Publication Date


Document Type


First Advisor

Perry, Eugene C., 1933-

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geology


Dolomite--Mexico--Yucatán (State)


The uppermost 53 meters of the northeastern Yucatan Peninsula has witnessed carbonate deposition in response to glacio-eustatic sea-level fluctuations during the Quaternary. Grainstones, wackestones, and coral boundstones are recognized; deposition took place in a reef to near-reef environment in agitated water of normal salinity. The section contains up to 50% dolomite by weight; dolomitization is of an erratic and patchy nature. Dolomite is found to occur as: 1) selective replacement of micritic matrix, 2) wholesale replacement of bioclasts and matrix, and 3) "corrugated fringes" of alternating bands of calcite and dolomite. Calcite cement exists as: 1) microcrystalline replacement of micrite, 2) bladed to fibrous submarine cement, and 3) coarse, euhedral spar of freshwater origin. Porosity is vuggy, ranging from 15% to 40%; evidence of subaerial weathering is recognized. Strontium and sodium are depleted, while manganese and iron are enriched relative to primary marine carbonates. This indicates re-equilibration of the primary marine carbonates with meteoric/ mixing-zone fluids. Carbon and oxygen isotope ratios indicate equilibrium precipitation from local meteoric water. Coexisting calcite-dolomite pairs show a consistent difference in isotopic composition (Δ¹⁸O(dol-cal) = +5.3°/∘∘; Δ¹⁸O(dol-cal) = +5.0°/∘∘), suggesting equilibrium. Computer modelling of mineral-phase stability in the freshwater seawater mixing zone indicates that calcite is destabilized and dolomite stabilized with increasing temperature. This temperature- induced stability inversion could have powerful implications for the study of ancient mixing-zone dolomites.


Bibliography: pages 148-154.


ix, 154 pages




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