Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments

Abstract

The long-standing controversy regarding the late Pleistocene megafaunal extinctions in North America has been invigorated by a hypothesis implicating a cosmic impact at the Ållerød-Younger Dryas boundary or YDB (Ϸ12,900 ؎ 100 cal BP or 10,900 ؎ 100 14 C years). Abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions, along with reductions in other animal populations, including humans. The hypothesis remains controversial due to absence of shocked minerals, tektites, and impact craters. Here, we report the presence of shock-synthesized hexagonal nanodiamonds (lonsdaleite) in YDB sediments dating to Ϸ12,950 ؎ 50 cal BP at Arlington Canyon, Santa Rosa Island, California. Lonsdaleite is known on Earth only in meteorites and impact craters, and its presence strongly supports a cosmic impact event, further strengthened by its co-occurrence with other nanometer-sized diamond polymorphs (n-diamonds and cubics). These shock-synthesized diamonds are also associated with proxies indicating major biomass burning (charcoal, carbon spherules, and soot). This biomass burning at the Younger Dryas (YD) onset is regional in extent, based on evidence from adjacent Santa Barbara Basin and coeval with broader continent-wide biomass burning. Biomass burning also coincides with abrupt sediment mass wasting and ecological disruption and the last known occurrence of pygmy mammoths (Mammuthus exilis) on the Channel Islands, correlating with broader animal extinctions throughout North America. The only previously known co-occurrence of nanodiamonds, soot, and extinction is the Cretaceous-Tertiary (K/T) impact layer. These data are consistent with abrupt ecosystem change and megafaunal extinction possibly triggered by a cosmic impact over North America at Ϸ12,900 ؎ 100 cal BP.Arlington Canyon ͉ biomass burning ͉ cosmic impact ͉ hexagonal nanodiamonds ͉ megafaunal extinctions

Late Quaternary sea-level history and the antiquity of mammoths (Mammuthus exilisandMammuthus columbi), Channel Islands National Park, California, USA

“…The possible causes of megafaunal extinction at the close of the Pleistocene have been hotly debated, and as the literature on this topic is voluminous, only a brief summary is given here. Three main mechanisms of extinction have been proposed for North America: (1) the human arrival hypothesis (Martin, 1967(Martin, , 1984(Martin, , 2005Haynes, 2013;Sandom et al, 2014, and references therein), wherein humans, newly arrived from Asia, extirpated an unwary North American fauna; (2) the climate change hypothesis, in which the shift from a glacial to an interglacial climate brought about extraordinary changes in ecosystems such that megafaunal species were unable to adapt (Graham and Lundelius, 1984;Meltzer, 2002, 2003 and references therein); and (3) the cosmic catastrophic event hypothesis, where an impact or airburst of an extraterrestrial body (comet or meteor) is thought to have brought about dramatic changes in climate, widespread fires, and demise of human (Clovis culture) and animal (megafauna) populations (Firestone et al, 2007;Kennett et al, 2008Kennett et al, , 2009). Other investigators have pointed out the possibility of a combination of human-caused and climate-related causes of extinction (see discussion in Barnosky et al, 2004).…”

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

“…Following the identification of NDs by Kennett et al (2009aKennett et al ( , 2009b, Daulton et al (2010) attempted to replicate that discovery at two wellknown archaeological sites, Murray Springs, Arizona, and Arlington Canyon, California. Daulton et al (2010) found no YDB NDs and concluded that their findings cast doubt on the presence of YDB NDs, although they pointed out that YDB NDs might "occur inhomogeneously and only in some of the YD-boundary carbons and hence are not observed in our study" (p. 16046).…”

Lonsdaleite is faulted and twinned cubic diamond and does not exist as a discrete material

“…Its formation was attributed to shock-induced transformation of graphite within the meteorite upon impact with Earth, and its occurrence was used as an indicator of shock [1][2][3] . It has since been reported from several meteorites as well as from terrestrial sediments and has been attributed to asteroidal impacts, both extraterrestrial and on Earth [4][5][6][7] .…”

“…1a,b) or match those of graphite, but well-resolved X-ray reflections for lonsdaleite have not been reported. Selectedarea electron diffraction (SAED), Raman, electron energyloss spectroscopy (EELS) and high-resolution transmission electron microscopy have also been used for identification of lonsdaleite [4][5][6][7]14,15,18,23,24 ; however, interpretation of data is ambiguous (Supplementary Note 1). In spite of the many diffraction and spectroscopic studies, unambiguous data that prove the existence of lonsdaleite as a distinct material have not been reported.…”

“…These patterns are consistent with diamond projected along o0114 or o1214, respectively, although the streaking and hexagonally arranged 111 reflections are incompatible with defect-free single-crystal cubic diamond. Such data have been interpreted as evidence for 'lonsdaleite' projected along o0104 and o0014 [4][5][6][7]14,15,20 . The circularly integrated intensity profiles of these SAED patterns ( Supplementary Fig.…”