Christopher R. Moore

The Australasian tektite strewn field, the largest known on Earth, extends ~13,000 km from Southeast Asia to Antarctica. Previous studies have relied largely on bulk geochemical analyses, which cannot resolve particle-scale processes associated with impact-plume formation and ejecta transport. Here we report, to our knowledge, the first integrated microparticle- and nanoparticle-scale investigation of tektites across the Australasian strewn field. We document quenched micrometer-scale spherules and metallic particles attached to or embedded within freshly fractured interior glass, including specimens whose exterior surfaces were removed before crushing. Electron microscopy was combined with single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS) to characterize more than 175,000 individual nanoparticles, including over 10,000 containing platinum-group elements (PGEs), from seven regions spanning >7,000 km. The metallic particles and spherules include Fe-, Ni-, and Cu-rich metals, oxides, sulfides, and aluminosilicate phases. Some spherules are vesicular or compound, and, to our knowledge, discrete Ni-Cu-rich metallic particles have not previously been documented within Australasian tektite glass. Quartz grains exhibiting progressive melting and vesicular SiO₂-rich domains are consistent with intense heating and possible silica volatilization at ~1900–2200 °C. PGE-bearing nanoparticle mass distributions and inter-element relationships are broadly similar among regions, while bulk multi-element patterns also show strong compositional coherence, suggesting that these characteristics were established before long-range transport. In contrast, recovered nanoparticle abundance and summed PGE mass vary geographically and generally decline toward distal parts of the strewn field, although Thailand and central Australia depart from a simple monotonic distance trend. Several non-PGE metal nanoparticle populations show distinct regional distributions, indicating that different elements were not transported or retained uniformly across the strewn field. Single-particle Ir/Fe and Pt/Fe ratios differ markedly from average crustal reference values and overlap broad ranges reported for cometary particles, refractory metal nuggets, micrometeorites, and iron meteorites. These overlaps are consistent with, but do not prove, incorporation of extraterrestrial metal and are not diagnostic of a specific impactor class. Hydrocode simulations indicate that multi-kilometer-scale impactors can generate high-velocity, strongly downrange ejecta under shallow-impact conditions, consistent with the first-order transport requirements of the Australasian strewn field.

Background Previous work identified a platinum anomaly at Wonderkrater, South Africa, within sediments modeled to the onset of the Younger Dryas (~12,800 cal BP). To investigate the nature of this anomaly, we analyzed sedimentary nanoparticles using single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS). Methods Nanoparticles were extracted from peat sediments spanning the modeled Younger Dryas Boundary (YDB) interval and analyzed for particle number concentrations, elemental compositions, elemental ratios, and multi-element nanoparticle clusters. Results from the YDB interval were compared with sediments above and below the anomaly. Results A pronounced geochemical anomaly is confined to a narrow interval between 357.5 and 362.5 cm depth. Total nanoparticle number concentrations increase by a factor of 4.6 relative to surrounding sediments (p < 0.01), accompanied by reduced average particle mass. The anomalous interval contains two distinct nanoparticle populations: one enriched in platinum-group and siderophile elements, and a second enriched in lithophile and rare earth elements. Eight elemental ratios exhibit elevated values relative to background sediments, including Au/Ir (3.80), Cr/Ni (3.75), and Au/Pt (1.16), each exceeding background values by more than a factor of two. Systematic fractionation among noble and siderophile elements is also evident, with Au, Pt, and Pd exhibiting greater enrichments than Os, Ir, and Ru, consistent with elemental fractionation during high-temperature vaporization, condensation, and atmospheric transport processes. Several multi-element nanoparticle clusters occur predominantly within the YDB interval. Conclusions The YDB layer at Wonderkrater contains a compositionally distinct nanoparticle assemblage characterized by elevated platinum-group elements, siderophile-element enrichments, unique elemental ratios, and changes in terrestrial dust-related signatures. The elemental ratio patterns and nanoparticle populations are consistent with a compositionally heterogeneous, volatile-bearing extraterrestrial component modified by high-temperature processes, together with enhanced terrestrial dust input. These observations are consistent with the introduction of geochemically distinct nanoparticle populations coincident with the onset of the Younger Dryas.

