Reliable C-14 AMS dates on bird and Pacific rat Rattus exulans bone gelatin, from a CaCO3-rich deposit

We tested the reliability of accelerator mass spectrometry (AMS) radiocarbo n dates on bone gelatin by dating samples whose maximum or minimum age was constrained by stratigraphic position relative to well-dated volcanic tephr a layers. The tephra layers were not reworked, and were thick enough to pre clude the possibility of redeposition resulting in specimens being found ou tside the age bounds set by the tephras. The damp, fossiliferous, carbonate -rich sediment was in a relatively constant, cool environment in a small ca ve at nearly 900 m altitude. Bones from four species of bird with different diets (a pigeon, a rail, an owlet-nightjar, and a large ratite) and one ro dent, the Pacific rat Rattus exulans, were dated. The calibrated (calendar) AMS age of each bone was compared to ages predicted from their stratigraph ic position and calculated sedimentation rates, inferred from the age of ea ch tephra layer. Samples of moa (Aves: Dinornithiformes) eggshell were also dated by AMS, providing an independent dating material. None of the bone g elatin or eggshell dates displayed any significant in-built (reservoir) age relative to the marker horizons, nor were any AMS ages significantly young er than expected. Our results agree with previous studies in showing that C -14 AMS dates on bone gelatin from deposits that have always had a relative ly cool, and stable physical environment are likely to be reliable. For bon es protected from weathering before burial, and then incorporated in a stab le, carbonate-rich environment, the filtered bone gelatin procedure used in this study is adequate to give reliable AMS ages. Possible reasons for dis crepancies in bone gelatin AMS dates relative to marine shell, or charcoal dates from archaeological sites in dune deposits, are also discussed.