The recognition of past climatic fluctuations in sedimentary sequences in central Mexico is relevant for understanding the forcing mechanisms and responses of climatic system in the northern American tropic. Moreover, in this active volcanic setting the sedimentary record preserves the history of past volcanic activity. Climatic and environmental variability has been documented for the last tenths of thousands of years from the upper lacustrine sediments in Chalco basin. A series of cores drilled down to 122 m depth in this basin offer a long, continuous and high resolution record of past climatic changes of the last ca. 150 kyr in this region. Here we present the detailed lithostratigraphy and some physical properties (magnetic susceptibility and density) of the master sequence. Sedimentary components and their abundance were identified and quantified in smear slides and direct core observations. Age model is based on 13 14C and one 230Th/U dates. Based on their facies association seven lithostratigraphic units were defined, which reflect the main stages of lake Chalco evolution. These phases closely match the marine isotopic stages. The data reveal that at the end of MIS6 Chalco was a relatively deep and stratified freshwater lake. During MIS5 the depositional environment fluctuated between low lake stands to marshy and marginal playa settings with sporadic flooding events, and severe arid periods resulted in aerial exposure of lake sediments. Low lake stands persisted during MIS4 and MIS3, with minor fluctuations towards slightly deeper phases. The Last Glacial Maximum (LGM) and the deglacial period (21-13 kyr) are characterized by intense volcanism. The early and mid-Holocene high calcareous content and alkaline-subsaline lake suggest dry conditions. The fluctuations of lake levels inferred provide the basis for future paleoclimatic works.
Bibliographical noteFunding Information:
This work was funded by projects Universidad Nacional Autónoma de México ( UNAM ) DGAPA-PAPIIT IN109012 , IN220609 , IN107013 and IV100215 , Coordinación de la Investigación Científica UNAM, and CONACyT 130963 . We thank T. Pi and S. Sosa for analytical work. A. González, T. Hernández, A. Rodríguez and D. Villanueva provided assistance during the field work. A. Ortiz-Beltrán collaborated in sedimentological descriptions. The following institutions provided scholarships to the students involved in this project: CONACyT (E. Torres-Rodríguez), UNAM-DGAPA (D. Avendaño-Villeda), Instituto Panamericano de Geografía e Historia (D. Herrera-Hernández). We thank the assistance of Anders Noren and Kristina Brady for the initial core processing carried out at LacCore, the National Lake Core Repository at the University of Minnesota. Special thanks to the local authorities of Ejido Santiago Tulyehualco, who helped and cooperated during the field work. We thank Dr. A. Sáez and two anonymous reviewers for their insightful reviews which improved the manuscript.
Copyright 2017 Elsevier B.V., All rights reserved.
- American tropics
- Lacustrine depositional environments
- Late Quaternary
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