T03_P13

Radiocarbon dating putative homonin coprolites

Roberts M¹, Trowbridge N¹, Lardie Gaylord¹, Sistiaga A^2,3, Haws J⁴, Mojarro A³, Summons R³

¹Woods Hole Oceanographic Institution, Woods Hole, United States of America, ²Center for Evolutionary Hologenomics, University of Copenhagen, Copenhagen, Denmark, ³Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, United States of America, ⁴Dept. of Anthropology, University of Louisville, Louisville, United States of America

Several coprolites from a homonin habitation site on the Iberian Peninsula were recently submitted for radiocarbon analysis. Coprolites are proxies of the presence and diet of ancient animal populations. Based on chronostratigraphy, an average age of at least 40 kyr BC was expected. Bulk analysis of the organic fraction of the individual coprolites returned an average calibrated age of 28,000 (+/- 1000) (calBC). To better understand the conflict between the expected and measured ages, and to accommodate the very low total organic carbon of the samples, the organic fraction of a composite coprolite sample was further analyzed using the ramped pyrolysis and oxidation (RPO) system at Woods Hole. The sample was sequentially oxidized from room temperature to 1000 C at 5 °C/min and the evolved carbon dioxide was collected from five different temperature ranges or fractions. The first four temperature fractions returned calibrated ages all less than 31,000 (calBC). However, the highest temperature fraction (525-705 ˚C) returned a calibrated age of 39,900 (+/- 8,800) (calBC) in agreement with the chronostratigraphy. Analysis of the fractions using pyrolysis-GC-MS showed that only the high temperature faction released steroid biomarkers consistent with fecal matter. Phytosterols were detected in addition to trace amounts of coprostanol. Furthermore, a high temperature fraction between 525-600 ˚C pyrolyzed in the presence of a silylating reagent (MTBSTFA/DMF) enabled the identification of cholesterol and cholestanol. Utilizing the RPO system for coprolite radiocarbon analysis may provide a more representative age than bulk organic analysis. Sample preparation and measurement procedures will be presented.