The temporal relationship between the Laacher See eruption (LSE), the Younger Dryas Boundary (YDB) layer, and the abrupt onset of Younger Dryas (YD) climate change has long been debated. The Körslättamossen fen in southernmost Sweden provides the first robustly dated Scandinavian record demonstrating that these events are clearly separated stratigraphically and temporally. The Laacher See Tephra (LST) layer at 288.5 cm (~13,006 cal BP) lies 6–10 cm below a discrete PGE-rich horizon (282–279 cm) marking YDB deposition, interpreted here as a 3-cm-thick impact fallout layer. This interval has an onset Bayesian-modeled age of 12,861 ± 54 cal BP, ~150 years after the eruption, indicating that the LST and YDB deposition represent separate events. Within this fallout layer, Fe–Si microspherules with dendritic quench textures peak at 282–281 cm, while maximum PGE-bearing nanoparticle mass occurs at 280–279 cm, consistent with delayed settling of submicron particles. LA-ICP-MS reveals Si-rich microspherules containing PGE-bearing microdomains but negligible Ni, Co, and Cr. These compositions indicate that the microspherules are dominated by terrestrial target material rather than meteoritic metal, while the associated PGE-rich microdomains and nanoparticle populations record a minor but detectable extraterrestrial component. Single-particle ICP-TOF-MS detects a sharp Pt anomaly with Pt-dominant elemental ratios (e.g., high Pt relative to Fe and Ir), consistent with the platinum enrichment reported in the YDB in the GISP2 ice core. Immediately above the fallout layer, a dark, organic-rich horizon records the abrupt hydroclimatic shift to cooler, wetter YD conditions. These observations document three stratigraphically distinct horizons: the LSE, a separate YDB fallout layer, and the near-synchronous onset of YD climate change, providing a well-constrained European stratigraphic framework for evaluating mechanisms proposed for the YD onset.

Geoarchaeological investigations at site 44PY152 near Smith Mountain Lake, Virginia, document stratified Late Pleistocene–Early Holocene archaeological occupations preserved within ~1.7 m of floodplain alluvium. These deposits contain both in situ and eroding fluted Paleoamerican and Early Archaic projectile points. Here, we analyze a contiguous, high-resolution sedimentary sequence to evaluate the presence and stratigraphic integrity of microspherule and platinum-group element (PGE) anomalies associated with the onset of the Younger Dryas (YD). Analyses include Bayesian radiocarbon modeling, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS), single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS), laser ablation ICP-MS (LA-ICP-MS), laser granulometry, bulk organic carbon and nitrogen, soot carbon, stable carbon isotopes (δ¹³C_OC and δ¹³C_soot), magnetic susceptibility, and mercury (Hg). Results reveal a narrow microspherule-rich interval centered within the 14–15 cmbd sample that is accompanied by pronounced PGE mass anomalies consistent with proxy assemblages reported near the Younger Dryas Boundary at multiple sites worldwide. Bayesian age modeling places this interval within the broader temporal range of the Younger Dryas onset, although the modeled age uncertainty exceeds the narrower age range proposed by Kennett et al. Chondrite-normalized elemental systematics indicate selective Pt-centered enrichment decoupled from comparatively conservative rare earth element behavior, arguing against simple sedimentological concentration processes. The stratigraphic position and internal coherence of this proxy suite identify a discrete marker horizon consistent with the onset of the Younger Dryas at 44PY152. Subtle excursions in δ¹³C_soot and Hg immediately above this interval may reflect associated environmental variability during the early Younger Dryas. Regardless of formation mechanism, the microspherule–PGE horizon provides a high-resolution stratigraphic marker confined to a 1-cm interval that may aid correlation and interpretation of pre- and post-12.8 ka archaeological sequences at stratified sites lacking abundant chronometric control.

