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Chalk is a soft, white, porous, sedimentary carbonate rock.It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor.
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.
Chalk is the rock type associated most closely with the National Park and, in common with the chalk which provides other key landscape features in the southeast of England, was formed by the settling to the sea floor of myriad coccoliths (microscopic plates of calcium carbonate formed by single-celled algae known as coccolithophores) during the Late Cretaceous epoch between about 100 and 70 ...
The chalk formations reach a height of up to 70 ft (21 m) and include formations such as buttes and arches. The carbonate deposits were laid down during the Cretaceous Period in what was then the Western Interior Seaway, which split the continent of North America into two landmasses. They are estimated to have been formed 80 million years ago.
Niobrara Chalk was weathered and opalized in the Valentine phase of the Ogallala Formation. 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 ...
Made of white chalk formed from the shells of a rare species of algae, the cliffs have always been vulnerable, but bad weather, storm waves, reduced sediment supply, and beach erosion has ...
Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, [1] [2] categorized as the variety of chert that occurs in chalk or marly limestone. Historically, flint was widely used to make stone tools and start fires. Flint occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones.
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]