%0 Journal Article %T Neoproterozoic peritidal facies of the Villa Monica Formation, Sierra la J uanita, Tandilia Facies Peritidales neoproterozpicas de la Formaci車n Villa M車nica, Sierra La Juanita, Tandilia %A Marcelo Manassero %A Patricia E Zalba %A Martin E Morosi %J Revista de la Asociaci車n Geol車gica Argentina %D 2012 %I Asociaci車n Geol車gica Argentina %X From field observations and petrographic studies, a complex association of peritidal carbonate and siliciclastic facies have been recognized in the Villa M車nica Formation (Neoproterozoic), Sierra La Juanita, outcropping at the quarries of Estancia La Siempre Verde, Estancia La Placeres and Estancia Don Camilo, where carbonate facies have not been described 'in situ since their discovery in 1967. Three different detailed stratigraphic sections are fully described. On the one hand, calcareous facies (well-preserved head stromatolites) have developed in a shallow subtidal to lower intertidal environment. Laminated microbial mats, with millimetric to centimetric scale siliciclastic intercalations, were deposited in low-energy intertidal conditions. Shortlived continental input of quartzose clastic sediments did not obliterate the microbial colonies, which grow following a pattern of thin cycles. On the other hand, heterolithic facies, developed in high-energy intertidal conditions towards the top of the succession illustrate progressive change in the paleoenvironmental conditions which evolved from a shallow prograding carbonate platform, with periodical sea level oscillations, to siliciclastic tidal influenced littoral conditions with minor development of microbial mat deposits. The recognition of MISS'(microbiall)< induced sedimentary structures) represented by microbial mats developed in siliciclastic facies was decisive for the evaluation of paleoenvironmental conditions and for the decision to assign heterolithic lithofacies described in this paper to the Villa M車nica Formation. These microscopical structures suggest and alternation of organic microbial activity with tractive and suspensive events. The coast line was probably oriented N-S with the deeper facies located to the west. A paleoenvironmental model is proposed for the area. Una asociaci車n compleja de facies carbon芍ticas y silicicl芍sticas peritidales ha sido reconocida en la Formaci車n Villa M車nica (Neoproterozoico) aflorante en las Estancias La Siempre Verde, La Placeres y Don Camilo sobre la base de observaciones de campo y estudios petrogr芍ficos de detalle. Se describen tres secciones estratigr芍ficas en las cu芍les las facies carbon芍ticas no hab赤an sido descriptas "in situ" desde 1967. Las facies calc芍reas basales (estromatolitos columnares) se desarrollaron en ambientes intertidales profundos a subtidales someros. Estromatolitos laminares con intercalaciones silicicl芍sticas milim谷tricas a centim谷tricas se depositaron en condiciones intertidales de baja energ赤a. El aporte espor芍dico de sedimen %K Paleogeografia %K Estromatolitos %K Planicie mareal %K Neoproterozoico %K MISS %K Paleogeography %K Stromatolites %K Tidalflats %K Neoproterozoic %K MISS %U http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0004-48222012000100004