Jebel Qatrani Formation

The Jebel Qatrani Formation (also Gebel Qatrani, Gabal Qatrani or Djebel Qatrani) is a geologic formation located in the Faiyum Governorate of central Egypt. It is exposed between the Jebel Qatrani escarpment and the Qasr el Sagha escarpment, north of Birket Qarun lake near Faiyum. The formation conformably overlies the Qasr el Sagha Formation and is topped by the Widan el Faras Basalt. The age of the formation has been subject to debate, but the most recent research indicates that it covers both the latest parts of the Eocene and the Early Oligocene, spanning over the boundary between these two time periods.

The geology and fauna of this formation gives a good idea of the environment and animals present during this time period. Research suggests that the Jebel Qatrani Formation featured a mix of subtropical to tropical forest, lowland swamps and marshes, ponds and rivers that would empty northward into the Tethys Sea. This is supported by the presence of water-dependent fauna including podocnemidid turtles, crocodilians, sea cows, various fish, jacanas, early flamingo-relatives, ospreys, herons and shoebills.

Besides these, the fossil record of the Jebel Qatrani Formation is especially well known for its value to understanding the early evolution of many modern mammal groups. Primates are represented by over a dozen genera, several forms of early elephants have been recovered from the sediments including the terrestrial ''Phiomia'' and the semi-aquatic ''Moeritherium''. The fossil rodents of the formation meanwhile are thought to be an important link between the African phiomorphs ( dassies, old world porcupines, mole rats and cane rats) and the caviomorphs of South America (capybaras, chinchillas and new world porcupines). Besides these early members of groups that would later rise to prominence, the formation was also home to a variety of unique groups no longer found today or only found in a greatly diminished diversity. This includes the enigmatic, possibly carnivorous ptolemaiids, large hyaenodonts, a vast number of highly diverse hyracoids including species the size of rhinos, anthracotheres and the bizarre embrithopod ''Arsinoitherium''.

Geography and history

Outcrops of the Jebel Qatrani Formation are present in the northern Fayum Depression southwest of Cairo. The Fayum Depression is an oasis west of the Nile in northern Egypt.

The formations of the Fayum have been studied for a significant amount of time by numerous paleontologists, with research dating back to as early as the 19th century. During this time the region was studied extensively by scientists including but not limited to Charles William Andrews, Henry Fairfield Osborn, René Fourtau and Ernst Stromer. Among the first names for what is now known as the Jebel Qatrani formation was the “Fluvio-Marine Series”, as coined by Hugh J. L. Beadnell. However, despite the bulk of research conducted in the late 19th and early 20th century, the Fayum localities would eventually enter a period of obscurity following the outbreak of World War I which continued throughout the mid 20th century and World War II. Research resumed during the 1960s, following an expedition under Elwyn LaVerne Simons. Previously, the formations of the region had been primarily known for the preservation of mammals, but Birds were also known from few specimens uncovered in the early 20th century. During the 60s, improved collection methods and additional expeditions by the Yale and Duke University gathered much additional material in association with the Egyptian Geological Survey and the General Petroleum Company. Around the 70s, the scope of the expedition was broadened to account for more diverse fields of study, leading to more precise datings of the strata.

Geology and stratigraphy

The formation overlies the Eocene Qasr el Sagha Formation and is overlaid by the Oligocene Widan el Faras Basalt. The formation contains at least two major fossil bearing layers, one in the upper sequence, which is used to refer to the top layers of the formation, and a second in the lower sequence. These two layers have also been called the Upper and Lower Fossil Wood Zones in older publications. Both sequences of the Jebel Qatrani Formation are separated from one another by the so-called Barite Sandstone, a layer with a thickness of .

