To further evaluate the compositional characteristics of nanoparticles within the Younger Dryas Boundary (YDB) interval at Wonderkrater, we examined platinum-group element (PGE) fractionation relative to iron using a biplot of (Os+Ir + Ru)/(Rh + Pd + Pt) versus Ir/Fe ( Figure 8). This approach allows simultaneous assessment of (1) relative extraterrestrial contribution, as reflected by Ir/Fe, and (2) the degree of fractionation among the platinum-group elements, particularly between the relatively refractory PGEs (Os and Ir) and the relatively more volatile PGEs (Rh, Pd, and Pt), providing insight into high-temperature processes such as vaporization, condensation, and particle sorting. These fields in Figure 8 are based on published third-party data but represent only approximate ranges for mixed particle populations. They are not intended to define strict compositional boundaries. Selected sources of comparative data include: Anders & Grevesse, ³³ Lodders, ³⁴ McDonough & Sun, ³⁵ Becker et al., ³⁶ Peucker-Ehrenbrink & Jahn, ³⁷ Walker, ³⁸ Walker et al., and Horan et al. ³⁹

Interpretation. The Wonderkrater YDB nanoparticles plot at elevated Ir/Fe (~10 ⁻⁴), several orders of magnitude above typical mantle, basaltic, and crustal values (~10 ⁻¹⁰ to 10 ⁻⁸), indicating a substantial enrichment in siderophile elements relative to terrestrial reservoirs. While Ir/Fe alone does not uniquely identify source, ⁴⁰ such elevated values are most consistent with the incorporation of extraterrestrial material. ^{19 – 21}

In contrast, the (Os+Ir + Ru)/(Rh + Pd + Pt) ratio is sub-chondritic and significantly lower than unity, indicating preferential enrichment of Pt, Pd, and Rh relative to Os, Ir, and Ru. This pattern is consistent with fractionation among the platinum-group elements during high-temperature vaporization and condensation processes. This pattern deviates from primary meteoritic compositions and instead is consistent with fractionation during high-temperature processing. In impact-generated vapor plumes, Os- and Ir-rich phases condense at higher temperatures and are incorporated into early forming phases, whereas more volatile PGEs remain in the vapor phase longer and condense later or at greater distances. ^{41 , 42} The Wonderkrater composition is therefore consistent with a fractionated condensate population rather than unfractionated meteoritic debris.

Importantly, the Wonderkrater YDB nanoparticle population does not fall within the compositional field of any single canonical meteoritic class. Instead, it occupies a region consistent with a mixture of components, including (i) a refractory PGE-rich phase contributing elevated Ir/Fe and (ii) a more volatile PGE-rich phase that lowers the overall (Os+Ir + Ru)/(Rh + Pd + Pt) ratio. This combination is consistent with heterogeneous material produced during high-temperature vaporization and subsequent condensation and transport. ^{18 , 41 , 43}

Although the Wonderkrater dataset does not resolve a well-defined background cluster in the Ir/Fe versus (Os+Ir + Ru)/(Rh + Pd + Pt) compositional framework, the broader SP-ICP-TOF-MS results ( Figures 2– 7) demonstrate the presence of persistent nanoparticle populations outside the YDB interval. These background particles exhibit compositions distinct from those observed within the YDB layer, indicating that the anomaly is superimposed upon a pre-existing nanoparticle population rather than representing the only occurrence of nanoparticles within the sequence. The YDB interval is distinguished not by the presence of nanoparticles alone, but by its unique combination of elevated siderophile element concentrations, distinctive PGE fractionation patterns, and increased nanoparticle abundance. Together, these characteristics indicate that the YDB layer represents a compositionally distinct enrichment relative to the surrounding sediments.

Direct comparison with the Greenland dataset reveals both similarities and differences. ⁴⁴ Both sites exhibit elevated Ir/Fe (~10 ⁻⁴), indicating comparable levels of extraterrestrial input. However, the Greenland nanoparticles cluster at higher (Os+Ir + Ru)/(Rh + Pd + Pt) values (~0.7–0.8), closer to refractory-rich compositions, whereas the Wonderkrater nanoparticle plots at lower values, indicating stronger enrichment in more volatile PGEs.

