2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 3
Presentation Time: 2:15 PM

Effects of An Extensive Evaporite-Rich Early Tertiary Sedimentary Unit on the Geology, Hydrogeology, and Geomorphology of the Yucatan Peninsula, Mexico


PERRY, Eugene C., Department of Geology and Environmental Geosciences, Northern Illinois Univ, 312 Davis Hall, De Kalb, IL 60115-2854, PAYTAN, Adina, Institute of Marine Sciences, University of California Santa Cruz, Santa Cruz, CA 95064, VELAZQUEZ-OLIMAN, Guadalupe, Centro de Investigacion Cientifica de Yucatan, Unidad Quintana Roo, Centro para el Estudio del Agua, Cancun, Quintana Roo, Mexico, PEDERSEN, Bianca, Department of Geology, University of Wisconsin, Eau Claire, Eau Claire, WI 54702 and WAGNER, Niklas, Department of Geology and Environmental Geosciences, Northern Illinois University, DeKalb, IL 60115, perry@geol.niu.edu

Correlation between 87Sr/86Sr and ion concentrations of sulfate, chloride, and strontium in the groundwater of the Yucatan Peninsula, Mexico indicates that 65.95 m.y. old Chicxulub impact ejecta have affected hydrogeology, geomorphology, and soil development of the region. Albion Formation ejecta are present at the surface along the Rio Hondo escarpment in Quintana Roo, and at relatively shallow subsurface depths in north-central Yucatan.  Anhydrite/gypsum and celestite are common in impact ejecta clasts and in beds and cements of overlying Paleocene and Lower Eocene rocks cored around the crater margin. Sulfate-rich minerals in rocks overlying the ejecta blanket, may either 1) be partially mobilized from the ejecta layer itself or 2) have been deposited after the K/T impact event in an extensive pre-Oligocene shallow sea. These deposits form a sedimentary package traceable by its Eocene-Cretaceous 87Sr/86Sr signal. A distinct Sr isotopic signature and high SO4/Cl ratios are observed in the groundwater of northwestern and north-central Yucatan that interacts with these rocks. Moreover, the distribution of the gypsum-rich stratigraphic unit provides a solution-enhanced subsurface drainage pathway for a broad region characterized by poljes, extending from Chetumal, Quintana Roo to Campeche, Campeche. Gypsum quarries in that area are also consistent with a sulfate-rich stratigraphic "package" that includes ejecta.

Chemistry of groundwater that has been in contact with evaporite/ejecta indicates flow directions and confirms a groundwater divide in the northern Peninsula. Information about groundwater flow directions and about deep subsurface zones of high permeability is useful for groundwater and liquid waste management. The unique chemistry of the groundwater that interacted with the evaporite/ejecta strata may have implications to coastal geomorphology. While groundwater-seawater mixing can dissolve and erode limestone, the mixing of water nearly saturated in CaSO4 with seawater is expected to have a less vigorous dissolution effect due to the high Ca content.