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A New Early Visean Coral Assemblage from Azrou-Khenifra Basin, Central Morocco and Palaeobiogeographic Implications Sergio Rodríguez1,2* , Ian D

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A New Early Visean Coral Assemblage from Azrou-Khenifra Basin, Central Morocco and Palaeobiogeographic Implications Sergio Rodríguez1,2* , Ian D Rodríguez et al. Journal of Palaeogeography (2020) 9:5 https://doi.org/10.1186/s42501-019-0051-5 Journal of Palaeogeography ORIGINAL ARTICLE Open Access A new early Visean coral assemblage from Azrou-Khenifra Basin, central Morocco and palaeobiogeographic implications Sergio Rodríguez1,2* , Ian D. Somerville3, Pedro Cózar2, Javier Sanz-López4, Ismael Coronado5, Felipe González6, Ismail Said1 and Mohamed El Houicha7 Abstract A new early Visean coral assemblage has been recorded from turbidite facies in the southern part of the Azrou- Khenifra Basin, northwest of Khenifra, central Morocco. The newly discovered Ba Moussa West (BMW) coral fauna includes Siphonophyllia khenifrense sp. nov., Sychnoelasma urbanowitschi, Cravenia lamellata, Cravenia tela, Cravenia rhytoides, Turnacipora megastoma and Pleurosiphonella crustosa. The early Visean age of the coral assemblage is supported by foraminiferal and conodont data, with the recognition of the basal Visean MFZ9 Zone. This confirms that the first transgression in the Azrou-Khenifra Basin was during the earliest Visean. The allochthonous coral assemblage was recovered from coarse-grained proximal limestone debris flow and turbidite beds within a fault- bounded unit, lying to the west of a thrust syncline containing upper Visean limestones. No evidence exists of the former early Visean shallow-water platform from which the corals were derived. All other in situ platform carbonate rocks around the southern margin of the Azrou-Khenifra Basin are probably of late Visean (Asbian–Brigantian) age. The early Visean Ba Moussa West coral fauna can be compared with that at Tafilalt in eastern Morocco, as well as in other Saharian basins of Algeria. Many of the genera and species in the Ba Moussa West assemblage are identical to those in NW Europe, with which it must have had marine connections. The new rugose species described, Siphonophyllia khenifrense, is probably endemic to North Africa. Its ecological niche in NW Europe was occupied by S. cylindrica or S. aff. garwoodi. Keywords: Mississippian, Visean, Corals, Foraminifers, Conodonts, Palaeobiogeography, Morocco 1 Introduction succession was considered quite continuous from the Mississippian rocks are common in the Moroccan Me- Devonian to the Serpukhovian (Michard et al. 2010). seta. They have been studied and described by French However, sedimentation in the eastern part of the cen- geologists since the beginning of the twentieth century tral Meseta (Azrou-Khenifra Basin) is more complicated. (Lecointre 1926; Termier 1936; Termier and Termier It took place in both a shallow-water carbonate platform 1950; Gigout 1951, etc.). The Mississippian stratigraphic and a deeper water flysch basin, within a tectonically ac- successions are clearly different in the western and in tive setting, involving movements of blocks, and trans- the eastern parts of the Meseta. The stratigraphy in both gressions and regressions that produced some gaps and areas, as well as in other regions from Morocco, has unconformities. Sedimentation during the Tournaisian, been summarized by Beauchamp and Izart (1987), early and mid Visean in the basin is regarded as being Hoepffner et al. (2005) and Michard et al. (2010). The absent by some authors (Huvelin 1969; Beauchamp and Izart 1987), whereas continuous or sporadic sedimenta- tion during that time interval is suggested by others * Correspondence: [email protected] (Bouabdelli 1989; Huvelin and Mamet 1997; Michard 1GEODESPAL, Universidad Complutense de Madrid, c/José Antonio Novais. 12, 28040 Madrid, Spain et al. 2010). 2Instituto de Geociencias (CSIC, UCM), c/ José Antonio Novais 12, 28040 The purpose of this paper is to report the recent dis- Madrid, Spain covery of a relatively rich Mississippian (early Visean) Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Rodríguez et al. Journal of Palaeogeography (2020) 9:5 Page 2 of 20 coral fauna in the southern part of the Azrou-Khenifra The limestones are variable in composition and texture, Basin, to describe the corals in detail and their host comprising coarse-grained, bioclastic and lithoclastic calcir- limestone rocks, as well as to comment on their com- udites, rich in crinoids, thick-shelled brachiopods and rela- parison and affinity with other coeval coral assemblages tively abundant corals. The limestone beds consist of in North Africa, Europe and SW Asia. The