Abstract
Marginal-marine to non-marine ostracod assemblages from the Bajocian (Mid-Jurassic) of southern Tunisia, precisely from the Krachoua Formation at the Kef El Anneba section near the Beni Kheddache area, are here described and tested for their utility to improve the stratigraphic accuracy and palaeoenvironmental reconstructions. This particular microfauna consists of 11 species belonging to 6 genera and represents 2 distinct types of species-rich assemblages from this time interval, allowing the interpretation of the depositional setting of the fossiliferous horizon from which the samples derive. The first ostracod assemblage is mainly composed of the brackish to shallow marine species Fastigatocythere sp. Mette, 1995; Vernoniella aff. V. bajociana Bate, 1965b; Paracypris sp. A, Paracypris sp. B, Fabanella sarda Malz et al., 1985; Marslatourella aff. M. bathonica Andreu, 1999; and Fabanella aff. F. bathonica Oertli, 1957. This ostracod biofacies reflects marginal marine (shallow platform, restricted lagoon) conditions in the studied area. In contrast, the second ostracod assemblage is exclusively dominated by the non-marine limnic species Alicenula sp., Theriosynoecum pusilla Rohr, 1976; Theriosynoecum aff. T. aveyronensis Rohr, 1976; and Theriosynoecum sp. Such ostracod biofacies reflects the establishment of (a) permanent freshwater lake(s) in the studied area, triggered by the total emersion of the Bajocian Krachoua platform, presumably as response to the short-term sea-level fall event JBj3 of Haq (2017). The recognized ostracod species from the upper part of the Krachoua Formation at Kef El Anneba section (Medenine area) are particularly similar to those already described from the neighbouring sections of Kezzani (Dhaher area) and Krachoua (Tataouine area), facilitating a stratigraphic calibration of the Krachoua Formation, as well as regional correlations of the respective Bajocian continental event within the southern Tunisian palaeogeographic domain. Moreover, the biogeography of the studied ostracod microfauna from the Mid-Jurassic of southern Tunisia provides further arguments to support the hypothesis of significant biological exchanges between Laurasian and Gondwanan islands, as recently demonstrated by means of a charophyte microflora, indicating that Peri-Tethyan biogeography remained relatively uniform during that time interval and challenging the previous assumption of their endemism.
Highlights
The detection of key emersion surfaces is fundamentally based on sedimentological criteria but can be revealed by remarkable changes in the microfaunistic assemblages in long-term marginal-marine depositional settings
We investigate the Mid-Jurassic (Bajocian) ostracod assemblages from the new Kef El Anneba section of the Krachoua Formation in the Medenine area, northern southern Tunisian domain
Bulk samples were collected from the marl KA 23a, the limestone KA 23b, and the marly limestone KA 24 levels (Figure 2B,C) of the Krachoua Formation
Summary
The detection of key emersion surfaces is fundamentally based on sedimentological criteria (e.g., desiccation cracks, karstification) but can be revealed by remarkable changes in the microfaunistic assemblages in long-term marginal-marine depositional settings. We use ostracods as tool to interpret the stratigraphy and the depositional palaeoenvironment of the Bajocian mixed series of the Krachoua Formation of southern Tunisia (Figure 1), northern margin of Gondwana. We investigate the Mid-Jurassic (Bajocian) ostracod assemblages from the new Kef El Anneba section of the Krachoua Formation in the Medenine area, northern southern Tunisian domain. These assemblages are compared with their coeval, poorly known microfauna from the Tataouine area in order to give more accuracy to the stratigraphy of the studied series in this palaeogeographic domain, its respective depositional environment, and its consideration for supra-regional correlation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
