Resumo

ALVAREZ, Luis A; DALENZ-FARJAT, Alejandra; HERNANDEZ, Roberto M  e  ALBARINO, Luis. Integration of facies and biofacies in a sequence analysis in detrital platforms from Devonian of southern Bolivia and northwestern Argentina. Rev. Asoc. Argent. Sedimentol. [online]. 2003, vol.10, n.2, pp.103-121. ISSN 1853-6360.

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 order eustatic fall, a forzed regression could be determinated in the development of the benthic fauna. During expanded periods, biofacies developed in normal regressions during Eifelian and Giventian are less diversified and less frequent than biofacies developed during similar conditions in the Coger Devonian (Fig. 12). This process is controlled by boreal benthic fauna until the Eifelian. We propose a biofacies distribution model for this siliciclastic ramp (Fig. 13 and Table 2).

Palavras-chave : Facies association; Siliciclastic Environments; Biofacies; Devonian; Argentina; Bolivia.

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