Hydrogeology of Carbonate Rocks

Abstract

Carbonate rocks are sedimentary type of rocks containing more than 50% carbonate minerals which are mainly calcite, CaCO₃, and dolomite, CaMg(CO₃)₂. The carbonate minerals could be a result of chemical precipitation, organic processes or may occur as detrital material. Some of the dolomites may be a result of diagenesis known as dolomitization which involves replacement of calcite by dolomite to a varying extent. The term limestone is used for those rocks which contain more than 90% carbonates. If the rock contains more than 50% but less than 90% carbonates, it is termed as arenaceous limestone or an argillaceous limestone, depending upon the relative amounts of quartz and clay minerals. Chalk is a type of limestone which is soft and white in colour and is rich in shell fragments. The carbonate rocks occupy about 10% of the Earth’ surface and supply nearly a quarter of the world’s population with water. Locally, their cumulative thickness may be 10 000 m (UNESCO 1984b). In the geological past, most limestones and dolomites were deposited during the intermediate phases of Caledonian, Hercynian and Alpine tectonic cycles and their ages are mainly Palaeozoic and Mesozoic. One of the largest carbonate aquifers in the world is the Floridan aquifer system of Palaeocene to Miocene age in the southeast United States consisting of gently dipping thick sequences of carbonate sediments separated by less permeable clastic sediments.