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High-Energy Carbonates on the Inner Shelf, Northeastern Yucatan Peninsula, Mexico
William C. Ward (1), Michael J. Brady (2)
High-energy carbonate sands and gravels are accumulating on the inner margin of the eastern Yucatan shelf. Carbonate sands are deposited in large spillover lobes, submarine dunes, seagrass banks, beaches, spits, and eolian dunes. Major factors controlling dispersal and deposition of these Holocene carbonate sediments are: (1) the northward flowing Yucatan current, (2) pre-Holocene topography on the limestone shelf, (3) littoral drift, (4) hurricanes, (5) normal waves and wind, and (6) biota.
Carbonate sediments on the inner Yucatan shelf are deposited in textural belts paralleling the strandline. Grain size generally decreases toward the mainland, with sand-size material concentrated in the nearshore-beach-coastal dune zone. Carbonate mud is deposited in lagoons landward of beach-dune barriers. The best-sorted sand is found along the landward margin of the sand belt in the beach-dune trend.
A partly submarine, partly subaerial belt of oolitically coated sand parallels this coastline. Ooids are formed in the nearshore zone of two high-energy segments of the coast and are reworked from submerged outcrops of older oolitic limestone. The belt of oolitic sediment is thickest on its landward edge, where coastal dunes accumulate. The carbonate dune-beach deposits are rapidly lithified, enhancing their chance of preservation. Effective porosity in the Holocene dune limestones ranges from 26-36%. The oolitic sand passes seaward into uncoated bioclastic, pelletoid, and lithoclastic sand and gravel. Periodic storm waves wash ooids landward into the muddy lagoons behind the dune and beach-ridge barriers.
Preservation of the carbonate facies deposited on the inner shelf of northeastern Yucatan would create stratigraphic traps in the most up-dip carbonate grainstones. Carbonate mudstones of the coastal lagoons would be both permeability barriers and source rocks for hydrocarbons.
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