SHORELINE FORMS AND DEPOSITS IN GALLOCANTA LAKE (NE SPAIN)

The Quaternary evolution of Gallocanta Lake (central Iberian Chain, Spain) is deduced from comparison between ancient deposits and present shoreline sedimentary forms. Present shoreline dynamics in the lake are controlled by persistent winds, parallel to the long-axis of the lake, creating wave fronts at the shore and net longshore currents. Present lake level fluctuations lead to a shoreline progradation during periods of lowering and to a partial erosion of ancient deposits during periods of rising level. Quaternary deposits in the region are represented by stepped lacustrine terraces which reflect a greater extension of the lake in the past. The sedimentological analysis of such deposits shows that their origin is linked to past lake-level fluctuations. Short-term (e.g. seasonal to multi-annual) fluctuations would have led to the building of a single terrace level by shoreline progradation processes. Long-term fluctuations, related to regional climatic changes, would have led to the present landscape of stepped terraces, reflecting a progressive aridification of the area.