GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 111-5
Presentation Time: 9:10 AM


STINCHCOMB, Gary E., Watershed Studies Institute & Dept. of Geosciences, Murray State University, 334 Blackburn Hall, Murray, KY 42071, LEVIN, Naomi E., Earth & Environmental Sciences, University of Michigan, 2534 C. C. Little Building, Ann Arbor, MI 48109-1005, PEPPE, Daniel J., Terrestrial Paleoclimatology Research Group, Dept. of Geosciences, Baylor University, One Bear Place #97354, Waco, TX 76798-7354, DIPIETRO, Lyndsay, Department of Geology, Baylor University, One Bear Place #97354, Waco, TX 76798, ROGERS, Michael J., Department of Anthropology, Southern Connecticut State University, 501 Crescent Street, New Haven, CT 06515 and SEMAW, Sileshi, Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), Sierra de Atapuerca 3, Burgos, 09002, Spain,

Previous work has shown that early Oldowan archaeological sites ≥2.0 Ma are associated with restricted areas on the landscape, often close to water and raw material; whereas Acheulian archaeological sites ≤1.7 Ma are found in a wider variety of settings, coinciding with the emergence and proliferation of Homo erectus. We provide more context to this understanding of hominin-landscape interaction using paleopedology and analyzing a sample (n=9) of paleosols from Gona, Ethiopia at artifact and hominin sites that are either ~2.6 Ma (Oldowan) or <1.7 Ma (mainly, but not exclusively, Acheulian). Paleosols at ~2.6 Ma sites are thin paleo-Entisols with A-C horizons; whereas paleosols at <1.7 Ma sites are thicker paleo-Inceptisols and –Vertisols with overprinted Ak-Bk or ABkss-Bkss horizons. The ~2.6 Ma paleosols often had many prominent very fine channel pores commonly created by grasses; whereas the <1.7 Ma paleosols occasionally had medium to coarse rhizoliths indicative of tree roots. Using bulk geochemistry, the mean integrated Na loss is ~9 times higher for <1.7 Ma paleosols (-6.0*10-3 mol cm-2) than for ~2.6 Ma paleosols (-6.8*10-4 mol cm-2).

The paleosol data suggest that ~2.6 Ma artifact sites occurred on relatively unstable landscapes that allowed little time for mature paleosol development. Conversely, sites <1.7 Ma occurred on or near paleosols that achieved relative stability that was long enough to develop calcareous subsoil. We quantified duration of weathering by calculating a Residence Time (RT) for each paleosol, where the integrated Na loss over the profile (mol cm-2) was divided by the inferred mean Na outflux for the basin (mol cm-2 y-1). The solution yields a rough estimate of how long, in years, Na was weathered out of the profile. The RTs for ~2.6 Ma sites leached Na on average for 540±290 years prior to burial, ranging from 349 to 970 years; whereas, RTs for <1.7 Ma sites leached Na on average for 3000±4300 years, ranging from 102 to 10,431 years. An F test for equality of variances shows that for the two RT groups, ~2.6 Ma and <1.7 Ma, the variances are not equal (p=0.0005). Our observation of longer and overall more variable residence times associated with <1.7 Ma sites is consistent with the hypothesis that Acheulian technology was found, or used, on a greater variety of landscapes than Oldowan sites.