Nemegt Formation
{{Short description|Geological formation in Mongolia}}
{{Infobox rockunit
| name = Nemegt Formation
| image = Avimimus excavation.jpg
| caption = Nemegt, the type locality of the Nemegt Formation
| type = Geological formation
| age = Maastrichtian
~{{fossilrange|70}}
| period = Maastrichtian
| prilithology = Shale, sandstone
| otherlithology = Mudstone, conglomerate
| namedfor =
| namedby =
| region = Bayankhongor Aimag, Omnogov, Ovorkhangai
| country = Mongolia
| coordinates = {{coord|43.5|N|101.0|E|display=inline,title}}
| paleocoordinates = {{coord|40.8|N|90.2|E|display=inline}}
| unitof =
| subunits = Lower, Middle and Upper units
| underlies = Alluvium
| overlies = Barun Goyot Formation
| thickness = Over {{convert|235|m|ft|abbr=on}}
| extent = Gobi Desert
| area =
| map = Cretaceous-aged dinosaur fossil localities of Mongolia.PNG
| map_caption = Cretaceous-aged dinosaur fossil localities of Mongolia. Nemegt localities at area A.
}}
The Nemegt Formation (also known as Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. The formation consists of river channel sediments and contains fossils of fish, turtles, crocodilians, and a diverse fauna of dinosaurs, including birds.
Description
The Nemegt Formation is composed of mudstones and sandstones that were deposited by ancient lakes, streams, and flood plains. The Altan Uul locality was described by Michael Novacek as "a canyon carved out of a very rich series of sedimentary rocks" with "steep cliffs and narrow washes". The climate associated with it was wetter than when preceding formations were deposited; there seems to have existed at least some degree of forest cover. Fossilized trunks have been also found. These petrified wood, and the remains of Araucariaceae conifers indicate that the forests of the Nemegt were thickly wooded, with a high canopy formed by tall conifer trees. When examined, the rock facies of this formation suggest the presence of stream and river channels, mudflats, and shallow lakes. Sediments also indicate that there existed a rich habitat, offering diverse food in abundant amounts that could sustain massive Cretaceous dinosaurs.Novacek, M. (1996). Dinosaurs of the Flaming Cliffs. Bantam Doubleday Dell Publishing Group Inc. New York, New York. {{ISBN|978-0-385-47775-8}}
Stratigraphy
File:Nemegt and Baruungoyot Formations.png
The most recent stratigraphy divides the Nemegt Formation into three informal members. The lower member is dominated by fluvial deposits, while middle and upper members consist of alluvial plain, paludal, lacustrine, and fluvial deposits. The colour of the sediments is usually light grey to tan in colour in comparison to the typically red colour of the underlying Barun Goyot Formation. It overlies and sometimes interfingers with the Barun Goyot Formation. Interfingering has been noted at the stratotype (Red Walls) and Hermiin Tsav.{{Cite journal|last=Eberth|first=David A.|date=1 April 2018|title=Stratigraphy and paleoenvironmental evolution of the dinosaur-rich Baruungoyot-Nemegt succession (Upper Cretaceous), Nemegt Basin, southern Mongolia|url=https://linkinghub.elsevier.com/retrieve/pii/S0031018217305771|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|language=en|volume=494|pages=29–50|doi=10.1016/j.palaeo.2017.11.018|bibcode=2018PPP...494...29E |url-access=subscription}} There has been no absolute dating of the Nemegt Formation. Historically the Nemegt has been considered late Campanian to Maastrichtian, based on comparisons of fossils present, but no exact dating has been performed. The age for the underlying Baruungoyot Formation (= Svita) has been suggested as Santonian to Campanian, and Shuvalov (2000) found K-Ar dating of basalts that they referred to the mid and upper Baruungoyot to be 75 to 80 million years old.