Geology, biostratigraphy and carbon isotope chemostratigraphy of the Palaeogene fossil-bearing Dakhla sections, southwestern Moroccan Sahara (original) (raw)
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The sabkha of Gueran in the Southwest Moroccan Sahara has yielded a rich and diverse fauna of late middle Eocene vertebrates that include the world's richest Bartonian age archaeocete assemblage. Archeocete remains were described previously and here we report on the rest of the vertebrate fauna. The Gueran fauna includes abundant chondrichthyan species belonging to Lamniformes, Carcharhiniformes and Rhinopristiformes, and actinopterygian assemblage consisting of Cylindracanthus, of a siluriform, and of Perciformes. Turtles are represented by at least two marine taxa referred to as Cheloniidae and Dermochelyidae. Crocodylian remains belong to at least two longirostrine species, including gavialoid remains. Snakes are represented by Pterosphenus cf. schweinfurthi (Palaeophiidae). Seabirds are represented by a pseudo-toothed bird (Pelagornithidae). The avian fossil belonged to a gigantic soaring bird and constitutes the earliest occurrence of the genus Pelagornis. The presence of proboscideans is attested by dental fragments. This fossil assemblage from Gueran shows affinities with those of the Eocene beds of Egypt and Libya. The numerous shared taxa support a close biogeographical connection between faunas from southeastern and southwestern coasts of the Mediterranean Sea.
The oldest Eocene marine vertebrate fauna from the Sahara desert in southwestern Morocco
2022
The Sabkha of El Breij has yielded the oldest marine Eocene vertebrate fauna known from the Sahara Desert in southwestern Morocco. Fossils come from three distinct layers in the Samlat Formation sequence. Selachian teeth are abundant in all levels. The selachian assemblage in the lower level indicates a Lutetian-early Bartonian age. The selachian taxa of the two upper levels indicates an upper Bartonian age. The lower horizon yields abundant fossil remains of two protocetids, the very large Pappocetus lugardi and a smaller medium-sized protocetid. Protocetids are associated with rare remains of bony fishes, turtles, crocodyliforms and a paleophiid snake (cf. Palaeophis moghrebianus). The two upper fossiliferous levels (Bartonian) are located about twenty meters above the lower level. They yielded remains of three genera of Basilosauridae: Chrysocetus, Platyosphys, and Eocetus, associated with abundant chondrichthyans, and remains of bony fish, turtles, crocodyliforms, and seabirds. Turtles are represented by a pleurodire species of the subtribe Stereogenyina, probably Cordichelys antiqua, and another pleurodire form which remains to be determined. The crocodile vertebrae show that it is a Eusuchian and the shape of the quadrate suggests a gavialoid. The two specimens of pseudo-toothed birds (Odontopterygiformes, Pelagornithidae) are tentatively assigned to the genus Pelagornis, which together with Pelagornis from the Bartonian of Gueran constitutes one of the earliest records of this genus.
The Oldest Eocene Marine Vertebrate Fauna from the Sahara Desert in Southwestern Morocco. MEDGU24
MEDGU, 2024
The Sabkha of El Breij has yielded the oldest marine Eocene vertebrate fauna from the Sahara Desert in southwestern Morocco. Fossils come from three distinct layers in the Samlat Formation sequence. Selachian teeth are abundant at all levels. The selachian assemblage in the lower level indicates a Lutetian-early Bartonian age. The selachian taxa of the two upper levels indicates an upper Bartonian age. The lower horizon yields abundant fossil remains of two protocetids, the very large Pappocetus lugardi and a smaller medium-sized protocetid. Protocetids are associated with rare remains of bony fishes, turtles, crocodyliforms, and a paleophiid snake (cf. Palaeophis moghrebianus). The two upper fossiliferous levels (Bartonian) are about 20 m above the lower level. They yielded remains of three genera of Basilosauridae: Chrysocetus, Platyosphys, and Eocetus, associated with abundant chondrichthyans, and remains of bony fish, turtles, crocodyliforms, and seabirds. Turtles are represented by a pleurodire species of the subtribe Stereogenyina, probably Cordichelys antiqua, and another pleurodire form remains to be determined. The crocodile vertebrae show that it is a Eusuchian, and the shape of the quadrate suggests a gavialoid. The two specimens of pseudotoothed birds (Odontopterygiformes, Pelagornithidae) are tentatively assigned to the genus Pelagornis, which together with Pelagornis from the Bartonian of Gueran constitutes one of the earliest records of this genus.
