Miami Natural Radiocarbon Measurements II

Abstract

The C14 dates given below are a continuation of the work presented in our first list (Miami I) using the same apparatus and techniques described previously. In addition to the dating of marine carbonate materials, however, we have extended our methods to the dating of wood and peat samples. All dated peat and wood samples have been given a standard pretreatment by successive washings with dilute HCl and 2% NaOH solution for removal of carbonates and humic acids (Olson and Broecker, 1958). Where sufficient alkali-soluble "humic acid" was recoverable for analysis, this fraction was dated separately and is included with the date obtained from either the wood or peat.The reported ages were obtained by using a 1.0-L CO2 proportional counter operating at 3 atm pressure. Samples were measured at least twice for a 1000-minute counting period each and a minimum of 14 days between counting periods. In cases where dilution was necessary because of small sample size, those samples were counted three times. Ages are C13 corrected and have been calculated in the usual way by comparison with the 95% activity of the NBS standard, using a half life of 5568 ± 30 yr, referred to A.D. 1950. From the calculated age of marine carbonate material we have subtracted 400 yr as an apparent sea-surface carbonate age (Miami I). No such correction is made for organic material. The uncertainty in the given ages includes the experimental standard deviation in the count rate of the modern standard, the unknown and the background, and the standard deviation of the half life of C14. ACKNOWLEDGMENTS

Insights into barrier-island stability derived from transgressive/regressive state changes of Parramore Island, Virginia

“…1000 years ago, as evidenced by washover deposits found overtopping in situ C. virginica in northern Parramore. This relative sequencing of deposits matches well with that identified along the southwestern side of Hog Island, where radiocarbon analyses from peat samples and in situ shells (Mercenaria campechiensis) from an underlying shell bed date to about 1100 years BP and 1400 years BP (re-calibrated ages), respectively (Rusnak et al, 1963;Harrison et al, 1965). Rice et al (1976) interpret these as evidence of an earlier, overwashdominated "proto-Hog Island".…”