Root calcretes and uranium-bearing silcretes at sedimentary discontinuities in the Miocene of the Madrid Basin (Toledo, Spain)

This paper reports a detailed study of the calcrete and silcrete profiles in the Miocene detrital deposits in the western area of Madrid, at the boundary of two main sedimentary units. The aims of this work were to better understand the pedogenic and diagenetic environments in which these profiles f...

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Autores: Bustillo Revuelta, María Ángeles, Plet, Chloé, Alonso Zarza, Ana María
Tipo de recurso: artículo
Fecha de publicación:2013
País:España
Institución:Universidad Complutense de Madrid (UCM)
Repositorio:Docta Complutense
Idioma:inglés
OAI Identifier:oai:docta.ucm.es:20.500.14352/33799
Acceso en línea:https://hdl.handle.net/20.500.14352/33799
Access Level:acceso abierto
Palabra clave:552.5(460.285)
Silcretes
Calcretes
Roots
Geochemistry
Continental basins
Petrología
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spelling Root calcretes and uranium-bearing silcretes at sedimentary discontinuities in the Miocene of the Madrid Basin (Toledo, Spain)Bustillo Revuelta, María ÁngelesPlet, ChloéAlonso Zarza, Ana María552.5(460.285)SilcretesCalcretesRootsGeochemistryContinental basinsPetrologíaThis paper reports a detailed study of the calcrete and silcrete profiles in the Miocene detrital deposits in the western area of Madrid, at the boundary of two main sedimentary units. The aims of this work were to better understand the pedogenic and diagenetic environments in which these profiles formed and to determine the cause(s) of their enrichment in uranium. Calcrete and silcrete duricrusts are characteristic features of closed continental basins in semiarid climates; this paper discusses the significance of duricrusts as indicators of important change in such basins. The detailed macromorphological, micromorphological, and geochemical study of three duricrust profiles revealed the sequence of pedogenic, vadose, and groundwater processes responsible for their formation. During the first stage of their development, carbonate laminae formed a white “grill-like” structure within the detrital parent materials. The microstructure and macrostructure of the carbonate, which includes alveolar septal structures and needle-fiber calcite, indicates the important role of roots and their associated microorganisms in calcrete formation. Early silicification occurred in the pedogenic-vadose environment affecting the detrital parent material, roots, and calcretes, forming an early silcrete defined by opaline glaebules and silica rhizoliths. The detailed preservation of the cells in the silicified roots denotes the early replacement of root organic matter. The green or green-yellowish fluorescence of the silicified root structures under short-wavelength UV shows their preferential enrichment in uranium. Calcitization and silicification coexisted in the pedogenic vadose environment, leading to several reversible replacements of calcite and silica. Later, the rise of the water table promoted silicification under phreatic conditions, as indicated by the good preservation of the texture of the detrital host rocks and calcretes. Other silcrete textures, such as ovoidal opaline accumulations, intraclasts produced by autobrecchification, and vadose silica cements, indicate later vadose environments, and consequently variations in the water table. The geochemical features of the calcretes and silcretes (major, minor, and rare earth elements) were inherited from their parent materials. The rare-earth-element patterns of some silcretes show them to have a positive Ce anomaly, suggesting that oxidizing conditions reigned during their formation. The good correlation between silica and uranium suggests that the silica phases acquired uranium through the direct silicification of roots that had fixed uranium from organic matter. This study shows that calcrete-silcrete duricrusts provide detailed information regarding the processes occurring in semiarid continental basins. In the studied basin, croots played a key role in both the development of the duricrust profiles and their enrichment in uranium. These duricrusts provide important information for understanding the overall stratigraphy of the studied basin and its large-scale sequential evolution.SEPM (Society for Sedimentary Geology)Universidad Complutense de Madrid20132013-01-0120132013-01-01journal articlehttp://purl.org/coar/resource_type/c_6501info:eu-repo/semantics/articleapplication/pdfhttps://hdl.handle.net/20.500.14352/33799reponame:Docta Complutenseinstname:Universidad Complutense de Madrid (UCM)Inglésengopen accesshttp://purl.org/coar/access_right/c_abf2info:eu-repo/semantics/openAccessoai:docta.ucm.es:20.500.14352/337992026-06-02T12:44:21Z
dc.title.none.fl_str_mv Root calcretes and uranium-bearing silcretes at sedimentary discontinuities in the Miocene of the Madrid Basin (Toledo, Spain)
title Root calcretes and uranium-bearing silcretes at sedimentary discontinuities in the Miocene of the Madrid Basin (Toledo, Spain)
spellingShingle Root calcretes and uranium-bearing silcretes at sedimentary discontinuities in the Miocene of the Madrid Basin (Toledo, Spain)
Bustillo Revuelta, María Ángeles
552.5(460.285)
Silcretes
Calcretes
Roots
Geochemistry
Continental basins
Petrología
title_short Root calcretes and uranium-bearing silcretes at sedimentary discontinuities in the Miocene of the Madrid Basin (Toledo, Spain)
