Reference : Opal-a Speleothems of Wei-Assipu-Tepui, Roraima Province, Brazil

	Document type :	Scientific journals : Article
	Discipline(s) :	Physical, chemical, mathematical & earth Sciences : Earth sciences & physical geography
	To cite this reference:	http://hdl.handle.net/2268/96884

Title :	Opal-a Speleothems of Wei-Assipu-Tepui, Roraima Province, Brazil
Language :	English
Author, co-author :	Urbani, Franco [> >]
	Compère, Philippe [Université de Liège - ULg > Département des sciences et gestion de l'environnement > Département des sciences et gestion de l'environnement >]
	Willems, Luc [Université de Liège - ULg > Département de géologie > Pétrologie sédimentaire >]
Publication date :	2005
Journal title :	Boletín de la Sociedad Venezolana de Espeleología
Volume :	39
Peer reviewed :	Yes
ISSN :	0583-7731
Keywords :	[en] cave mineralogy ; biomineralization ; opal-A ; quartzite ; Roraima ; Brazil
Abstract :	[en] Bol. Soc. Venezolana Espel. v.39 Caracas dic. 2005 ®download el artículo en el formato PDF Como citar este artículo Opal-a Speleothems of Wei-Assipu-Tepui, Roraima Province, Brazil Franco Urbani1, Phillipe Compère2 & Luc Willems2 1Universidad Central de Venezuela. Fac. Ingeniería. Escuela de Geología. Lab. de Geología y Geoquímica. Caracas 1053 y Sociedad Venezolana de Espeleología. Apartado 47028. Caracas 1041A. urbani@cantv.net 2Université de Liège, Laboratoire de Morphologie Ultrastructurale, Département des sciences et gestion de l'environnement, allée de la Chimie, 3, B-4000 Liège 1,Belgium. 3University of Liège. Laboratoire de Pétrologie Sédimentaire, Département de Géologie, B20, B-4000 Liege, Belgium.Lucwillems65@versateladsl.be ABSTRACT Coralloid-shaped speleothems samples were collected from a small cave in a mountain of the Roraima massif, Brazil. They were mineralogically identified as opal-A and show two concentric growth zones: A massive light colored inner one, and a darker outer zone with a spongy texture. On the surface the presence of some filaments probably of algae suggest biomineralisation. Chemically the outer zone shows impurities with high values of Cl and P. The leaching of bird nest guano may be the source of P. The two zones were probably formed in two different climatic conditions, the outer one in the current wet and vegetated period, and the inner zone during a former drier period.
Target :	Researchers ; Professionals ; Students
Permalink :	http://hdl.handle.net/2268/96884
Other URL :	http://www2.scielo.org.ve/scielo.php?script=sci_arttext&pid=S0583-77312005000100004&lng=es&nrm=is

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