江汉平原及邻区海相碳酸盐岩的古岩溶特征及控制因素

对于露头剖面的观察、相关样品分析及钻井资料的研究表明,区内碳酸盐台地在形成、发展及消亡过程中,由于不同级次的相对海平面下降,台地沉积过程中断,出现暴露并伴随溶蚀作用,在台地埋藏后还受到地下热水的溶蚀改造。将区内古岩溶划分为同生期层间岩溶、裸露期古风化壳岩溶、埋藏期热水岩溶等三类。同生期层间岩溶多与相对短时间的海平面下降有关,以发育溶蚀残积物、溶孔(铸模孔)等为特征。裸露期古风化壳岩溶表现为台地长时间的暴露及溶蚀,一般可见明显的古风化壳岩溶垂向分带;埋藏期热水岩溶以非选择性溶蚀为特征。控制碳酸盐台地古岩溶发育的主要因素有气候、全球性海平面变化、古地形、古构造等因素。初步探讨了区内古岩溶与储层发育的关系。

Palaeokarst Characteristics and Controlling Factors of Marine Carbonate Rocks in Jianghan Plain and its Neighboring Areas

Carbonate platforms underwent several interruptions of sedimentary process, subaerial dissolution and karstification during their formation and development in Jianghan Plain and its neighboring areas because of multistage relative sea-level descent in Sinian, Palaeozoic and early Mesozoic. The carbonate rocks are corroded further by subterranean thermal water after burial. The palaeokarst in the studied area is divided into hypergenic depositional karst, the palaeoweathering crust karst and the burial thermal-water karst. The hypergenic depositional karst is characterized by ground residual deposits or selective dissolution pores (or casting pores) related to short-term depositional interruptions. The palaeoweathering crust karst generally shows weathered layers and obvious belts of karstification in vertical because of long-term exposure. The burial thermal-water karst displays nonselective dissolution pores and dissolution fissures caused by subterranean thermal-water corrosion. It is considered that main factors of controlling karstification development in the carbonate platforms are paleoclimate, eustatic sea level changes, palaeotopography, tectonic event, etc. The relationship of paleokarst and reservoirs is discussed also.