The Bissekty Formation (sometimes referred to as Bissekt) is a geologic formation and Lagerstätte which crops out in the Kyzyl Kum desert of Uzbekistan, and dates to the Late Cretaceous Period. Laid down in the mid to late Turonian, it is dated to about 92 to 90 Ma (million years ago).^[1]

Quick Facts Type, Underlies ...

Bissekty Formation
Stratigraphic range: Mid-Late Turonian ~92–90 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Underlies	Aitym Formation
Overlies	Dzheirantui Formation
Thickness	up to 80 m (260 ft)
Lithology
Primary	Sandstone
Other	Conglomerate, mudstone, siltstone
Location
Coordinates	42.1°N 62.7°E / 42.1; 62.7
Approximate paleocoordinates	36.8°N 57.0°E / 36.8; 57.0
Region	Navoiy & Xorazm Regions
Country	Uzbekistan
Extent	Kyzylkum Desert
Bissekty Formation (Uzbekistan)

Close

The lithology of the sediment largely consists of cross bedded sandstones with interbeds of massive sandstone, well cemented intraformational conglomerate, siltstones and mudstones. Most of the fossils are found as clasts within the conglomerates.^[2]

The Bissekty Formation is characterised by a mix of marine, brackish, freshwater, and terrestrial animal fossils. This stands in contrast the strictly marine fossils found in the underlying Dzheirantui Formation, and indicates that the Bissekty was formed during the regression of a saltwater sea. The coastline expanded inland again in the upper portion of the Bissekty, represented by a proportional increase of fully aquatic species, which were almost completely absent from the middle period of the formation. Semi-aquatic species remained abundant during this middle period, and the geology of the formations indicates that a braided river system took the place of the coastline. Eventually the area was again completely underwater, during the time period represented by the later Aitym Formation, which preserves coastal marine sediments.^[2]