In short: the Oulad Abdoun Basin, near Khouribga in central Morocco, is a vast phosphate deposit that preserves one of the richest marine vertebrate fossil records in the world. Its lowest fossil beds date to the Maastrichtian, the last stage of the Cretaceous, and record the oceans just before the extinction event about 66 million years ago.
Where is the Oulad Abdoun Basin?
The basin lies in Khouribga Province, roughly an hour’s drive from Casablanca. Also called the Khouribga Basin, it covers about 100 by 45 kilometres, an area of around 4,500 square kilometres. It is one of several Moroccan phosphate basins; the Ganntour Basin near Benguerir is another important source of fossils.
Why are there so many fossils?
At the end of the Cretaceous, a shallow sea covered this part of Morocco. Nutrient-rich water supported abundant marine life, and the phosphate sediments that accumulated on the seafloor preserved bones and teeth exceptionally well. Researchers describe the fossils as plentiful, diverse and well preserved, including complete skulls and articulated skeletons of mosasaurs and crocodyliforms.
The phosphates have been known since 1908 and mined since the 1920s. Large-scale mining exposes enormous volumes of fossil-bearing rock, which is a major reason so much material has been found.
A record spanning 24 million years
The Moroccan phosphate series runs from the Maastrichtian into the Eocene, about 24 million years of nearly continuous deposition. Miners and geologists divide it into layers called “Couches.” Couche III is Maastrichtian, while the higher Couches are Paleocene and Eocene. Shark fossils and chemical analysis show that the upper part of Couche III formed less than one million years before the end of the Cretaceous.
This long record is why the basin produces both Cretaceous marine reptiles and younger fossils such as the shark Otodus obliquus from the Paleocene and Eocene.
What lived in the Oulad Abdoun sea?
Mosasaurs
The Maastrichtian phosphates of Morocco contain the most diverse mosasaur assemblages known. Species include Mosasaurus beaugei, known only from these phosphates, several species of Prognathodon, the shell-crushing Globidens, the slender Halisaurus and rare tylosaurines. In 2022, researchers described Thalassotitan atrox, a giant mosasaur with a skull about 1.4 metres long and massive conical teeth, closely related to Prognathodon currii. Its discovery suggests mosasaurs were still thriving right up to the extinction.
Plesiosaurs
Plesiosaurs are rarer than mosasaurs in the phosphates. The long-necked elasmosaurid Zarafasaura oceanis is the best-known species from the basin.
Sharks, fish and more
The basin also yields large numbers of shark teeth, including Cretolamna, Squalicorax and Otodus, along with fish such as Enchodus, marine turtles and crocodyliforms such as Dyrosaurus.
Sidi Chennane
Sidi Chennane is one of the best-known phosphate mining areas within the basin. Several mosasaur species have been described from its layers, and many Moroccan fossils on the market are reported from this area.
What this means for collectors
A specimen’s locality and layer help confirm its age and identity. When you see “Oulad Abdoun Basin,” “Khouribga” or “Sidi Chennane” on a mosasaur listing, it points to these latest-Cretaceous phosphates.
Explore fossils from the Moroccan phosphates
Sources
- Muséum national d’Histoire naturelle, The phosphates of Morocco
- Longrich et al. (2022), Cretaceous Research. doi:10.1016/j.cretres.2022.105315
- First record of a tylosaurine mosasaur from the latest Cretaceous phosphates of Morocco, Open Journal of Geology (2022). doi:10.4236/ojg.2022.1211042
- New plesiosaur specimens from the Maastrichtian Phosphates of Morocco. HAL archive
- Ouled Abdoun Basin, Wikipedia