EGU22-3106, updated on 10 Jan 2024
EGU General Assembly 2022
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Palaeo-environmental and palaeo-climatic significance of Tunisian calcretes

Farah Jarraya1, Barbara Mauz2, Mike Rogerson3, Noureddine Elmejdoub4, Abdeljalil Sghari5, and Nejib Kallel1
Farah Jarraya et al.
  • 1Faculty of Sciences, University of Sfax, Sfax, Tunisia (
  • 2School of Environmental Sciences, University of Liverpool, Liverpool, UK
  • 3School of Environmental Sciences , University of Northumbria, New castle, UK
  • 4High Institute of Water Sciences and Techniques , University of Gabes, Gabes, Tunisia
  • 5University of Sfax, Faculty of Letters and Human Sciences, University of Sfax, Sfax, Tunisia

Continental carbonates constitute an interesting topic of study since they are important archives recording climate and paleoenvironmental changes. In Tunisia, calcretes are formed during the Pliocene-early Pleistocene (Villafranchian). They mainly occur in the center and on the coastal plain of Djeffara (Southern East) while their presence is more sporadic in the North of the country. Continental carbonates may form in the soil, groundwater, and palustrine and lacustrine environments. Four criteria are used to differentiate these different environments: host rock, components and micromorphological texture, subaerial exposure (seasonality), and flora and fauna.

The purpose of this study is to investigate the palaeoenvironmental significance of Tunisian calcretes for the Plio-Pleistocene. For this aim, well-developed carbonate beds were studied along a north-south transect that crosses the climatic boundaries between the latitudes 33 ° and 37 ° N: North (N36º.43.713 E10º.06.681’) Center (N35º.07.077 'E10º. 14.545 ') and South (N33º.28.898' E10º.20.597 ').

Based on the macroscopic, petrographic, and cathodoluminescence observations in association with scanning electron microscopy results, we classified thin sections extracted from the massive horizons in all sites into 8 facies types:

The Northern site is characterized by 1) pisolithic calcretes and 2) laminar calcretes showing several beta microfabrics such as rhizolith, peloids, intraclasts, coated grains, bioclast debris, cracks, alveolar septal, spherulite, and organic matter. Moreover, 3) pseudo microkarst carbonates were detected in Northern Tunisia by the presence of vertical layers, peloids, intraclasts, circum crack grain, pedotubules, and rhizoconcretions, and bioclasts.

At the central site, 4) laminar calcretes are characterized by planar layers. Both 5) massive brecciated calcretes and 6) mottled nodular brecciated calcretes are distinguished by the abundance of cracks. All these facies types’ shows similar pedogenic components such as peloids, coated grains, gastropod shell, alveolar septal, ooids, and bioclasts.

The southern site is characterized on the one hand by 7) laminar calcretes composed of peloids, nodules, coated grains, cracks, and on the other hand by 8) groundwater nodules showing a massive aspect with alpha microfabrics. In all sites, the nodular horizons are pedogenic.

Thus, our Plio-early Pleistocene calcretes formed in three main depositional environments: pedogenic, groundwater, and palustrine. The groundwater calcretes are formed under phreatic conditions while the Tunisian pedogenic calcretes and palustrine carbonates exhibit subaerial exposure characteristics (cracks). Except for southern groundwater calcretes, all other types of carbonates show biogenic traces. The palustrine carbonates developed above lacustrine mud. Whereas, pedogenic and groundwater calcretes, develop on different types of host rocks (siliceous and clayey). The difference between fabrics indicates that during the Pliocene-early Pleistocene calcrete form in the north in palustrine settings while it forms in groundwater context in the south. Furthermore, the transition between the different environments is controlled mainly by variation in the water table suggesting a variable but generally more humid climate during the Plio-Pleistocene in North Africa.

How to cite: Jarraya, F., Mauz, B., Rogerson, M., Elmejdoub, N., Sghari, A., and Kallel, N.: Palaeo-environmental and palaeo-climatic significance of Tunisian calcretes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3106,, 2022.