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Carbonate muds deposited in extensive coastal lagoons bordering the northeast Yucatan Peninsula have been subjected to a variety of diagenetic environments. The sediment in each of these environments is characterized by a particular suite of diagenetic features which provides additional insight for determining the early processes involved in carbonate-mud diagenesis.
Several finely crystalline cements are present in the supratidal and back-lagoon sediments associated with the lagoons. Those formed in the vadose zone are typically calcite and include calichelike cryptocrystalline cement, microstalactitic druse, and "needle-fiber" (whisker crystal) cement. Submarine cements are composed of Mg-calcite and consist of grain-skin druse and void-filling blocky spar. Coalescent neomorphism results in the gradation from micrite to microspar in both subaerial and submarine environments; in the submarine environment the mineralogy apparently remains Mg-calcite, whereas a conversion from Mg-calcite to calcite occurs in the vadose zone.
Dolomitic and Mg-calcite cemented crusts have formed on the beaches, on tidal-flat surfaces, and in the subsurface in sediments influenced by hypersaline waters. In places, fresh water draining from the mainland and flowing through the lagoonal sediments has resulted in the formation of pisolithlike calcite concretions.
Aragonite constituents are being leached from sediments in contact with hypersaline interstitial waters rich in Mg, whereas Mg-calcite grains are dissolved in sediments affected by fresh water. Dissolution of fine mud and corrosion of coarser skeletal grains also occur in association with mangrove peats.
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