Absence of geochemical evidence for an impact event at the Bølling–Allerød/Younger Dryas transition

Paquay, François S.; Goderis, Steven; Ravizza, Greg; Vanhaeck, Frank; Boyd, Matt; Surovell, Todd A.; Holliday, Vance T.; Haynes, C. Vance; Claeys, Philippe

doi:10.1073/pnas.0908874106

Cited by 77 publications

(68 citation statements)

References 73 publications

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“…S1), which points strongly toward a terrestrial (upper crustal) source. This finding is similar to that of Paquay et al (13), who analyzed platinum group elements and osmium isotopes in Younger Dryas (YD)-age sediments from different depositional settings and arrived at the same conclusion. If the iridium is carried in the magnetic sediments, as it appears to be based on Firestone et al's data (1), then the REE results imply that the iridium likely has a terrestrial origin as well.…”

Section: Discussionsupporting

confidence: 90%

“…(Note that Ir bs was measured on bulk samples of 10 g or larger to avoid any "nugget effects"; ref. 13). The highest concentrations were found in an 8.2 ka black mat at Tilomonte (1.20 AE 0.21 ppb), a 10.6 ka mat at Quebrada Agua de Cascabel (QAC 4; 0.86 AE 0.21 ppb), a 13.0 ka mat at El Salto 1 (1.65 AE 0.10 ppb), and a >40 ka mat at Rio Salado (2.51 AE 0.15 ppb).…”

Section: Resultsmentioning

confidence: 99%

“…Shortly after the impact hypothesis was proposed, critics began questioning whether some of the markers were necessarily related to an ET impact event (5-11), whereas others argued against the hypothesis after they were unable to find supporting evidence in other depositional settings (12,13) or existing datasets (4,14). Still others raised concerns over issues of replicability and laboratory protocols used in the original study (15).…”

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confidence: 99%

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Accumulation of impact markers in desert wetlands and implications for the Younger Dryas impact hypothesis

Pigati

Latorre

Rech

et al. 2012

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

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The Younger Dryas impact hypothesis contends that an extraterrestrial object exploded over North America at 12.9 ka, initiating the Younger Dryas cold event, the extinction of many North American megafauna, and the demise of the Clovis archeological culture. Although the exact nature and location of the proposed impact or explosion remain unclear, alleged evidence for the fallout comes from multiple sites across North America and a site in Belgium. At 6 of the 10 original sites (excluding the Carolina Bays), elevated concentrations of various “impact markers” were found in association with black mats that date to the onset of the Younger Dryas. Black mats are common features in paleowetland deposits and typically represent shallow marsh environments. In this study, we investigated black mats ranging in age from approximately 6 to more than 40 ka in the southwestern United States and the Atacama Desert of northern Chile. At 10 of 13 sites, we found elevated concentrations of iridium in bulk and magnetic sediments, magnetic spherules, and/or titanomagnetite grains within or at the base of black mats, regardless of their age or location, suggesting that elevated concentrations of these markers arise from processes common to wetland systems, and not a catastrophic extraterrestrial impact event.

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Section: Discussionsupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Accumulation of impact markers in desert wetlands and implications for the Younger Dryas impact hypothesis

Pigati

Latorre

Rech

et al. 2012

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

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“…18-21. Many of the impact markers reported in YD black mats have been widely discredited (22)(23)(24)(25)(26)(27) with the exception of the enigmatic nanodiamonds.…”

