Paleogene Calciclastic Deposits in Southern Tunisia
The Paleogene outcrops of the abandoned open pit mine near El Mdhilla, Gafsa display calciclastic deposits encased in phosphorite-rich marls and limestone alternations of Chouabine Formation. Lithostratigraphic investigation of the quarry sections allows recognizing chaotic lenticular bodies that spread uniformly within Ypresian layers. The individual lens is concave up in cross section. The lens width range from 9 to 12 m; whereas, the height ranges between 1 and 3 m. These lenticular bodies are composed of skeletal-rich (Ostrea, bivalve shells, e.g. pecten) and coarse-grained sediments with low amount of mud (calcirudite). Thin sections analysis shows mixed depositional environments indicated by high-energy grainstone (mostly bivalve shell fragments) and intertidal sediment textures. The sediments originated from isolated carbonate platform via submarine gravity flow processes and redeposited in the phosphorite-rich basin. The predominance of coarse-grained sediment textures indicates that the carbonate platform, probably made up of organogenic limestone, allows steep slope paleotopography. Textural analysis of calciclastic deposits shows that the sediment main source is related to the Late Paleocene carbonate/lagoonal platform of Thelja Formation. The formation of these calciclastic deposits involves submarine erosion process that stripped lithified sediments from submarine uplifted the carbonate platform edge and slope controlled by the conjunction of tectonic activity (e.g. normal faults) and possibly low sea level. Rockfalls along faulted escarpments (platform margin) are not excluded to produce calciclastic deposits since that grain shape roundness indicates little transport of sediments.
KeywordsSouthern Tunisia Paleogene Calciclastic submarine deposits Carbonate platform slope Gravity mass flow
- 1.Cook, H.E., Hine, A.C., Mullins, H.T.: Platform margin and deep water carbonates. Society of Economic Paleontologists and Mineralogists (1983)Google Scholar
- 2.Shanmugam, G., Moiola, R.J., Damuth, J.E.: Eustatic control of submarine fan development. In: Submarine Fans and Related Turbidite Systems, pp. 23–28. Springer, New York, NY (1985)Google Scholar
- 5.Coniglio, M., Dix, G.R.: Carbonate slopes. Facies models: response to sea level change, pp. 349–373 (1992)Google Scholar
- 7.Kocsis, L., Ounis, A., Baumgartner, C., Pirkenseer, C., Harding, I.C., Adatte, T., Chaabani, F., Neili, S.M.: Paleocene–Eocene palaeoenvironmental conditions of the main phosphorite deposits (Chouabine Formation) in the Gafsa Basin, Tunisia. J. Afr. Earth Sci. 100, 586–597 (2014)Google Scholar
- 8.Einsele, G.: Sedimentary basins: evolution, facies, and sediment budget, 2nd edn., Springer Science & Business Media (2013)Google Scholar