Contribution to the Evidences of an Interhemispheric Cosmic Impact During the Younger Dryas. Distinctive Proxies from Central and South Mexico

The Younger Dryas chronozone is the last and coldest abrupt climatic change that took place at the end of the late Pleistocene producing a significant environmental disruption in America Europe and Asia. These changes include diversity and abundance of vegetation, and are often associated with a large amount of charcoal recorded in several paleoenvironmental records and coincide with high mortality of large vertebrates. This abrupt YDB (Younger Dryas Boundary) change has been always associated with major drainage of Lake Agassiz producing a major change in southern overturning driving freshwater draining into the western Arctic Ocean. The mechanism of this overturning is not well understood. Several authors suggest that there was a comet affecting the atmosphere that occurred at around the YD Boundary as observed in a widespread anomaly in 50 YDB sites in all latitudes. This anomaly is found in lacustrine, fluvial, glacial and aeolian systems that date to around 12,800 y bP. The YDB layer has been proposed as a widespread correlation datum in America (North, and South), Europe and Asia. In order to investigate in Mexico sites potentially affected by the Younger Dryas event, we collected sediment samples from four ancient lakes in central Mexico (Chapala, Cuitzeo, Acambay, Chalco lake) and two rivers in the south Mexico (Oaxaca and Chiapas). All contain distinctive characteristics as determined by sedimentological, geochemical, micropaleontogical and paleopedological analyses. The retrieved and dated lake and fluvial sediments encompass the Pleistocene-Holocene transition and provide good materials for studying the YD transition. The detailed stratigraphical analyses in the buried YDB layer intervals show anomalous values for bulk chemistry, pollen, stable isotopes, diatoms, nanodiamond polytypes, TOC, charcoal, soot, and platinum. All show higher concentrations than average background values associated with numerous quenched Fe spherules. These are morphologically and geochemically identical to quench-textured YDB spherules found elsewhere. The nanodiamonds in the Mexican samples show the skeletal iron crystallization typical of rapid quenching, with about 96% iron oxide. Ternary diagrams make it clear that the spherules are not cosmic, volcanic, or anthropogenic in origin. In some river systems in Oaxaca Mexico, the quaternary landscape displays widespread evidence of outburst floods that produce extensive lag deposits.. These sedimentological characteristcs may indicate a sudden flood event that buried Late Pleistocene vertebrate remains. In Chiapas State, river sediments show clear fluvial traction deposits, with large channels, associated with lag deposits which incorporated Late Pleistocene vertebrate fossils. All the anomalous changes found could be associated with a large extraterrestrial object, possibily a comet that produced abundant debris. The evidence suggest that the impact event causes a sudden influx of water into the atmosphere inducing abundant rainfall that may have caused a major shift in precipitation and fluvial patterns across the Northern hemisphere.