Pedro Morales-Puente

Mineral and organic components of the buried paleosols of the Nevado de Toluca, Central Mexico as indicators of paleoenvironments and soil evolution

Abstract Results of earlier studies of Quaternary tephra–paleosol sequences in Central Mexico revealed contradictions between paleopedological and lacustrine records. To settle the contradictions, selected quantitative characteristics of mineral and organic components of the paleosols PT1–PT7 from the Nevado de Toluca sequence were studied as independent paleoclimate proxies. Mineralogical composition of sand and clay fractions allows assessment of weathering and secondary mineral formation, both being climate-dependent processes. Stable carbon isotope ratios of humus and phytolith morphology indicate paleovegetation. In all paleosols, the sand fractions consist mainly of unstable volcanogenic minerals, although the grains have weathering features. Short durations of pedogenesis are responsible for limited weathering status. The clay fraction is dominated by halloysite and dehydrated halloysite in units PT1–PT4, which suggests drier periods during paleosol formation, whereas major amounts of kaolinite in the units PT5–PT7 indicate extended humid pedogenesis. δ 13C values of PT2–PT4 humus are intermediate between those characteristic of C3 and C4 plants. Phytolith assemblages which include both forms of C3 (dominant) and C4 (minor quantities) grasses agree with carbon isotope data. These data indicate plant cover changes driven by wet/dry paleoclimate oscillations. The new results, showing drier stages during the formation of Late Pleistocene paleosols PT2 and PT3, correct the primary interpretation of these units as indicating only humid pedogenesis, and settles the contradiction between paleopedological and lacustrine records.

Diet and habitat definitions for Mexican glyptodonts from Cedral (San Luis Potosí, México) based on stable isotope analysis

Values for δ 13 C and δ 18 O obtained from molar samples from three individuals pertaining to Glyptotherium sp. from Cedral (San Luis Potosi, Mexico) are provided and are utilized to infer general aspects of glyptodont diet and habitat. On average this animal showed a C 3 /C 4 mixed diet, with a high consumption of C 4 plants. Comparisons of the δ 13 C VPDB and δ 18 O VPDB values for glyptodonts with horses, mastodons, mammoths and tapirs from the same locality show that glyptodonts from Cedral lived in an open habitat.

Fluid characteristics of the world-class, carbonate-hosted Las Cuevas fluorite deposit (San Luis Potosi´, Mexico)

Abstract Las Cuevas is a world-class high-grade fluorite district that accounts for over 7% of the world total fluorite production. This district is mainly hosted in the Cretaceous limestones of the El Doctor Formation, and is in fault contact with Tertiary rhyolites. This preliminary study is focused on the “G” orebody, a mass of fine-grained fluorite, with abundant cavities lined up by fluorite, sometimes stalactitic, late calcite and clays. Fluid inclusions in cavity filling minerals have salinities up to 0.18 wt.% NaCl eq. with homogenization temperatures ranging from 60 to 110 °C, with the T h decreasing consistently from early cavity filling fluorite to late calcite. δ 18 O and δ 13 C values suggest that both an organic matter maturation and a decarbonation process might have occurred during the formation of the deposit. All the characteristics of the deposit suggest an MVT related origin rather than a magmatic-hydrothermal one as previously proposed by other authors.

Modern Radiocarbon Levels for Northwestern Mexico Derived from Tree Rings: A Comparison with Northern Hemisphere Zones 2 and 3 Curves

The radiocarbon variation for northwestern Mexico during the period 1950-2004 was studied by accelerator mass spectrometry (AMS) and liquid scintillation counting (LSC) analyses of tree rings. Two tree-ring sequences of Pseudotsuga menziesii, sampled in a site isolated from urban centers and active volcanoes (26.18°N, 106.3°W, 3000 m asl), were dendrochronologically dated and separated in annual rings prior to 14C analysis. Results obtained show a similar profile to the values reported for the Northern Hemisphere (NH), having significant correlation coefficients with the compilation curves for NH zone 2 (r = 0.987, p < 0.001) and NH zone 3 (r = 0.993, p < 0.001). The maximum peak is centered at 1964.5 with a ∆14C value of 713.15 ± 9.3‰. The values obtained for the period 1958-1965 are lower than zone 2 values and higher than zone 3 values. For the period 1975-2004, the values obtained are higher than the NH compilation curve and other NH records. We attribute the first divergence to the North American monsoon that may have carried 14C-depleted air from the south during the summer months; the second divergence may be attributable to 14C-enriched biospheric CO2.

