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The Paleobiodiversity of the Famennian Ammonoid Genera on the Northern Margin of Gondwana: A Case from the Western Sahara of Algeria

2023; Springer International Publishing; Linguagem: Inglês

10.1007/978-3-031-43744-1_34

2522-8722

Abdelkader Abbache, Aicha Fetati, Mansour Zaagane,

Geology and Paleoclimatology Research

The Devonian is a cardinal stratigraphic period of the Paleozoic era due to major faunal, environmental, climatic and atmospheric changes. It contains one of the major biological crises during the Late Devonian (Frasnian-Famennian boundary). This coincides with a global eustatic fall and consequently the disappearance of large faunal groups. After the Frasnian, the dispersal of the ammonoid Order Goniatita and the appearance of the new Order Clymenida originated after these variations, and both are central to define the subdivisions and biozonation of the Famennian. From north to south, in NW Algerian Sahara and on the northern Gondwanan margin, three sedimentary basins were studied: the Bechar basin in the north (Ben-Zireg); the Ougarta basin (Saoura) in the south, and the Timimoun basin (Gourara) further south. During the Late Devonian and especially the Famennian, these regions had epicontinental sea as a consequence of paleocontinental collision and the extension of carbonate platforms. This led to the development of “griotte” facies, as a mixed sedimentation (clay-sandstone-limestone) controlled by tectonic activity (subsidence and resistance) and deposited in different sedimentary environments ranging from a shallow platform to a deep subsiding basin. In these basins, the generic ammonoid (Goniatitida, Clymeniida) biodiversity is interesting especially in the red carbonate facies of griotte types, highly rich in ammonoid macrofauna. Here, 13 families with 28 genera were identified, distributed unequally among families. This pelagic fauna enabled us to examine biodiversity at the generic level of this faunal group. The objective was to show fluctuations in the indices of diversity between the different sectors. The generic diversity and abundance index show fluctuating values among the respective sectors, with a higher relative abundance in the Saoura sector (Ougarta).