Mississippian Platform and Basin Successions from the Todrha Valley (northeastern Anti‐Atlas), southern Morocco

Abstract

AbstractCarboniferous rocks of Mississippian age are exposed in Jebel Asdaf and Jebel Tisdafine, south and north respectively of the fault‐controlled Todrha Valley, between the towns of Tinerhir and Tinejdad in the Anti‐Atlas of southern Morocco. The age, as determined by microfossils, and facies of the dominantly siliciclastic successions of the two areas are different. The Jebel Asdaf Formation (245 m exposed; base and top not seen) is a shallow shelf sequence of late Tournaisian age. The Jebel Tisdafine Formation is a succession of turbidites (at least 1500 m thick), which rests unconformably on Devonian limestones and is of late Viséan age. Limestone beds in each formation have different origins. Skeletal grainstones and packstones in the Jebel Asdaf Formation formed when sand supply to the shelf was episodically reduced. Ooid‐rich skeletal packstones and grainstones in the Jebel Tisdafine Formation, characterized also by the presence of well‐rounded, coarse‐sand grade quartz grains, were derived from a contemporary carbonate platform. Individual beds in the Jebel Tisdafine Formation are essentially tabular and can be followed for long distances. Channelling is very rare. The turbidites, which are quartz‐rich, were transported from west to east across a basin floor with low slopes. Jebel Azguine, northwest of Tinejdad, is separated from Jebel Tisdafine by a major shear zone. It is made up of quartz sandstones that differ from those of both the Jebel Asdaf and Jebel Tisdafine formations in not containing any carbonate or body fossils, in its trace fossil assemblage dominated by vertical burrows, and in the presence of very thick beds. It is tentatively suggested that the Jebel Azguine sandstones are older than Carboniferous, to which they are assigned on some geological maps. The conclusions of this research are markedly different from accounts of the geology of the area published previously. Copyright © 2007 John Wiley & Sons, Ltd.