The Late Cretaceous polygenic breccias succession of Rouana formation in central Tunisia: implication for the comparison of stratigraphy and depositional environment

Abstract

The Rouana formation consists of Turonian interbedding dolostones, breccias and marls that developed in Sidi Bouzid area in middle central Tunisia. The study of a geological section in the Jebel Rouana, complemented by the microscopic observations of thin sections allowed distinguishing different types of breccias and non-breccias deposits. The Rouana formation includes five different types of breccias arranged into eight levels generally interbedded by laminated tidalitic dolomites. The succession of breccias occurred in a marginal paleogeographic environment between continental and marine domains; it consists of a shallow-water uplift on which developed alternating shallow-marine and continental deposits. The sedimentation was controlled by third-order sea level variation. Indeed, during the sea level rise, the Sidi Bouzid uplift was covered with shallow-marine waters where tidalitic dolomites occurred, simultaneously the shoreline extended southward beyond this uplift and reaches the supratidal evaporitic domain in Gafsa area. During the sea level fall, the shoreline retreats toward the North and the uplift became exposed and continental conditions occurred materialized especially by the development of polygenic, alluvial, palustrine, collapse and desiccation breccias. The Rouana formation records third-order eustatic fluctuation during the Turonian interval, materialized by the development of depositional sequences bounded by subaerial exposure surfaces. The studied depositional sequences may be correlated, respectively, with the coeval open-marine sequences (Annaba and Bireno formations) in North central Tunisia as well as with the coeval supratidal evaporitic sequences (Beida formation) in south central Tunisia.