The Two Ordovician Unconformities in N. China Their Origins and Related Regional Reservoirs Prediction
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摘要: 发育于下奥陶统亮甲山组顶部（UF1）和中奥陶统马家沟组或峰峰组顶部（UF2）的两个不整合面是控制华北早古生代与古岩溶有关的区域性储层形成及展布的关键性面。UF1F2原被认为分别代表了短期或长期的基底构造隆升，但是，基于新的证据，我们认为二者受控于不同成因机制，因而与之相关的储层预侧也应有所不同。UF１原被解释为是板块南部基底上翘的结果，但层序地层分析却支持其海平面变动成因解释。海面下降会通过切蚀水平岩层产生一个倾向盆地的卡斯特侵蚀斜面。UF1从西北仅蚀亮甲山组到东南下切至下寒武统顶部。因此，与之相关的储层亦从西北至东南发育于相应层位内。在空间上，有利区域性储层主要分布于强烈混合带白去化并有随后轻度淡水淋滤的华北地区中心地带。UF2由全球性构造事件形成。这一构造运动导致板块内部下弯及相应的边缘上凸，在下凹的华北中心地带保存了较新的地层（峰峰组），而在凸起区这些新地层却被天水侵蚀殆尽。与UF2有关的潜在区域性储层趋于分布在边缘抬升区，特别是峰峰组分布的周边地区。Abstract: The two unconformities developed on the tops of Lower Ordovician Liangjashan Fm(U F1)and M a-jagou or the Middle Ordovician Fengfeng Fm(UF2) are essential boundaries that controlled the formationand distribution of the Early Paleozoic karstification related reservoirs. U F1 and U F2 have beeninterpret-ed to represent short and long terms of tectonic uplift, respectively，but the new evidence led us to con-clude that they were crested by different original mechanisms and therefore the related reservoirs shouldbe predicted in different ways. UF1 was commonly interpreted as the result of southern upwarping ofbasement, but sequence stratigraphic analysis supports its origin of eustatic sealevel changes. Sealeve1fall can produce a tilted karst denudation plane dipping basinward by truncating horizontal strata. TheU F1 cut Liangjashan Fm. in the NW and gradually went down to the top of Upper Cambrian Series inthe S Etherefore, the related reservoirs〔orrespon dingly developed in these different strata from NW to SESp atially，the most favorable regional reservoirs should be located in the central area of N. China,where the carbonate sediments experienced dolotion with the following light leaching. UF2was cre-ated by global event that resulted in the intraplate downward flexure, and subsequent perispheral bulge.The younger strata(Fengfeng Fm.)were protected in the concave belt of central N.China and erodedaway by the meterior water along the bulge. As a result, the potential regional reservoirs related rocksof Fengfeng Fm. and the potential regional reservoirs related to U F2 are likely to distribute along the pe-ripheral uplift belts, especially around the remanent Fengfeng Fm.
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Key words:
- nnconformity /
- sealevel change /
- karstification /
- reservoir
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