Northwestern Yucatan Research Articles

Hydrogeological Investigations in Northwestern Yucatan, Mexico, Using Resistivity Surveys

AbstractEight Schlumberger soundings and four Wenner anisotropy measurements were conducted in the northwestern section of the Yucatan Peninsula for hydrogeological investigations of a karst aquifer. This system is influenced by a circular high permeability zone (Ring of Cenotes) probably related to the Chicxulub Impact Crater. Schlumberger soundings and Wenner anisotropy measurements show that the karst aquifer can be modeled as an electrically anisotropic medium. Anisotropy is related to preferential permeability directions channeling ground‐water flow within the aquifer. Directions of maximum permeability were determined using Wenner anisotropy measurements. Electrical soundings were conducted at different sites near the Ring of Cenotes. Resistivity values decrease toward the Ring of Cenotes supporting the hypothesis that selected segments of the Ring have high permeability. Several soundings were conducted in order to study lateral permeability variations along the Ring. A high permeability section can be identified by low resistivity models and is related to a zone of high cenote density. A low permeability section of the Ring was found showing high resistivity models. This zone overlaps with an area of low cenote density. Electrical soundings were used to determine the depth of the fresh‐water lens; the interface was detected along two profiles perpendicular and parallel to the Ring of Cenotes resulting in a depth that ranged from 18 m near the coast up to 110 m in the southeastern part of the study area. The predicted depths of the interface using electrical methods showed a good correlation with Ghyben‐Herzberg and measured interface depths at some sites. Discrepancies between calculated and interpreted interface depths at two sites may be explained by horizontal‐to‐vertical permeability anisotropy.

The hydrogeology and contamination potential of north-western Yucatan, Mexico : L. E. Marin & E. C. Perry, Geofisica Internacional, 33(4), 1994, pp 619–623

The hydrogeology and contamination potential of north-western Yucatan, Mexico : L. E. Marin & E. C. Perry, Geofisica Internacional, 33(4), 1994, pp 619–623

Yucatán subsurface stratigraphy: Implications and constraints for the Chicxulub impact

Much of the discussion about the effects of an end-of-Cretaceous impact by a large extraterrestrial body in northwestern Yucatan has been done in the context of limited and partly erroneous published data on the Mesozoic stratigraphy of that area. Reexamination of cores and geophysical logs taken in several Pemex wells has produced improved lithologic and biostratigraphic correlation of the Jurassic to Maastrichtian section across the northern Yucatan peninsula. These data suggest that major disturbance of strata by an impact would have been confined to within about 100 km of the proposed impact center near Chicxulub. The only unusual lithologic unit is polymict breccia, which apparently was penetrated at or near the top of the Cretaceous section in all the deep wells of northern Yucatan. This breccia in Pemex wells Yucatan 1, 2, 4, 5A, and 6 is composed predominantly of detrital dolomite, limestone, and anhydrite clasts set in dolomitized carbonate mud matrix, which contains upper Maastrichtian foraminifers. These constituents, mixed with fragments of altered glass or melt rock, shocked quartz and feldspar, and basement rock, suggest an impact as the most likely origin for the breccia. The timing of brecciation is poorly constrained by biostratigraphic data. There is some evidence, however, that the breccia unit is overlain by about 18 m of uppermost Maastrichtian marls, suggesting an impact before the Cretaceous-Tertiary boundary. In addition, there may have been more than one episode of breccia deposition.

Surficial geology of the Chicxulub impact crater, Yucatan, Mexico.

The Chicxulub impact crater in northwestern Yucatan, Mexico is the primary candidate for the proposed impact that caused mass extinctions at the end of the Cretaceous Period. The crater is buried by up to a kilometer of Tertiary sediment and the most prominent surface expression is a ring of sink holes, known locally as cenotes, mapped with Landsat imagery. This 165 +/- 5 km diameter Cenote Ring demarcates a boundary between unfractured limestones inside the ring, and fractured limestones outside. The boundary forms a barrier to lateral ground water migration, resulting in increased flows, dissolution, and collapse thus forming the cenotes. The subsurface geology indicates that the fracturing that created the Cenote Ring is related to slumping in the rim of the buried crater, differential thicknesses in the rocks overlying the crater, or solution collapse within porous impact deposits. The Cenote Ring provides the most accurate position of the Chicxulub crater's center, and the associated faults, fractures, and stratigraphy indicate that the crater may be approximately 240 km in diameter.

Low marine terraces of Grand Cayman Island

Twenty levelling profiles across the shore zone of Grand Cayman Island reveal the presence of six low marine terraces above present sea level. The lowest and youngest one at about 2 m elevation is the most widespread and probably represents Sangamon interglacial high sea level. Higher terraces are much eroded and probably much older, but none provides evidence of post-terrace warping. Similarities in age and elevation of the 2 m terrace on this island to those in north-western Yucatan, northern Jamaica, the Bahamas and Florida suggest that vertical movements at Grand Cayman Island have been minor during at least the past 125 000 years, even with its nearness to the tectonically active Cayman Trough.

The Analysis and Distribution of Volcanic Ash-Tempered Pottery in the Lowland Maya Area

Petrographic analysis of potsherds from Dzibilchaltun and other Maya sites conclusively establishes the presence of volcanic ash temper in ceramics from northern Yucatan. The distribution of ash-tempered ceramics in time and space suggests import of ash in bulk from sources in highland Guatemala or El Salvador in exchange for salt. The homogeneous nature of the ash in northwestern Yucatan supports the idea that certain trading organizations enjoyed exclusive access to that region, while competing for markets in other lowland areas.

The Olmec gulf coast region and northwestern Yucatan during the middle formative

The Olmec gulf coast region and northwestern Yucatan during the middle formative