microfossil numerous sedimentary events. Some have sharp, erosive content was also studied to enhance the biostratigraphic bases and show grading with laminated tops. Large angular discussion and significance of the coral fauna. lithoclasts of sandstone and siltstone (up to 20 cm in diam- eter) occur in some beds (Fig. 2b–d). Other limestones are 2 Geological setting buff weathered, fine-grained, laminated calcarenites. Under The beginning of Carboniferous sedimentation in the the petrological microscope two microfacies are differenti- Khenifra region, which lies in the southern part of the ated. The first microfacies, which is less common, is a lami- Azrou-Khenifra Basin and contains the largest Mississip- nated crinoidal wackestone-packstone containing small pian outcrops in the eastern central Meseta, is usually fragments of crinoidal plates, corals and bryozoans. The considered to occur within the widely known late Visean second one, which is dominant, is a polymictic rudstone transgression (Huvelin 1969; Chanton-Güvenç et al. 1971; with fragmented corals, crinoids, bryozoans, brachiopods, Semenoff-Tian-Chansky 1985; Beauchamp and Izart 1987; trilobites, gastropods, bivalves, foraminifers and angular to Michard et al. 2010; Aretz and Herbig 2010; Rodríguez subangular grains of quartzite (Fig. 2b) sandstone and silt- et al. 2012;Somervilleetal.2012;Saidetal.2013). How- stone (Fig. 2e, f). The disposition of siliciclastic clasts and ever, Huvelin and Mamet (1997) cited two early Visean bioclasts is random in some beds (Fig. 2e), suggesting rapid transgressions. The first one is imprecisely located as “to sedimentation, but in some beds, most clasts are disposed the north of Ba Moussa (point 1)”. The second one was mainly parallel to the stratification (Fig. 2c). The fragmenta- equated with the base of V2b (= Cf5 Zone of Conil et al. tion of bioclasts is also variable. 1990; Livian or Holkerian) of mid Visean age. The limestones can be regarded as proximal debris In the southwestern margin of the Azrou-Khenifra flow and multistorey high-density turbidite bodies, with Basin at Sidi Lamine and Tabainout (Fig. 1b), a thick numerous event beds, deposited in a prevailing succes- shallow-water carbonate succession with basal Mississip- sion of distal turbidite beds. Thus, the coral assemblage pian conglomerate and sandy limestone can be seen to is allochthonous and may have been transported far rest unconformably on older (Ordovician) tilted silt- from its original depositional shelf setting. stones and sandstones (Aretz and Herbig 2010; Somer- ville et al. 2012; Said et al. 2013). A similar relationship 3 Methodology is seen at the southeastern margin of the basin at Tioui- The two limestone horizons (BMW1 and BMW2) were nine (Fig. 1b) where shallow water sandy limestones rest sampled and corals were collected. Samples from BMW1 unconformably on red Ordovician sandstones (Rodrí- contain almost entire brachiopods and corals (Fig. 2d), guez et al. 2012). whereas in BMW2 most bioclasts are completely broken The eastern part of the Azrou-Khenifra Basin, north- and very few coral specimens are identifiable at generic or west of Khenifra, is a region of mostly deep-water ryth- specific level. The coral assemblage is relatively rich, but mic mudstones. However, recent field investigations at their diversity is quite low (5 genera and 7 species). The Ba Moussa West, northwest of a nappe folded as a N–S- assemblage comprises solitary rugose corals and tabulate trending syncline, and approximately 3 km northwest of colonies. Many corals are well preserved and nearly Khenifra city margins (Figs. 1 and 2a), have discovered complete, missing only the apexes and showing sometimes two pale gray weathering limestone units within a thick compressed calices when they show few skeletal elements dark gray siltstone and shale rhythmic succession. These and are filled with muddy sediment. However, others are limestones contain abundant corals that form the focus completely fragmented or crushed or have lost much of of this paper. The limestone units form two distinct par- their dissepimentaria. Fifty specimens were collected, of allel ridges, some 50 m apart, and traceable laterally for which 38 have been definitively identified. over 200 m (Fig. 1c). They form prominent features on Thin sections of samples were studied to describe the the landscape, compared to the subdued topography of microfossil content. Owing to the brecciated character the more easily eroded mudstones which encase the of many beds, including boulders of large size, only the limestones (Fig. 2a). The beds dip steeply to the east fine-grained limestones yield foraminifers. Assemblages (70°) and in places can be vertical
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