Braided stream and flood-plain deposition in a rapidly aggrading basin: the Escanilla formation, Spanish Pyrenees

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Abstract
Models of braided stream deposition have largely been developed from studies of regionally degrading and laterally confined alluvial environments. Glacial outwash streams, in particular, have supplied important and widely cited descriptions of intra-channel processes. These fluvial systems are typically confined within quite narrow valleys. It is felt that such systems have low long-term preservation potential and are unlikely to be present in the geologic record in large quantities. Therefore, the study of these modern laterally confined degradational systems may not provide holistic analogs of the larger-scale alluvial architecture developed in braided river environments in the ancient. The Escanilla Formation of the Spanish Pyrenees provides a well-exposed example of an Eocene fluvial system flowing axially within the Pyrenean foreland basin. Sedimentologic study shows coarse channelized deposits of braided character wholly enclosed within large amounts of fine-grained overbank mudstones and siltstones (>40% by volume), with both being deposited coevally across the Escanilla floodplain.