This divergence is most parsimoniously explained by spatial and/or temporal fractionation within a high-temperature plume. The Greenland record is consistent with earlier-condensing, refractory-rich phases, whereas the Wonderkrater signal represents a more volatile-enriched component, possibly representing later-stage condensates or more distal plume material.

The key observation is that Ir/Fe remains similar between the two sites, whereas PGE fractionation varies substantially. This decoupling indicates that total siderophile input and PGE fractionation are governed by different processes: Ir/Fe is consistent with bulk extraterrestrial contribution, whereas (Os+Ir + Ru)/(Rh + Pd + Pt) records plume-scale fractionation and phase partitioning.

These data are consistent with the interpretation that the YDB nanoparticle signal reflects a broadly distributed but compositionally heterogeneous extraterrestrial input that has been modified by high-temperature vaporization, condensation, and atmospheric transport processes. These observations are more consistent with a heterogeneous or fractionated source than with a single homogeneous compositional source.

The elemental ratio analysis of nanoparticles from the Younger Dryas Boundary layer at Wonderkrater provides multiple, internally consistent lines of evidence for a geochemically distinct nanoparticle population within the anomaly interval, in agreement with the two compositional populations identified through SP-ICP-TOF-MS analysis. Eight key elemental ratios exhibit systematic enrichments within the YDB interval relative to background sediments ( Table 1). These enrichments significantly exceed analytical variability and indicate that the YDB nanoparticles differ compositionally from the surrounding nanoparticle population. We acknowledge that individual geochemical proxies are not uniquely diagnostic; however, the co-occurrence of multiple independent elemental-ratio anomalies within a narrow stratigraphic interval strengthens the interpretation that the YDB nanoparticles formed through processes distinct from those responsible for the background sedimentary signal.

The systematic fractionation among platinum-group elements observed in the 357.5–362.5 cm interval is accompanied by extreme enrichments documented in this study, including iridium (~24,000× crustal abundance), osmium (~16,000×), ruthenium (~2,100×), platinum (~1,500×), palladium (~1,100×), and rhodium (~132×). The Au/Ir ratio of 3.80 ( Table 1) indicates relative enrichment of Au compared with Ir. Because Au is generally more volatile than Ir during high-temperature processes, elevated Au/Ir ratios may reflect fractionation during vaporization, condensation, and atmospheric transport rather than primary meteoritic compositions. ^{18 , 41 , 45} Similarly, the Pt/Ir ratio of 3.58 indicates enrichment of platinum relative to iridium compared with background sediments and is consistent with fractionation among platinum-group elements during high-temperature processing. ^{20 , 41}

The preferential enrichment of Au, Pt, and Pd relative to Os and Ir is consistent with high-temperature vaporization, condensation, and transport processes associated with hypervelocity impacts or atmospheric airburst events. ^{41 , 46} Such fractionation patterns have been documented at confirmed impact sites, including the Sudbury structure ⁴⁷ and the Chicxulub crater, ⁴⁸ where impact-generated vapor plumes produced substantial redistribution and fractionation of platinum-group elements. Importantly, several of the elemental ratios reported here differ from both average crustal compositions and primitive chondritic values, indicating that the YDB nanoparticles do not represent simple mixtures of terrestrial material and unfractionated meteoritic debris. Instead, the observed compositions are more consistent with fractionated condensates produced during high-temperature impact-related processes.

