The Caledonian paleokarstification of Longwangmiao Formation, Lower Cambrian in the central Sichuan basin, China

• Autores: Xuefei Yang, Xingzhi Wang, Hao Tang, Yueming Yang, Jirong Xie, Wenjun Luo, Lincheng Dai
• Localización: Carbonates and Evaporites, ISSN 0891-2556, Vol. 32, Nº. 3, 2017, págs. 325-335
• Idioma: inglés
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• Resumen

  • Longwangmiao Formation in Lower Cambrian is one of the key petroleum systems in Sichuan basin. The reservoir is well developed in the Longwangmiao Formation which was deposited in the restricted carbonate platform. It is indicated that the karstification occurred in the reservoir of Longwangmiao Formation during the Caledonian tectonic movement on the basis of seismology, petrology, sedimentology and geochemistry. Distinguishable markers of the paleo-karstification include: the lost strata and unconformable contact occurring between Middle-Upper Cambrian carbonates and Lower Permian Liangshan Formation; the occurrence of collapse breccias and fillings in caves and karrens; the evident difference between cave fill dolostones and matrix dolomite in the Sr/Ba ratio; and the log response of cavernous formations. The karstification lasted for a long time. According to the residual thickness between the top of Longwangmiao Formation and the bottom of the Permian, paleo-geomorphology during the Caledonian karstification had been recovered. In that time, Longwangmiao Formation was not directly exposed to the surface in central Sichuan basin; lots of meteoric fresh water flowed through faults and cracks from Gaotai Formation and a series of vertical dissolved caverns and karrens were formed. Meanwhile, due to the denudation window of Leshan-Longnvsi paleo-uplift lying in the west of the study area, meteoric fresh water flowed from the denudation window and the Longwangmiao Formation became a karstic confined aquifer. Under the pressure, diagenetic fluid migrated along the formation. Consequently, elongated dissolved pores and vugs formed and bedding karst reservoir developed in Longwangmiao Formation. The intensity of the karstification weakened with the distance from the paleo-uplift increasing, which indicates that the karstification was deeply influenced by the paleo-uplift. Finally, the supergene karstification model of Longwangmiao Formation has been established on the basis of the synthesis of the above-mentioned research results.