APPLYING BAHAMIAN MODELS TO THE EOLIANITES OF QUINTANA ROO, MEXICO

Bahamian studies produced criteria for determining the age of eolianites from field relationships alone. Those criteria were applied to eolianites in Quintana Roo, Mexico. The Quintana Roo coast, and the islands Cozumel and Isla Mujeres, expose Pleistocene eolianites previously described as regressive-phase, formed at the end of the last interglacial, OIS 5c (Puerto Viejo and Contoy Eolianites) and 5a (Mujeres Eolianite). Two Holocene units, the Blanca Eolianite and the Cancun Eolianite in Quintana Roo are similar in character to the Hanna Bay and North Point Mbrs of the Rice Bay Fm in the Bahamas.

In Mexico, Pleistocene eolianites are recognizable by a complex paleosol and micritic surface crust, containing a fossil epikarst. Fossilized root structures that disrupt fine-scale laminations are abundant. These observations are indicative of regressive-phase eolianites. However, certain eolianites, such as at Playa Tulum, contain phreatic flank margin caves, similar to those in the Bahamas. The altitude of the caves (2-6 m), in a tectonically-stable setting, indicates development during the OIS 5e sea-level highstand. The eolianites could not have formed on the regression from that highstand, as they must already have been in existence for the flank margin caves to form during OIS 5e. Therefore, the eolianites must either be transgressive-phase eolianites developed at the beginning of the OIS 5e sea-level highstand, or eolianites of either phase from an earlier sea-level highstand. In addition, subtidal marine facies that onlap notches in eolianites on the west side of Cozumel indicate that substage 5e transgressive-phase eolianites must be present. These trangressive and regressive-phase eolianites could be the same age as the French Bay and Cockburn Town Mbrs of the Grotto Beach Fm in the Bahamas. At Tulum, a paleosol-covered eolianite beneath the OIS 5e eolianites indicates that the Owl’s Hole Fm equivalent of the Bahamas may be present as well.

Substage 5c eolianites are not reported from the Bahamas, and substage 5a eolianites there have been controversial. Given that substage 5e transgressive-phase eolianites are present in Quintana Roo, regressive-phase eolianites from that highstand also should be present in the Bahamas and have most likely been incorrectly assigned to substages 5c and 5a.