RADICOARBON ACTIVITY OF SHELLS FROM LIVING CLAMS AND SNAILS
Measurements were made of the natural C/sup 14/ activity of shells from living clams and snails collected from a variety of environments. Three samples were measured, representing growth in lime-poor, fairly soft, and lime-rich waters. The tracer study indicated that a snail can incorporate 10 to 12% inorganic C in making its shell and the remainder of the C in the shell carbonate must come from food or the atmosphere, and the resulting C/sup 14//C/sup 12/ ratio will be essentially the same as in those sources. The control laboratory snails ate modern food (lettuce), whereas the natural snails ate food with a C/ sup 14/ /C/sup 12/ ratio similar to their environment and so showed the greater deficiency in C/sup 14/. The limiting value of a system in contact with the atmosphere is 50% dead C, theoretically possible, but not yet measured anywhere. Even such a great deficiency in C /sup 14/ as this produces a constant error in the dating of unknown nonmarine carbonate samples of one C/sup 14/ half life (5568 or 5730 years). Of greater significance is the postdepositional alteration and replacement of the original shell composition, which can add or subtract material. Neither visual nor mineralogic criteria can be used to predict the degree of this alteration. This can be determined only by mass spectrometric isotopic studies. (auth)
- Research Organization:
- Geological Survey, Washington, D.C.
- NSA Number:
- NSA-17-034136
- OSTI ID:
- 4668405
- Journal Information:
- Science See Saiensu, Journal Name: Science See Saiensu Vol. Vol: 141; ISSN SIENDS1
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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