CLIMATIC AND NON-CLIMATIC LAKE-LEVEL CHANGES INFERRED FROM A PLIOPLEISTOCENE LACUSTRINE COMPLEX OF CATALONIA (SPAIN) - PALYNOLOGY OF THE TRES-PINS SEQUENCES

A 27-m sequence of deposits from the Plio-Pleistocene Banyoles-Besalu lacustrine complex, at Tres Pins, N.E. Spain, shows lithological, carb onate, pollen and spores, and ostracode-gastropod evidence of climatic and lake-level change. Upland pollen taxa from the lowermost zones 1, 3 and 5, show that the area was forested and indicate a progressive d eterioration of the climate. Zone 2 (steppe vegetation) corresponds to a global glacial stage, with mild temperatures, if the comparison Co modern analogues is valid. Only minor climate fluctuations occurred su bsequently. Aquatic vegetation and micritic sediment facies show a pel agic environment during pollen zones 1 and 3 and a littoral one during pollen zone 5. A short-term lowering of the water level (sandy algal micrite and slightly brackish waters) occurred in zone 2, as a result of severe droughts. Subzone 2c records progressive recovery of the for est. The coarse lithology and the high carbonate content, however, con tinue to indicate shallow waters. The fluctuation marked by zone 4 (ex tensive marsh vegetation and spring waters) may be due to a lake-level decrease caused by karst activity, or by lower precipitation with onl y slight cooling, or more probably by a relative lake-level decrease c aused by natural infilling. The sediment of pollen zone 4, a sandy alg al micrite, indicates the development of a littoral bench at the core site. From pollen zone 4 to pollen zone 5 an evolution from lakeward t o landward position occurred. In zone 2, droughts existed at least dur ing the spring growing season, and probably also during the rest of th e year. In subzone 2c, a shift to spring precipitation occurred. In co ntrast, during pollen zone 4, if there was a decrease in precipitation , it did not take place during the summer growing season.