AN UPPER VISÉAN (ASBIAN-BRIGANTIAN) AND SERPUKHOVIAN CORAL SUCCESSION AT DJEBEL OUARKZIZ (NORTHERN TINDOUF BASIN, SOUTHERN MOROCCO)

Abstract

The Djebel Ouarkziz Formation, located in the northern part of the Tindouf Basin, in western Algeria and southern Morocco, is composed mainly of shales with interbedded limestones, dolostones and sandstones. The limestone beds are relatively thin, but are laterally persistent, and can be followed along strike for tens of kilometres. We have identified 19 limestone beds in three main sections; one logged along the road from Assa to Zag, a second in the Tinguiz-Remz Valley, 15 km to the east, and a third section 10 km west of the Assa-Zag road section. Rugose coral assemblages are recorded in most limestone beds, but the stratigraphically higher beds become more diverse However, many rugose genera and species are persistent throughout much of the succession. The oldest coral assemblages are Asbian in age and the youngest coral assemblages indicate a Serpukhovian age, as confirmed by foraminiferal biostratigraphy. The first appearance of rugose corals shows a different pattern than that in northern Moroccan basins; some common genera that first appear in the Asbian and lower Brigantian in northern Morocco and Europe, appear much later, in the upper Brigantian or Serpukhovian in the Djebel Ouarkziz. The genus Kizilia , which is rare in the Upper Visean in northern Moroccan basins, is, however, abundant in the Tindouf Basin. Interestingly, the occurrence of the genus Lonsdaleia in the Serpukhovian from Djebel Ouarkziz poses a palaeogeographic problem because of its absence in northern Moroccan basins (except as transported elements in Serpukhovian conglomerates). Similarly, Actinocyathus in the Serpukhovian in the Tindouf Basin is not present north of the Anti-Atlas Mountains. A possible coral migration route to the Tindouf Basin may be from the northeast via the Bechar Basin in Algeria, similar to that already inferred for foraminifers and calcareous algae.