Comparative Research On Sedimentary Characteristics And Provenance Of Zhiluo Formation In The Northern Ordos Basin And Southern Ordos Basin

Tracing sediment sources and research the sedimentary characteristics of strata in sedmentary basin are not only the important content of basin analysis,but the basic work and necessary premise for the exploration of energy mineral resource. This paper chooses the Northern Ordos Basin and Sorthern Ordos Basin as the study area and aim at the Zhiluo Formation which is the main position of uranium ore and have a relatively weak study.Based on the study of a large number of typical outcrops,the catalog of drilling core and the correlation analysis tests,we made the systematic and comprehensive study on sedimentary structure, sedimentary environment, sedimentary system, provenance and uranium source by multi-disciplinary theories and methods of sedimentology, geochemistry,basin geology. The main conclusions can be drawn as follows:(1) Viewing the sedimentary characteristics of Zhiluo Formation in Northern Ordos Basin and Sorthern Ordos Basin as a whole,we got the comparative research on it and combined with previous studies.Our research reveals that there are four types of sedimentary systems developed in Zhiluo Formation in the Northern Ordos Basin, they are braided river system, braided river delta system, meandering river system and meandering river delta system.The sedimentary systems which in Zhiluo Formation in the Sorthern Ordos Basin are braided river system, meandering river system and shallow lake system,meanwhile,the braided river delta system and meandering river delta system are not exist in the Sorthern Ordos Basin.(2) The delicate restore of the paleoenvironment during the sedmentary period of Zhiluo Formation strata shows that the paleoclimate transformed from warm and humid to dry and hot, the palaeosalinity have a gradual increase trend and the redox conditions which belong to the reducing environment and the water column stratification is not obvious.(3) Based on the provenance analysis by many methods indicate that the provenance ofthe Zhiluo Formation in the Northern Ordos Basin mainly came from the gneisses,granulites,khondalite and Hercynian intermediate-acid intrusive rock from Yinshan Terrane and Daqingshan-Wulashan Mountain.the rock from Langshan Mountain and the khondalite from Jining area also provided part of the source.The tectonic setting of source area is the active continental margin that associated with the continental island arc. The provenance of Zhiluo Formation in Huangling area which in the southeastern Ordos Basin mainly came from the intermediate-acid intrusive rocks and metamorphic rocks from Alxa Block.The provenance of the sandstones in Binxian area which in the southern Ordos Basin mainly came from the intermediate-acid intrusive rocks.the basic intrusive rocks and the metamorphic rocks from the North Qilian orogenic belt, the Central Qilian orogenic belt and the North Qinling orogenic belt.The volcanic rocks,detrital rocks and meta-detrital rocks from the source area also provided part of the source.(4) The intrusive rock and metamorphic rock in the northern source area were not only provided sediment sources for study area,but the importent uranium source. The intensive crustal overthrusting which caused by the intraplate orogeny of the northern source area during the Mesozoic eventually led to the extremely favorable conditions of uranium source supply in the sedimentary period of Zhiluo Formation.(5) The intermediate-acid intrusive rock and metamorphic rock which had a high uranium contents and widely exposed in Alxa Block,North Qilian orogenic belt and the Central Qilian orogenic belt.It is indicate that the Alxa Block and the North-Central Qilian orogenic belt are respectively as the source area of the provenance and uranium to Huangling area and Binxian area.