The Fayum is a region and an important fossil Lagerstätte in northern Egypt. The region comprises the Fayum Basin, which is intensively used for agriculture, and adjoining areas; the important areas of discovery are mostly north and west of Lake Qarun. The Wadi al-Hitan, known for its numerous whale fossils and, since 2005, a UNESCO World Natural Heritage Site, forms the south-western end. The deposits of the Fayum belong to various geological formations. They are mainly composed of limestone, siltstone and sandstone. The lower sections consist of marine sediments, while the upper, continental sediments were formed in a coastal landscape. The formation period ranges from the Middle to the Upper Eocene to the Lower Oligocene, which corresponds to an age of around 41 to 28 million years ago. The entire sedimentary complex is overlain by basalt, which dates back to volcanic activity around 24 million years ago.
The very rich fossil evidence of the Fayum includes plants, invertebrates and vertebrates, and numerous trace fossils have also survived. Vertebrates include fish, reptiles, birds and mammals. Some forms represent important evolutionary links in the development of individual lineages, particularly in the proboscideans, manatees and cetaceans. Among the fossil primates are early forms of Old World monkeys. In addition, marsupials, tenrec-like, even-toed ungulates, bats and rodents also occur. Some groups such as the giant herbivorous Embrithopoda or the predatory Hyaenodonta or the insectivorous Ptolemaiida have no descendants living today. Due to this diversity, the Fayum is the most important fossil site of the African Paleogene. On the basis of the terrestrial vertebrates, a delta-like landscape crisscrossed by watercourses can be distinguished. landscape near the sea coast under tropical climate conditions can be reconstructed.
The first fossil finds in the Fayum date back to the middle of the 19th century. A major phase of investigation took place at the transition from the 19th to the 20th century, when English, American, German and French researchers were active on the site at different times. During this time, numerous fossils were recovered; this led to some important discoveries that contributed to the supra-regional fame of the Fayum region. In addition, the first investigations into geology were also carried out. Modern research began in the 1960s and continues to this day. It is organized internationally. Analyses of the finds lead to the description of new fossil forms from the Fayum almost every year.
Geographical location
The Fayum region covers an area of around and is located around southwest of Cairo, situated west of the Nile and in the middle of the Libyan Desert. The center is formed by the Fayum Basin, a depression area of about . It has a triangular shape with the tip pointing south. The central town is Faiyum, which is also the capital of the Faiyum Governorate. In the north of the basin lies the approximately large Lake Qarun, a drainless lake, which has a length of from northeast to southwest, an average depth of around and a maximum depth of . The island of Geziret el-Qorn rises out of the water as a single land mass. Lake Qarun (German for "Lake of Horns", after the two pointed peninsulas that reach into the lake from the north) is the largest lake in northern Africa, but it is only the remnant of an even larger lake. This existed in the prehistoric and historic past and is known as Lake Moeris. The depression descends from south to north. While the central town of al-Fayyūm is around above sea level, the water surface of Lake Qarun is around below sea level. The entire Fayum basin is used for agriculture, with two water collectors (El Bats in the east and El Wadi in the west) draining the excess water into Lake Qarun.
The surroundings of the Fayum Basin consist largely of desert-like terrain. In the east, a wide ridge separates the depression from the Nile Valley, its upper edge is about above sea level. These marginal mountains show an approximately wide breakthrough, through which the Bahr Yussef also runs. The canal connects the Nile with the Fayum depression over a length of . It ends at al-Fayyūm and branches out here into numerous small branches.
To the south is the small basin of el-Gharaq, which has a maximum depth of below sea level. It is followed by the Wadi el-Rayyan in the southwest and west of the Fayum basin. This is an approximately large depression, with its deepest point at about below sea level. The Wadi is fed by its own springs and is today partly filled by lake El Rayan, a two-part artificial lake measuring respectively.
However, the northern border of the Fayum basin is significant, where several escarpments rise. They run from southwest to northeast, over a length of around , and are separated from each other by plateau-like plains. The terrain thus rises from Lake Qarun at its lowest point to an average of above sea level. The most important escarpments from south to north are the Birket Qarun Escarpment, the Qasr el-Sagha Escarpment and the Gebel Qatrani Escarpment. In between, there are smaller steps, such as the el-Ekhwat Escarpment and the Talata Escarpment.
The south-western end of the escarpments marks the Wadi al-Hitan ("Valley of the Whales" or Zeuglodon Valley), around from Lake Qarun. The area has been a UNESCO World Natural Heritage Site since 2005. It is a broad, flat, approximately long valley that is not an actual wadi in the geomorphologic sense. It is bordered to the northwest by the Birket Qarun Escarpment. In the southwest, on the other hand, a series of flat-topped hills forms the end and are called the "border hills". These two geographical boundaries narrow the valley from about wide in the northeast to about in the southwest. About further northeast towards the Fayum basin, another group of hills extends, among them the Garet Gehannam, which rises about above the surrounding area as an important landmark.
