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Evolution of mixed shelf at the Jurassic-Cretaceous boundary: Case study of the S Setifian shelf (NE Algeria)
El Hadj Youcef Brahim, Mohammed Chadi, Rami Djeffal, Wahid Chettah

Building: Muséum d'Histoire Naturelle de Genève
Room: Lobby /Hall/
Date: 2018-12-05 11:17 AM – 11:20 AM
Last modified: 2018-11-24

Abstract


This study focuses on an area located at the convergence of the allochthonous and the Atlasic forelands of the Northren Algerian Alpine Belt. The objective of this work is to reconstruct the paleogeographica history of the Jurassic-Cretaceous carbonate shelf and discuss its relationship with the geodynamic evolution of the Southern Tethysian margin.

The Jurassic series are characterized by various facies and depositional environments, all of which record low bathymetry. During the Kimmeridgian and the Portlandian, the bioclastic character becomes increasingly more marked with the presence of bioclasts, gravels and oolites, characteristic of high energy deposits in the northern part  of the study area (Dj. Messaouda and Dj. Mestaoua). On the other hand, the southern part (Belezma-Batna Mts.) individualized by deep facies consisting of mudstones with intercalations of marl and clay limestones.

The lower Cretaceous is represented by clay-sandstone sedimentation, typical of a deltaic environment in a shelf context. In order to better constrain the interpretation of facies in terms of depositional environments (foreshore, shoreface, offshore ...) and bathymetric zonation, three facies associations were defined and recognized in the several sections studied.

The Jurassic-Cretaceous boundary is characterized by the presence of a pelagic fauna where the Ammonites (Malbosiceras aff. parmimounum, Mazenoticeras affuralense, Fauriella boissieri, Jabronella isaris, Spiticeras sp.) are dominant. Calpionellids (Calpionella alpina Lorenz, etc.) allow to ascribe a higher Berriasian age to the pelitic-sandy complex with rare intercalations of thin beds of argillaceous limestones with ripple marks, and marls.

The regional distribution of facies and thicknesses has a relationship with a complex structural heritage.