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The Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of marine limestone, a rock type that is formed under warm, shallow marine conditions.
The Chalk Group (often just called the Chalk) is the lithostratigraphic unit (a certain number of rock strata) which contains the Upper Cretaceous limestone succession in southern and eastern England.
In northwestern Sonora, in addition to the Glance Conglomerate, the Morita Formation, the Mural Limestone, and the Cintura Formation, the group includes the Cerro de Oro Formation and Arroyo Sásabe Formation. [12] The group was deposited in the Bisbee basin, which was the central basin of the Jurassic-Cretaceous border rift belt.
Limestone (calcium carbonate CaCO 3) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of CaCO 3. Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place ...
The Niobrara Formation / ˌ n aɪ. ə ˈ b r ær ə /, also called the Niobrara Chalk, is a geologic formation in North America that was deposited between 87 and 82 million years ago during the Coniacian, Santonian, and Campanian stages of the Late Cretaceous.
The putative galloanseran bird Austinornis lentus has been found in the Austin Chalk. [2] [3] The general absence of dinosaurs is a reflection of the Austin limestone being marine in origin, primarily composed of microscopic shell fragments from floating sea organisms known as "coccolithophores" (the same organisms that contributed to the White Cliffs of Dover, on the south coast of England). [4]
The Mancos Shale or Mancos Group is a Late Cretaceous (Upper Cretaceous) geologic formation of the Western United States. The Mancos Shale was first described by Cross and Purington in 1899 [ 1 ] and was named for exposures near the town of Mancos, Colorado .
Other features of interest are several different post-metamorphic breccia formations. The North Pyrenean Zone can be subdivided into three subzones bounded by major faults: a northern subzone. Its sedimentary cover has detached from the basement uplifts farther south. It contains flysch from the Upper Cretaceous. an intermediate subzone.