New Computerized Method for the Geochemical Classification of Precambrian Carbonate Rocks: Case of a Set of African Cap Carbonates

Post-sedimentary transformations have masked or completely obliterated the structures and textures of Precambrian carbonate rocks. Therefore, methods of classification of the carbonate rocks founded on the observation of primary structures or textural characteristics are ill-adapted. Consequently, only certain geochemical classification methods al- low us to distinguish the various rock-types in the case of Neoproterozoic carbonates. After presenting the most suit- able geochemical classifications, we propose a new classification into 14 groups based on a regular ternary diagram with computerized data input. For each sample of carbonate rock, analysis of calcium and magnesium contents allows us to calculate the input data for our diagram i.e. the percentages of Calcite, Dolomite and Insoluble Residue. To auto- mate the application of this diagram, input parameters are created in a descriptive file "Roches.ternaires.txt" using an option called "Ternaires" in the "Diagrammes" software developed by Roland Simler. Thirty cap carbonates of Africa are used to validate this new method.