ENVIRONMENTAL CHANGES IN HIGHLAND VALLEY HEAD AREAS DURING THE LATE PLEISTOCENE OF SANTA CATARINA STATE, SOUTHERN BRAZIL

Pedostratigraphic units have been studied in the North of Santa Catarina State, Southern Brazil. The study area is situated on a plateau at about 1.000 meters elevation. According to Köppen’s nomenclature the local climate is of the "Cfb" type. Although degraded, multi-layer Araucaria forests and Campos (grassland) compose the dominant vegetation today. Hills and valleys dominate geomorphology, under the structural influence of the area’s Eo-Paleozoic basement. Two sites have been studied, near the interior border of the "Serra do Mar" mountain ranges. The sites are located in valley heads, above smooth Quaternary floodplains.

Thick histic paleosoils and peat bogs developed over Bw cambic horizons during the Quaternary. These soils alternate with colluvial strata, indicating pulses of erosion and sedimentation. Older layers are lenticular, while the younger develop cut and fill structures.

In one site, radiocarbon ages for the histic horizons suggest the development of paleosoils around 19,130 years BP ±110 and 15,260 years BP ±80. Colluvial lenses covered the last glacial maximum soil while the younger soil was dissected by gullies. This sedimentary pattern was interpreted as evidence for a change in environmental conditions.

At the second site a peat bog buried under 4.5 meters of colluvium had been described. Radiocarbon ages for the 150 cm long peat section gives >50,000 years BP for its base and 49,300 years BP ±6,970 for its top. Pollen analytical studies on that peat indicate the predominance of Campos with small areas of forest during the glacial period record. Subtropical Araucaria forests probably occurred as gallery forest in the valleys. Araucaria angustifolia itself was not presented in that record. Pollen composition of the samples suggests two periods of stable conditions. The higher representation of Podocarpus trees during the younger period (0-45cm) suggests a climate colder than that of the older period, where trees of Weinmannia were stronger represented.

Radiocarbon dates for the Late Pleistocene record of the sites are correlative to marine isotopic stages 2 and 3. Morphogenesis and pedogenesis alternate along this period. Dryer climate seems to have been dominant during the period, although an excess of precipitation over evaporation is needed to explain the development of water logged soils.