Abstract

PERRY, Eugene C.; VELAZQUEZ-OLIMAN, Gudalupe; LEAL-BAUTISTA, Rosa M.  and  DUNNING, Nicholas P.. The Icaiche Formation: Major contributor to the stratigraphy, hydrogeochemistry and geomorphology of the northern Yucatán Peninsula, Mexico. Bol. Soc. Geol. Mex [online]. 2019, vol.71, n.3, pp.741-760.  Epub Dec 06, 2019. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2019v71n3a7.

The Paleogene-Eocene Icaiche Formation, which contains bedded gypsum deposits that cover an estimated minimum area of 10000 km2, is located in the southern parts of the Mexican states Yucatan, Campeche and Quintana Roo. The formation has been little studied because it crops out in an area with limited access, few people, and little economic activity. Low population density is a consequence of the sulfate-contaminated water that is produced during weathering and dissolution of the gypsum deposits in the formation. The Icaiche Formation occupies a considerable part of the physiographic area known as the Elevated Interior Region (EIR) of the Yucatán Peninsula, which encompasses a terrain that the Maya occupied with varying success for almost two millennia and finally almost completely abandoned by about 950 CE. During their tenure, the Maya survived and at times prospered in this region of unpalatable groundwater by using and adapting natural depressions (called bajos) for water supply and, somewhat later, by using abundant impermeable local clays in construction of dams and ingenious systems for water storage and transport. Because of the relatively high solubility of gypsum, the Icaiche Formation has had an outsize influence on hydrologic and geomorphic features and groundwater geochemistry beyond where it crops out and into parts of the Yucatán Peninsula where it is present in the subsurface, particularly those places where it encounters flowing groundwater. In this study, we propose that gypsum dissolution, followed by collapse of overlying rock, was important in: 1) the formation of poljes (large, partly or completely enclosed karst basins with flat floors and interior drainage) along the east and west margins of the EIR; 2) the development of deep karst in north central Yucatán state; and 3) the formation of irregular terrains, extensive brecciation of rock, and highly varying water quality in the area at the eastern margin of the EIR (between Lake Chichancanab and Felipe Carrillo Puerto, Quintana Roo). Argillaceous sediment released during weathering of the Icaiche Formation, perhaps mixed with siliceous components of impact deposits from the Chicxulub Impact may have affected the permeability of post-Eocene marine sedimentary rocks, perhaps including local facies of the Carrillo Puerto Formation, formed on the southeast margin of the Peninsula. The resulting rocks have markedly lower permeability than rocks of the more northerly lowlands of the Mexican portion of the Yucatán Peninsula that host a pervasive fresh water lens overlying a saline intrusion.

Keywords : Yucatan Peninsula; gyp-sum; stratigraphy; hydrogeochemistry; karst.