Publication: Unidades estratigráficas en el registro sedimentario neógeno del sector occidental de la Cuenca de Madrid
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Publication Date
2004
Authors
López Olmedo, F.
Díaz de Neira, A.
Martín Serrano, A.
Morales, J.
Peláez-Campomanes, P.
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Sociedad Geológica de España
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Abstract
El sector occidental de la Cuenca de Madrid está constituido por depósitos siliciclásticos, en general areniscas arcósicas y lutitas, fundamentalmente de edad neógena. A partir de la cartografía y del estudio estratigráfico detallado de los materiales terciarios presentes en varias hojas geológicas a escala 1:50.000 de la zona SO de la cuenca, se han reconocido cinco unidades estratigráficas cuya denominación alude a las áreas donde aparecen mejor representadas. De base a techo, son: 1) Unidad de arcosas y lutitas de El Carpio, 2) Unidad de arcosas con cantos y conglomerados del Embalse de Castrejón, 3) Unidad de arcosas y lutitas de Los Vergales, 4) Unidad de arcosas gruesas con cantos de Batres, y 5) Unidad de arcosas blancas de Carranque-Griñón. Los límites entre ellas quedan definidos
por cambios en la evolución en la vertical de los depósitos siliciclásticos, sobre todo relativos a su granulometría. Los materiales reconocibles en cada una de estas unidades se depositaron en su mayor parte en sistemas de abanicos aluviales, con variaciones en el carácter permanente o efímero de los sistemas distributarios y, en menor medida, en ambientes lacustres someros y palustres. La edad del
conjunto estratigráfico analizado abarca esencialmente el Mioceno inferior y medio, no descartándose que la base de la Unidad de arcosas y lutitas de El Carpio sea Paleógeno y que la parte superior de la Unidad de arcosas blancas de Carranque-Griñón alcance el Mioceno superior (Vallesiense).
The western part of the Madrid Basin, central Spain, shows widespread siliciclastic deposits consisting mainly of arkosic sandstone and mudstone. The age of the deposits is mostly Neogene. Both mapping and detailed stratigraphic analysis of the sedimentary record present in several topographic sheets (scale 1:50,000) in the western part of the basin allow recognition of five major stratigraphic units, which have been named according to places where the units are better exposed. From bottom to top, the units are: 1) Arkoses and mudstones of El Carpio, 2) Gravelly-sandstones and mudstones of the Castrejón Reservoir, 3) Arkoses and mudstones of Los Vergales, 4) Gravelly-arkosic sandstones of Batres, and 5) White arkoses of Carranque-Griñón. The boundaries between the units are outlined by upward grain-size changes of the deposits as well as facies variation in vertical. Most of the sediments were deposited in alluvial fan systems, where some changes in the character of the distributary streams, i.e. permanent to ephemeral, is observed. Local deposits representative of shallow-lake to palustrine environments, including carbonate paleosols, are recognised especially towards the top of the stratigraphic units. The age of the units spans Early to Middle Miocene although a Paleogene age is not ruled out for the lower part of the Arkoses and mudstones of El Carpio Unit. Similarly, the White arkoses of Carranque-Griñón Unit could reach the lower part of the Late Miocene (Vallesian).
The western part of the Madrid Basin, central Spain, shows widespread siliciclastic deposits consisting mainly of arkosic sandstone and mudstone. The age of the deposits is mostly Neogene. Both mapping and detailed stratigraphic analysis of the sedimentary record present in several topographic sheets (scale 1:50,000) in the western part of the basin allow recognition of five major stratigraphic units, which have been named according to places where the units are better exposed. From bottom to top, the units are: 1) Arkoses and mudstones of El Carpio, 2) Gravelly-sandstones and mudstones of the Castrejón Reservoir, 3) Arkoses and mudstones of Los Vergales, 4) Gravelly-arkosic sandstones of Batres, and 5) White arkoses of Carranque-Griñón. The boundaries between the units are outlined by upward grain-size changes of the deposits as well as facies variation in vertical. Most of the sediments were deposited in alluvial fan systems, where some changes in the character of the distributary streams, i.e. permanent to ephemeral, is observed. Local deposits representative of shallow-lake to palustrine environments, including carbonate paleosols, are recognised especially towards the top of the stratigraphic units. The age of the units spans Early to Middle Miocene although a Paleogene age is not ruled out for the lower part of the Arkoses and mudstones of El Carpio Unit. Similarly, the White arkoses of Carranque-Griñón Unit could reach the lower part of the Late Miocene (Vallesian).