The external morphology and its variability, myocardinal apparatus, and shell structure of both valves of the radiolitid rudist Eoradiolites plicatus (Conrad) are described, based on the examination of about one hundred well-preserved, fairly complete specimens that are free of sediment matrix, found in a single bed of an ammonite-bearing Albian succession ('Knemiceras beds', Zebbag Formation) in central Tunisia. This study provides the most nearly complete knowledge of any Eoradiolites species to date. With this background, all previous records of E. plicatus, as well as the taxonomic status of the other Albian species of the genus, are revised considering both original material, when available, and published papers. As a result, the systematics of Eoradiolites is simplified.

No abstract

A series of sections from the Ouled Nail, Hodna and Aurès massifs of Algeria have been studied to analyse the palaeogeographic evolution of the eastern part of the Saharan Atlas prior to and after the Cenomanian/Turonian (C/T) boundary event. Three periods are distinguished in the interval studied. During the middle to late Cenomanian, an overall ramp setting prevailed from the Saharan platform to the deeper environments of the Saharan Atlas. The latest Cenomanian and the earliest Turonian was marked by an episode of marked palaeogeographic change. Prior to the deposition of C/T boundary black shales, a rise in sea level occurred. Shallow-water carbonates were locally able to accommodate the sea-level rise. A “keep-up” response created a palaeogeography made up of isolated carbonate platforms separated by saddles, where a 1–20 m thick bed of deeper water mudstones was deposited as the lateral equivalent of the platform carbonates. At a larger scale, these saddles probably acted as corridors that allowed marine communication with the intra-Saharan basins (Tinrhert, Tademaït basins). Correlations show that the boundary black shales later filled up the saddles of the Saharan Atlas, and onlapped the carbonate platforms, before the deposition of lower Turonian open marine marls that everywhere blanket the successions. During the early to late Turonian, the palaeogeography again changed to restore a N-S oriented ramp setting, similar to that of the middle Cenomanian. Correlation with the deeper-water facies of nearby northern Tunisia, suggests that the uppermost Cenomanian mudstone immediately underlying the black shale facies in the Saharan Atlas is the lateral equivalent of the uppermost bed of the Fahdene Formation (the so-called “pre-Bahloul”) underlying the Bahloul black shale facies in the Tunisian Kalaat Senan reference section. Our platform-to-basin correlations show that the base of this bed is a regional transgressive surface, not a type II sequence boundary as suggested by previous authors. Finally, it is proposed that this mudstone bed correlates with Bed 63 of the Pueblo global reference section in the North American western Interior Basin, which also marks the beginning of the strong C/T boundary transgression.

Les formations carbonatées de l'Aptien supérieur (Gargasien) du Djebel Ouenza livrent une abondante faune de rudistes. Les Requieniidae sont largement représentés notamment par les espèces : Requienia migliorinii, Toucasia carinata et T. patagiata. Les Monopleuridae sont également fréquents et variés, on peut citer en particulier : Monopleura sp. Petalodontia sp. Agriopleura darderi et Himeraelites sp.

The Ouenza carbonate platform is a decakilometric sedimentary system surrounded by marly formations, which have been acting during the main part of the Gargasian and have been interrupted at Clansayesian. The platform is made of an outer coral facies zone and an inner Rudist facies one. A triasic diapirism had initiated the platform statement, the main history of which is also determined by diapiric activity probably controled by the reactivation of an hercynian fault.