Publication Date


Document Type


First Advisor

Perry, Eugene C., 1933-

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geology


Hydrology; Karst--Mexico--YucataÌ�n (State); Water--Composition--Mexico--YucataÌ�n (State); Groundwater--Mexico--Yucatán (State)


Deep water-filled, sinkholes, cenotes, at least one of them greater than 120 meters deep, are common in the karst region of the northern Yucatan Peninsula, Mexico. The deepest of these sinkholes (cenote. Xcolac) extends through a fresh water lens that is approximately 50 meters thick. This fresh water is meteoric in origin (δ¹⁸O = -3.2°/oo, δD = -20°/∘∘ (SMOW)). Saline water that approaches sea water composition lies below. It has been proposed (Salvador Gaona and others, 1980) that these sinkholes are drilled through the nearly pure Tertiary carbonates of the Yucatan Peninsula by H₂CO₃ produced by vegetation decaying at the bottom. Sulfur isotope data from this and another cenote (Ucil) support the interpretation of Salvador Gaona and others (1980). Under these conditions anaerobic bacterial reduction of sulfate is also expected, resulting in strong δ³⁴S enrichment of residual sulfate and δ³²S enrichment of produced sulfide. A shift in isotope composition of sulfur in the deepest, largest cenote from a sea water value of 21°∘∘(CDT) to 42.6°/∘∘ indicates conversion of a major amount of SO₄ˉ² to sulfide. Enrichment is observed to take place in water from deep cenotes, but not from deep wells. Furthermore, sulfur isotope enrichment is correlated with capture cross-section for vegetation of the cenote. Most sulfide production takes place near the bottom, and as it moves upward in the cenote, sulfide becomes oxidized back to sulfate upon contact with phototrophic sulfur bacteria. Sulfide not affected by sulfur bacteria is quickly oxidized above 55 meters, where it contacts oxygen.


Bibliography: pages 59-61.


vii, 61 pages




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