Mid-Holocene Climate in the South-Central Andes: Humid or Dry?

) have concluded thatgenerally drier conditions prevailed.We argue that wet conditions result in high-er river discharge and erosion, whereas accu-mulation of fine materials in a steep valleyrequires overall decreased river flow and a low-energy environment. With dry conditions, fine-grained but permeable sediments that accumu-late in the valley bottom may form local aqui-fers and raise the groundwater table, despite alarger cross section in the valley and reduceddischarge overall. Modern analogs show thatgroundwater tables in such wetlands are oftenself-sustained, very local, and disconnectedfrom their surroundings, and are thus difficult tointerpret in terms of climate conditions. Today,the rivers in both the Tula´n and Puripica valleysare erosive and have dissected the mid-Holo-cene sediments down to bedrock. Typically,sediments from between 14 and 9 ky B.P., aperiod of well-documented, extreme humidity,are missing in these valleys because of strongerosion, whereas, as expected, sediments fromthis humid period are present in fossil springcomplexes [Tilomonte Springs, figure 4 in (