Radiocarbon reservoir effects occur when organisms incorporate carbon that is not in equilibrium with the modern atmosphere. These reservoir effects often result in 14C ages of fossils shells that are too old, often by thousands of years. Dissolution of limestone bedrock in southwestern Ohio may lead stream water to be enriched in old, dissolved carbon and cause radiocarbon reservoir effects. This is especially relevant to mollusks as they use the dissolved inorganic carbon pool for shell construction. Gastropod and bivalve shells, which can be used to constrain ages of channel deposits, can thus yield erroneous 14C ages when dated if the age offset is not taken into account. The aim of this study is to examine the extent and spatial variability of a potential radiocarbon reservoir effect in Four Mile Creek, Ohio.
Six samples of live gastropods (unidentified sp.) and bivalves (Corbicula sp.) were collected from four study sites located along Four Mile Creek. These samples were chemically pretreated and sent off for accelerator mass spectrometry (AMS) 14C analysis. Shells yielded percent modern carbon (pMC) values between 92.86 – 94.64, with apparent radiocarbon ages ranging from 445 – 595 years BP. These data indicate the presence of a radiocarbon reservoir effect in Four Mile Creek. However, the analysis of only live specimens has limitations. Anthropogenic modifications may have altered the hydrologic system such that modern samples do not show the full extent and spatial variability of the radiocarbon reservoir effect over time. Future work will focus on radiocarbon dating paired charcoal and fossil shell samples to assess potential changes in 14C reservoir effects with climatic changes over the Holocene. By determining the radiocarbon reservoir effect in a humid stream environment in the Midwest, we will be able to determine the viability of shells as an age dating method for dating fluvial systems.
Authors: Alexander Baldasare, Christina Tenison
Faculty Advisor: Jason A. Rech, Geology
Graduate Student Advisor: Christina Tenison, Geology
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