The Two Ordovician Unconformities in N. China Their Origins and Related Regional Reservoirs Prediction

Liu Bo; Wang Yinghua; Qian Xianglin

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.

The Two Ordovician Unconformities in N. China Their Origins and Related Regional Reservoirs Prediction

Geology Department Beijing University Beijing 100871

Received Date: 1996-11-27

Publish Date: 1997-03-10

Key words:

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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The Two Ordovician Unconformities in N. China Their Origins and Related Regional Reservoirs Prediction

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