Soft-Sediment Deformation Associated with Mass Transport Deposits of the Ainsa Basin (Spanish Pyrenees)

摘要

Mass-transport deposits (MTDs) are well developed on the slope of the Eocene Sobrarbe delta (Ainsa Basin, Spanish Pyrenees) and are studied in order to improve the understanding of soft sediment deformation in MTDs. The five examples illustrate the distinction between the extensional zone and the compressional domain. The upslope domain is illustrated by a set of three stacked nummulite-rich slid layers. They are deformed by load structures suggesting density inversion and sinking of nummulite gravel down into the underlying silty-shaly material. Post-sliding deformation is evidenced from small-scale roll-overs, neptunian dykes and syn-sedimentary normal faults. Slow extensive deformation has continued in the substratum of the scar after the main sliding episode. Soft-sediment deformation is less obvious in large displaced blocks where deformation is limited at the periphery of the blocks. Imbricate thrusts, formed on the side of a sliding layer, illustrate structures related to displacement. Striations on the thrust planes indicate that sliding occurred along the strike of the imbricate slices. The km scale Castellazo outcrop shows slump folds resting over a basal debris flow.