New Computerized Method for the Geochemical Classification of Precambrian Carbonate Rocks: Case of a Set of African Cap Carbonates
- 1 Aix-Marseille Université, CNRS, IRD, CEREGE UM 34, Aix en Provence, France
- 2 Université d’Avignon et des pays du Vaucluse, INRA, EMMAH, UMR 1114, LHA, Avignon, France
- 3 Aix-Marseille Université, CNRS, IRD, CEREGE UM 34, Aix en Provence, France
- 4 Aix-Marseille Université, CNRS, IRD, CEREGE UM 34, Aix en Provence, France
- 5 Département de Géologie, Faculté des Sciences et Techniques, Université Marien Ngouabi de Brazzaville, Brazzaville, République du Congo
- 6 Département de Géologie, Université des Sciences et Techniques de Masuku, Franceville, Gabon
Abstract
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 allow us to distinguish the various rock-types in the case of Neoproterozoic carbonates. After presenting the most suitable 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 allow s us to calculate the input data for our diagram i.e . the percentages of Calcite, Dolomite and Insoluble Residue. To automate 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.
- R. J. Dunham, “Classification of Carbonate Rocks According to Their Depositional Texture,” In: W. E. Ham, Ed., Classification of Carbonate Rocks: Tulsa, OK, American Association of Petroleum Geologist Memoirs, 1962, pp. 108-121.
- A. F. Embry and J. E. Klovan, “A Late Devonian reef tract on northeastern Banks Island,” Bulletin of Canadian Petroleum Geology, Vol. 19, No. 4, 1971, pp. 730-781.
- R. L. Folk, “Practical Petrographic Classification of Limestones,” American Association of Petroleum Geologist Bulletin, Vol. 43, No. 1, 1959, pp. 1-38.
- R. L. Folk, “Spectral Subdivision of Limestones Types,” In: W. E. Ham, Ed., Classification of Carbonates Rocks. A Symposium, Tulsa, OK, American Association of Petroleum Geologist Memoirs, 1962, pp. 62-84.
- V. P. Wright, “A Revised Classification of Limestones,” Sedimentary Geology, Vol. 76, No. 3-4, 1992, pp. 177-185. http://dx.doi.org/10.1016/0037-0738(92)90082-3
- G. V. Chilingar, “Use of Ca/Mg ratio of Limestones and Dolomites as a Geological Tool,” Ph.D. Dissertation, Univ. Southern California, 1956.
- G. V. Chilingar, “Classification of Limestones and Dolomites on Basis of Ca/Mg Ratio,” Journal of Sedimentary Petrology, Vol. 27, No. 2, 1957, pp. 187-189.
- A. Carrozi, “Petrographie des Roches Sédimentaires,” F. Rouge et cie, Lausanne, 1953, 250 p.
- R. W. Fairbridge, “The Dolomite Question,” In: R. J. Le Blanc and J. G. Breeding, Eds., Regional Aspects of Carbonate Deposition, Tulsa Society of Economic Paleontologists and Mineralogists, Special Publications, 1957, p. 128. http://dx.doi.org/10.2110/pec.57.01.0125
- J. Rodgers, “Terminology of Limestone and Related Rocks: An Interim Report,” Journal of Sedimentary Petrology, Vol. 24, No. 4, 1954, pp. 225-234.
- B. Martinet and J. Sougy, “Utilisation Pratique des Classifications Chimiques des Roches Carbonatées,” C. R. Somm. Soc. Géol. Fr., 1957, p 367 (résumé), Annales de la Faculté des Sciences de Dakar, 1957[1961], pp. 81-92.
- K. E. Chave, “Aspects of the Biochemistry of Magnesium,” Journal of Geology, Vol. 62, 1954, pp. 266-283.
- B. Martinet, M. Deynoux and R. Trompette, “Méthode de Dosage de CaO et MgO dans les Roches Carbonatées,” Travaux des Laboratoires des Sciences de la Terre, Série B, No. 2, St Jérome, Marseille, 1969.
- W. E. Dean, “Determination of Carbonate and Organic Matter in Calcareous Sediments and Sedimentary Rocks by Loss on Ignition: Comparison with Other Methods,” Journal of Sedimentary Petrology, Vol. 44, No. 1, 1974, pp. 242-248.