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

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.