Douiret Formation

{{Short description|Geologic formation in Tunisia}} {{Infobox rockunit | name = Douiret Formation | image = | caption = | type = Geological formation | period = Barremian | age = Hauterivian-Aptian<br>~{{fossil range|129|115}} | prilithology = Sandstone, claystone | otherlithology = | namedfor = | namedby = | region = Tatouine | country = Tunisia | coordinates = {{coord|32.7|N|10.2|E|display=inline,title}} | paleocoordinates = {{coord|17.8|N|11.9|E|display=inline}} | unitof = Merbah el Asfer Group | subunits = | underlies = Chenini Formation | overlies = Boulouha Formation | thickness = | extent = | area = | map = {{Location map+ | Tunisia | relief = 1 | width = 250 | float = center | places = {{Location map~ | Tunisia | lat_deg = 32.7 | lon_deg = 10.2 | mark = Green pog.svg | marksize = 12 }} }} | map_caption = }}

The '''Douiret Formation''' is a geologic formation in Tunisia, near the Berber village of Douiret. It is part of the larger Continental Intercalaire Formation, which stretches from Algeria and Niger in the west to Egypt and Sudan in the east.<ref name="Anderson">{{cite journal|title=Palaeoenvironments of vertebrates on the southern shore of Tethys: The nonmarine Early Cretaceous of Tunisia |author= Paul E. Anderson, Michael J. Benton,⁎ Clive N. Trueman, Bruce A. Paterson, Gilles Cuny |date=2007|journal= Palaeogeography, Palaeoclimatology, Palaeoecology |volume=243 |publisher=Elsevier |issue=1–2|pages=118–131|doi=10.1016/j.palaeo.2006.07.015 |bibcode= 2007PPP...243..118A }}{{dead link|date=May 2021|bot=medic}}{{cbignore|bot=medic}}</ref><ref name="Fanti" /> The Douiret Formation is located in the Tataouine basin in southern Tunisia, stretching into Algeria and Libya, and is part of the Merbah el Asfer Group of rock formations.<ref name="Anderson" /><ref name="Fanti">{{cite journal|title= The ''Continental Intercalaire'' of southern Tunisia: Stratigraphy, paleontology, and paleoecology |author= Federico Fanti, Michela Contessi, Fulvio Franchi |date=2012|journal= Journal of African Earth Sciences |volume= 73 |issue=73–74 |publisher=Elsevier |pages=1–23|doi= 10.1016/j.jafrearsci.2012.07.006 |bibcode= 2012JAfES..73....1F }}{{dead link|date=May 2021|bot=medic}}{{cbignore|bot=medic}}</ref> The Douiret is 80 metres thick and consists of a 30-metre layer of sand beneath a 50-metre layer of clay.<ref name="Fanti" /><ref name="Tawadros">{{cite book|url= https://books.google.com/books?id=lyLOBgAAQBAJ&pg=PA475 |title= Geology of North Africa |author= Edward Tawadros |date=2 November 2011|publisher= CRC Press |access-date=23 October 2018|page=475|isbn= 9780203130612 }}</ref>

A few fossil-bearing beds have been discovered in the sand layer.<ref name="Anderson" /><ref name="Fanti" /> The fossils range from the Aptian to Albian period<ref name="Fanti" /> and include freshwater and marginal marine sharks, skates, fish, turtles, crocodilians, pterosaurs, bivalves, pollens and plants, including trees.<ref name="Fanti" /> The fish are the most abundant type of fossil found.<ref name="Anderson" /> The orientation of the fossils suggests the earlier ones were deposited by a westward flowing paleocurrent while the later ones were laid down in waves.<ref name="Fanti" /> Dinosaur remains consisting of the remains of a single indeterminate iguanodontid ornithopod are also among the fossils that have been recovered from the formation,<ref name="Fanti" /> although none have yet been referred to a specific genus.<ref name="Weishampel">{{cite book|title=The Dinosauria |edition=2nd |author=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.) |date=2004|publisher=University of California Press |location=Berkeley |pages=517–607|isbn= 0-520-24209-2 }}</ref>

The green clay layer contains plant remains (ferns and conifers), but no vertebrate or flowering plant remains.<ref name="Fanti" />

The Douiret formation dates from the Early Cretaceous period, more than 100 million years ago.<ref name="Anderson" /> Scientists have dated the sandy layer to the Hauterivian, Barremian or Aptian periods (132 to 113 million years ago) and the clay layer to the Barremian or Aptian periods (130 to 113 million years ago).<ref name="Anderson" /><ref name="Fanti" /><ref name="Tawadros" />

Based on both the geology of the formation and the fossils found, scientists agree that the sandy part of the Douiret Formation was a lush coast or more likely river delta on the shore of the Tethys Sea,<ref name="Anderson" /><ref name="Tawadros" /> but by the time of the clay layer, tectonic subsidence and the northward migration of the Tethys Sea had turned the area into a huge freshwater lagoon that periodically dried into a salt flat, hostile to vegetation.<ref name="Fanti" /><ref name="Anderson" />

== References == {{Reflist}}

Category:Geologic formations of Tunisia Category:Aptian Stage Category:Barremian Stage Category:Hauterivian Stage Category:Sandstone formations Category:Shale formations Category:Deltaic deposits Category:Paleontology in Tunisia Category:Lower Cretaceous Series of Africa