Publication Date

1984

Document Type

Dissertation/Thesis

First Advisor

Perry, Eugene C., 1933-

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geology

LCSH

Dolomite--Mexico--Yucatán (State)

Abstract

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.

Comments

Bibliography: pages 148-154.

Extent

ix, 154 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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