Qasr-el-Sagha formation

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The Qasr-el-Sagha Formation is a sedimentary formation in the Fayyum Basin of northern Egypt . The shallow sediments are primarily of marine origin and come from the Upper Eocene . She is the carrier of many Fayyum fossils .

Name and initial description

The formation was created by Hugh John Llewellyn Beadnell described in 1901 for the first time by him to Qasr el-Sagha ( Arabic : Golden Fortress named an unfinished, about 10 kilometers north of) Qarun lake lying temple complex from the Middle Kingdom .

stratigraphy

Whale skeleton in Wadi al-Hitan, in the background the transition area from the Birket-Qarun formation to the Qasr-el-Sagha formation

The 175 to 200 meters thick Qasr-el-Sagha Formation , originating from the Priabonian , overlays the sandbar sandstones of the Birket-Qarun Formation , but can still erosively reach down almost to the Gehannam Formation below . It consists mainly of fine-grain sandstones , siltstones and dark claystones , but formation-internal parasequences can also be enriched in shells at their upper limits . The layers lie flat (angle of incidence less than 1 ° to the NW) and are quite regularly banked. The continental Gebel Qatrani Formation from the Lower Oligocene ( Rupelian ) , containing mangrove remains, lies discordantly over the Qasr-el-Sagha Formation .

The Qasr el Sagha Formation built up of the following layer members ( engl. Member ) to:

  • You Abu Lifa Member - Deltafazies
  • Temple Member - inner lagoon area with shill limes
  • Harab Member - middle lagoon area
  • Umm Rigl Member - outer lagoon area

A gradual flattening of the sedimentation area can be seen within the Qasr-el-Sagha formation. During the sedimentation of the basal Umm Rigl member based on sequence stratigraphic results, there was still a sea high level, but regressive tendencies were already noticeable from the Harab member onwards, which ended in the advance of a delta during the Dir Abu Lifa member . Within the individual layers, however, there was always a gradual rise in sea level at the beginning, which was accompanied by a sudden drop towards the end of the respective sequence. The drop in sea level at the end of Dir Abu Lifa Member was drastic and reached 90 meters; it marks the transition from the Priabonian to the Rupelian (so-called Grande Coupure at the turn of the Eocene / Oligocene with great extinction of species and deterioration in the climate). In this context, 76 meters of sediment were removed from the discordance following the Dir Abu Lifa Member .

Harab member

During the sedimentation of the Harab member , delta arms cut deep into the Umm Rigl member and the underlying Birket-Qarun formation ( incised valley fill ).

Temple Member

The Temple Member has conglomerate mussel shells ( Schillkalke or Coquina ), which Bown & Kraus in 1988 interpreted as fossil beach lines. However, this interpretation is contradicted by PD Gingerich in 1992.

You Abu Lifa Member

The Dir Abu Lifa Member is made up of huge, obliquely layered sandstone bodies, which, however , can contain intermediate layers of scleractine corals and other marine invertebrates . This member is also crossed by delta arms cut into the subsoil. It usually ends with a layer of limestone only 2 meters thick , the so-called bare limestone . In places, however, a second sandstone sequence has been preserved above the limestone horizon.

The discordance to the Oligocene Gebel-Qatrani Formation is regionally important, namely it can still be observed in the Cairo area and in the eastern desert.

Age

On the basis of the mollusc fauna , P. Oppenheim was able to determine an Upper Oocene age for the Qasr-el-Sagha formation as early as 1903. There is no absolute age for the formation yet. Its upper limit coincides with the Priabon-Rupel transition and is therefore around 34 million years old. The lower limit is slightly above the transition between Bartonium and Priabone, i.e. H. at around 37 million years BP .

Simultaneous or equivalent formations in northern Egypt are the Wadi Hof Formation (eastern desert) and the Maadi Formation (Cairo area).

Fossil content

The fossils in the Qasr-el-Sagha Formation were mainly washed into the various detritic delta arms. The following significant finds were made, among others:

Reptiles

Mammals

Paleogeography

The lagunar to the beach near Qasr-el-Sagha formation was deposited in the Tethys Sea on the then unstable, slowly sinking, passive continental margin of North Africa (Egypt). The coast passed through northern Egypt at this time in a WSW-ONE direction. During the Eocene (and also in the Oligocene) continental sediments slowly progressed north and west with a simultaneous long-lasting decline in sea level. This explains why shallow marine and continental sequences overlay deeper marine sequences in large parts of northern Egypt.

See also

Web links

Individual evidence

  1. ↑ M. Blanckenhorn: New geological-stratigraphic observations in Egypt . In: Session reports of the mathematical-physical class of the Royal Bavarian Academy of Sciences . tape 32 . Munich 1903, p. 353-433 .
  2. ↑ HJL Beadnell: The Fayum depression: a preliminary notice of the geology of a district in Egypt containing a new Palaeogene vertebrate fauna . In: Geol. Mag. Band 8 (IV), 1901, pp. 540-546 .
  3. ↑ CF Vondra: Upper Eocene transitional and near-shore marine Qasr el Sagha Formation, Fayum Depression, Egypt . In: Ann. Geol. Surv. Egypt . tape 4 , 1974, p. 79-94 .
  4. ↑ TM Bown, MJ Kraus: Geology and paleoenvironment of the Oligocene Jebel Qatrani Formation and adjacent rocks, Fayum Depression, Egypt . In: US Geol. Surv. Prof. Pap. Volume 1452 , 1988, pp. 1-60 .
  5. ↑ PD Gingerich: Marine Mammals (Cetacea and Sirenia) from the Eocene of Gebel Mokattam and Fayum, Egypt: stratigraphy, age, and paleoenvironments . In: Univ. Michigan Pap. Paleont. tape 30 , 1992, pp. 1-84 .
  6. ^ P. Oppenheim: On the knowledge of ancient tertiary fauna in Egypt . In: Palaeontographica . tape 30 . Stuttgart 1903, p. 1-164 .