|Variations in the O18/O16 and C13/C12 ratios of diagenetically altered limestones in the Bermuda Islands|
Grant Gross, M. (1964). Variations in the O18/O16 and C13/C12 ratios of diagenetically altered limestones in the Bermuda Islands. J. Geol. 72(2): 170-194
In: The Journal of Geology. University of Chicago Press: Chicago,. ISSN 0022-1376, more
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Marine and eolian Pleistocene sediments in the Bermuda Islands are composed largely of fragments of mollusks, Foraminifera, lithothamnoid algae, and Halimeda. The Pleistocene sediments range from unconsolidated carbonate sands to well-consolidated limestones. Recent carbonate sediments and major sediment-contributing organisms (except Halimeda) have similar O18/O16 and C13/C12 ratios which are distinctly different from the O18/O16 and C13/C12 ratios observed in the stalactites, soil bases, and secondary calcites from the limestones. Precipitation of secondary calcite in the limestones and alteration of the constituent grains cause the O18/O16 and C13/C12 ratios of the limestones to approach the values observed in stalactites and soil bases. Secondary calcites, precipitated from fresh water on the Bermuda Islands, have O18/O16 ratios which are controlled primarily by the average O18/O16 ratio of the rain water on the island. The C13/C12 ratios of the secondary calcites are controlled by the amount of carbon dioxide derived from the soil zone which is mixed with carbon derived from solution of the limestones through which the water has passed. Some of the limestones from the intertidal or surf-spray zone have O18/O16 and C13/C12 ratios which are distinctly different from the majority of the well-consolidated limestones. These limestones may have been lithified by cement precipitated from sea water or from fresh water which had been subjected to evaporation and to exchange of carbon with atmospheric carbon dioxide.