Carbonate Deposit Microfacies and Carbonatogenesis of Abiod Formation (Campanian/Maastrichtian) in Jebel Kebar (Central Tunisia)
The present work aims to study the origin of limestones and carbonatogenesis of the Abiod Formation (Campanian Maastrichtian) in Jebel Kebar area (Central Tunisia). This work is based on the examination of a geological section in Jebel Kebar area. The polarizing microscopic observation of thin sections of limestone allowed us to determine four depositional facies: (i) Planctonic foraminifera-rich mudstone-wackestone, (ii) Calcisphera-rich mudstone, (iii) Bioclastic-bioturbated mudstone and (iv) Bioturbated mudstone, which is developed in turn in open circalittoral, circalittoral and infralittoral environments. These different carbonate facies correspond respectively to Transgressive and Regressive systems tracts that determine carbonate depositional sequences. The SEM observation shows that the Abiod Formation limestone is essentially micritic with three kinds of micrite (i) biodetrital micrite (ii) Chemical micrite (chemical precipitation) and (iii) Biological micrite (bacteria product?). The biodetrital micrite is the most represented in the studied limestones in comparison with the other kinds of micrite. The mineralogy, calcimetry, geochemical element concentrations and magnetic susceptibility (SM) show cyclic vertical changes which are related to the deposit facies (systems tracts) variation in the same way the maximum carbonate production rates are related to the transgressive intervals and mainly resulted from the biodetrital micrite accumulation. Accordingly, it seems that the carbonatogenesis was at least in part controlled by the sea-level fluctuation.
KeywordsFacies Carbonatogenesis Bacteria Campanian maastrichtian Jbel kebar
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