冀中坳陷奥陶纪岩相古地理*

碳酸盐岩是冀中坳陷下古生界重要的古潜山油气储集层。研究表明,冀中坳陷奥陶系属于陆表海型台地,进一步划分为潮上带、潮间带、局限潮下和开阔潮下4个沉积亚相,以及泥云坪、膏云坪、云坪和云质潟湖等11种沉积微相,并构成了4个三级层序(SQ1~SQ4),其中SQ4仅发育海侵域。奥陶纪首次海侵期沉积的冶里期(SQ1-TST)在区内由北向南发育了开阔潮下—潮间—潮上亚相沉积。亮甲山期(SQ1-HST)主要发育潮间亚相沉积,局部为潮上亚相。下马家沟期(SQ2-TST)和上马家沟组沉积晚期(SQ3-TST)分别为第2次和第3次海侵,区内均以局限潮下和开阔潮下亚相为主,局部发育生屑滩和砾屑滩;上马家沟组沉积早期(SQ2-HST)和峰峰组沉积早期(SQ3-HST)以发育潮间和潮上亚相为主,是白云岩的稳定沉积期。峰峰组沉积晚期(SQ4-TST)记录了第4次海侵,以发育开阔潮下亚相为主,北部地区零星发育潮间云灰坪微相。受加里东构造运动影响,华北地台整体抬升,冀中坳陷奥陶系顶部受到剥蚀,直至石炭纪再次接受沉积。

Lithofacies palaeogeography of the Ordovician in Jizhong Depression

Carbonate rocks are the important buried-hill oil and gas reservoirs in the Lower Paleozoic in Jizhong Depression. The researches show that the Ordovician developed on a typical epicontinental platform with four sedimentary subfacies including supratidal zone,intertidal zone,restricted subtidal and open subtidal zone,while it was further divided into 11 sedimentary microfacies,such as muddy-dolomitic flat,gypseous-dolomitic flat,dolomitic flat and dolomite-dominated lagoon etc. It is constructed with four third-order sequences(SQ1~SQ4),while sequence-4 only developed transgressive systems tract. The Yeli stage(SQ1-TST)which belonged the first Ordovician transgressive period developed open subtidal-intertidal-supratidal subfacies from north to south,while the Liangjiashan stage(SQ1-HST)mainly developed intertidal subfacies with locally distributed supratidal subfacies. The early Majiagou stage and late late Majiagou stage which were the second and third transgression mainly developed restricted subtidal flat and open subtidal flat,while bioclastic shoal and gravel shoal were locally developed. The early late Majiagou stage(SQ2-HST)and the early Fengfeng stage(SQ3-HST)were dominated by intertidal and supratidal subfacies,which were stable depositions of dolomites. The fourth transgression systems tracts were recorded in the late Fengfeng stage(SQ4-TST),which mainly developed open subtidal subfacie,and intertidal flat microfacies and dolomitic flat sporadically developed in the northern of Jizhong Depression. Due to the Caledonian tectonic movement,the North China Platform was uplifted as a whole,and the top of the Ordovician in the Jizhong Depression was eroded until the Carboniferous.