Paper No. 11
Presentation Time: 10:50 AM

PALEOENVIRONMENT AND HUMAN OCCUPATION IN MAYA LOWLANDS AT USUMACINTA RIVER, SOUTH MEXICO


SOLLEIRO, Elizabeth, Instituto de Geología, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica S/n, Mexico, 04510, Mexico, SOLIS CASTILLO, Berenice, Posgrado en Ciencias de la Tierra, UNAM, Instituto de Geologia, Mexico, 04510, Mexico, SEDOV, Sergey, Dept. of Soil Science, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica s/n, Ciudad Universitaria, Mexico D.F:, 04510, Mexico and LIENDO, Rodrigo, Instituto de Investigaciones Antropológicas, UNAM, Mexico, 04510, Mexico, solleiro@geologia.unam.mx

In this work, we use four paleosol-sedimentary sequences (Tierra Blanca I and II, El Pochote, and Vicente Guerrero) along the lowest terrace of the Usumacinta River at Maya lowlands, in order to reconstruct Holocene environmental changes and examine human-environmental interactions. Correlation of the four sections was established through paleosol morphology, radiocarbon dating, and artifact seriation (Early Holocene, Formative, Classic and Postclassic ceramics). Present only at Tierra Blanca, the oldest paleosols are characterized by their gleyic features. Although they contain hard carbonate concretions dated at 5450-5380 cal yr., these Gleysols are considered to be formed in Late Pleistocene - Early Holocene. Separated by laminated silty sediment with crossed stratification, the uppermost paleosols lack gleyic features and appear at all the sites. The oldest has strong vertic features (its radiocarbon age is 3000 cal BP and contains abundant ceramics from the Formative period). Upper paleosol is less developed, with dark A horizons and less proportion of clay. Ages between 1300 - 2000 cal BP and ceramic allow establishing their stratigraphic position belonging to the Maya classic. The uppermost paleosol is also weakly developed and is strongly affected by human activities. Because of the archaeological evidences as well as radiocarbon dating, this paleosol corresponds to the Maya Postclassic. Vertic paleosols formed during Formative period, found in all the study sections, clearly reflects the shift to major landsurface stability and pedogenesis under seasonal climate with periodic strong drying. The stable C isotope composition demonstrates the highest d13C value of -16.5‰ of the whole sequence, clearly pointing to the dominance of C4 plants, as maize (which is confirmed by phytolith identification). Paleosol development during the Classic and Postclassic evidences a more dynamic environment, where sedimentation is more pronounced and pedogenesis is lower. The soil forming processes are limited to humus accumulation and development of dark A horizon. The d13C values of soil organic matter in these cases are much lower (-19 - -20‰) and point to a higher proportion of C3 plants typical for humid environments.