The Cenomanian-Turonian boundary in central Tunisia in the context of a sequence-stratigraphic interpretation

Abstract The Cenomanian-Turonian section in central Tunisia offers an excellent opportunity to consider the stage boundary events in a basin margin setting. The deposits of the Kalaat Senan section combine a diverse biostratigraphic record with sufficient change in the lithofacies to identify the position of depositional sequences in a detailed stratigraphic framework. A preliminary evaluation of the position of the depositional sequences in the middle and upper Cenomanian relative to the standard ammonite zones shows a sequence boundary in the upper part of the middle Cenomanian and one in the upper Cenomanian. The sequence boundary in the upper middle Cenomanian coincides, as in Normandy and in the type area of the Cenomanian, with the chronozonal boundary between Acanthoceras rhotomagense and A. jukesbrownei . The sequence boundary in the upper Cenomanian falls within the Calycoceras naviculare ammonite zone. Because of incompleteness of the platform sections in France this sequence boundary appeared to fall between the C. naviclare and Metoicoceras geslinianum zones. The Cenomanian-Turonian boundary, as defined by ammonites, falls just below the maximum, second-order transgression of the Cretaceous sea. The boundary coincides with a flooding surface in the transgressive systems tract of a third-order sequence that has its lower boundary in the uppermost Cenomanian C. naviculare zone.