Paula Medina-Varea

Potential foraminiferal markers for the Visean–Serpukhovian and Serpukhovian–Bashkirian boundaries—a case-study from Central Morocco

Abstract The Carboniferous succession in Adarouch (Central Morocco, north of the Atlas Transform Fault) contains thick carbonate beds including upper Visean, Serpukhovian and basal Bashkirian rocks. Foraminifers enable precise recognition of the Visean/Serpukhovian (V/S), early/late Serpukhovian (eS/lS) and Serpukhovian/Bashkirian (S/B) boundaries. Insolentitheca horrida, Loeblichia ukrainica, “Millerella” spp. and Endostaffella? sp. 2 are regarded as regionally useful indices to the V/S boundary, whereas Eostaffellina spp., Eostaffella pseudostruvei and some evolved species of Archaediscus exhibit greater reliability for worldwide correlation of this level. Similarly, the eS/lS boundary is marked locally by Brenckleina rugosa, Eosigmoilina sp., and Monotaxinoides spp. and globally by Loeblichia minima, Bradyina cribrostomata, Plectostaffella spp., Eostaffellina “protvae” and “Turrispiroides”, and the S/B boundary is marked locally by Globivalulina bulloides and globally by Seminovella elegantula, and Novella?. Occurrences of these taxa in Morocco allow correlations with the Moscow Basin, the Urals, the Donetz Basin and North America. The Moroccan assemblages share few taxa in common with Saharan basins south of the Atlas Transform Fault. Correlations with western European basins are difficult because of the paucity in the latter of foraminiferal-bearing carbonate strata.

Palaeobiogeographical constraints on the distribution of foraminifers and rugose corals in the Carboniferous Tindouf Basin, South Morocco

Abstract The northern flank of the Tindouf Syncline in southern Morocco exhibits a continuous, well exposed Carboniferous succession with limestones of Late Asbian to Early Bashkirian age containing rich and diverse foraminiferal and rugose coral assemblages. Analysis of these assemblages provides new data on the relatively poorly known Saharan basins. The palaeobiogeographical relationship of the Tindouf Basin with other Palaeotethyan basins is complex. Although there is a predominance of cosmopolitan taxa for the Palaeotethys, it is recognized that there was an influence of basins from NW Europe, such as the UK and Ireland. Some taxa are recorded in both NW Europe and Tindouf without any characteristic contributions from intermediate basins in northern Morocco. The neighbouring Bechar Basin in Algeria presents distinct assemblages. The bulk of the data analyzed suggest that this sector of the western Palaeotethys can be subdivided into four palaeobiogeographical subprovinces: the Atlantic Subprovince (UK, Ireland, N France and Belgium), the Mediterranean Subprovince (Pyrenees, Montagne Noire, Betic Cordillera, Rif (N Morocco) and Balearic Islands), and the Saharan Subprovince (Bechar, Reggan, Ahnet-Mouydir and Tindouf). In between, mobile belts of mixed faunal assemblage characteristics are observed ( e.g. , SW Spain and Central Meseta) forming the West peri-Gondwanan Subprovince. Analysis of the Tindouf Basin faunas shows that, as in other Saharan basins, there is a high diversity and abundance of foraminiferal taxa, with a higher proportion of survivors and longer stratigraphic ranges; these features also are mirrored by rugose corals. This emphasizes the longevity of the carbonate platform in a tropical setting, where periodic transgressions introduced new assemblages, and oceanic currents are interpreted as one of the main controlling factors for the distribution of the taxa in these subprovinces. Moreover, not only were water temperatures on the platform higher, but also tectonic stability greater. It is considered that the effects of the first phases of the Gondwanan glaciation were minimal on the Tindouf faunas.

Lithofacies and biostratigraphical correlation of marine Carboniferous rocks in the Tindouf Basin, NW Africa

Spatial and temporal variations of Carboniferous sediment accumulation within the northwestern part of the northern flank of the Tindouf Syncline in Saharan Morocco allowed to distinguish 16 lithofacies types. The predominant sedimentation pattern is cyclic, with the overall succession recording a major regressive trend. Outer platform siliciclastics in the lower part (Tournaisian and Viséan) pass up to middle and inner platform mixed siliciclastic and carbonate sediments (late Viséan–Serpukhovian) and finally to continental sandstones in the Bashkirian capping the marine carbonate sedimentation. The lack of similarities in a correlation with southern outcrops in the Tindouf Syncline suggests tectonically controlled sedimentation. The upper Tournaisian to lower Bashkirian succession records the incipient uplift of the Anti-Atlas Mountains, changing the paleogeography and, therefore, affecting the paleoecologic conditions, as well as the sedimentary environments in the Tindouf Basin. It is suggested that from the Serpukhovian onwards, much of the Anti-Atlas was uplifted, leading to subaerial conditions, while during the late Viséan, only a few small inliers had emerged. Although the number of Proterozoic emergent inliers of the Anti-Atlas is unknown, during the late Viséan, the Anti-Atlas Mountain belt is regarded as an emerging structure, with a distinct influence on the paleobiogeography of the region.