PP13A-2269
C and N Isotopes in Ostrich Eggshell as Proxies of Paleovegetation and Paleoprecipitation: Extraction, Preservation, and Application to Pleistocene Archaeological Samples

Monday, 14 December 2015
Poster Hall (Moscone South)
Elizabeth M Niespolo, University of California Berkeley, Earth and Planetary Science, Berkeley, CA, United States, Warren D. Sharp, Berkeley Geochronology Center, Berkeley, CA, United States, Christian A Tryon, Harvard University, Cambridge, MA, United States, J. Tyler Faith, University of Queensland, St Lucia, Australia, Melanie Miller, University of California Berkeley, Anthropology, Berkeley, CA, United States and Todd E Dawson, University of California Berkeley, Center for Stable Isotope Biogeochemistry, Berkeley, CA, United States
Abstract:
Paleoenvironmental change is commonly invoked as a factor in the development of modern human behaviors and the successful expansion of H. sapiens out of Africa, and paleoenvironmental information from archaeological sequences is central to addressing such questions. Ostrich eggshell (OES) are common in many African archaeological sequences and may be dated by 14C and U-series methods. In modern ratite eggshells (large flightless birds including the ostrich and emu), the δ13C in eggshell calcite and the δ13C and δ15N in eggshell organic fractions have been shown to vary systematically across climate gradients in South Africa and Australia with δ15N varying inversely with mean annual precipitation, and δ13C varying with the C isotopes of vegetation (1,2). Thus, if primary C and N isotopic signatures are preserved, assemblages of OES can provide dated records of paleovegetation and paleoprecipitation at archaeological sites. Since the C isotopic fractionation between calcite and eggshell organics is constant in modern OES (Δ13Ccalcite-organic = 14.7 ± 1.3‰) (3), evaluating that offset in ancient OES provides a test for preservation of primary isotopic signatures. Johnson et al. (3) showed that OES from Equus Cave (South Africa) retained the expected fractionation for up to 17 ka. We present a new protocol to extract C and N of OES organics for online analysis that preserves pristine δ13C and δ15N values and C and N contents. We find that using sodium hydroxide (NaOH), common to many bone collagen extraction procedures, destroys and degrades the organic component of OES, resulting in low C and N and altered δ13C and δ15N values. Analysis of a series of OES samples directly dated by 14C and U-series from the GvJm-22 rockshelter (Lukenya Hill, Kenya) (4,5) will demonstrate the first application of this protocol to OES from the last ~50,000 yr.

1. Johnson, B.J. et al. (1998) Geochim. Cosmochim. Acta 62, 2451-2461.

2. Newsome, S.D. et al. (2011) Oecologia 167, 1151-1162.

3. Johnson, B.J. et al. (1997) Palaeogeog. Palaeoclimatol. Palaeoecol. 136, 121-137.

4. Tryon, C.A. et al. (2015) PNAS 112, 2682-2687.

5. Sharp, W.D. et al. (2015) Abstract for AfQUA, Cape Town, South Africa.

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