"Source-to-sink" System Research Of He8-shan1 Member In Longdong Area, Ordos Basin

Based on geologic setting,petrological and geochemistry analyses,the research develops source direction,parent rock types and tectonic setting of He8 and Shan1 Member in Longdong area,Ordos basin.The type of sedimentary facies and distribution of sedimentary systems are confirmed by using cores,outcrops and well-logging.Depending on provenance and sedimentary facies,“source-to-sink” system is studied and favorable zones are predicted by combination of palaeo-landform,sedimentary environments and hydrodynamics.The main results are as follows.Longdong area is highly related to the north Qinling orogenic belt of the Late Paleozoic era.The main source of He8 Member comes from the southwest,followed by the northern source.The main source of Shan1 Member comes from the southwest,followed by the southern source.The results suggest that the provenance of He8 and Shan1 Member are silimar,which are formed from the silimar parent rock and tectonic setting.The provenance of those two members is mainly affected by passive continental margin source until the end of Late Paleozoic,the under the influence of active continental margin.The parent rocks of He8 and Shan1 Member are mainly from gneiss,quartzite of Qingling Group and chlorite schist,actinolite schist of Kuanping Group in the north Qinling orogenic belt,a few from igneous rocks of Late Paleozoic era in the north Qinling orogenic belt.Braided river delta is developed in He8 Member,which mainly developed delta plain and delta front,and delta plain is larger than delta front.Meandering river delta is developed in Shan1 Member,which mainly developed delta plain and delta front,in which delta front is larger.There is a “source-to-sink” system of gentle slope pattern in Longdong area.During the sedimentary period of Shan1 Member,the climate is warm and humid,the terrain is gentle and the hydrodynamic force is strong.Distributary channels carry sediments under water for a long distance,which formed banded sandbody.During the period of He8 Member,the supply of terrestrial debris is sufficient,the climate is dry and hot,with a fairly gentle terrain and very strong hydrodynamic conditions.The migration of Multi-stage channels is frequently in He8 Member,which formed large contiguously sandbody.The organic matter maturity of the hydrocarbon source rocks from Taiyuan Formation and Shan2 Member are not high,almost in the stage of high maturity,and consists mainly of kerogen of ? type.There are three types of source-reservoir-seal assemblages in research area.The favorable predicting standard is established,and favorable exploration areas of He8 and Shan1 Member are predicted.