Tectonic Evolution And Middle-upper Proterozoic Petroleum Geological Setting In South-western Ordos Basin

Breakthroughs have been made in exploration of unconventional resources,deep water resources,and onshore deep resources for years,which further promote the exploration practice.Ordos Basin belongs to the western part of the North China Craton,with ancient strata of the Middle and Upper Proterozoic exposed on the periphery.Studies on its sedimentary tectonic environment and evolution is of great significance for the exploration of ancient strata.This study systematically observed and sampled the field profiles of the Precambrian in the southwestern Ordos Basin.Based on previous studies,we fully use the lithology characteristic,analysis of sedimentary environment,geochemical methods and organic petrological results,so that discuss the tectonic characteristics and evolution since the Sino-Neoproterozoic era,and link it to the hydrocarbons accumulation conditions in the Middle-Upper Proterozoic,providing the evaluation basis for petroleum accumulation in study area.Research holds that:(1)south-western Ordos Basin keeps a passive continental marginal tectonic setting in the Meso-Neoproterozoic,with series of intracontinental and marginal rifts existing in the early Changcheng Period and gradually transforming to the stable shallow shelf in the Jixian Period,which inherits the previous tectonic pattern;the strata of Proterozoic and Paleozoic in the research area shows that the tectonic transformation mainly based on uplift and erosion with tectonic-thermal events;(2)differences comes in the evolution of the tectonic pattern among areas in south-western Ordos Basin,and the influence of the Caledonian and Yanshanian movements on the Proterozoic are of more importance;in Caledonian,basin pattern is divided between inside basin and marginal,which thrust belt forms over the basin margin,setting a limited zone for subsequent movements;The Yanshanian movement was the most severe one in study area,as the folds and tilted structure develops overthe margin while deep faults are formed cutting through the Proterozoic,and the preservation condition is worse than that inside the basin;(3)the continental trough zone under the control of Qing-yang paleo-uplift could be the possible favorable area for the Proterozoic source rock;sedimentary tectonic evolution in Paleozoic period are critical to the thermal history and hydrocarbon generation history;the Yanshanian movement played a key role in the preservation of the Upper-Proterozoic reservoirs in study area.