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The Pleistocene footprints are younger than we thought: correcting the radiocarbon dates of Ruppia seeds, Tularosa Basin, New Mexico

Published online by Cambridge University Press:  10 January 2024

David M. Rachal Open the ORCID record for David M. Rachal [Opens in a new window] ,
Robert Dello-Russo Open the ORCID record for Robert Dello-Russo [Opens in a new window]  and
Matthew Cuba Open the ORCID record for Matthew Cuba [Opens in a new window]
David M. Rachal*
Affiliation:
Tierra Vieja Consulting LLC, Las Cruces, New Mexico 88005, USA Jornada Research Institute, Tularosa, New Mexico 88352, USA
Robert Dello-Russo
Affiliation:
Director Emeritus—University of New Mexico, Office of Contract Archeology, Livingston, Montana 59047, USA
Matthew Cuba
Affiliation:
Holloman Air Force Base, Alamogordo, New Mexico 88330, USA
*
Corresponding author: David M. Rachal; Email: geoarchnewmexico@gmail.com
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Abstract

Past studies have demonstrated that Ruppia cirrhosa (Ruppia), which typically grows in brackish water, is far too unreliable to serve as the chronological basis for radiocarbon dating because of the hard water effect (HWE). Despite this unreliability, Ruppia seeds have been used to date footprints along the margins of paleo-Lake Otero in southern New Mexico to around 23,000–21,000 cal yr BP. In this study, we employ a modern analog approach using δ13C values and radiocarbon dates from modern Ruppia plants growing in Salt Creek to calculate a maximum limiting age range for the footprints. Those plant samples with higher δ13C values produced greater age discrepancies. This simple relationship can be used to correct for the HWE and demonstrates that the human footprints purported to have been made during the local last glacial maximum could be at least ~7500 yr younger.

Keywords

Hard water effectPleistocene footprintsNew MexicoModern Ruppia

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Type
Research Article
Information
Quaternary Research , Volume 117 , January 2024 , pp. 67 - 78
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Copyright © The Author(s), 2024. Published by Cambridge University Press on behalf of Quaternary Research Center

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