Vertebrate assemblages from the early Late Cretaceous of southeastern Morocco: An overview
Fossils of vertebrates have been found in great abundance in the continental and marine early Late Cretaceous sediments of Southeastern Morocco for more than 50 years. About 80 vertebrate taxa have so far been recorded from this region, many of which were recognised and diagnosed for the first time based on specimens recovered from these sediments. In this paper, we use published data together with new field data to present an updated overview of Moroccan early Late Cretaceous vertebrate assemblages. The Cretaceous series we have studied encompasses three Formations, the Ifezouane and Aoufous Formations, which are continental and deltaic in origin and are often grouped under the name ‘‘Kem Kem beds”, and the Akrabou Formation which is marine in origin. New field observations allow us to place four recognised vertebrate clusters, corresponding to one compound assemblage and three assemblages, within a general temporal framework. In particular, two ammonite bioevents characterise the lower part of the Upper Cenomanian (Calycoceras guerangeri Zone) at the base of the Akrabou Formation and the upper part of the Lower Turonian (Mammites nodosoides Zone), that may extend into the Middle Turonian within the Akrabou Formation, and allow for more accurate dating of the marine sequence in the study area. We are not yet able to distinguish a specific assemblage that characterises the Ifezouane Formation when compared to the similar Aoufous Formation, and as a result we regard the oldest of the four vertebrate ‘‘assemblages” in this region to be the compound assemblage of the ‘‘Kem Kem beds”. This well-known vertebrate assemblage comprises a mixture of terrestrial (and aerial), freshwater and brackish vertebrates. The archosaur component of this fauna appears to show an intriguingly high proportion of large-bodied carnivorous taxa, which may indicate a peculiar trophic chain, although collecting biases alter this palaeontological signal. A small and restricted assemblage, the OT1 assemblage, possibly corresponds to a specific, localised ecosystem within the Kem Kem beds compound assemblage. Microfossils and facies from the Aoufous Formation, corresponding to the top of the compound assemblage, provide evidence of extremely abiotic conditions (hypersalinity), and thus of great environmental instability. At the base of the Akrabou Formation the first ammonite bioevent, Neolobites, corresponds to the onset of the marine transgression in the early Late Cenomanian while the Agoult assemblage (Late Cenomanian?) contains a variety of small fish species that have Central Tethyan affinities. Finally, the youngest Mammites bioevent in the late Early Turonian corresponds to a deepening of the marine environment: this sequence is isochronous with the Goulmima assemblage, a diverse collection of fish and other marine taxa, and shows affinities with taxa from the South Atlantic, the Central Tethys and the Western Interior seaway of North America, and further highlights the biogeographical importance of these North African Late Cretaceous assemblages.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2021
We performed different geochemical analyses of Paleogene terrestrial mammal remains to establish their taphonomy, stratigraphic provenance, and palaeoenvironmental conditions. Rare earth element (REE) results indicate a similar diagenetic history to that of previously investigated marine taxa from these beds. Therefore, the mammal remains were initially deposited in a marine setting, and probably not long after the death of the animals their bodies were washed into the sea. The Ce/Ce* and Pr/Pr* ratios for the mammal fossils were compared with the background dataset from the phosphate mines, which varies with time. This allowed us to characterize the stratigraphic levels bearing the fossils. The provenances of fossils with known origins were confirmed, while remains with unknown origins could be assigned to certain stratigraphic horizons that are compatible with previously proposed phylogenic relationships. Marine diagenesis affected the various skeletal tissues differently, with the largest alteration in the bone and the least or none in the enamel. This is mostly demonstrated by the high F concentration, high Ca/P, and seawater related 87 Sr/ 86 Sr in the bone/dentine samples. Enamel shows the opposite, and retained the most pristine terrestrial values. The δ 18 O PO4 and δ 13 C results from mammal enamel revealed warm (>20°C mean annual temperature-MAT) and dry (<500mm mean annual precipitation) conditions for Paleocene-Eocene period in the region. From the early to mid-Ypresian about +5°C ∆MAT is recorded that might be linked to the Early Eocene Climatic Optimum. Furthermore, the 87 Sr/ 86 Sr ratios derived from shark tooth enameloid fit the global open ocean Sr-isotope record during the latest Paleocene and early Eocene providing further evidence for the age of these phosphate beds in the Ouled Abdoun Basin. However, older marine fossils yielded higher ratios than the global Sr-isotope curve, reflecting an alteration and/or somewhat restricted conditions in the Moroccan coastal basins, possibly triggered by global sea-level changes.
