Interpreting carbonate particles in modern continental sands: an example from fluvial sands (Iberian Range, Spain)



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Arribas Mocoroa, José and Arribas Mocoroa, María Eugenia (2007) Interpreting carbonate particles in modern continental sands: an example from fluvial sands (Iberian Range, Spain). In Geological Society of America. Special Paper. Geological Society of America. Special Paper, 420 . Geological Society of America, Boulder, CO, pp. 167-179. ISBN 9780813724201

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We analyzed modern fluvial sands in the Iberian Range in order to obtain an accurate description of the different typologies of carbonate grains and to interpret their origin. Head streams of the Iberian Range mainly receive carbonate sediments as (1) fragments from ancient carbonate rocks, and (2) penecontemporaneous car­ bonate grains generated in the fluvial channels or in associated subenvironments. The erosion of proximal carbonate sources (Jurassic and Cretaceous in age) contributes to the generation of carbonate rock fragments. In addition, erosion of recent freshwater tufas, carbonate soils, and other recent carbonates produces an important volume of penecontemporaneous carbonate particles. Temperate to subhu mid climate and short transport conditions promote good preservation of the composition and textures of carbonate grains in modern fluvial sands. Detailed petrographic analyses on penecon­ temporaneous carbonates provide diagnostic clues of their origin. Four main petro­ graphic classes of penecontemporaneous grains have been established: (1) penecon­ temporaneous micritic grains, which are composed of microcrystalline calcite with a filamentous or laminated microfabric, are derived from erosion of recent freshwa­ ter carbonate tufas. Penecontemporaneous micritic grains with alveolar microfabric are derived from recent carbonate soils. (2) Penecontemporaneous sparitic grains, which are composed of single crystals or of mosaics with filamentous microfabric, are the result of erosion of carbonate tufas. Other penecontemporaneous sparitic grains include Microcodium and speleothems fragments. (3) Penecontemporaneous coated grains, which are composed of a nucleus plus a coating of penecontemporane­ ous carbonate, represent bioinduced carbonate particles (cyanoliths) that originate in streams. (4) Penecontemporaneous bioclasts, made from charophytes, ostracods, and mollusks, are rare. ldentification of these grain categories in ancient deposits has implications for coeval carbonate supplies during fluvial sedimentation.

Item Type:Book Section
Uncontrolled Keywords:Provenance; Coeval grains; Carbonate grains; Freshwater carbonate tufa; Fluvial sands; Iberian Range; Sand composition
Subjects:Sciences > Geology > Geochemistry
Sciences > Geology > Petrology
ID Code:45985
Deposited On:11 Jan 2018 08:41
Last Modified:11 Jan 2018 08:43

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