Quaternary paludal tufas from the Ben Younes spring system, Gafsa, southwestern Tunisia: Interactions between tectonics and climate

Abstract

Tufa deposits that can be fit into a single depositional model are restricted to relatively few publications in the geological literature. This paper presents a detailed sedimentological study of Quaternary (Early Holocene) paludal tufas partly exposed in the Ben Younes piedmont. Field data reveal five main paludal lithofacies: phytoherm framestones, sapropelitic tufa, microdetrital tufa, microbial laminites and lime muds. Radiocarbon dating of residual organic matter in tufa shows that the tufa ranges in age from 8790 ± 50 to 3230 ± 60 BP. Most tufa deposits appear to remain preserved during the different stages of their development. Lithification and diagenetic modifications of tufa show two major trends, an increase in the average carbonate grain size and non-selective dissolution of the fabric where deposits are exposed to meteoric diagenesis. The studied tufas are “water-limited” and the importance of climate in their formation is as major as implied in other Mediterranean equivalents. The predominance of paludal conditions in this area is controlled by the flat substrate, the spring locations, and the water supply. The Gafsa Strike-slip Fault, aside its tectonic role, acts as a major regional sill that controlled paleoflow directions, discharge locations, content, volume, rate and fluctuations of the water supply.