Öösh Formation

The Öösh Formation, also known as the Tevsh Formation is a geological formation of Lower Cretaceous strata in Övörkhangai Province, Mongolia. Dinosaur remains are among the fossils that have been recovered from the formation.^[1] It overlies folded and metamorphosed basement strata of the Gobi region, and is capped by basalt. The succession is around 600 metres thick and consists of red claystones and sandstones, along with black thinly laminated shales. The claystones and sandstones were deposited as part of an alluvial fan system, while the shales were deposited in lakes present in the foot of the fan.^[2] Many of the fossils come from the "Cannonball beds", which comprise the lowest 60 metres of the unit and consist of green siltstone.^[2]

TypeGeological formation

Sub-unitsCannonball beds

UnderliesBasalt

OverliesBasement

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Öösh Formation
Stratigraphic range: Berriasian-Barremian ~141–125 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Sub-units	Cannonball beds
Underlies	Basalt
Overlies	Basement
Thickness	600 m (2,000 ft)
Lithology
Primary	Sandstone, claystone, shale
Other	Siltstone
Location
Coordinates	44.2°N 102.7°E / 44.2; 102.7
Approximate paleocoordinates	45.0°N 103.3°E / 45.0; 103.3
Region	Ovorkhangai
Country	Mongolia
Öösh Formation (Mongolia)

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