ROCK VARNISH MICROLAMINATION, THE MID-HOLOCENE CLIMATE SIGNAL, AND THE RECORD OF HUMAN OCCUPATION IN THE SEMI-ARID INTERMOUNTAIN BASINS OF NORTHWESTERN ARGENTINA

CARLOS ALBERTO BAIED; CAROLINA SOMONTE

Congreso; 55 Congreso Internacional de Americanistas; 2015

We advance results of ongoing research on past environmental conditions and human occupation in the western piedmont of Cumbres Calchaquies, Argentina. We focus on two proxies that provide geochronological control and the possibility of extracting a palaeoclimatic signal: rock-varnish microlaminations and palynological studies. Ultrathin sections from  surface lithic scatters, gathered at the Amaicha Archaeological Locality (AAL), were analyzed providing varnish layering sequence that correlates with the age scale of radiometrically calibrated and climatically correlated Holocene millennial-scale varnish microstratigraphy of the western USA drylands varnish and the SPECMAP MIS 1 record. The applied technique provided minimum-limiting surface exposure ages of 7.3-5.9 ka for initial rock varnish formation on rocks and on non-chipped sections of human made tools, and on the negative scars of tools respectively. These dates represent the minimum age of rock varnish formation on lithic artifacts, meaning that artifacts are probably older. Beyond chronology, Amaicha varnish provided the first reliable data to date on regional scale mid-Holocene-to-recent climate change and variability.  Within the regional context of Holocene widespread arid-to-semiarid conditions, seven wetter intervals bracketed between 7.3 and 0.3 ka were identified. These wet events largely correlate with Holocene cooling events represented by pulses of detrital carbonate in the GISP2.