High resolution calpionellid biozonation of Upper Tithonian reference sections in NE Algeria (Jebel Azreg, Aurès Range; Jebel Toumbaït, Aïn Yaghout Mounts): correlations and geodynamic implications

Abstract

The stratigraphic problem of the Jurassic-Cretaceous boundary (JKB) is still the object of a warm international debate. Around this limit, the Upper Tithonian substage has been the subject of significant stratigraphic investigations throughout the Tethyan Realm areas. On the southern Tethys Margin of the Maghreb, our recent works in NE Algeria have revealed sections, where good Upper Jurassic outcrops are considered as promising for the definition of a Global Standard Section and Point (GSSP) for the Jurassic-Ctretaceous boundary. In this line of interest, a high resolution calpionellid biozonation of Upper Tithonian successions from two bed-by-bed sampled key sections in the Aurès (Jebel Azreg) and Aïn Yaghout Mounts (Jebel Toumbaït) of NE Algeria is proposed here for the first time. The Crassicollaria and Calpionella Zone limits, encasing two subzones and six stratigraphic horizons, are identified. Within these sections, calpionellid distribution and resulting biostratigraphic units fit the standards referred to for the Tethyan Realm. The identified marker bioevents and associations confirm the high biostratigraphic potential of calpionellids for the JKB definition in the North Africa Maghrebian Chains. Correlation transects reveal important thickness and facies variations interpreted as the result of a synsedimentary tectonic control implying NW–SE, E-W and NE-SW major faults that led to the individualization of a mozaic of highs and depressions where Upper Tithonian deposits onset. A proposed interpretative model replaces the Upper Tithonian study successions in their regional geodynamic context.