PALEOWETLAND DEPOSITS IN THE NORTHERN ATACAMA DESERT: ARCHIVES OF CLIMATE CHANGE AND HUMAN MIGRATIONS

Recent climate reconstructions gained from the radiometric dating of paleowetland deposits indicate a protracted history of wetter conditions coeval with the Central Andean Pluvial Event (CAPE) in the Atacama Desert of northern Chile during the latest Pleistocene and early Holocene. Moreover, as wetlands are often a focal point of human activity in arid environments, paleowetland deposits often contain archaeological sites. Although more hospitable conditions prevailed during this time, the archaeological record is still quite sparse. A recently discovered archaeological site (QM12c), which dates from 12.8-11.6 ka, has shed new light upon the relationship between climate and Paleoindian culture in the Atacama. Past climate change facilitated the settlement of the Atacama by early hunter-gatherers and demonstrates new prospects for understanding the complex peopling of South America.

Quebrada Mani is a hyperarid watershed in the northern Atacama that is sourced in the high Andes. Through the analysis of the alluvial stratigraphy of Quebrada Mani, along with the identification and analysis of the paleowetland deposits associated with QM12c, the latest Pleistocene and early Holocene climate history reveals evidence of wetter conditions coeval with CAPE. Terrace surfaces abound with organic material by which over twenty-five AMS radiocarbon dates indicate that these terraces were formed during a brief interval characterized by high water tables between 17.6-11.4 ka. Two distinct stratigraphic units, separated by an unconformity, were identified among the wetland facies which correspond with the two pluvial phases of CAPE Coiposa and Tacna (ca. 15,900-13,800 and 12,700-9,700 ka). Unit 1 is characterized by interbedded alluvial gravels and diatomaceous silts with interspersed organic mats and has been ¹⁴C dated to 15,108-16,022 ka (Coiposa) and 9,238 ka (Tacna). Such ecosystems would have constituted attractive oases to groups of hunter-gatherers in an otherwise barren landscape.