The elevated Au/Pt ratio of 1.16 ( Table 1) indicates enrichment of Au relative to Pt within the anomaly interval. Because Au is generally more volatile than Pt during high-temperature processes, this pattern is consistent with fractionation during melting, vaporization, condensation, and atmospheric transport. ^{49 , 50} The anomalous elemental ratios, including enrichments in Cr/Ni, Au/Pt, Pd/Ir, and Pt/Ir, deviate systematically from the surrounding background nanoparticle population and indicate a geochemically distinct assemblage within the YDB interval. The systematic enrichment of multiple siderophile elements, including chromium (~38×), cobalt (~34×), and tungsten (~50×) relative to crustal abundances, within a narrow stratigraphic interval parallels patterns reported from impact-related deposits and is consistent with high-temperature processes capable of concentrating siderophile elements into discrete nanoparticle populations. The confinement of these enrichments to the YDB interval further suggests that they represent a transient depositional event rather than prolonged background sedimentary processes or low-temperature geochemical mobilization.

The elemental ratio patterns observed at Wonderkrater are consistent with a growing body of evidence for extraterrestrial input at YDB sites globally. At Arlington Canyon, California, Kennett et al. ⁵¹ reported elevated Ir concentrations and anomalous PGE ratios at the YDB. Similarly, Bunch et al. ⁵² documented PGE enrichments in conjunction with magnetic spherules at multiple North American sites, paralleling PGE enrichments from confirmed impact sites such as Sudbury and Morokweng. ⁴⁷ The consistency of these signatures across diverse geographical locations and depositional environments suggests a shared high-temperature process affecting extraterrestrial material. Recent work by Pino et al. ²⁸ at the Pilauco site in Chile demonstrated elevated Pt concentrations at the YDB, extending the geographical range of documented anomalies to the Southern Hemisphere. The Wonderkrater data provide additional Southern Hemisphere evidence consistent with a multi-continent extraterrestrial input event.

Several elemental concentrations and ratios begin to increase in the sample immediately below the principal anomaly interval. This pattern may reflect background environmental variability, age-model uncertainty, gradual onset of atmospheric deposition preceding peak enrichment, or incorporation of locally derived detrital material. Similar stratigraphic offsets have been reported at other proposed Younger Dryas Boundary sites, where different particle populations appear to have been deposited over a short interval rather than as a single instantaneous event. ^{53 , 54} However, maximum enrichments, the highest nanoparticle concentrations, and the most pronounced elemental-ratio anomalies remain confined to the principal anomaly interval, indicating that the strongest geochemical signal is stratigraphically restricted rather than distributed uniformly throughout the sequence.

Nanoparticle number concentrations and total particle mass (Supplementary Figure S4) show a pronounced increase in particle abundance at the YDB, accompanied by a decrease in average particle mass. This pattern, characterized by a high abundance of low-mass nanoparticles, is consistent with the fallout of fine-grained material generated during a high-energy cosmic impact or atmospheric airburst, which can produce widespread dispersal of PGE-rich nanomaterials that settle as a discrete depositional layer. The co-occurrence of elevated nanoparticle concentrations and platinum-group element enrichments strengthens the interpretation of an extraterrestrial contribution.

Several alternative mechanisms for PGE enrichment have been proposed, but these do not readily account for the specific combination of elemental ratio patterns observed at Wonderkrater. Volcanic processes typically produce PGE signatures reflecting mantle-derived compositions, characterized by relatively uniform siderophile element distributions and lacking strong enrichment in refractory elements such as Ir relative to crustal materials. ^{45 , 55}

Diagenetic remobilization does not readily account for the systematic enrichment of multiple siderophile elements within such a narrow stratigraphic interval. Platinum-group elements are generally considered relatively immobile under most diagenetic conditions, and post-depositional processes typically produce diffuse redistribution rather than the sharply defined, multi-element anomalies observed here. ³⁷ The coherent fractionation patterns documented in this study are therefore inconsistent with low-temperature diagenetic alteration. Anthropogenic contamination is likewise unlikely, as industrial PGE inputs exhibit distinct compositional signatures and are not expected in Late Pleistocene sedimentary contexts. ²²

Although the observed elemental enrichments and fractionation patterns are not individually diagnostic of a specific impactor type or impact process, they are consistent with extraterrestrial input. Alternative terrestrial mechanisms cannot be completely excluded on the basis of nanoparticle geochemistry alone, but no currently recognized terrestrial process readily accounts for the combined observations. The stratigraphic confinement of the anomalies, coherent multi-element enrichments, platinum-group element fractionation, and agreement with previously reported Younger Dryas-age geochemical anomalies collectively support an extraterrestrial interpretation more readily than any currently known terrestrial alternative.

