Guttulatic calcite: A carbonate microtexture that reveals frigid formation conditions

Abstract

The paragenesis of carbonate pseudomorphic textures in the rock record that are inferred to represent replaced metastable ikaite (CaCO3·6H2O), which forms at frigid temperatures, isuncertain. Petrographic analysis of Mono Lake (California, USA) Pleistocene tufas allowedrecognition of a distinctive calcite microtexture, termed guttulatic calcite, that forms duringcarbonate dehydration and is diagnostic for precursor ikaite. The texture is characterized bypseudo-hexagonal or spherical low-Mg cores, which likely formed initially as vaterite, withan ellipsoidal overgrowth, and a secondary high-Mg sparry or micritic cement. Observationsof Mono Lake ikaite pseudomorphs, combined with a review of more ancient examples, indicatethat guttulatic texture records carbonate dehydration of precursor ikaite and can beused to infer frigid paleotemperatures