Sedimentary lobes in a tidally influenced alluvial area, Capella Formation, Tremp-Graus Basin, Southern Pyrenees, Spain

Abstract

Among the coarse clastic deposits of the mainly alluvial Capella Formation several sediment bodies with characteristics of depositional lobes are recognized. These lobes are characterized and distinguished from other macroforms by their geometry, basal contact and lithofacies. A classification of the lobes is proposed on the basis of the geometry and the lithofacies. The most common geometrical type is tabular to wedge-shaped; a second geometrical type is sigmoidal. Two main lithofacies types are distinguished on the basis of the bedding pattern: a horizontally and an inclined bedded type. The lobes were deposited in the lower part of an alluvial fan system. The sedimentation of some of the lobes was influenced by tidal currents. Several models of sedimentary lobes are recognized: overbank splay lobes, terminal lobes, debris flow lobes and spillover lobes.