title_full Root calcretes and uranium-bearing silcretes at sedimentary discontinuities in the Miocene of the Madrid Basin (Toledo, Spain)
title_fullStr Root calcretes and uranium-bearing silcretes at sedimentary discontinuities in the Miocene of the Madrid Basin (Toledo, Spain)
title_full_unstemmed Root calcretes and uranium-bearing silcretes at sedimentary discontinuities in the Miocene of the Madrid Basin (Toledo, Spain)
title_sort Root calcretes and uranium-bearing silcretes at sedimentary discontinuities in the Miocene of the Madrid Basin (Toledo, Spain)
dc.creator.none.fl_str_mv Bustillo Revuelta, María Ángeles
Plet, Chloé
Alonso Zarza, Ana María
author Bustillo Revuelta, María Ángeles
author_facet Bustillo Revuelta, María Ángeles
Plet, Chloé
Alonso Zarza, Ana María
author_role author
author2 Plet, Chloé
Alonso Zarza, Ana María
author2_role author
author
dc.contributor.none.fl_str_mv Universidad Complutense de Madrid
dc.subject.none.fl_str_mv 552.5(460.285)
Silcretes
Calcretes
Roots
Geochemistry
Continental basins
Petrología
topic 552.5(460.285)
Silcretes
Calcretes
Roots
Geochemistry
Continental basins
Petrología
description This paper reports a detailed study of the calcrete and silcrete profiles in the Miocene detrital deposits in the western area of Madrid, at the boundary of two main sedimentary units. The aims of this work were to better understand the pedogenic and diagenetic environments in which these profiles formed and to determine the cause(s) of their enrichment in uranium. Calcrete and silcrete duricrusts are characteristic features of closed continental basins in semiarid climates; this paper discusses the significance of duricrusts as indicators of important change in such basins. The detailed macromorphological, micromorphological, and geochemical study of three duricrust profiles revealed the sequence of pedogenic, vadose, and groundwater processes responsible for their formation. During the first stage of their development, carbonate laminae formed a white “grill-like” structure within the detrital parent materials. The microstructure and macrostructure of the carbonate, which includes alveolar septal structures and needle-fiber calcite, indicates the important role of roots and their associated microorganisms in calcrete formation. Early silicification occurred in the pedogenic-vadose environment affecting the detrital parent material, roots, and calcretes, forming an early silcrete defined by opaline glaebules and silica rhizoliths. The detailed preservation of the cells in the silicified roots denotes the early replacement of root organic matter. The green or green-yellowish fluorescence of the silicified root structures under short-wavelength UV shows their preferential enrichment in uranium. Calcitization and silicification coexisted in the pedogenic vadose environment, leading to several reversible replacements of calcite and silica. Later, the rise of the water table promoted silicification under phreatic conditions, as indicated by the good preservation of the texture of the detrital host rocks and calcretes. Other silcrete textures, such as ovoidal opaline accumulations, intraclasts produced by autobrecchification, and vadose silica cements, indicate later vadose environments, and consequently variations in the water table. The geochemical features of the calcretes and silcretes (major, minor, and rare earth elements) were inherited from their parent materials. The rare-earth-element patterns of some silcretes show them to have a positive Ce anomaly, suggesting that oxidizing conditions reigned during their formation. The good correlation between silica and uranium suggests that the silica phases acquired uranium through the direct silicification of roots that had fixed uranium from organic matter. This study shows that calcrete-silcrete duricrusts provide detailed information regarding the processes occurring in semiarid continental basins. In the studied basin, croots played a key role in both the development of the duricrust profiles and their enrichment in uranium. These duricrusts provide important information for understanding the overall stratigraphy of the studied basin and its large-scale sequential evolution.
publishDate 2013
dc.date.none.fl_str_mv 2013
2013-01-01
2013
2013-01-01
dc.type.none.fl_str_mv journal article
http://purl.org/coar/resource_type/c_6501
dc.type.openaire.fl_str_mv info:eu-repo/semantics/article
format article
dc.identifier.none.fl_str_mv https://hdl.handle.net/20.500.14352/33799
url https://hdl.handle.net/20.500.14352/33799
dc.language.none.fl_str_mv Inglés
eng
language_invalid_str_mv Inglés
language eng
dc.rights.none.fl_str_mv open access
http://purl.org/coar/access_right/c_abf2
dc.rights.openaire.fl_str_mv info:eu-repo/semantics/openAccess
rights_invalid_str_mv open access
http://purl.org/coar/access_right/c_abf2
eu_rights_str_mv openAccess
dc.format.none.fl_str_mv application/pdf
dc.publisher.none.fl_str_mv SEPM (Society for Sedimentary Geology)
publisher.none.fl_str_mv SEPM (Society for Sedimentary Geology)
dc.source.none.fl_str_mv reponame:Docta Complutense
instname:Universidad Complutense de Madrid (UCM)
instname_str Universidad Complutense de Madrid (UCM)
reponame_str Docta Complutense
collection Docta Complutense
repository.name.fl_str_mv
repository.mail.fl_str_mv
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score 15,300719

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