Integración de facies y biofacies en un análisis secuencial en plataformas clásticas Devónicas del sur de Bolivia y noroeste Argentino Integration of facies and biofacies in a sequence analysis in detrital platforms from Devonian of southern Bolivia and northwestern Argentina

Se exponen los resultados obtenidos del análisis de facies, asociaciones de facies, ambientes y estudio de biofacies en la cuenca silúrico-devónica del subandino sur de Bolivia y del noroeste de Argentina, analizada en su tramo devónico. Se expone la bioestratigrafía utilizada en esta cuenca, tanto en base a palinomorfos como fauna bentónica. Se caracterizan los ambientes y subambientes en una plataforma silicoclástica marina desarrollados en 19 Secuencias Genéticas, entre el Lochkoviano y el Frasniano. Se plantea un modelo de distribución de facies y de ambientes. Finalmente se estudian las biofacies desarrolladas durante etapas de contracción y de expansión de esta cuenca. A silurian-devonian basin of southern Bolivia and northwestern Argentina (Figs. 1, 2) is interpreted as a backarc basin developed in a noncontracted margin, like a Java system (Fig. 3). In this basin, 19 Genetical Sequences are described in a continuous sedimentation from Ludlowian to Frasnian (Fig. 8). In this paper we analize the Devonian interval. Data from facies analysis, facies associations, environments and biofacies of this basin are presented (Figs. 4, 5). The biostratigraphy of the basin is based in palynomorphs and benthic fauna. Palynological analysis is based in world wide associations and First Occurrence Biozone for each association. Chitinozoans, acritarchs, spores, and others are considered to determine the age of each sample. Benthic fauna are divided in two types, specialized and non-specialized. The former is considered an important fauna to date. This fauna is calibrated with other basins outside Gondwana (Table 1). Facies and environmental conclusions are placed in an eustatic curve designed for this period. 21 facies associations are described and exposed (Figs. 4, 6, 7). Environmental determinations in a marine siliciclastic platform developed in 19 Genetical Sequences from Lochkovian to Frasnian are characterized (Fig. 8). Seven marine environments are described and placed in a model where facies associations and environments present a logical distribution (Fig. 5). Biofacies are studied during contracted and expanded periods. During contractions, in normal regressions of Pragian and Emsian age, biofacies are more diversified and frequent than biofacies developed in the same conditions during Eifelian expansions of the basin (Fig. 10). During forced regressions, biofacies are less diversified and poorly distributed in space (Fig. 11). In this platform type, development of benthic fauna is a function of available space and eustatic changes. During a second or