{{cite book|last=Shuvalov|first=V.F.|year=2000|chapter=The Cretaceous stratigraphy and palaeobiogeography of Mongolia|pages=[https://archive.org/details/agedinosaursruss00bent/page/n294 256]–278|editor-last=Benton|editor-first=Michael J.|editor2-last=Shishkin|editor2-first=Mikhail A.|editor3-last=Unwin|editor3-first=D.M.|editor4-last=Kurochkin|editor4-first=E.N.|title=The Age of Dinosaurs in Russia and Mongolia|url=https://archive.org/details/agedinosaursruss00bent|url-access=limited|publisher=Cambridge University Press|isbn=0-521-55476-4}}
Paleobiota of the Nemegt Formation
=Amphibians=
| class="wikitable" align="center" width="100%" |
| Genus
! Species ! Location ! Stratigraphic position ! Material ! Notes ! Image |
|---|
| Altanulia
| A. alifanovi | Altan Uul II |Middle or Upper | "Partial maxilla."{{cite journal |last1=Gubin|first1=Y. M.|date=1993|title=Cretaceous anurans of Mongolia|journal=Paleontological Journal|pages=51−56|language=ru}} | A discoglossid. Its classification has been criticized.{{cite book|last1=Sanchíz|first1=B.|year=1998|chapter=Salientia Part 4|editor-last1=Wellnhofer|editor-first1=P.|editor-last2=Verlag|editor-first2=F. P.|title=Handbuch der Paläoherpetologie|location=Munich|pages=1−275}} | |
=Crocodylomorphs=
| class="wikitable" align="center" width="100%" |
| Genus
! Species ! Location ! Stratigraphic position ! Material ! Notes ! Image |
|---|
| Paralligator{{cite journal|first1=A. H.|last1=Turner|date=2015|title=A Review of Shamosuchus and Paralligator (Crocodyliformes, Neosuchia) from the Cretaceous of Asia|journal=PLOS ONE|volume=10|issue=2|page=e0118116|bibcode=2015PLoSO..1018116T|doi=10.1371/journal.pone.0118116|doi-access=free|pmc=4340866|pmid=25714338}}
| Nemegt, Nogon Tsav, Ulaan Bulag |Lower | "Partially complete skulls with sparse body elements." | A paralligatorid. | 150px |
=Fish=
=Flora=
=Invertebrates=
| class="wikitable" align="center" width="100%" |
| Genus
! Species ! Location ! Stratigraphic position ! Material ! Notes ! Image |
|---|
| rowspan=3| Altanicypris
| A. bispinifera | Altan Uul IV, Nemegt |Lower | An ostracod. | |
| A. multispina
| Altan Uul IV, Nemegt |Lower | "Nine carapaces and some detached valves." | An ostracod. | |
| A. szczechurae
| Altan Uul IV, Nemegt |Lower | "Multiple carapaces and detached valves." | An ostracod. | |
| rowspan=2| Candona
| C. altanulaensis | Altan Uul IV, Bügiin Tsav, Nemegt | | "Multiple specimens with carapaces and valves." | An ostracod. | |
| cf. C. fabaeformis
| Altan Uul IV, Nemegt |Lower | "Several carapaces and detached valves." | An ostracod. | |
| rowspan=2| Candoniella
| C. altanica | Altan Uul IV, Bügiin Tsav, Nemegt | | "Multiple specimens with carapaces and valves." | An ostracod. | |
| C. mordvilkoi
| Altan Uul IV |Lower | An ostracod. | |
| Cyclocypris
| C. transitoria | Bügiin Tsav, Nemegt | | An ostracod. | |
| Cypria
| C. elata | Bügiin Tsav, Hermiin Tsav | | "Several carapaces and valves." | An ostracod. | |
| rowspan=2| Cypridopsis?
| C. bugintsavicus | Altan Uul IV, Bügiin Tsav, Nemegt, Tsagan Khushu | | An ostracod. | |
| Indeterminate
| Nemegt |Lower | "Several complete carapaces." | An ostracod. | |
| Cypris?