The temporal relationship between the Laacher See eruption (LSE), the Younger Dryas Boundary (YDB) layer, and the abrupt onset of Younger Dryas (YD) climate change has long been debated. The Körslättamossen fen in southernmost Sweden provides the first robustly dated Scandinavian record demonstrating that these events are clearly separated stratigraphically and temporally. The Laacher See Tephra (LST) layer at 288.5 cm (~13,006 cal BP) lies 6–10 cm below a discrete PGE-rich horizon (282–279 cm) marking YDB deposition, interpreted here as a 3-cm-thick impact fallout layer. This interval has an onset Bayesian-modeled age of 12,861 ± 54 cal BP, ~150 years after the eruption, indicating that the LST and YDB deposition represent separate events. Within this fallout layer, Fe–Si microspherules with dendritic quench textures peak at 282–281 cm, while maximum PGE-bearing nanoparticle mass occurs at 280–279 cm, consistent with delayed settling of submicron particles. LA-ICP-MS reveals Si-rich microspherules containing PGE-bearing microdomains but negligible Ni, Co, and Cr. These compositions indicate that the microspherules are dominated by terrestrial target material rather than meteoritic metal, while the associated PGE-rich microdomains and nanoparticle populations record a minor but detectable extraterrestrial component. Single-particle ICP-TOF-MS detects a sharp Pt anomaly with Pt-dominant elemental ratios (e.g., high Pt relative to Fe and Ir), consistent with the platinum enrichment reported in the YDB in the GISP2 ice core. Immediately above the fallout layer, a dark, organic-rich horizon records the abrupt hydroclimatic shift to cooler, wetter YD conditions. These observations document three stratigraphically distinct horizons: the LSE, a separate YDB fallout layer, and the near-synchronous onset of YD climate change, providing a well-constrained European stratigraphic framework for evaluating mechanisms proposed for the YD onset.

Geoarchaeological investigations at site 44PY152 near Smith Mountain Lake, Virginia, document stratified Late Pleistocene–Early Holocene archaeological occupations preserved within ~1.7 m of floodplain alluvium. These deposits contain both in situ and eroding fluted Paleoamerican and Early Archaic projectile points. Here, we analyze a contiguous, high-resolution sedimentary sequence to evaluate the presence and stratigraphic integrity of microspherule and platinum-group element (PGE) anomalies associated with the onset of the Younger Dryas (YD). Analyses include Bayesian radiocarbon modeling, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS), single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS), laser ablation ICP-MS (LA-ICP-MS), laser granulometry, bulk organic carbon and nitrogen, soot carbon, stable carbon isotopes (δ ¹³ C_OC and δ ¹³ C_soot), magnetic susceptibility, and mercury (Hg). Results reveal a narrow microspherule-rich interval centered within the 14–15 cmbd sample that is accompanied by pronounced PGE mass anomalies consistent with proxy assemblages reported near the Younger Dryas Boundary at multiple sites worldwide. Bayesian age modeling places this interval within the broader temporal range of the Younger Dryas onset, although the modeled age uncertainty exceeds the narrower age range proposed by Kennett et al. [1]. Chondrite-normalized elemental systematics indicate selective Pt-centered enrichment decoupled from comparatively conservative rare earth element behavior, arguing against simple sedimentological concentration processes. The stratigraphic position and internal coherence of this proxy suite identify a discrete marker horizon consistent with the onset of the Younger Dryas at 44PY152. Subtle excursions in δ ¹³ C_soot and Hg immediately above this interval may reflect associated environmental variability during the early Younger Dryas. Regardless of formation mechanism, the microspherule–PGE horizon provides a high-resolution stratigraphic marker confined to a 1-cm interval that may aid correlation and interpretation of pre- and post-12.8 ka archaeological sequences at stratified sites lacking abundant chronometric control.

