Abstract

SANCHEZ-GONZALEZ, Ma. de Jesús; ISRADE ALCANTARA, Isabel; MORALES, Juan Julio  and  GOGUITCHAICHVILI, Avto. Paleoenvironmental evolution of the Agostitlán diatomite, Michoacán, during the Pleistocene-Holocene transition. Bol. Soc. Geol. Mex [online]. 2021, vol.73, n.1, 00006.  Epub Oct 11, 2021. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2021v73n1a080620.

The Chapala Acambay graben is characterized by several Quaternary diatomite deposits of variable thickness where dominates flora indicative of' ancient deep lakes. The 6.70 m thickness diatomite-deposit of the Agostitlan dammed basin contains the paleoenvironmental record that show the transitionfrom less cold conditions of 37,000 yr cal AP until the onset of the late Glacial period (ca. 25,000yr cal AP). At the beginning of the lake formation a deep-water body was developed, characterized mostly by Stephanodiscus niagarae with little contribution of detrital material, mostly composed of argillaceous lithology. The magnetic susceptibility values in this first episode of tie lake are relatively low, at least in the first two meters, with two notorious maxima associated with periods of erosion of the high-mountain ranges. Successively towards the Early Glacier the lake conditions become fluctuating; the sedimentation is more detrital, alternating with episodes of fine sedimentation in which the lowest values of magnetic susceptibility are revealed, which are accompanied by the decrease of Stephanodiscus spp communities and an increase of Aulacoseira ambigua and Fragilaria spp. This indicates an environment of dominantly cold and alkaline conditions. The top of the succession is characterized by an increase in the concentration of magnetic minerals, as well as by a significantly decrease of planktonic that becomes substituted by littoral benthic and periphytic species, which are interpreted as the response to the increase in aridity in this area at the beginning of the Last Glacial Maximum.

Keywords : Diatomitas; Central Mexico; Environmental Magnetism; MIS3; late Wisconsin.

        · abstract in Spanish     · text in Spanish     · Spanish ( pdf )