6000-7000 Year Old Nautilus Shells Found

DWhatley

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THE NAUTILUS DEATH CENOTE

MAPES, Royal, Dept of Geological Sciences, Ohio University, 316 Clippinger Laboratories, Athens, OH 45701, mapes@ohio.edu, LIGNIER, Vincent, Laboratoire PPME, Université de la Nouvelle-Calédonie, BP R4, Nouméa, 98851, New Caledonia, LANDMAN, Neil H., Division of Paleontology (Invertebrates), American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192, HEMBREE, Daniel I., Department of Geological Sciences, Ohio University, 316 Clippinger Laboratories, Athens, OH 45701, GOIRAN, Claire, Biologie et Ecologie Marine LIVE, Université de la Nouvelle-Calédonie, BP R4, Noumea, 98851, New Caledonia, COCHRAN, Kirk, School of Marine & Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000, FOLCHER, Eric, Institut de Recherche pour le Développement, BP A5, Nouméa, 98848, New Caledonia, and BRUNET, P., AVENS, Ivry sur Seine, 94200, France

Exploration of a cenote on Lifou (Loyalty Islands, South Pacific) revealed more than 35 empty shells of the cephalopod Nautilus macromphalus in saltwater on the cenote floor, ~35-40 meters below the piezometric surface. This is the first known occurrence of modern Nautilus shells in a karstic system. The shells are scattered and oriented randomly on the sloping scree of the cenote floor. Most are mature individuals and are unbroken with faded brown stripes. Some have cemented carbonate mud partly filling the umbilical opening and body chambers. Seven shells were collected for analysis. These shells have a chalky outer surface but no mineral precipitates. No other organisms, living or dead, were observed on the Nautilus shell surfaces, attached to the limestone rubble, or anywhere in the cenote. Radiocarbon dating of the shells indicated ages of 6380 ± 30 to 7095 ± 30 y BP, making these the oldest Nautilus shells known since the Pleistocene. The [SUP]238[/SUP]U series radionuclides [SUP]210[/SUP]Pb (half-life = 22.3 y) and [SUP]226[/SUP]Ra (half-life = 1600 y) were also measured and generally showed radioactive equilibrium between these nuclides, consistent with their old radiocarbon ages. At least one specimen showed excess [SUP]210[/SUP]Pb, however, suggesting an age of
 

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