Rb diagram analysis.3.The deltaic materials of Shan 2 Member-He 8 Member can be classified into 7 types of sandstone lithofacies,4 types of mudstone lithofacies and 4 types of conglomerate lithofacies.6types of lithofacies association and 6 types of sedimentary sequences are also identified.The sedimentary models of a meandering river delta and a braided river delta are erected.4.4 3-order sequences are determined based on core description,well log analysis and outcrop measurements.A delta front mainly delveloped in Shan 2 Member-He 8 Member of the study area.A delta plain developed in the northwestern area.The deltaic evolution and sandstone distribution is determined based on sandstone distribution in profiles and plans.