Diagenetic process as tool to diagnose paleo-environment conditions, bathymetry and oxygenation during Late Paleocene-Early Eocene in the Gafsa Basin

Abstract

Late Paleocene–Early Eocene deposits cropping out in Tamerza area were settled on a carbonate homoclinal ramp. Deposits which are ranged in six main facies record a gradual transition from intertidal to upper circatidal environment. Lateral variations in terms of facies and thickness infers to the main role of synsedimentary tectonics. The characterization of paleoenvironments was established in respect to the lithology, fauna content, sedimentary structures and diagenetic features. Detailed analysis of deposits shows that the diagenetic processes are reliable tools to reconstruct each depositional environment. Moreover, they bring out precious information concerning the chemical and physical parameters and the sedimentary dynamics of the studied interval. The early stage cementation is favored under low rates of sedimentation and a calm sea floor. The arrangement and the morphology of crystals permit to appreciate the bathymetry and to better characterize the depositional environment. Phosphogenesis seems in a tight relation with silicification requiring both an acidic environment. The occurrence of upwelling currents engendered the blooming of fauna guarantying test preservation after death and allowed to establish a linkage between fauna content and diagenetic features. Silicification processes concern test replacement and the genesis of chert beds included within the enclosing deposits. Micritization processes, occurring in the inner ramp, advocate calm environments and are engendered by endolithic algae, bacteria and fungi. The X-Ray diffraction shows the frequency of smectites associated with clinoptilolites, sepiolite and palygorskite. The clay paragenesis helps to identify several diagenetic contexts occurring under xeric and confined conditions.