Palaeoecology and palaeobiogeography of the Middle Jurassic ostracods of southern Tunisia

Abstract

Abstract The results of a palaeoecological, biostratigraphical and palaeobiogeographical analysis of Jurassic ostracods from southern Tunisia are presented. The shallow to marginal marine deposits of Bajocian-Bathonian (Krachoua and Techout formations) and Callovian-?Oxfordian age (Tataouine Formation), which accumulated under predominantly warm humid climatic conditions, yielded diverse ostracod faunas from limnic, brackish and marine environments which have been analysed statistically. A qualitative cluster analysis yielded fourteen associations and two assemblages which are characterised by different percentages of marine, brackish and freshwater species. The distribution of the associations in the Middle Jurassic reflects temporal and spatial salinity gradients which are interpreted to reflect climatic variations (humid-arid) and global eustatic sea level changes. In the Callovian the ostracods and macrofaunas probably also reflect minor relative sea level changes. In accordance with other biostratigraphical data the ostracods support a Bajocian-Bathonian age for the upper Krachoua and the lower Techout formations, and a Callovian age for the lower Tataouine Formation. The palaeobiogeographical relationships suggest faunal exchange between southern Tunisia and Europe (southern France, Sardinia, England) in the Bajocian-Bathonian, and an isolation of the south Tunisian ostracod faunas from the European faunas in the Callovian, probably due to the deepening of the central Western Tethys. Predominantly in the Bajocian-Bathonian but also in the Callovian brackish conditions resulted in an endemicity of the ostracod faunas. As a consequence of the eustatic sea level rise in the Callovian species from the eastern North Gondwana shelf (Israel, Jordan, Egypt, Saudi Arabia), respectively, the Ethiopian Province, invaded southern Tunisia. Palaeobiogeographically the ostracods from southern Tunisia are intermediate between the ostracods from the Arabic-Northeast African region and Northwest Africa (Morocco).