Deep‐water delivery model of Ruppia seeds to a nearshore/terrestrial setting and its chronological implications for Late Pleistocene footprints, Tularosa Basin, New Mexico

Abstract

Ruppia cirrhosa (Ruppia) seed layers have been used to constrain the age of footprints along the eastern shoreline of Paleolake Otero in southern New Mexico to around 21,000–23,000 calibrated years before the present. However, there remain two unresolved questions that can affect the reliability of the age(s) of the footprints. First, what is the nature of the geological context of the seed layers? Second, did the hard‐water effect impact the accuracy of the radiocarbon dates? It has been argued that the dated Ruppia plants grew in situ in a very shallow, freshwater‐infused system that minimized the hard‐water effect. Many of these Ruppia seed layers contain ball‐like aggregations made of Ruppia plant materials. We provide new evidence that these balls and seed layers were introduced to the discovery site by high wind seiche events during Late Pleistocene thunderstorms. In our proposed site formation model, the Ruppia plants and seeds originated in deeper water settings outside the site, thus it is very likely that the hard‐water effect has impacted the accuracy of the radiocarbon dates. As such, the radiocarbon assays of Ruppia seeds previously used to date the prehistoric footprints along Paleolake Otero could be thousands of years too old.