Coquina

For the small marine bivalves, see Donax variabilis and Donax trunculus.
For George Shields who went by the pseudonym Coquina, see George Oliver Shields.
Coquina strata from Caleta Hornos (Coquimbo Formation)

Coquina (/koʊˈkiːnə/) is a sedimentary rock that is composed either wholly or almost entirely of the transported, abraded, and mechanically sorted fragments of mollusks, trilobites, brachiopods, or other invertebrates.[1][2] The term coquina comes from the Spanish word for "cockle" and "shellfish".[3][4]

For a sediment to be considered to be a coquina, the particles composing it should average 2 mm (0.079 in) or greater in size. Coquina can vary in hardness from poorly to moderately cemented. Incompletely consolidated and poorly cemented coquinas are considered grainstones in the Dunham classification system for carbonate sedimentary rocks.[5] A well-cemented coquina is classified as a biosparite (fossiliferous limestone) according to the Folk classification of sedimentary rocks.[6]

Coquinas accumulate in high-energy marine and lacustrine environments where currents and waves result in the vigorous winnowing, abrasion, fracturing, and sorting of the shells that compose them. As a result, they typically exhibit well-developed bedding or cross-bedding, close packing, and good orientation of the shell fragments. The high-energy marine or lacustrine environments associated with coquinas include beaches, shallow submarine raised banks, swift tidal channels, and barrier bars.[6][7]

  1. ^ Dictionary of Mining, Mineral, & Related Terms. Report SP-96-1. Washington, DC: U.S. Department of Interior, U.S. Bureau of Mines. 1996.[ISBN missing][page needed]
  2. ^ Neuendorf, K. K. E.; J. P., Jr, Mehl; Jackson, J. A., eds. (2005). Glossary of Geology (5th ed.). Alexandria, VA: American Geological Institute. ISBN 978-0-922152-76-6.[page needed]
  3. ^ "Definition of coquina in English". English Oxford Dictionaries. Oxford University Press. 2018. Archived from the original on September 25, 2016. Retrieved 10 December 2018. Mid 19th century: from Spanish, literally 'cockle', based on Latin concha.
  4. ^ English Wiktionary: concha mussel, shell."
  5. ^ Dunham, R. J. (1962). "Classification of carbonate rocks according to depositional texture". In Ham, W. E. (ed.). Classification of Carbonate Rocks. American Association of Petroleum Geologists Memoir, no. 1. pp. 108–121.
  6. ^ a b Folk, R. L. (1980). The Petrology of Sedimentary Rocks. Austin, TX: Hemphill Publishing Company. ISBN 978-0-914696-14-8.[page needed]
  7. ^ Scholle, P. A.; Bebout, D. G.; Moore, C. H. (1983). Carbonate Depositional Environments. Memoir no. 33. Tulsa, OK: American Association of Petroleum Geologists. ISBN 978-0-89181-310-1.[page needed]