Late Pleistocene clastic tufa from Gafsa, southern Tunisia: Implications for paleo-landscape interpretation

Abstract

The landscape reconstruction in the Jebel El Mida area during the Late Pleistocene was based on the continental carbonate record, particularly on the clastic tufa deposits. Four main lithofacies types of clastic tufa were recorgnized in the Jebel El Mida area, these are: (1) grain-supported macrodetrital phytoclast tufa, (2) grain-supported macrodetrital oncolith tufa, (3) grain-supported macrodetrital lithoclast tufa, and (4) matrix-supported microdetrital tufa. The interpretation of depositional environment reveals spring-fed streams and pools with highly CO2-enriched water helped in carbonate precipitation and incrustation on the vegetation cover. Dating of tufa deposits has been based on archeological content and radiometric (U/Th) age dating. A major lag exists between the age of the archeological content and the radiometric age for tufa (170 ky) indicating transport and re-sedimentation of older reworked tufa within the stone tool-rich sandsone and conglomeratic substrates. The major fault of Gafsa that cross-cuts the studied area is the main conduit for upwelling carbonated waters for tufa precipitation and also the re-organization of the landscape after the recurrent tectonic activity during the Late Pleistocene. The deposition of Jebel El Mida tufa indicates particular depostional settings characterized by (1) abundant rainfall on the recharge areas with high water table, (2) acidic water infiltrations through plant cover and soils, and (3) dissolution of aquiferous Cretaceous carbonates resulting in water mineralization of the groundwater during a time span that predates Late Pleistocene.