Modelo de sedimentacion arenosa y fangosa en canales fluviales: Grupo Neuquen Inferior, Cretacico, Argentina Occidental

Abstract

ABSTRACT. The lowermost section of a thick Albian(?)-Campanian redbed sequence in the central part of the Neuquen Basin is composed of fine sandstones and pelites with subordinated extra and intraformational conglomerates. Several facies and sedimentary bodies have been recognized and described in the 35-40 m thick studied sequence. The most typical sediment bodies are: a. cross-bedded and ripple-bedded sandstones formed by sandwave, dune and current-ripple migration; b. tabular sections of intraconglomerates, massive and rippled mudstones; and c. large sea le IHS pelite rich sets characterized by successive 15 m long sigmoidal bundles; paleocurrent trends suggest that these IHS sets were built by lateral accretion processes. The tabular, multistorey and amalgamated cross-bedded sandstone bodies of the lower section suggest a low sinuosity and bed-Ioad fluvial depositional system. This system is followed by an association of aeolian and poorly channelized fluvial sediments represented by loess-type muddy deposits and levee-crevasse splay intraconglomerates and rippled mudstones. The third and most interesting model, identified towards the top of the sequence, is a suspended load dominated fluvial system, mainly represented by the IHS pelite rich sets. This model resembles the deposits of tidally influenced point bars, but is assigned here to a high sinuosity meandering system with very wide bends, developed in a low gradient-poorly vegetated continental flood plain.