Section: Uring the End Of The Last Glacial Period In The Northernmentioning

confidence: 99%

No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event

Daulton

Pinter

Scott

2010

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

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The causes of the late Pleistocene megafaunal extinctions in North America, disappearance of Clovis paleoindian lithic technology, and abrupt Younger-Dryas (YD) climate reversal of the last deglacial warming in the Northern Hemisphere remain an enigma. A controversial hypothesis proposes that one or more cometary airbursts/ impacts barraged North America ≈12,900 cal yr B.P. and caused these events. Most evidence supporting this hypothesis has been discredited except for reports of nanodiamonds (including the rare hexagonal polytype) in Bølling-Ållerod-YD-boundary sediments. The hexagonal polytype of diamond, lonsdaleite, is of particular interest because it is often associated with shock pressures related to impacts where it has been found to occur naturally. Unfortunately, previous reports of YD-boundary nanodiamonds have left many unanswered questions regarding the nature and occurrence of the nanodiamonds. Therefore, we examined carbon-rich materials isolated from sediments dated 15,818 cal yr B.P. to present (including the Bølling-Ållerod-YD boundary). No nanodiamonds were found in our study. Instead, graphene-and graphene/ graphane-oxide aggregates are ubiquitous in all specimens examined. We demonstrate that previous studies misidentified graphene/graphane-oxide aggregates as hexagonal diamond and likely misidentified graphene as cubic diamond. Our results cast doubt upon one of the last widely discussed pieces of evidence supporting the YD impact hypothesis.archaeology | paleoclimate | Quaternary extinctions | carbon spherules | fungal sclerotia

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“…In North America and the Middle East, Bunch et al (2012) identified YDB melt-glass that formed at high temperatures (1730Њ to 12200ЊC), as also reported by three independent groups, Mahaney et al (2010) in South America and Fayek et al (2012) and Wu et al (2013) in North America. This study focuses solely on nanodiamonds (NDs), and so, for independent discussions of other proxies, see Haynes et al (2010) and Paquay et al (2009), who found no evidence for the platinum-group elements iridium or osmium. Alternately, Wu et al (2013) found large YDB anomalies in osmium, as discussed below.…”

Section: Introductionmentioning

confidence: 99%

Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP

Kinzie¹,

Hee

Stich

et al. 2014

The Journal of Geology

170

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. A B S T R A C TA major cosmic-impact event has been proposed at the onset of the Younger Dryas (YD) cooling episode at ≈12,800 ‫ע‬ 150 years before present, forming the YD Boundary (YDB) layer, distributed over 150 million km 2 on four continents. In 24 dated stratigraphic sections in 10 countries of the Northern Hemisphere, the YDB layer contains a clearly defined abundance peak in nanodiamonds (NDs), a major cosmic-impact proxy. Observed ND polytypes include cubic diamonds, lonsdaleite-like crystals, and diamond-like carbon nanoparticles, called n-diamond and i-carbon. The ND abundances in bulk YDB sediments ranged up to ≈500 ppb (mean: 200 ppb) and that in carbon spherules up to ≈3700 ppb (mean: ≈750 ppb); 138 of 205 sediment samples (67%) contained no detectable NDs. Isotopic evidence indicates that YDB NDs were produced from terrestrial carbon, as with other impact diamonds, and were not derived from the impactor itself. The YDB layer is also marked by abundance peaks in other impact-related proxies, including cosmic-impact spherules, carbon spherules (some containing NDs), iridium, osmium, platinum, charcoal, aciniform carbon (soot), and high-temperature melt-glass. This contribution reviews the debate about the presence, abundance, and origin of the concentration peak in YDB NDs. We describe an updated protocol for the extraction and concentration of NDs from sediment, carbon spherules, and ice, and we describe the basis for identification and classification of YDB ND polytypes, using nine analytical approaches. The large body of evidence now obtained about YDB NDs is strongly consistent with an origin by cosmic impact at ≈12,800 cal BP and is inconsistent with formation of YDB NDs by natural terrestrial processes, including wildfires, anthropogenesis, and/or influx of cosmic dust.

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Absence of geochemical evidence for an impact event at the Bølling–Allerød/Younger Dryas transition

Cited by 77 publications

References 73 publications

Accumulation of impact markers in desert wetlands and implications for the Younger Dryas impact hypothesis

Accumulation of impact markers in desert wetlands and implications for the Younger Dryas impact hypothesis

No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event

Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP

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