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Environmental significance of 13C/12C and 18O/16O ratios of modern land-snail shells from the southern great plains of North America

Published online by Cambridge University Press:  20 January 2017

Meena Balakrishnan
Affiliation:
Department of Geological Sciences, Southern Methodist University, Dallas, TX 75275-0395, USA
Crayton J. Yapp*
Affiliation:
Department of Geological Sciences, Southern Methodist University, Dallas, TX 75275-0395, USA
James L. Theler
Affiliation:
Department of Sociology and Archaeology, University of Wisconsin-La Crosse, La Crosse, WI 54601, USA
Brian J. Carter
Affiliation:
Oklahoma Museum of Natural History, University of Oklahoma, Norman, OK 73019, USA
Don G. Wyckoff
Affiliation:
Oklahoma Museum of Natural History, University of Oklahoma, Norman, OK 73019, USA
*
*Corresponding author. Fax: +1 214 768 2701.E-mail address:cjyapp@mail.smu.edu (C.J. Yapp).

Abstract

13C/12C and 18O/16O ratios of aragonite shells of modern land snails from the southern Great Plains of North America were measured for samples from twelve localities in a narrow east–west corridor that extended from the Flint Hills in North Central Oklahoma to the foothills of the Sangre de Cristo Mountains in Northern New Mexico, USA. Across the study area, shell δ18O values (PDB scale) ranged from −4.1‰ to 1.2‰, while δ13C values ranged from −13.2‰ to 0.0‰. δ18O values of the shell aragonite were predicted with a published, steady state, evaporative flux balance model. The predicted values differed (with one exception) by less than 1‰ from locality averages of measured δ18O values. This similarity suggests that relative humidity at the time of snail activity is an important control on the δ18O values of the aragonite and emphasizes the seasonal nature of the climatic information preserved in the shells. Correlated δ13C values of coexisting Vallonia and Gastrocopta suggest similar feeding habits and imply that these genera can provide information on variations in southern Great Plains plant ecology. Although there is considerable scatter, multispecies, transect average δ13C values of the modern aragonite shells are related to variations in the type of photosynthesis (i.e., C3, C4) in the local plant communities. The results of this study emphasize the desirability of obtaining isotope ratios representing averages of many shells in a locale to reduce possible biases associated with local variations among individuals, species, etc., and thus better represent the “neighborhood” scale temporal and/or spatial environmental variations of interest in studies of modern and ancient systems.

Information

Type
Research Article
Copyright
University of Washington

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