Here, we present a multidisciplinary investigation of a late-Pleistocene Greenland ice-margin sequence near Kangerlussuaq that spans the Bølling-Allerød, Younger Dryas, and early Holocene. This study investigates the cause of the Younger Dryas (YD) cooling event (~12,800 years ago) and its possible relationship to a cosmic impact. The Kangerlussuaq interval was previously identified using visible dust stratigraphy, oxygen-isotope measurements, and a peak in nanocarbon particles interpreted as nanodiamonds. We expand that record using bulk ICP-MS, single-particle ICP-time-of-flight mass spectrometry (SP-ICP-TOF-MS), microscopy, mineralogical observations, and hydrocode modeling. The Kangerlussuaq sequence preserves a dark, dust-rich YD interval bounded by clearer Holocene and Bølling-Allerød ice. Stable δ ¹⁸ O values and dust-related geochemical changes support correlation of this interval with the YD cooling episode, although the ice-margin setting introduces uncertainties related to compression, ablation, meltwater infiltration, and multi-season sample alignment. Within this framework, the Greenland record resolves three superimposed signals. First, bulk geochemistry and nanoparticle mineral-phase associations document a sustained YD-scale reorganization of atmospheric dust provenance and transport, consistent with colder, drier, and windier conditions and enhanced mineral-dust flux throughout much of the ~1,200–1,300-year YD interval. Second, a narrow proxy-rich horizon at the YDB layer (~5.5 m along the sloping ice) contains peak abundances of multiple particulate proxies, including nanocarbon particles previously interpreted as nanodiamonds, quartz grains with shocked planar microstructures, meltglass, glass-filled lithic aggregates, Fe- and Si-rich spherules, carbon-rich spherules, glasslike carbon, charcoal, and soot. Third, nanoparticle concentrations begin to rise at the YDB layer (~5.5 m), marking the onset of enrichment, but reach their maximum immediately above, at ~5.2 m. SP-ICP-TOF-MS identifies this overlying interval as the peak in nanoparticle-scale terrestrial and siderophile components, including Nb, Ta, U, As, Pb, Sb, PGEs, Ni, Co, and Re. Elemental behavior across the nanoparticle dataset can be grouped into three principal populations: climate-driven terrestrial mineral dust, high-temperature plume-derived possible ET condensates, and lower-temperature terrestrial plume derivatives. This offset between the boundary layer and the nanoparticle maximum is a key observation: concentrations are lowest within the YDB layer, increase at the boundary, and peak in the overlying sample, indicating temporally structured deposition involving initial boundary-layer input followed by delayed fallout or redistribution of fine particles. This delay is supported by independent evidence from the GISP2 ice core of a platinum anomaly coincident with the onset of Younger Dryas climate change, including a delayed peak over ~21 years, supporting non-instantaneous deposition of impact-related material and suggesting a temporal link to YD climate change. The PGE-bearing nanoparticle population provides the strongest geochemical evidence for a non-crustal contribution. At ~5.2 m, PGE sum, Ir, Pt, Os, Pd, Ni, Co, and Re are enriched relative to the YDB layer; these elements are strongly enriched in extraterrestrial (ET) materials relative to crustal abundances, suggesting a non-terrestrial source. Ratio-ratio diagrams and PGE fractionation versus Ir/Fe comparisons indicate that the YDB nanoparticle population is compositionally distinct from Greenland background dust and typical terrestrial reservoirs. The Greenland YDB value of (Os+Ir+Ru)/(Rh+Pd+Pt) is sub-chondritic, while Ir/Fe is highly elevated, consistent with a heterogeneous mixture containing a refractory PGE-rich component, possibly from ET refractory metal nuggets (RMNs), together with more volatile PGE-bearing material. This signature does not match any single impactor class (e.g., bulk chondrite, iron meteorite, or achondrite), but is consistent with a mixed, fractionated nanoparticle population superimposed on background cosmic dust influx. Hydrocode modeling demonstrates that a high-velocity impact or airburst interacting with an ice-sheet target can plausibly generate high pressures, elevated temperatures, shocked quartz, melt products, spherules, and widespread nanoparticle dispersal; however, this modeling is intended to illustrate a viable mechanism for proxy formation and does not imply that such an impact occurred at the Greenland site. Instead, these results are consistent with broader Younger Dryas Impact Hypothesis scenarios involving regionally or globally distributed impact and airburst phenomena. The combined proxy assemblage is difficult to explain by volcanism, biomass burning, authigenesis, anthropogenic contamination, or climate-driven dust deposition alone. No single proxy is uniquely diagnostic of impact; rather, the interpretation rests on the stratigraphic co-occurrence of multiple high-temperature, shocked, carbonaceous, siderophile-enriched, and PGE-bearing materials within the YD onset interval. Together, the Greenland record is consistent with a short-duration, high-energy airburst or impact-related depositional episode superimposed on and possibly a major trigger of the broader climatic transition into the Younger Dryas.

