Implications from chemical, structural and mineralogical studies of magnetic microspherules from around the lower younger dryas boundary (new mexico, usa)

Abstract

Hollow magnetic microspherules from along the lower Younger Dryas boundary (c. 12.9 ka bp) in New Mexico (USA) were studied using scanning electron microscopy, electron probe microanalysis, X‐ray diffraction, and laser‐ablation inductively coupled‐plasma mass spectrometry methods. The shell of the microspherules (10–15% of the spherule's diameter) displays dendritic surface textures, which are likely due to quenching during rapid cooling of molten material. Structurally, multiple single‐magnetite crystals attached together form the bulk of the microspherules. Iron dominates the microspherules’ composition (∼90% FeOtot), Mn is the second most abundant element (up to 0.4% MnO), Al is detected in low concentrations (<0.30% of Al2O3). Among the trace elements, the rare earth elements display slightly fractionated patterns with concentrations of 0.1–1.0× CI chondrite. The microspherules contain elevated concentrations of Ni relative to detrital magnetite (up to 435 ppm) and very low concentrations of Ti (down to 5 ppm). Chemical, structural and mineralogical features of the microspherules do not contradict the existing models of the formation during ablation while a meteoroid goes through the Earth's atmosphere. Elevated concentrations of the magnetic microspherules in sediments can be a stratigraphic marker for the lower Younger Dryas boundary in North America.

Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences

“…Andronikov et al 19. reported that Pt, Ir, and Os values were near detection limits for spherules, and therefore, have high uncertainties.…”

“…Specifically, questions have been raised regarding the nature or replicability of the reported impact proxies, the accuracy of the established chronology, and its purported effects on humans and animals at the YD onset12131415161718. All of these criticisms have been addressed by additional and independent studies replicating the original findings of Firestone et al 371920…”

“…investigated sediments from Belgium, the Netherlands, Lithuania, and NW Russia near Finland, reporting sharp YDB enrichment in Pt at the YD onset, as well as other meteoritic elements such as nickel, chromium, copper, and iridium. In a separate study, Andronikov et al 19. analyzed YDB magnetic microspherules from Blackwater Draw, New Mexico using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and laser-ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS).…”

Cosmic Airburst on Developing Allerød Substrates (Soils) in the Western Alps, Mt. Viso Area

“…Smaller fragments, such as the near clay size grain in Fig. 8A, with small bulbous protrusions, depict a melted/quenched morphology similar to that described by Andronikov et al, 2016a) suggestive of an airburst origin. The chemistry of this grain and its coating, Ni and Sn in particular, is suggestive of a cosmic impact (De Laeter and Jeffrey, 1965), with a high content of Fe supporting an impact interpretation, although no crater has been conclusively identified yet.…”

Sediments from around the lower younger dryas boundary (se arizona, usa): implications from la‐icp‐ms multi‐element analysis

“…(), but were not observed in such spherules by Andronikov et al . (). The sample 1PLM1320‐1 from Palominas Arroyo displays trace element patterns that are similar to those in the Murray Springs LYDB sediments, but the features are not as strongly pronounced (Fig.…”