The elemental ratio data are consistent with a model in which high-temperature vaporization and condensation processes produced PGE fractionation followed by atmospheric dispersal. The spatial distribution and transport mechanisms of such material remain an area of active investigation, particularly with respect to plume dynamics and atmospheric residence times. Quantitative constraints on plume dispersal, atmospheric residence times, and nanoparticle survivability remain limited, and resolving these factors is important for linking distal nanoparticle signatures to specific impact scenarios. Experimental and modeling studies of hypervelocity impacts demonstrate that such events can generate impact vapor plumes and condensation products capable of producing fractionated platinum-group element signatures similar to those observed in impact-related deposits. ^{56 , 57} The sharp stratigraphic confinement of the anomalies to a narrow (~5 cm) interval indicates rapid deposition from a discrete event, consistent with atmospheric fallout from a cosmic impact or airburst. This temporal restriction, combined with the coherent elemental signatures across multiple independent ratios, supports the interpretation that the anomaly is unlikely to reflect gradual accumulation processes.

The observed elemental ratio patterns ( Table 1) further suggest that the extraterrestrial component was modified by high-temperature fractionation processes during impact, atmospheric entry, plume evolution, or deposition. The enrichment of the more volatile PGEs relative to the more refractory PGEs is consistent with selective volatilization and condensation effects documented in experimental and natural impact systems. ^{49 , 58} Distinguishing primary compositional signatures from secondary fractionation effects remains an important area for future investigation.

The elemental ratio evidence for extraterrestrial input at Wonderkrater occurs within a broader interval of paleoenvironmental change documented by pollen and sedimentological data that demonstrate synchronous and abrupt environmental change at the YDB. The paleoecological record at Wonderkrater, reconstructed from high-resolution pollen data, reveals a marked transition in vegetation composition coinciding with the onset of the YD. This interval is characterized by a decline in arboreal taxa, including warm savanna woodland elements like Combretaceae and a concurrent increase in small shrubs associated with high-lying vegetation like certain Asteraceae and fynbos elements, indicative of a shift toward cooler conditions. ^{7 – 9}

Multivariate statistical analyses of the pollen spectra, including the Summary Statistic based on Factor 1 (SSF1) temperature index, demonstrate a significant negative excursion in paleotemperature estimates at this time ( Figure 9). ^{5 , 9} The timing of this temperature decline broadly coincides with the nanoparticle enrichment anomalies of Pt, Ir, Os, Rh, Pd, Co, Cr, and other elements detected with SP-ICP-TOF-MS, providing strong support for the temporal association between extraterrestrial input and abrupt climate change.

These findings are consistent with deuterium isotope records from Vostok (Antarctica) and oxygen isotope data from Sumxi Co (Tibet), suggesting that the climatic perturbation at Wonderkrater reflects a broader, potentially global signal. ^{59 – 61} Sedimentological analyses further corroborate these interpretations, with a reduction in peat accumulation rates and organic productivity evident in the upper sections of the core, consistent with increasingly xeric conditions during and after the YD. ^{62 , 63}

The coincidence of significant nanoparticle enrichment anomalies with vegetation restructuring, inferred temperature decline, and reduced peat accumulation supports the hypothesis that the YD in southern Africa was part of a hemispherically synchronous event with possible extraterrestrial forcing. This paleoclimate evidence supports an interpretation in which extraterrestrial material deposition is associated with rapid and sustained environmental changes affecting regional ecosystems.

