Petrología y evolución diagenética de las facies silicoclásticas del Grupo Sierras Bayas, Sistema de Tandilia, Argentina

the neoproterozoic sedimentary sequences of the tandilia system basin are represented in the olavarría area by interstratified shallow marine, silicoclastic and carbonate units comprising, from oldest to youngest, for the villa mónica, cerro largo and olavarría formations of the sierras bayas group (fig. 1). these almost undeformed and unmetamorphosed siliciclastics sedimentary units allowed studying the different diagenetic regimes due to the preservation of postdepositional features and, also, of many depositional and eodiagenetic ones. in the study area de sierras bayas group is composed of the villa mónica (conglomerates, sandstones, shales and dolostones), cerro largo (chert breccias, quartz-sandstones and siltstones), olavarría (mudstones) and loma negra (limestones) formations with a thickness up to 185 m (figs. 2 and 3; i？iguez, et al., 1989; poiré, 1987a, 1993; gómez peral, 2008). the siliciclastics facies of the sierras bayas group are composed of conglomerates, sandstones and mudstones, represented in the basal section of the villa mónica formation and the cerro largo and olavarría formations (fig. 4). the objective of the present study was to reveal the sequence of diagenetic processes represented in the silicoclastic facies from a detailed petrological analysis. it included the recognition of the allogenic and authigenic components, the characterization of the diagenetic microfabrics (chemical and compactational), the definition of microfacies and the interpretation of the postdepositional burial history from the determination of paragenetic sequences. besides, a revision of the classical depositional facies chart was performed. considering that different factors may influence the diagenesis of sediments at different times during its evolution (kantorowicz, 1985), the general controls on diagenesis include the depositional mineralogy, the depositional-water chemistry, the change in pore fluid composition, the inferred burial pressures and the temperatur