Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub-aquatic opaline stromatolite formation (Terceira, Azores)

© 2014 International Association of Sedimentologists. Silica stromatolites occur in a number of modern hydrothermal environments, but their formation in caves is very rare. The silica stromatolitic speleothems of the Branca Opala cave (Terceira Island, Azores), however, provide an excellent opportun...

Descripción completa

Detalles Bibliográficos
Autores: Daza, Raquel, Bustillo, Mª Ángeles
Tipo de recurso: artículo
Estado:Versión aceptada para publicación
Fecha de publicación:2014
País:España
Institución:Consejo Superior de Investigaciones Científicas (CSIC)
Repositorio:DIGITAL.CSIC. Repositorio Institucional del CSIC
OAI Identifier:oai:digital.csic.es:10261/126076
Acceso en línea:http://hdl.handle.net/10261/126076
Access Level:acceso abierto
Palabra clave:Bacterial activity
Geochemistry
Opal
Silica-tufa
Stromatolitic-speleothems
id ES_fe0e2ee915af3b3b6a2e682cb8babc87
oai_identifier_str oai:digital.csic.es:10261/126076
network_acronym_str ES
network_name_str España
repository_id_str
spelling Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub-aquatic opaline stromatolite formation (Terceira, Azores)Daza, RaquelBustillo, Mª ÁngelesBacterial activityGeochemistryOpalSilica-tufaStromatolitic-speleothems© 2014 International Association of Sedimentologists. Silica stromatolites occur in a number of modern hydrothermal environments, but their formation in caves is very rare. The silica stromatolitic speleothems of the Branca Opala cave (Terceira Island, Azores), however, provide an excellent opportunity for their study. These formations may be analogous to ancient silica stromatolites seen around the world. Petrographic, mineralogical and geochemical analyses were undertaken on the silica speleothems of the above cave, and on the silica-tufa deposits outside it, with the aim of understanding their genesis. The possible hydrothermal origin of their silica is discussed. X-ray diffraction analyses showed opal-A to be the sole silica phase. Negligible ordering of this opal-A showed ageing to be insignificant, as expected for recent silica deposits. Most of the silica speleothems examined were definable as sub-aquatic opaline stromatolites that are not currently growing. Optical microscopy clearly revealed a lower microlaminated, an intermediate and an upper microlaminated zone within the stromatolites. Stromatolite types (I, II and III) were classified with respect to their internal structure and distribution throughout the cave. Scanning electron microscopy showed silicified bacterial filaments within the stromatolites, the silicified plant remains and the silica-tufa deposits. Bacteria therefore played a major role in the precipitation of the opal-A. Plasma emission/mass spectrometry showed major, minor and rare earth elements to be present in only small quantities. The rare earth elements were mainly hosted within volcanic grains. Rapid silica precipitation from highly super-saturated water would explain the intense silicification of the plant remains found inside and outside the cave. The opaline stromatolites, the silica-tufa deposits and the above-mentioned intense general silicification suggest a local hydrothermal source for the silica. Indeed, these deposits strongly resemble plant-rich silica sinter associated with low-temperature hot spring deposits that include bacterial filaments. However, no geochemical signals that might indicate a hydrothermal origin could be found.This research was funded by the Spanish Ministry of Economy and Competitiveness; project CGL2011-27826-CO2-02.Peer ReviewedJohn Wiley & SonsInternational Association of SedimentologistsConsejo Superior de Investigaciones Científicas [https://ror.org/02gfc7t72]20142015info:eu-repo/semantics/articlehttp://purl.org/coar/resource_type/c_6501Postprintinfo:eu-repo/semantics/acceptedVersionhttp://hdl.handle.net/10261/126076reponame:DIGITAL.CSIC. Repositorio Institucional del CSICinstname:Consejo Superior de Investigaciones Científicas (CSIC)InglésSíinfo:eu-repo/semantics/openAccessoai:digital.csic.es:10261/1260762026-05-22T06:33:51Z
dc.title.none.fl_str_mv Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub-aquatic opaline stromatolite formation (Terceira, Azores)
title Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub-aquatic opaline stromatolite formation (Terceira, Azores)
spellingShingle Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub-aquatic opaline stromatolite formation (Terceira, Azores)
Daza, Raquel