To test two competing hypotheses for the Younger Dryas trigger (extraterrestrial impact versus volcanism), we analyzed a high-resolution multiproxy record from Hall’s Cave, Texas, which preserves a continuous sedimentary archive from the Last Glacial Maximum through the Holocene. A Bayesian age–depth model based on 61 radiocarbon dates places the Younger Dryas Boundary (YDB) at 12,780 ± 170 cal BP, coincident with abrupt cooling, aridification, and sharply reduced sedimentation. At this boundary, biotic indicators record major ecological disruption, including a collapse of megafaunal dung-fungus spores and declining species richness. Geochemical profiles (magnetic susceptibility, δ ¹⁵ N, C/N, Hg/TOC) document hydroclimatic change and show no pronounced Hg/TOC enrichment at the YDB, indicating no evidence for a significant Hg-rich volcanic input at Hall’s Cave. In contrast, the YDB layer contains multiple high-temperature and shock proxies, including melted microspherules, carbon spherules, soot, nanodiamonds, and shocked quartz, identified using SEM-EDS and TEM analyses. Single-particle ICP-TOF-MS detects enrichments in Ni–Fe, Co–Fe, Fe–Si, Al–Ir, and Ti–Ir nanoparticle associations, including element combinations characteristic of meteoritic material and high-temperature condensation. These proxies define a two-step sequence consisting of a condensed boundary layer containing high-temperature and high-pressure (shock metamorphism) materials, followed by an early Younger Dryas interval characterized by increased dust input consistent with regional aridification. Collectively, the chronological, geochemical, mineralogical, and faunal evidence indicates a high-temperature and high-pressure event at ~12.8 ka and supports an extraterrestrial airburst or impact as the most consistent explanation for the Younger Dryas Boundary, in agreement with the Younger Dryas Impact Hypothesis (YDIH).

The Younger Dryas Boundary (YDB), dated to ~12.8 ka, marks the onset of an abrupt return to near-glacial conditions across much of the Northern Hemisphere. Numerous terrestrial sites contain unusual assemblages of high-temperature materials and geochemical anomalies near this boundary, but marine records remain comparatively sparse. Here we report a multiproxy investigation of four sediment cores (52, 64, 67, and 77) from Baffin Bay, a climatically sensitive region adjacent to the Laurentide Ice Sheet and downstream of major North Atlantic circulation pathways. Within glaciogenic marine sediments dated to the YD onset, we identify distinct layers enriched in inferred impact-related proxies, including meltglass, spherules, carbonaceous particles, metallic dust particles, cometary dust particles, and platinum-group element (PGE) anomalies. Nanoparticles (<1 μm) extracted from bulk sediments were analyzed using single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS), allowing determination of elemental masses and ratios within individual particles. Concentrations of Pt, Ir, Ni, and Co show pronounced peaks associated with the YDB interval across all cores. Elemental mass ratios within nanoparticles, including Ir/Pt, Pt/Pd, Pt/Fe, Co/Ni, and Ni/Fe, also increase sharply within the same stratigraphic interval, with maxima typically occurring slightly above peaks in microspherules and carbonaceous particles. The diagnostic ratio of Pt/Fe is most similar to that of metal-rich extraterrestrial compositions, including comets, and is also strongly enriched relative to average crustal material. The stratigraphic coherence of these enrichments across cores spanning shelf to deep-basin environments indicates a basin-wide depositional signal rather than localized sedimentary processes. The slight offset between peaks in larger melted spherules and submicron nanoparticles is consistent with delayed atmospheric fallout of fine material and subsequent settling through the water column, potentially enhanced by aggregation into marine snow. Background nanoparticle abundances outside the YDB interval are comparatively low, suggesting that the observed enrichments represent a short-lived pulse of metal-rich particulate input. Taken together, the multiproxy evidence from Baffin Bay supports the presence of an unusual depositional layer at the onset of the Younger Dryas marked by high-temperature materials and PGE-enriched nanoparticles. While these anomalies and individual proxies may have alternative explanations, their co-occurrence, stratigraphic confinement, and replication across multiple, widely separated marine cores argue for a common origin. The data are consistent with the addition of extraterrestrial material from a high-energy event capable of injecting large quantities of fine particulate matter into the atmosphere and ocean. Such an event could have contributed to rapid environmental perturbations at the Younger Dryas onset, including atmospheric dust loading and disruption of regional climate. These findings extend the geographic range of YDB proxies into the marine realm of Baffin Bay and provide independent evidence for a sudden, basin-wide depositional episode at ~12.8 ka.