%0 Journal Article
%T Estratigraf¨ªa, Paleontolog¨ªa y Edad de la Formaci¨®n Las Ventanas (Neoproterozoico, Uruguay)
%A Blanco
%A Gonzalo
%A Gaucher
%A Claudio
%J Latin American journal of sedimentology and basin analysis
%D 2005
%I Scientific Electronic Library Online
%X las ventanas formation (fmlv), defined and mapped by midot (1984), is composed by a thick, finingand thinning-upward sequence covering an area in excess of 120 km2 of the southern nico perez terrane, uruguay (fig. 1). the structure in its type area corresponds to an ample syncline (cerro las ventanas syncline) with an axis oriented s20w (figs. 2, 7f). las ventanas formation is here subdivided into the following members: la rinconada member, quebrada de viera member and el perdido member (figs. 2, 4-5). la rinconada member is made up of basic volcanics, mainly basalts, vulcanoclastic breccias and subordinate basic tuffs, reaching 500 m in thickness (fig. 6). it is overlain with erosional unconformity by the quebrada de viera member, which is composed by polymictic conglomerates, grading to conglomerate-sandstone intercalations up section (fig. 7a-d). maximum thickness reaches 3800 m. lithoclast composition shows provenance from a mixed volcanic (basic and acid) and granitic source area (fig. 8a-b). whereas basalt clasts are more common at the base, rhyolitic clasts and intercalated rhyolitic tuffs occur at the top of the quebrada de viera member (fig. 5). the overlying el perdido member (600 m measured thickness) is characterized by laminated siltstones and shales (figs. 7e-f, 9), showing reddish colours at the base and green and grey colours at the top. abundant pyrite at the top of this member indicates disoxic or anoxic conditions (fig 7e-8d). thus, las ventanas formation represents a deepening-upward sequence, recording evolution from an alluvial fan-dominated environment to shallow marine conditions with occasional storms indicated by hummocky cross stratification at the top of quebrada de viera member (fig. 9). petrography shows compositional and textural immaturity of conglomerates and sandstones which together with sedimentary structures point to a steep palaeorelief. las ventanas formation is intruded by syenites of the sierra de animas formation, which yiel
%K neoproterozoic
%K vendian
%K ediacaran
%K acritarchs
%K uruguay.
%U http://www.scielo.org.ar/scielo.php?script=sci_abstract&pid=S1851-49792005000200004&lng=en&nrm=iso&tlng=en