Magnetic spherules from Pleistocene sediments in Alberta, Canada

Bi, Dong

doi:10.1111/j.1945-5100.1994.tb00658.x

Cited by 5 publications

(1 citation statement)

References 31 publications

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“…Since samples of this type that had been previously analyzed by other authors using more sensitive techniques (1,5,36,38) and had been found to contain only metallic oxides, our analyses assume that all of the metallic elements are oxidized. The quantities of the various elements were determined by standardless EDS analysis and then converted to oxides by stoichiometry.…”

Section: Methodsmentioning

confidence: 99%

Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis

LeCompte

Goodyear

Demitroff

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Firestone et al. sampled sedimentary sequences at many sites across North America, Europe, and Asia [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 106:16016–16021]. In sediments dated to the Younger Dryas onset or Boundary (YDB) approximately 12,900 calendar years ago, Firestone et al. reported discovery of markers, including nanodiamonds, aciniform soot, high-temperature melt-glass, and magnetic microspherules attributed to cosmic impacts/airbursts. The microspherules were explained as either cosmic material ablation or terrestrial ejecta from a hypothesized North American impact that initiated the abrupt Younger Dryas cooling, contributed to megafaunal extinctions, and triggered human cultural shifts and population declines. A number of independent groups have confirmed the presence of YDB spherules, but two have not. One of them [Surovell TA, et al. (2009) Proc Natl Acad Sci USA 104:18155–18158] collected and analyzed samples from seven YDB sites, purportedly using the same protocol as Firestone et al., but did not find a single spherule in YDB sediments at two previously reported sites. To examine this discrepancy, we conducted an independent blind investigation of two sites common to both studies, and a third site investigated only by Surovell et al. We found abundant YDB microspherules at all three widely separated sites consistent with the results of Firestone et al. and conclude that the analytical protocol employed by Surovell et al. deviated significantly from that of Firestone et al. Morphological and geochemical analyses of YDB spherules suggest they are not cosmic, volcanic, authigenic, or anthropogenic in origin. Instead, they appear to have formed from abrupt melting and quenching of terrestrial materials.

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Section: Methodsmentioning

confidence: 99%

Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis

LeCompte

Goodyear

Demitroff

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling

Firestone

West²,

Kennett³

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

493

639

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A carbon-rich black layer, dating to Ϸ12.9 ka, has been previously identified at Ϸ50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at Х12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at Ϸ12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.comet ͉ iridium ͉ micrometeorites ͉ nanodiamonds ͉ spherules

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Magnetic spherules in coastal plain sediments, Sullivan's Island, South Carolina, USA

Taylor

Nusbaum

Fronabarger

et al. 1996

Meteorit & Planetary Scien

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Abstract— We extracted black, magnetic spherules from well cuttings of Oligocene sediments in the coastal plain of South Carolina, USA. Three possible origins were considered: industrial, volcanic, and extraterrestrial. An extraterrestrial origin by ablation of parent meteoroid material is proposed, based on the spherule morphologies, the presence of metallic Fe cores in many of the spherules, and the detection of wüstite in some of the oxide rims. Low Ni contents are problematic but may be attributed to the ablation of a low‐Ni parental body, such as hexahedrite. The presence of spherules in somewhat clay‐like, sandy sediments is unusual, as most magnetic spherules are found in abyssal muds. Based on benthic foraminiferal assemblages and sediment distribution above, within, and below the beds containing spherules, it is unlikely that the spherules were transported from a deep‐sea environment.

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Magnetic spherules from Pleistocene sediments in Alberta, Canada

Cited by 5 publications

References 31 publications

Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis

Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis

Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling

Magnetic spherules in coastal plain sediments, Sullivan's Island, South Carolina, USA

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