Diet and habitat of mesomammals and megamammals from Cedral, San Luis Potosí, México

Using carbon and oxygen isotopic relationships from dental enamel, diet and habitat were inferred for both mesomammals and megamammals that lived in Cedral (San Luis Potosi, north-central Mexico) during Late Pleistocene time. δ 13 C and δ 18 O values show that bison, some horses and mammoth were eating C 4 plants and lived in open areas, while tapir, camel and some llamas ate C 3 plants and inhabited closed areas. All other studied herbivores (pronghorn, glyptodont, mylodont ground sloth, javelina, mastodon, and other llamas, horses and mammoth) had a C 3 /C 4 mixed diet, living in areas with some percentage of tree coverage. On the other hand, American lion and dire wolf ate either C 4 or mixed-diet herbivores, and short-faced bear ate C 3 herbivores. At Cedral, more humid conditions existed than presently, allowing the presence of a forested area near the grassland.

Preliminary data on the diet and habitat preferences of Capromeryx mexicana (Mammalia: Antilocapridae) from the late Pleistocene of Cedral, San Luis Potosí, Mexico

Abstract We inferred the diet and habitat preferences of three individuals of the dwarf pronghorn Capromeryx mexicana from Cedral, Mexico, using stable isotope analysis and the mesowear method. Both approaches showed that the individuals were C3/C4 mixed feeders which inhabited open forest. These results differ from previous hypotheses that suggested this species only fed on grasses and lived in grasslands.

Diet of rinchothere (Proboscidea, Gomphotheriidae, Rhynchotherium Species) of Taxco, Guerrero, México

Abstract The diet of a gomphothere (Proboscidea, Gomphotheriidae, Rhynchotherium species) from the Mexican Pliocene was determined using carbon and oxygen stable isotopes relationships in dental enamel. The analyses demonstrated that this individual exclusively fed on C3 plants, similar to some specimens found in Florida, United States.

The diet of Leptomeryx sp. from the Late Eocene Yolomécatl Formation, NW Oaxaca, Sierra Madre del Sur Morphotectonic Province, SE México and its palaeoecological significance

The diet and habitat of Leptomeryx sp. from the Late Uintan Yolomecatl Formation of NW Oaxaca, SE Mexico were inferred using dental enamel carbon and oxygen isotopic relationships, and compared with those of congeneric species from temperate North America. Results show that Leptomeryx sp. fed on C3 plants and lived in open forest or forest/savanna ecotone. The palynoflora and co-occurrence of perissodactyls and artiodactyls that live in an environment like that of Leptomeryx support this interpretation. Further, both records disclose that in NW Oaxaca (southern North America) tropical conditions prevailed at that time, unlike that of temperate North America.

Preliminary Paleodiet of a Specimen of the Pliocene Rhinoceros (Teleoceras fossiger) from Michoacán, México

Abstract Using the isotopic carbon and oxygen ratios present in dental enamel, the diet and the habitat of an individual of the Pliocene rhinoceros Teleoceras fossiger from San Francisco de los Reyes, Michoacán, México, were inferred. The values of δ13C and δ18O indicate that this animal fed on C3 plants and lived in enclosed areas similar to those found in some Florida specimens. However, because only one specimen was analyzed, it is not possible to determine if these rhinoceroses in Mexico were specialists or generalists in their diet.

Stratigraphy of the Basal Paleocene Carbonate Sequence and the Impact Breccia-Carbonate Contact in the Chicxulub Crater: Stable Isotope Study of the Santa Elena Borehole Rocks

We present results of a stable isotope study of the carbonate sedimentary sequence recovered in the Santa Elena borehole (located 110 km from the crater center) of the UNAM Scientific Drilling Program, immediately above the impact breccia-carbonate contact at a depth of 332 m. Sixty samples spaced in a 17 m thick section representing the basal Tertiary sequence were analyzed for oxygen and carbon isotopes. The δ13C ranges from about 1.2 to 3.5‰, and the δ18O ranges from about -1.4 to -4.8‰. We correlate the isotopic records for bulk carbonate for the Paleocene with the DSDP Hole 577, assuming a tie point for the Cretaceous/Paleocene (K/T) boundary. The variation pattern in the Santa Elena borehole correlates well with the global pattern defined for marine carbonate sediments. In the Santa Elena borehole, δ13C values are slightly more positive; δ13C values reach ~3.5‰ and there is a gradual increase from the Lower to the Middle Paleocene strata. The trend of δ18O values from Santa Elena borehole are also similar to δ18O DSDP Hole 577, however values in the Chicxulub Tertiary sequence are more negative; δ13C values reach ca. -4% in the Lower Paleocene rocks. Paleomagnetic data for the study section document four geomagnetic polarity zones for the impact breccias and basal sedimentary sequence, which span from chron 29r (K/T boundary) to chron 28n. The combined stable isotope and magnetic polarity data provide a stratigraphic framework for the first 2.5 Ma after the K/T boundary, and permit inferences about the paleoceanographic conditions following the Chicxulub impact and into the Early Paleocene.