The late Aptian-early Albian transgressions in the Chott area, southern Central Tunisia

The detailed sedimentological and biostratigraphic study of the upper Aptian-Albian series in the Chott area, southern Central Tunisia, leads to the identification of several, well-dated depositional sequences. The upper Aptian sequences are marked by very shallow marine, first partly evaporitic, then mainly clastic deposits. The last sequence yielded latest Aptian ammonites (H. jacobi zone). The Aptian-Albian boundary is assumed to be marked by a long-lasting hiatus, and by the abrupt change from clastic to carbonate deposits. The overlying ?Knemiceras Beds? express the Albian transgression, and comprise four depositional sequences. New findings of ammonites allow to date these beds to the lower Albian (D. mammillatum superzone), and to correlate the four sequences with those defined in Central Tunisia. Five distinct morphologies of Knemiceras sp. are recognized in the ?Knemiceras beds?. Because of their stratigraphic position, the overlying massive shelf carbonates (Radhouane Member) are ascribed to the uppermost lower Albian (T. camatteanum and L. pseudolyelli zones), and correlated with the Allam Limestone of Central Tunisia. This carbonate series is capped by a major discontinuity, correlated with the middle Albian discontinuity known in Central Tunisia. The ammonites and rudists fauna are presented and illustrated