Perry, Eugene C., 1933-
M.S. (Master of Science)
Department of Geology
Geochemistry--Mexico--Yucatán (State)||Petrology--Mexico--Yucatán (State)
A confining layer, termed the lower laja, exists near or at the surface south of the swamp/lagoon system. The lower laja is a dense, impermeable confining layer which resembles a calcrete or caliche profile. The calcrete consists predominantly of a wackestone which grades into grainstone with depth and distance away from the Gulf of Mexico. Prior to the initiation of calcrete formation, rocks and sediments consisted of carbonates of marine origin. Subaerial exposure, evaporation of surface water and degassing of C02 resulted in extensive meteoric diagenesis which caused carbonate cement precipitation resulting in the stabilization and formation of the calcrete profile. During formation of the calcrete profile, extensive alteration of the profile by groundwater discharging from the Yucatan aquifer resulted in the occlusion and sealing of most pores and fractures causing the formation of a nearly impermeable confining layer. Studies of the age of the lower laja indicate that a maximum age of formation is 23,000 years old and it may be continuing to form at present beneath and adjacent to the swamp/lagoon system. Dolomite crystals were collected from two locations from the western Yucatan Peninsula: MITZA quarry and Noc Ac cenote. The dolomite from MITZA appears to be a replacive phase while the dolomite from Noc-Ac may be a direct precipitate from water composed of less than 10% seawater. U C studies of the dolomite from Noc-Ac indicate that a maximum age of the dolomite deposit appears to 22,000 years old. However, the actual age may be much younger because the carbon isotopic composition of the dolomite is out of equilibrium with the bulk aquifer water suggesting precipitation within a micropore system closed with respect to carbon from the bulk aquifer.
Sanborn, Robert K., "Petrography and geochemistry of a calcrete profile from the northwestern coast of the Yucatan Peninsula, Chuburna, Yucatan, Mexico" (1991). Graduate Research Theses & Dissertations. 4352.
xi, 209 pages, maps
Northern Illinois University
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