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1 School of Earth Sciences, University of Birmingham, PO Box 363, Birmingham B15 2TT, UK
2 NERC Isotope Geoscience Laboratory, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
Various subglacial, proglacial, periglacial and glacimarine parageneses of carbonates are known, but have not been systematically compared. Precipitation-triggering mechanisms include subglacial regelation, lacustrine photosynthesis and evaporation, freezing in permafrost, skeletal biomineralization, and bacterial oxidation of organic matter in organic-rich sediments. New data from late Proterozoic carbonates suggest another, potentially important mechanism: recrystallization of glacially transported (and hence chemically unstable) carbonate.
Unlike the bulk of warm-water carbonate sediments, most glacial carbonates have been precipitated as stable phases which therefore preserve a good memory of environmental parameters. Carbon stable isotopic data have been used to constrain precipitation mechanisms whilst oxygen isotopes together with minor element chemistry can characterize salinity and distinguish the effects of evaporative from freezing processes. Elevated Fe and Mn contents point to anoxic precipitational conditions. Petrographic data on crystal size, shape and internal zonation are vital to avoid misinterpretations of diagenetically-altered material.
Carbonate geochemistry has proved valuable in interpretation of Quaternary and older palaeoenvironments, and could even yield information to aid Proterozoic palaeogeographic reconstructions.
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  References Geological Society, London, Memoirs, 1997; 17: 477 - 514. [PDF]
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