Coastal Quintana Roo, Mexico, including islands such as Cozumel and Isla Mujeres, contains numerous ridges of Quaternary eolian calcarenite in two packages, one Pleistocene and one Holocene. The Pleistocene eolianites are recognizable in the field by well-developed terra rossa paleosol and micritic crust on the surface, containing a fossil epikarst. The foreset beds of these eolianites commonly dip below modern sea level, and fossilized plant root structures are abundant. The Holocene
eolianites lack a well-developed epikarst, and have a calcernite protosol on their surfaces. The degree of cementation, and the grain composition, are not reliable indicators of the age of Quaternary eolianites.
The Pleistocene eolianites have been previously described (e.g. Ward, 1997) as exclusively regressive-phase eolianites, formed by the regression during the oxygen isotope substages (OIS) 5a and 5c. However, certain eolianites, such as those at Playa Copal, contain flank margin caves, dissolution chambers that form by sea water/fresh water mixing in the fresh-water lens. For such mixing dissolution to occur, the eolianite must already be present. As the flank margin caves are found at elevations of 2-6 m above current sea level, the caves must have developed during the last interglacial sea-level highstand, and the eolianites could not have formed on the regression from that or younger highstands. Therefore the eolianites must be transgressive-phase
eolianites developed at the beginning of the last interglacial sea-level highstand, or either transgressive- or regressive-phase eolianites from a previous sea-level highstand that occurred earlier in the Pleistocene. There is no field evidence of oxygen isotope substage 5c or 5a eolianites as suggested by Ward (1997).
Most coastal outcrops show classic regressive–phase Pleistocene eolianites as illustrated by complex and well-developed terra rossa paleosols and epikarst, and dense arrays of fossilized plant roots. However, in addition to flank margin caves, other evidence of transgressive-phase eolianites includes notches in eolianites on the west side of Cozumel, with subtidal marine facies onlapping the notches. The absence of a paleosol between those two units indicates that the eolianite is a transgressive-phase deposit from the last interglacial. All Holocene eolianites are, by definition, transgressive-phase units.
Eolianites and Karst Development in the Mayan Riviera, Mexico
- Written by News Manager
- Republished from: Davis, R. L., and Gamble, D. W., eds., 2006, Proceedings of the 12th Symposium on the Geology of the Bahamas and Other Carbonate Regions, p. 88-99
- PDF: /pdf/seka_pdf9854.pdf