A Study On The Ordovician Tectonic-sedimentary Evolution In Southern Ordos Region

Southern Ordos region is located in a special tectonic domain, which is up to the Ordos Basin in the north, to Liupanshan tectonic belt in the west, to North Qilian -North Qinling tectonic belt in the south and to Fenhe rift in the east. Due to its particular tectonic location, the region of interest is characterized by variable stratigraphy and various depositional patterns in Ordovician. As a result, a comprehensive research on the Ordovician tectonic-sedimentary and paleo-tectonic form evolution in Southern Ordos region can provide theoretical basis and information for the research of natural gas distribution and accumulation rule. What's more, this research also conduce to ascertain some stratigraphy age that has been disputed for a long period.Using the principles of continental dynamics and basin analysis theory, based on surface and subsurface geologic analysis, geophysical, geochemical techniques and kinds of testing data analysis, combined with outdoors and indoors researching are available to draw up the figures of tectonic-sedimentary evolution and tectonic pattern of each sedimentary stage in Ordovician. Afterwards, reappearing the tectonic-sedimentary framework and tectonic evolution history in Ordovician. At the same time, through the researching of geochemical characteristics of granite mass and granite in conglomerate are available to provide evidences for the understand of tectonic setting of Ordovician in Southern Ordos Region and adjacent areas.Based on previous research, the evolution of the southern Ordos region can be divided into three stages. The region of interest has undergone the process of passive continental margin in early Ordovician to positive continental margin in middle Ordovician and rise to surface which absence deposition in the end of Ordovician. The key point of tectonic reverse happened in the end of early Ordovician. Ordovician palaeo-tectonic study shows that in Majiagou and Fengfeng period there was a Xunyi - Chunhua Depression in Southern Ordos region.