The Upper Cenomanian-Turonian (Upper Cretaceous) of the Saharan Atlas (Algeria)

Long-distance correlations 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 depo-sition of C/T boundary black shales, a rise in sea level occurred. Shallow-water carbonates were locally able to accom-modate 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 dee-per-water facies of nearby northern Tunisia, suggests that the uppermost Cenomanian mudstone immediately underlyin