| C. ectypa | Altan Uul IV, Bügiin Tsav, Nemegt, Ulan Bulag | | "Complete carapaces and some detached valves." | An ostracod. | |
| rowspan=5| Cypridea
| cf. C. punctilataeformis | Nemegt | | An ostracod. | |
| C. barsboldi
| Altan Uul IV, Bügiin Tsav, Nemegt | | "Multiple specimens with carapaces and valves." | An ostracod. | |
| C. cavernosa
| Altan Uul IV, Bügiin Tsav, Nemegt, Nogon Tsav | | "Multiple specimens with carapaces and valves." | An ostracod. | |
| C. rostrata
| Bügiin Tsav, Nemegt, Nogon Tsav | | An ostracod. | |
| Indeterminate
| Altan Uul IV, Nemegt |Lower | An ostracod. | |
| Gobiella
| G. prima | Altan Uul IV, Nemegt |Lower | "Several carapaces and detached valves." | An ostracod. | |
| Khandia
| K. stankevitchae | Altan Uul IV, Nemegt |Lower | "Multiple carapaces and valves." | An ostracod. | |
| rowspan=2| Leiria
| Indeterminate | Nemegt |Lower | An ostracod. | |
| Indeterminate
| Nemegt |Lower | An ostracod. | |
| Limnocythere sp.
| Indeterminate | Nemegt |Lower | An ostracod. | |
| Lycopterocypris?
| cf. L. profunda | Altan Uul IV, Nemegt |Lower | "Multiple complete carapaces and left valve." | An ostracod. | |
| Mongolianella
| M. palmosa? | Altan Uul IV, Bügiin Tsav, Nemegt | | An ostracod. | |
| Mongolocypris
| M. distributa | Altan Uul IV, Bügiin Tsav, Nemegt, Tsagan Khushu | | "Multiple specimens with complete carapaces and valves." | An ostracod. | |
| rowspan=3| Nemegtia
| N. biformata | Altan Uul IV, Bügiin Tsav, Nemegt, Tsagan Khushu | | "Multiple complete carapaces and several detached valves." | An ostracod. | |
| N. obliquecostae
| Altan Uul IV, Nemegt |Lower | "Multiple carapaces and valves." | An ostracod. | |
| N. reticulata
| Altan Uul IV, Bügiin Tsav, Nemegt, Nogon Tsav, Tsagan Khushu | | "Several carapaces and detached valves." | An ostracod. | |
| Paracypridea?
| P. mongolica | Altan Uul IV, Nemegt |Lower | "Multiple carapaces and detached valves." | An ostracod. | |
| Rhinocypris sp.
| Indeterminate | Nemegt |Lower | An ostracod. | |
| rowspan=2| Scabriculocypris
| S. ingenicus? | Altan Uul IV, Bügiin Tsav, Naran Bulag, Nemegt, Tsagan Khushu | | "Multiple carapaces and valves." | An ostracod. | |
| S. rasilis?
| Altan Uul IV, Nemegt |Lower | "Several carapaces and detached valves." | An ostracod. | |
| rowspan=4| Timiriasevia
| cf. T. miaogouensis | Altan Uul IV, Nemegt |Lower | An ostracod. | |
| cf. T. opinabilis
| Altan Uul IV |Lower | An ostracod. | |
| T. minuscula
| Altan Uul IV, Bügiin Tsav, Nemegt | | "Multiple specimens with carapaces and valves." | An ostracod. | |
| T. naranbulakensis
| Altan Uul IV, Bügiin Tsav, Nemegt | | "Four carapaces and one right valve." | An ostracod. | |
| Ziziphocypris
| Z. costata | Altan Uul IV, Bügiin Tsav, Nemegt | | An ostracod. | |
=Mammals=
| class="wikitable" align="center" width="100%" |
| Genus
! Species ! Location ! Stratigraphic position ! Material ! Notes ! Image |
|---|
| Buginbaatar{{cite journal|last1=Kielan-Jaworowska|first1=Z.|last2=Sochava|first2=A. V.|date=1969|title=The first multituberculate from the Uppermost Cretaceous of the Gobi Desert (Mongolia)|journal=Acta Palaeontologica Polonica|volume=14|issue=3|pages=355−367|url=https://www.app.pan.pl/archive/published/app14/app14-355.pdf}}
| Bügiin Tsav |Middle or Upper | A multituberculate. | |
| "Gurlin Tsav skull"
| Indeterminate | |Middle or |Partial skull | A mysterious metatherian, possibly a sparassodont. | |
=Pterosaurs=
| class="wikitable" align="center" width="100%" |
| Genus
! Species ! Location ! Stratigraphic position ! Material ! Notes ! Image |
|---|
| Unnamed azhdarchid
| Indeterminate | Guriliin Tsav |Middle or Upper | A giant azhdarchid. | 150px |
