The Shell Chemistry of Some Recent and Pleistocene Mollusks and its Environmental Significance

Citation

Lloyd, Ronald Michael (1960) The Shell Chemistry of Some Recent and Pleistocene Mollusks and its Environmental Significance. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Q1WZ-Z134. https://resolver.caltech.edu/CaltechETD:etd-07052006-082708

Abstract

In Part I Florida Bay is used as a model to describe some influences of environment on chemical variations of shell material. Geographic isolation and high evaporation in the Bay coupled with the influx of fresh water enriched in O18 produce a gradient of increasing H2O18 going into the Bay. Dilution of Bay water by Ca rich fresh water lowers the Sr/Ca ratio in the Bay. The gradient of H2O18 in the water is clearly reflected in a similar gradient in the carbonate oxygen of mollusk shells. The effect of temperature on the carbonate isotopic composition is shown to be inadequate to explain the variations. Sr/Ca ratios of the shells vary but show no simple relationship to environment. A gradient of decreasing C13 in shells going into the Bay is attributed to the equilibration of CO2 derived by oxidation of organic debris with the carbonate of the water. Analyses of mollusks from sediment cores show that the present environmental framework of Florida Bay has existed for the last 3700 years. Analysis of the fine-grained sediment of the Bay suggests that part of it is washed in from the mainland. In Part II fossil mollusks from the Pleistocene Caloosahatchee formation are analyzed. The O18/O16 ratios coupled with geological and faunal data indicate an environmental framework strikingly similar to the Florida Bay model. A land mass immediately west of the outcrop area is postulated for most of Caloosahatchee time. The carbon isotope and strontium data reveal little environmental information.

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