Geology General and underground
The geological situation of the Fayum region has been the subject of intensive research since the end of the 19th century. Significant work on this was carried out in 1905 by Hugh John Llewellyn Beadnell, published in 1988 by Thomas M. Bown and Mary J. Kraus, and in 1992 by Philip D. Gingerich. The Fayum Basin is a tectonic structure that was formed in the Triassic underground. However, rock layers from this period, such as the Bahariya Formation, only come to the surface in the outermost parts of the region, for example in the north-east. The main faults run from southwest to northeast and belong to the Syrian arc fold belt, which runs in an S-arc from the Levant across the Sinai Peninsula to North Africa. They are also responsible for the formation of the large escarpments north of Lake Qarun. There are also subordinate fault zones running from northwest to southeast and from east to west. They frame the Fayum Basin on all sides. It can, therefore, be assumed that the basin was formed by tectonic tensile forces. These formed the depression in the transition from the Oligocene to the Miocene, possibly in connection with local volcanism. In the region itself, mainly Eocene and Oligocene deposits are formed, with a total thickness of up to .
Eocene to Oligocene sedimentary sequence Mokattam Group
The Fayum region's base is generally assigned to the Mokattam group (also called the Wadi el-Rayyan series), named after Gebel Mokattam east of Cairo. It is of marine origin and consists of four rock units: the Muweilih Formation, the Midawara Formation, the Sath El-Hadid Formation and the Gharaq Formation. All four formations are composed of limestones, but they differ in their structure and in the content of nummulites and glauconites. The upper end of the Mokattam Group is defined by a rapid decrease in nummulites and an increase in glauconites. The Gharaq Formation is the most widely outcropped unit of the Mokattam Group in the region and is mostly found in the southwestern Fayum area from Wadi el-Rayyan to the southern part of Wadi el-Hitan and to Garet Gehannam.
Maadi Group The Gehannam Formation (also called the ravine beds) is the base member of the Maadi Group. It consists mainly of marine clays, siltstones and sandstones, into which marls and clayey limestones are incorporated. Their total thickness is around . The base consists of glauconitic claystone/siltstones, which are finely laminated and merge upwards into limestone-rich sandstones. This is followed by siltstone, limestone and marls. In some outcrops, limestone again forms the upper end. In some cases, individual gypsum layers are embedded in the upper sections of the Gehannam Formation. The Gehannam Formation is particularly well exposed in the western Fayum area near Wadi el-Hitan and at Garet Gehannam. It also forms the bedrock of most of the cultivated land in the basin.
All other formations are largely distributed in the escarpments north of Lake Qarun. The Birket Qarun Formation forms the lower escarpment immediately to the north of Lake Qarun, the Birket Qarun Escarpment. It presents itself as a rock unit up to thick, whose main components are composed of fine to very fine sands and silts, some of which are highly calcareous. Basically, there is a sandstone rich in sea urchins, which is referred to as Schizaster-lybica sandstone. Gypsum precipitates are formed in individual areas. In general, the deposits can be traced back to a coastal sea. In the outcrops to the north of Lake Qarun, they appear as a uniform sedimentary complex, which fans out to the west towards the Wadi el-Hitan and interlocks with the Gehannam Formation in its lower and middle sections. Here, the Birket-Qarun Formation can be subdivided into four individual bodies, which can generally be clearly separated from the Gehannam Formation. A conspicuous feature is a series of narrow, sometimes only thick, block-like sandstone layers, the uppermost of which is known as the Camp White Layer. The latter is very striking, as it contains numerous whale bones and conspicuous vertical structures, which are interpreted either as roots of mangrove or burial traces of the trace genus Thalassinoides. The Camp White Layer is interpreted in some older works as a boundary layer between the Gehannam and Birket-Qarun formations; however, more recent investigations see it within the upper rock unit.
The Garet-el-Naqb Formation was only defined as a possible rock formation in 2014, but it had already attracted attention as a special formation before then. It is a dark gray clay whose thickness increases from south to north. It reaches its greatest thickness north of the Wadi el-Hitan at around . The rock unit occurs largely only in the western Fayum region; it is not documented north of Lake Qarun. In the outcrops of the western Fayum, the Garet-el-Naqb Formation divides the Birket-Qarun Formation as a strikingly dark horizon or directly overlies the Gehannam Formation.