The Evolution Of Ordos Basin's South Zhangxia-Fengshan Period Sequence Lithofacies Paleogeography

Ordos basin is a large inland basins in China and the largest coal bearing basin Mesozoic era, is also the earliest area of China petroleum exploration and development, has been through nearly a century of exploration course, and scored remarkable achievements. Basin clastic rock series as a large-scale lithologic reservoir has been a huge benefit. Among them, the lower palaeozoic era of Cambrian— upper palaeozoic of Permian is an important stage of gas accumulation. So far, the Ordos Basin Cambrian carbonate oil and gas exploration has not got enough attention, its oil and gas geological conditions research is still in its infancy. In this paper by using sedimentology, stratigraphic paleontology, sequence stratigraphy, geochemistry and geophysics methods the ories and technologies, With field outcrop, logging and seismic data as the foundation data, combining the previous research results, with "structure controlled basin, basin controlled sedimentary, sedimentary is the response of basin " as the starting point, using point(drilling, field profile), line(profile correlation), surface(the sedimentary pattern and lithofacies palaeogeography ?s analysis method, combine basin tectonic evolution and global tectonic background to research, building a isochronous sequence stratigraphic framework, compiled a sequence lithofacies paleogeographic map which can well describe the dynamic evolution of the basin, analysis of ordos basin‘s south in the Cambrian zhangxia-fengshan period sedimentary framework and evolution process. The main knows are as follow:First, based on predecessors ‘achievements, to divide Cambrian stratum of lower Paleozoic,and establish stratigraphy division plan and comparison framework.Second, based on comprehensive analysis on data of outcrop, drilling core and logging, by study on sedimentary facies mark,dividing the ordos basin‘s south in the Cambrian zhangxia- fengshan sedimentary system, Three sedimentary systems and several sedimentary units were distinguished, which include carbonate platform,carbonate tidal flat and platform edge.Third, through the study of the different times of the backbone section observation, key drilling core observation, logging data and detailed study of the existing seismic profile data, the sequence interface in the area has five kinds of form: unconformity surface, erosion scouring surface, lithology and lithofacies transition surface, overlap, the sea surface.Fourth, based on study on sequence boundary characteristic, genetic type of sequence boundary and sequence division mark, sequence stratigraphy have been divided, the Cambrian system in the study area was divided the 1 super sequence and 6 third-order sequences, and this paper focuses on Cambrian zhangxia group – fengshan group, Then,the characteristic of each super sequence is studied,and sequence is compared in each different period.Fifth, based on study of sedimentary facis characteristic and establishment of sequence stratigraphy framework, taking third-order sequence as mapping unit, have studied study area of zhangxia- fengshan sequence of lithofacies palaeogeographic characteristics, in stage of ?SQ4 to ?SQ8, sedimentary environment transited to epicontinental sea, and the central paleouplift emerged the rudiment. Huge cratonic basin formed in stage of ?SQ9 to ?SQ12.