THE ARCHEOLOGICAL RECORD OF HUMANS AROUND SPRINGS

Spring deposits and their associated wet meadows, marshes, and outflow channels (ground-water discharge deposits, for short) are very widespread in the geologic record, but probably under-recognized because of their similarity to lake deposits. Ground-water discharge deposits appear differently in the geologic record depending on spring water chemistry, local geomorphology, and sources of detritus. Actual cauldrons associated with the springs themselves are rarely preserved. Commonly preserved features of ground-water discharge deposits are (1) green (reduced) but extensively bioturbated sediments associated wet meadows and wetlands, (2) localized extent, (3) a mix of terrestrial semi-aquatic, and aquatic snail taxa, and (4) lack of associated high-energy shoreline deposits. In this talk we examine the sedimentology, paleontology, and associated archeology of two springs systems in the deserts of northern Chile and central Tibet. The Chilean spring deposits in the hyperarid Atacama Desert are dominated by diatomites, phreatic salts, and abundant, well-preserved plant remains. The deposits date to the 17 to 9 ka period, when the Atacama in general was wetter, and the deposits contain abundant Paleoindian archeology. The Tibetan ground-water discharge deposits developed on the margins of the Tsangpo River, as a result of rising ground-water invading dune fields. They are distinguished by abundant sand, wet sediment and possibly cryogenic deformation, and black mats. The deposits date to the first half of the Holocene, consistent with high lake levels in Tibet, and contain in situ microlithic archeology.