Multiple lines of evidence suggest that climate responses to the Younger Dryas onset (∼12,800 cal BP) varied significantly across different regions of the Southern Hemisphere, highlighting the complex regional modulation of global scale forcing mechanisms. Paleoenvironmental records from central-southern South America, including pollen and sediment data, suggest a continued warming trend during the YD interval rather than the cooling observed at Wonderkrater. Pino et al. ²⁸ document a lack of cold-adapted taxa and stable or rising temperatures in central Chile, interpreting this as part of an antiphased hemispheric response associated with the bipolar seesaw mechanism. ^{64 – 66} Supporting studies from sites such as Lago Cipreses, ⁶⁷ Lago El Salto, ⁶⁸ and Lago Condorito ⁶⁹ likewise show no cooling at the onset of the YD and instead indicate warmer or stable conditions.

At the Pilauco site in southern Chile, Pino et al. ²⁸ report both a platinum anomaly and elevated soot and charcoal levels at the YD boundary, consistent with the global signal of an extraterrestrial impact and associated biomass burning. ^{53 , 70} However, they emphasize that these changes did not lead to significant vegetation disruption or abrupt cooling, suggesting a muted climatic response in that region compared to the pronounced cooling documented at Wonderkrater.

In contrast, the multiproxy data from Wonderkrater demonstrate a significantly different pattern, with pollen-based reconstructions revealing a sharp decline in temperatures around ∼12,800 cal BP, consistent with pronounced cooling. ^{5 , 9} Concurrent shifts in vegetation composition, including a decline in forest and wetland taxa and an expansion of grasses and savanna elements, suggest that this cooling was accompanied by drier conditions. ⁹ The presence of both the platinum anomaly and the comprehensive nanoparticle enrichments at Wonderkrater, coinciding with these environmental changes, is consistent with extraterrestrial input at the YD onset. ⁵

These contrasting regional signatures underscore the spatial heterogeneity in Southern Hemisphere climate responses during the Younger Dryas, highlighting the importance of local climate systems in modulating the impacts of hemispheric or global-scale events while remaining consistent with evidence for extraterrestrial material input at the onset of the Younger Dryas.

The elemental ratio evidence from Wonderkrater, when considered alongside similar signatures from other YDB sites, is consistent with extraterrestrial material input occurring within the broader Younger Dryas Boundary interval. ^{26 , 71 , 72} The similarity of PGE fractionation patterns across multiple continents suggests a shared high-temperature process affecting extraterrestrial material, rather than independent local sources. ^{6 , 73} The Pt and other PGE enrichments at Wonderkrater exhibit profiles comparable to those reported from YDB sites across multiple continents ^{26 , 44 , 71 , 74} and in the Greenland ice sheet, supporting the interpretation of a widespread depositional signal of possible cosmic origin. ¹⁷ Nanoparticle enrichments reported here align temporally with anomalies documented at numerous YDB sites worldwide, including Patagonia, ²⁸ and are consistent with the broader body of evidence associated with the Younger Dryas Boundary interval. ^{5 , 6 , 17 , 26 , 71 – 73}

While the PGE ratios provide evidence consistent with extraterrestrial input, several elemental signatures in the 357.5–362.5 cm interval also indicate an enhanced influx of non-local terrestrial dust coinciding with the Younger Dryas onset, consistent with the second nanoparticle population identified in this study. The pronounced enrichment of lithophile and refractory elements, such as rare earth elements, Al, Nb, Ti, and Zr, relative to iron, as documented through terrestrial-signature element analysis ( Figures 5- 6), indicates enhanced aeolian input from distal crustal sources during the YDB interval. The calculated elemental ratios are inconsistent with known terrestrial sedimentary processes under normal climatic conditions, suggesting a fundamental shift in dust provenance and/or atmospheric transport mechanisms.

The distinct fractionation between heavy rare earth elements (HREEs; Gd to Lu) and light REEs (LREEs; La to Eu) observed in the YDB layer indicates mobilization patterns that differ from typical weathering-derived profiles. This REE signature may reflect the activation of previously isolated crustal reservoirs or the preferential transport of specific REE-bearing mineral phases under altered atmospheric conditions. Additionally, the systematic enrichment in refractory elements suggests either enhanced wind strength capable of long-range transport of coarser dust particles, or the mobilization of new dust source regions with unique geochemical signatures.