Through the Late Jurassic and Early Cretaceous, the southern shore of the Tethys Ocean migrated north and south over short distances. These vicissitudes are documented in the ‘continental intercalaire’, a long series of mainly non-marine sediments deposited across North Africa. A combined taxonomic, physical and chemical taphonomic study provides independent lines of evidence for reconstruction of palaeoenvironments within this marginal marine setting. The Douiret, Chenini and Oum ed Diab formations from the Tataouine basin of southern Tunisia span the later part of the Early Cretaceous. Microvertebrates from four sites in these formations show different modes of physical abrasion, time averaging, and mixing, based on a taphonomic analysis using a combination of physical and chemical methods. The taxonomic composition of each assemblage, and trends in rare earth element (REE) compositions of bones, from each locality were used as independent lines of evidence to indicate differences in early depositional environments. The Jebel Boulouha assemblage (Douiret Formation) is interpreted as a terrestrial carbonate-rich environment with relatively little mixing. The Touil el Mra assemblage (Oum ed Diab Formation) suggests a marginal marine environment with some mixing of previously interred bones. The Oued el Khil assemblage (Chenini Formation) and the Oum ed Diab assemblage (Oum Ed Diab Formation) are more equivocal, suggesting mixed freshwater and marine influences. Interpreting salinity in marginal marine settings is difficult, and best attempted from multiple, independent lines of evidence. We suggest that REE geochemistry can contribute to palaeoenvironmental reconstruction when used in combination with other, independent physical, palaeontological and /or geochemical methods.
The discovery of Upper Miocene vertebrates at Tizi N'Tadderht in the Ouarzazate basin (Morocco) helps to fill a gap in our knowledge of Neogene faunas in North Africa. The new fauna includes an ostrich cf. Struthio sp, a turtle cf. Centrochelys sp., Crocodylus cf. niloticus, and a relatively diverse fauna of large mammals. The mammal assemblage probably includes three hipparion species, including a very small form not previously reported from Africa, aff. Cremohipparion periafricanum, two species of rhinoceros cf. Ceratotherium sp. and aff. Chilotherium sp., a Proboscidean cf. Tetralophodon sp., a large member of the Giraffidae similar to "Palaeotragus" germaini and two bovids of which one is likely related to Prostrepsiceros, while the other is a new medium-sized antelope with spiral horns, certainly a representative of the Caprinae, a group that is rare in Africa. A late Miocene age, corresponding to the European Turolian Mammal age, is most likely for this fauna.
The Maastrichtian to Ypresian dated sediments of the Tahar Cut [1, 2], Western Outer Rif (Northwest Morocco), are studied here for paleoenvironmental and paleoclimatic reasons. The results of quantitative and qualitative analyses of dinoflagellate cysts and other palynomorphs of continental origin (spores and pollen) allowed the reconstruction, in ascending order, of twelve different marine depositional environments: (1) outer neritic without productivity and thus without continental influence at the base of the section (Th1-Th3: Upper Maastrichtian); (2) inner neritic without productivity (Th4: Upper Maastrichtian:); (3) shallow outer neritic with low productivity (Th5-Th7: Upper Maastrichtian); (4) inner neritic in a phase of marine regression and widespread cold climatic conditions at the end of the Maastrichtian (Th7a-Th7b': Upper Maastrichtian); (5) outer neritic of very low productivity marking thus a slight marine transgression (Th7c : Danian); (6) inner neritic, reflecting a relative decrease in sea level (Th7d: Danian); (7) outer neritic with very low biological productivity for interval G, reflecting a rise in sea level compared to the previous interval (Th7e-Th7f: Selandian-Thanetian); (8) indeterminate paleoenvironment due to the scarcity of palynomorphs in this interval (Th8: Selandian-Thanetian); (9) marine oceanic without productivity which would result in a marine transgression (Th8a: Selandian-Thanetian); (10) neritic external (Th9: Selandian-Thanetian); (11) neritic internal without productivity for the K interval with a drop in sea level, under relatively warm climatic conditions (Th9a: Ypresian); (12) outer neritic, which would result in a marine transgression (Th10-Th11: Ypresian). These variations in paleoenvironments coincide with global climate changes at the Cretaceous-Paleocene (K-Pg) and Paleocene-Eocene (P-E) boundaries.