Bacterial activity
Geochemistry
Opal
Silica-tufa
Stromatolitic-speleothems
title_short Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub-aquatic opaline stromatolite formation (Terceira, Azores)
title_full Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub-aquatic opaline stromatolite formation (Terceira, Azores)
title_fullStr Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub-aquatic opaline stromatolite formation (Terceira, Azores)
title_full_unstemmed Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub-aquatic opaline stromatolite formation (Terceira, Azores)
title_sort Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub-aquatic opaline stromatolite formation (Terceira, Azores)
dc.creator.none.fl_str_mv Daza, Raquel
Bustillo, Mª Ángeles
author Daza, Raquel
author_facet Daza, Raquel
Bustillo, Mª Ángeles
author_role author
author2 Bustillo, Mª Ángeles
author2_role author
dc.contributor.none.fl_str_mv Consejo Superior de Investigaciones Científicas [https://ror.org/02gfc7t72]
dc.subject.none.fl_str_mv Bacterial activity
Geochemistry
Opal
Silica-tufa
Stromatolitic-speleothems
topic Bacterial activity
Geochemistry
Opal
Silica-tufa
Stromatolitic-speleothems
description © 2014 International Association of Sedimentologists. Silica stromatolites occur in a number of modern hydrothermal environments, but their formation in caves is very rare. The silica stromatolitic speleothems of the Branca Opala cave (Terceira Island, Azores), however, provide an excellent opportunity for their study. These formations may be analogous to ancient silica stromatolites seen around the world. Petrographic, mineralogical and geochemical analyses were undertaken on the silica speleothems of the above cave, and on the silica-tufa deposits outside it, with the aim of understanding their genesis. The possible hydrothermal origin of their silica is discussed. X-ray diffraction analyses showed opal-A to be the sole silica phase. Negligible ordering of this opal-A showed ageing to be insignificant, as expected for recent silica deposits. Most of the silica speleothems examined were definable as sub-aquatic opaline stromatolites that are not currently growing. Optical microscopy clearly revealed a lower microlaminated, an intermediate and an upper microlaminated zone within the stromatolites. Stromatolite types (I, II and III) were classified with respect to their internal structure and distribution throughout the cave. Scanning electron microscopy showed silicified bacterial filaments within the stromatolites, the silicified plant remains and the silica-tufa deposits. Bacteria therefore played a major role in the precipitation of the opal-A. Plasma emission/mass spectrometry showed major, minor and rare earth elements to be present in only small quantities. The rare earth elements were mainly hosted within volcanic grains. Rapid silica precipitation from highly super-saturated water would explain the intense silicification of the plant remains found inside and outside the cave. The opaline stromatolites, the silica-tufa deposits and the above-mentioned intense general silicification suggest a local hydrothermal source for the silica. Indeed, these deposits strongly resemble plant-rich silica sinter associated with low-temperature hot spring deposits that include bacterial filaments. However, no geochemical signals that might indicate a hydrothermal origin could be found.
publishDate 2014
dc.date.none.fl_str_mv 2014
2015
dc.type.none.fl_str_mv info:eu-repo/semantics/article
http://purl.org/coar/resource_type/c_6501
Postprint
info:eu-repo/semantics/acceptedVersion
format article
status_str acceptedVersion
dc.identifier.none.fl_str_mv http://hdl.handle.net/10261/126076
url http://hdl.handle.net/10261/126076
dc.language.none.fl_str_mv Inglés
language_invalid_str_mv Inglés
dc.relation.none.fl_str_mv Sí
dc.rights.none.fl_str_mv info:eu-repo/semantics/openAccess
eu_rights_str_mv openAccess
dc.publisher.none.fl_str_mv John Wiley & Sons
International Association of Sedimentologists
publisher.none.fl_str_mv John Wiley & Sons
International Association of Sedimentologists
dc.source.none.fl_str_mv reponame:DIGITAL.CSIC. Repositorio Institucional del CSIC
instname:Consejo Superior de Investigaciones Científicas (CSIC)
instname_str Consejo Superior de Investigaciones Científicas (CSIC)
reponame_str DIGITAL.CSIC. Repositorio Institucional del CSIC
collection DIGITAL.CSIC. Repositorio Institucional del CSIC
repository.name.fl_str_mv
repository.mail.fl_str_mv
_version_ 1869425650380570624
score 15,811543

Similares en LA Referencia