The dating of the Jebel Qatrani Formation has historically been under debate, with some research having placed it either entirely within the Eocene or Oligocene and some arguing that it spans both periods. Rasmussen and colleagues for instance argued that the central Barite Sandstones separating both fossil bearing layers mark the exact Eocene-Oligocene Boundary. Part of the reasoning for this connects to the primate fauna of the formation, with propliopithecids and parapithecines only appearing in the upper localities. Other dating methods meanwhile have generally not been applicable. According to Seiffert, the mammal fauna of the formation on its own is too endemic and marine invertebrates are absent, preventing biostratigraphic dating. Radioisotopic dating was conducted on the overlying Widan el Faras Basalt, however the results of this suggested an age of 23.6 million years for its lower units, much younger than prior estimates for the Jebel Qatrani Formation. However, in a 2006 publication Seiffert draws a comparison between the Fayum fauna and the fossil record of the Ashawq Formation in Oman, which notably preserved vertebrates as well as foraminifera useful in dating. Foraminifera biostratigraphy and magnetostratigraphy suggest that the examined localities in Oman date to approximately 31-31.5 (Taqah locality) and 33.7-33.3 Ma (Thaytiniti locality). Seiffert argues that the mammal fauna from Oman most closely resembles those found in the oldest localities of the Lower Sequence of the Jebel Qatrani Formation (L-41) and the oldest localities of the Upper Sequence (quarries G and V). The hyraxes '' Thyrohyrax'' and '' Saghatherium'' occur in both formations, as does the primate '' Moeripithecus''. More generally, both formations preserve propliopithecids and parapithecine parapithecids as well as oligopithecids. While the former two groups are restricted to the younger Fayum sequence, the latter is the most common primate family in the older sediments. Assuming the traditional interpretation of the Jebel Qatrani Formation, this would mean that many of these taxa would have had to appear 2 to 4 million years earlier in Egypt than in Oman, which is considered to be unlikely by Seiffert. According to them the formation spans approximately 8 million years, with its oldest localities situated in latest Eocene strata. Locality BQ-2 has been estimated to be 37 million years old (early Priabonian), while L-41 falls into an age range of 34.8–33.7 million years old, a timespan that includes the Eocene-Oligocene Boundary. Although an earliest Oligocene age could not be disproven by Seiffert, he argues that a latest Eocene age should be considered more likely based on an unconformity present just above the locality (one also acknowledged as a possible candidate for the EOB by Rasmussen). This means that only the lower of the formation are Eocene in age, including both the BQ-2 and L-41 localities. The remainder of the Lower Sequence, as well as the entire Upper Sequence, would subsequently fall within the Oligocene. The position of quarries A and B in regards to the boundary is ambiguous, however Quarry E on the other hand is considered without doubt Oligocene (ca. 33 Ma) in age by Seiffert.

Paleoenvironment

The environment of the Jebel Qatrani formation has been described as a subtropical to tropical lowland plain by Bown, who further suggests the presence of streams and ponds. Based on the fossil bird remains, which includes the fossils of a variety of animals highly associated with water (ospreys, early flamingos, jacanas, herons, storks, cormorants and shoebills), Rasmussen and colleagues inferred that the environment featured slow-moving freshwater with a substantial amount of aquatic vegetation, which matches the prior hypothesis. Although lithology suggests that most fossils were deposited on sandbanks after being transported by currents, the authors argue that swamps could have easily formed along the banks of the river that was present during the Oligocene and may account for the mudstone found in certain quarries. They furthermore suggest that the fossil birds of Fayum, due to their affinities with modern groups, should be considered a more valuable indicator of the environment when compared with the fossil mammals, many of which belonged to families lacking modern examples. The absence of other birds typical for such an environment may be explained either through sampling bias or due to the fact that said groups had simply not yet been present in Oligocene Africa. Generally, Rasmussen and colleagues compare the environment of Jebel Qatrani to freshwater habitats in modern Central Africa. The discovery of snakehead fossils seem to support Rasmussen's interpretation, as the genus ''Parachanna'' today prefers slow-moving backwaters with plenty of vegetation. Other fish present meanwhile, notably ''Tylochromis'', suggest that deep, open water was likewise present. The river channels may have been overgrown with reeds, papyrus and featured floating vegetation like water lilies and ''Salvinia''. In a 2001 paper Rasmussen ''et al.'' argued that the sandstone and mudstone of the formation likely formed as sediments were aggraded by a system of river channels that emptied towards the west into the Tethys. Here they reconstructed the environment as a tropical lowland swamp forest intermingled with marshes. They furthermore suggest that the environment would have experienced monsoons. Overall this indicates that this region was a part of an extensive belt of tropical forest that stretched across what is now northern Africa, which would gradually give rise to open woodland and even steppe the further one was to travel inland.

Paleobiota

Fish

Actinopterygii

Chondrichthyes

Sarcopterygii

Reptiles

Birds

Accipitriformes

Charadriiformes

Ciconiiformes

Cuculiformes

Gruiformes

Palaeognathae

Pelecaniformes

Phoenicopteriformes

Suliformes

Mammals

Afroinsectivora

Artiodactyla

Chiroptera

Embrithopoda

Hyaenodonta

Holroyd also identified several indetermined pterodontine hyaenodonts from various sequences of the Jebel Qatrani Formation, but doesn't identify them beyond subfamily level.

Hyracoidea

Marsupalia

Rodentia

Pholidota

Ptolemaiida

Primates

Proboscidea

Sirenia

Flora

See also

*
* List of fossil sites

References

{{coord missing, Egypt

Geologic formations of Egypt
Eocene Africa
Oligocene Africa
Faiyum Governorate
Geology of Egypt
Paleontology in Egypt
Eocene Series of Africa
Oligocene Series of Africa