UPDATED CALPIONELLID ZONATION AROUND THE JURASSIC–CRETACEOUS BOUNDARY IN NE ALGERIA (“RAVIN BLEU” SITE, BATNA MOUNTAINS): A POTENTIAL REGIONAL STRATOTYPE FOR THE NORTH AFRICA MAGHREBIAN RANGES

Abstract

: In NE Algeria and the Tunisia–Algeria border chains, detailed stratigraphic investigations across the Jurassic– Cretaceous boundary (JKB) are scarce and this important stratigraphic interval remains poorly known. This work attempts fulfilling this gap of our knowledge on the JKB successions in this area. It represents unpublished data on calpionellid zonations, based on bed-by-bed sampling, of two sections from the “Ravin Bleu” site of Batna Mountains. In the Jebel Kasserou and J. Bou Merzoug study sections, most of the standard Upper Tithonian–lowermost Valanginian calpionellid zones and subzones are first identified here. Their limits correspond to main calpionellid bioevents allowing to recognize a new Alpelliptica Subzone of the Calpionella Zone in the Lower–Middle Berriasian; subsidiary bioevents being useful to delimit six horizons in the Upper Tithonian Crassicollaria Zone and two others in the Middle Berriasian Elliptica Subzone. All these biostratigraphic units are correlated with their lateral equivalents in other Tethyan sections, mainly from Morocco, Tunisia, SE France, Spain, the Carpathian Ranges and the Balkanides. Chitinoidellid and most of the calpionellid species from Eastern Algeria are first illustrated here. In addition to their easy access and good outcrops, the continuous, complete and thick marine study successions are devoid of strong diagenetic alteration, synsedimentary features and tectonic effects. The “Ravin Bleu” site is proposed herein as a potential reference section for the JKB interval in the North Africa Maghrebian Ranges of the SW Tethys Margin.