The abrupt YD climate transition fundamentally reorganized Southern Hemisphere atmospheric circulation patterns, potentially enhancing long-distance dust transport from arid regions, including the Kalahari and Namib deserts. These source regions, characterized by distinct geochemical signatures enriched in refractory elements, could contribute to the observed terrestrial elemental anomalies through enhanced wind strength and altered transport pathways. The multi-elemental ratios of primarily terrestrially-enriched elements identified in this study (Ti-Fe-Al, Ce-Nd-La) support the interpretation of enhanced input from aluminosilicate-rich source regions and evolved crustal compositions (Supplementary Figure S2).

The coeval occurrence of extraterrestrial and non-local terrestrial signatures supports an interpretation in which extraterrestrial material deposition was accompanied by atmospheric perturbations that altered regional dust transport. This coupled signal, extraterrestrial input alongside reorganized terrestrial dust sources, offers a more complete view of the environmental changes associated with the onset of the Younger Dryas.

The specific elemental ratio patterns observed at Wonderkrater provide constraints on the nature of the extraterrestrial component. A YDB Au/Ir ratio of 3.80 indicates enrichment of Au relative to Ir. Because Au is generally more volatile than Ir during high-temperature processes, this pattern is consistent with fractionation accompanying melting, vaporization, condensation, and atmospheric transport. ^{49 , 58} The elevated Au/Pt ratio of 1.16 is likewise consistent with volatile enrichment and/or high-temperature fractionation processes that can enhance Au relative to refractory PGEs. ^{49 , 58}

A YDB Pd/Ir ratio of 16.6, together with the observed enrichments in Pd (~1,100× crustal abundance), indicates fractionation of Pd relative to the more refractory PGEs. Similar Pd-Ir fractionation has been documented in high-temperature condensation and evaporation environments where volatility exerts a primary control on siderophile element behavior. ^{41 , 75} Similarly, the observed YDB Pt/Ru ratio of 2.20 reflects enrichment of Pt relative to Ru and is consistent with fractionation among platinum-group elements during high-temperature processing. ^{18 , 41 , 46} The coupled enrichment in Au and Pt further supports the presence of a volatile-rich component and/or substantial fractionation within the nanoparticle population.

Although some elemental ratios overlap with values reported for specific meteoritic groups, several differ substantially from both primitive chondritic compositions and average crustal values, indicating that the YDB nanoparticles do not represent simple mixtures of terrestrial material and unfractionated meteoritic debris. In particular, ordinary and enstatite chondrites exhibit more uniform siderophile element distributions and do not readily account for the elevated Au/Pt ratios and the preferential enrichment of Au, Pt, and Pd relative to Os and Ir observed within the YDB interval. Moreover, the coexistence of both siderophile-enriched and lithophile-rich nanoparticle populations is not characteristic of a single, homogeneous meteoritic source.

The elemental ratio patterns are not readily explained by any single canonical meteoritic class and instead are consistent with a compositionally heterogeneous extraterrestrial source. The systematic enrichment of Au, Pt, and Pd relative to Os and Ir suggests either a primary volatile-rich component or high-temperature fractionation during atmospheric entry and impact. ^{23 , 41} Cometary material, with its elevated volatile content and susceptibility to atmospheric disruption, provides a plausible contributor, although the moderate but significant PGE enrichments argue against a purely cometary source. ^{49 , 58 , 76}

Critically, no single meteoritic group reproduces the full suite of observed relationships. Ordinary and enstatite chondrites exhibit more uniform siderophile element distributions and do not account for the combined enrichment patterns or the preferential enrichment of Au, Pt, and Pd relative to Os and Ir observed here. These observations are consistent with a mixture of extraterrestrial components modified by high-temperature processes, rather than the direct deposition of unfractionated meteoritic material.

