Abstract:

The Early Paleozoic of Ordos massif underwent the evolution processes of siliciclastic→carbonate ramp→rimmed shelf→distally steepened ramp→aulocogen→evaporate platform which correspond to five superseguences developed respectively in Early Cambriam,the early stage of Middle Cambrian,Middle Late Cambrian,the Yeli Liangjiashan period of Early Ordovician,the Majiagou period of Early Ordovician and Middle Ordovician.Take the huge unconformity in the bottom of Middle Ordovician as the boundary,the sequences could be classified into Sauk and Tippecanoe suppersequence sets.The formation of the boundaries of the supersequences and supersequence sets was related to the mutation of tectonic subsidence and tectonic movement.Most periods of sea level changes of Cambrian in Ordos Basin coupledwith global identity of eustatic cycle,except the high frequency in low frequence in Gushan period.Tectonic movement was weakend during Early Ordovician,high frequency sequences developed well.Late Ordovician contained 5 6 sequence periods.According to the analysis of organic geochemistry,the main source rocks are the condensed sections with dark limestones and shales in the Zhangxia Formation of Cambrian,the Majiagou and Wulalike Formations of Ordovician.Favorable reservoirs are paleo karst related to regional unconformity,carbonate buildup and bioclastic limestone in TST and HST,turbidite in LST and dolostone or grainstone in lower LST and higher HST.