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Published August 1994 | public
Journal Article Open

Tracing ground-water evolution in a limestone aquifer using Sr isotopes: Effects of multiple sources of dissolved ions and mineral-solution reactions


Uplifted Pleistocene coral-reef terraces on Barbados, West Indies, constitute an aquifer that is built on low-permeability Tertiary pelagic rocks that overlie the Barbados accretionary prism. The downdip segments of the aquifer are composed of younger reef limestones that contain more aragonite and have higher ^(87)Sr/^(86)Sr and Sr/Ca ratios than the updip parts of the aquifer. Ground waters and host limestones display similar stratigraphic trends in ^(87)Sr/^(86)Sr and Sr/Ca. The ground waters have lower ^(87)Sr/^(86)Sr values, however, indicating that they acquire a significant fraction of their dissolved Sr through interaction with components of Tertiary rocks, which compose the underlying aquitard and parts of overlying soils. Geochemical modeling results indicate that ground-water evolution is controlled by (1) variations in the age and composition of the aquifer and aquitard rocks and (2) the relative roles of calcite dissolution, calcite recrystallization, and the transformation of aragonite to calcite. Sr isotopes can provide unique information for tracing ground-water evolution, which requires consideration of the multiple components and processes that make up even relatively simple limestone aquifer systems.

Additional Information

© 1994 Geological Society of America. Manuscript received December 30, 1993. Revised manuscript received May 18, 1994. Manuscript accepted May 25, 1994. Supported by the Geology Foundation of the University of Texas. We thank the following for scientific discussions and technical assistance: the Barbados Water Authority and Ministry of Health, T. Kimbell, J. Humphrey, R. Speed, E. Holder, T. Housh, M. Denham, G. Wasserburg, D. Papanastassiou, D. Porcelli, and J. Saleeby. R. Major, L. Vacher, and an anonymous reviewer provided helpful reviews.

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August 20, 2023
August 20, 2023