Integration of the PGE ratio patterns with the observed multi-elemental clusters (Ti-Fe-Al, Cr-Fe-Ba, Ce-Nd-La) and associated fractionation trends suggests that high-temperature processing played a major role in producing the observed nanoparticle compositions, potentially involving a compositionally heterogeneous extraterrestrial source and substantial fractionation during atmospheric entry, vaporization, condensation, and transport. ^{23 , 77} The absence of typical iron meteorite signatures argues against a purely metallic impactor.

A parsimonious interpretation is that the Wonderkrater YDB signal reflects a compositionally heterogeneous, volatile-bearing extraterrestrial input modified by high-temperature processes during atmospheric entry and deposition, rather than the direct deposition of a single, homogeneous meteoritic source. ^{6 , 49 , 58} Distinguishing between primary compositional variability and secondary fractionation effects remains an important area for further investigation. Alternative explanations involving volcanic, diagenetic, or authigenic processes were evaluated but do not readily account for the combined elemental ratios, particle-scale associations, and stratigraphic confinement observed in this study.

Sediment Sampling. Samples selected for SP-ICP-TOF-MS analysis were targeted to evaluate the stratigraphic interval previously identified as containing anomalous platinum enrichment together with adjacent background sediments. ⁵ Consequently, sampling was not intended to provide continuous high-resolution coverage of the entire core sequence. Rather, the objective was to compare nanoparticle compositions within the interval of interest with those from stratigraphically adjacent sediments above and below. While the analyzed samples capture the principal interval investigated in this study, additional unsampled geochemical variability elsewhere in the sequence cannot be excluded and should be evaluated through future higher-resolution sampling.

Particle Extraction. For SP-ICP-TOF-MS analysis, 100 mg aliquots of sediment were suspended in 10 mL of ultrapure water (Millipore Advantage System, Merck Millipore) in acid-washed 15 mL centrifuge tubes. The suspensions were vortexed (Scientific Industries G560) and ultrasonicated (Branson 2800, 40 kHz) for 15 minutes to ensure dispersion. After settling for 24 hours, the upper 5 mL of the supernatant was transferred to clean centrifuge tubes and stored at 4 °C. Before analysis, samples were diluted 5000-fold with ultrapure water and sonicated before and after dilution.

Elemental Analysis. Elemental composition of individual nanoparticles was determined using a TOFWERK SP-ICP-TOF-MS system, as outlined in prior work. ^{78 – 80} Samples were introduced via a 2DX autosampler (Element Scientific) with a MicroMist U-series nebulizer and a quartz cyclonic spray chamber. Instrument settings and monitored isotopes are provided in Supplementary Tables S3 and S4. Calibration standards included multi-element ICP reference solutions (0, 1, 2, 5, 10 μg/L in 1% HNO3) and certified nanoparticle standards (NIST RM 8013 Au) for determining transport efficiency using the known size method. ⁸¹ A 4.5% H2/He gas mixture was used as a collision gas, optimized for ⁵⁶Fe + and ²⁸Si + signals. Data processing, including signal thresholding using the Poisson algorithm ⁸² and event correction, was conducted using TOFpilot v2.11.3 (TOFWERK). Samples and blanks were analyzed in triplicate, and data were collected for 200 seconds per replicate. Replicates were combined for final interpretation.

Statistical Significance and Analytical Validation. To assess the robustness of the observed nanoparticle anomaly, statistical analyses were conducted using triplicate analytical measurements. Total nanoparticle concentrations within the YDB interval were approximately 4.6 times higher than in surrounding sediments (Mann-Whitney U test, p < 0.01), demonstrating that the observed enrichment substantially exceeded analytical replicate variability. Although particle mass measurements exhibited elevated standard deviations, the increase in nanoparticle abundance was consistently observed within the 357.5–362.5 cm interval. Accordingly, the anomaly is interpreted as a reproducible analytical signal rather than an artifact of instrumental or analytical noise.