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Golden, CO, United States

Kurbatov A.V.,University of Maine, United States | Mayewski P.A.,University of Maine, United States | Steffensen J.P.,Copenhagen University | West A.,Packer Geoscience Consulting , LLC | And 19 more authors.
Journal of Glaciology | Year: 2010

We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5×106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy, the ND-rich layer appears to be coeval with ND abundance peaks reported at numerous North American sites in a sedimentary layer, the Younger Dryas boundary layer (YDB), dating to 12.9±0.1 ka. However, more investigation is needed to confirm this association.

Anderson D.G.,University of Tennessee at Knoxville | Goodyear A.C.,University of South Carolina | Kennett J.,University of California at Santa Barbara | West A.,Packer Geoscience Consulting , LLC
Quaternary International | Year: 2011

Three approaches are used to test whether or not human populations across North America were affected by abrupt climate change and/or other environmental factors associated with the onset of the Younger Dryas (YD) cooling episode at ca. 12,900 cal BP. They are: (1) frequency analyses of Paleoindian projectile points from across North America; (2) time series of lithic assemblages from eleven Paleoindian quarry sites in the southeastern United States; and (3) summed probability analyses (SPA) of radiocarbon dates from cultural (human-related) sites across North America and parts of the Old World. The results of each analysis suggest a significant decline and/or reorganization in human population during the early centuries of the YD, varying in extent by region. Archaeological settings formerly heavily utilized, such as stone quarries in the southeastern U.S., appear to have been largely abandoned, while over large areas, a substantial decline occurred in the numbers of diagnostic projectile points and cultural radiocarbon dates. Later in the YD, beginning after about 12,600 cal BP, there was an apparent resurgence in population and/or settlements in many areas, as indicated by increases in projectile points, quarry usage, and human-related radiocarbon ages. © 2011 Elsevier Ltd and INQUA.

Mahaney W.C.,Quaternary Surveys | Mahaney W.C.,York University | Keiser L.,University of Oklahoma | Krinsley D.,University of Oregon | And 3 more authors.
Journal of Geology | Year: 2013

Previous work has ascribed a cosmic impact origin to black, high-temperature, carbon-encrusted beds (2-3 cm thick), associated with the Younger Dryas readvance of ice at 12.8 ka during the Late Glacial in the northern Andes of Venezuela. The evidence for this includes carbon spherules, aluminosilicate melt rocks, melted coatings of glass-like amorphous carbon, and Fe-Mn on sands and clasts derived from local felsic gneiss and granite. These sediments have been subjected to renewed investigation using high-resolution scanning electron microscopy and energy-dispersive spectrometry, and new data show that spherules at site MUM7B exhibit unique morphologies and compositions. Molar oxide weight percentages prove the spherules are not volcanic and show little overlap with cosmic materials. Spherule microstructures display quench melting and, thus, could not have formed from slow geological authigenic, diagenetic, or metamorphic processes. Instead, geochemical values for the Venezuelan samples plot within the limits of impact-related materials, including tektites, ejecta, and impact spherules from a number of craters and strewnfields (cf. Chicxulub Crater, Chesapeake Bay Crater, Tunguska, Australasian tektite field, Lake Bosumtwi Crater, Ries Crater, and others). These results are identical to previously reported spherules from the Younger Dryas boundary layer (YDB) on three continents, North America, Europe, and Asia, and the most likely origin is from a cosmic impact/ airburst 12.8 ka, as previously proposed. The MUM7B site is one of the two southernmost sites (Venezuela and Peru) in South America, thus extending the evidence supporting the YDB impact event into a new hemisphere on a new continent. © 2013 by The University of Chicago. All rights reserved.

Mahaney W.C.,Quaternary Surveys | Mahaney W.C.,York University | Keiser L.,University of Oklahoma | Krinsley D.H.,University of Oregon | And 10 more authors.
Journal of the Geological Society | Year: 2013

Weathering rinds have been used for decades as relative age indicators to differentiate glacial deposits in long Quaternary sequences, but only recently has it been shown that rinds contain long and extensive palaeoenvironmental records that often extend far beyond mere repositories of chemical weathering on both Earth and Mars. When compared with associated palaeosols in deposits of the same age, rinds often carry a zonal weathering record that can be correlated with palaeosol horizon characteristics, with respect to both abiotic and biotic parameters. As demonstrated with examples from the French and Italian Alps, rinds in coarse clastic sediment contain weathering zones that correlate closely with horizon development in associated palaeosols of presumed Late Glacial age. In addition to weathering histories in both rinds and palaeosols, considerable evidence exists to indicate that the black mat impact (12.8 ka) reached the European Alps, a connection with the Younger Dryas readvance supported by both mineral and chemical composition. Preliminary metagenomic microbial analysis using density gradient gel electrophoresis suggests that the eubacterial microbial population found in at least one Ah palaeosol horizon associated with a rind impact site is different from that in other Late Glacial and Younger Dryas surface palaeosol horizons. © 2013 The Geological Society of London.

Mahaney W.C.,Quaternary Surveys | Mahaney W.C.,York University | Keiser L.,University of Oklahoma | Krinsley D.H.,University of Oregon | And 5 more authors.
Geografiska Annaler, Series A: Physical Geography | Year: 2014

Recent analyses of sediment samples from "black mat" sites in South America and Europe support previous interpretations of an ET impact event that reversed the Late Glacial demise of LGM ice during the Bølling Allerød warming, resulting in a resurgence of ice termed the Younger Dryas (YD) cooling episode. The breakup or impact of a cosmic vehicle at the YD boundary coincides with the onset of a 1-kyr long interval of glacial resurgence, one of the most studied events of the Late Pleistocene. New analytical databases reveal a corpus of data indicating that the cosmic impact was a real event, most possibly a cosmic airburst from Earth's encounter with the Taurid Complex comet or unknown asteroid, an event that led to cosmic fragments exploding interhemispherically over widely dispersed areas, including the northern Andes of Venezuela and the Alps on the Italian/French frontier. While the databases in the two areas differ somewhat, the overall interpretation is that microtextural evidence in weathering rinds and in sands of associated paleosols and glaciofluvial deposits carry undeniable attributes of melted glassy carbon and Fe spherules, planar deformation features, shock-melted and contorted quartz, occasional transition and platinum metals, and brecciated and impacted minerals of diverse lithologies. In concert with other black mat localities in the Western USA, the Netherlands, coastal France, Syria, Central Asia, Peru, Argentina and Mexico, it appears that a widespread cosmic impact by an asteroid or comet is responsible for deposition of the black mat at the onset of the YD glacial event. Whether or not the impact caused a 1-kyr interval of glacial climate depends upon whether or not the Earth had multiple centuries-long episodic encounters with the Taurid Complex or asteroid remnants; impact-related changes in microclimates sustained climatic forcing sufficient to maintain positive mass balances in the reformed ice; and/or inertia in the Atlantic thermohaline circulation system persisted for 1kyr. © 2013 Swedish Society for Anthropology and Geography.

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