ESR ANALYSES AN OPEN-AIR PALEOLITHIC SITE: HINTS ABOUT U UPTAKE, WATERTABLE MIGRATION, REWORKING, AND PALEOENVIRONMENTAL CHANGE AT ATTIRAMPAKKAM, INDIA

At Attirampakkam, in Tamil Nadu, India, a stratified open-air Paleolithic site, that has never been successfully dated, yielded Acheulian artefacts from Pleistocene fluvial sediment. Near the Kortayallar River and the Indian Ocean, Attirampakkam is prone to sealevel fluctuations, fluvial channel migrations, abandonment, and avulsions. Interbedded in laminated clay, ferricalcrete, calcrete, and ferruginous gravel beds, Attirampakkam is the type site for the Mandras Handaxe Tradition of the Indian Acheulean (Lower Paleolithic). The archaeological layers have yielded six Pleistocene vertebrate fossils, including the three teeth dated here.

Electron spin resonance (ESR) can date tooth enamel between 5 ka and 5 Ma. Few ESR studies have used teeth from open-air sites, which often suffer from severe, pervasive, and rapid diagenetic alteration and weathering, producing teeth that are difficult to prepare for ESR analysis. All the available teeth were analyzed ESR. Despite their diagenetic alteration, the teeth yielded 20 independent ESR enamel ages, and three ESR isochron analyses. Diagenetic alteration features in two teeth indicated rapid submergence in quiet saline to hypersaline water, following a short subaerial exposure, while the third remained constantly buried in reducing conditions. Hence, their dates also indicate the timing for the geochemical and sedimentological events affecting the site. All the geochemical, standard and isochron ESR analyses indicate that the teeth experienced at least three independent U uptake events during diagenesis, including two that occurred long after the samples' burial by sediment. Assuming linear U uptake (LU) adjusted for the multiple U uptake events, the teeth averaged 45-50 ka. Numerous animal burrows, the geochemistry of the teeth's coatings, and artefact displacement, suggest that the teeth were reworked from the Middle or Upper Palaeolithic layers higher in the site which, therefore, correlate with Oxygen Isotope Stage 3.