Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA at the Younger Dryas onset (12.8 ka)

Abstract

Sediment sequences spanning the 12,800-year-old lower Younger Dryas boundary (YDB) were investigated at three widely separated sites in eastern North America (Parsons Island, Maryland, a Newtonville sandpit in southern New Jersey, and Flamingo Bay, South Carolina). All sequences examined exhibit peak abundances in platinum (Pt), microspherules, and meltglass representing the YDB cosmic impact layer resulting from the airbursts/impacts of a fragmented comet ∼12,800 years ago. The evidence is consistent with the Younger Dryas impact hypothesis (YDIH) recorded at ∼50 other sites across North and South America, Europe, Asia, and the Greenland ice sheet. These sequences were also examined for shock-fractured quartz, based on a recent study suggesting that low-shock metamorphism may result from low-altitude bolide airbursts similar to that observed during near-surface atomic detonations. Now, for the first time in a suite of well-separated sites in North America, we report in the YDB the presence of quartz grains exhibiting shock fractures containing amorphous silica. We also find in the YDB high-temperature melted chromferide, zircon, quartz, titanomagnetite, ulvöspinel, magnetite, native iron, and PGEs with equilibrium melting points (∼1,250° to 3,053°C) that rule out anthropogenic origins for YDB microspherules. The collective evidence meets the criteria for classification as an “impact spherule datum.”

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Airbursts and Cratering Impacts
2024 | Volume 2 | Pages: 1–31 | e-location ID: e20240003
DOI: 10.14293/ACI.2024.0003
Research Article
Platinum, shock-fractured quartz,
microspherules, and meltglass widely
distributed in Eastern USA at the Younger
Dryas onset (12.8 ka)
Christopher R. Moore1,2,* , Malcolm A. LeCompte3, James P. Kennett4, Mark J. Brooks1, Richard B. Firestone5,
Andrew H. Ivester6, Terry A. Ferguson7
, Chad S. Lane8, Kimberly A. Duernberger9, James K. Feathers10, Charles B.
Mooney11, Victor Adedeji12, Dale Batchelor13, Michael Salmon13, Kurt A. Langworthy14, Joshua J. Razink14, Valerie
Brogden14, Brian van Devener15, Jesus Paulo Perez15, Randy Polson15, Michael Martínez-Colón16 , Barrett N.
Rock17
, Marc D. Young18, Gunther Kletetschka19,20 , Ted E. Bunch21,a and Allen West22
1South Carolina Institute for Archaeology and Anthropology, University of South Carolina, 1321 Pendleton Street, Columbia, SC 29208,
USA; 2SCDNR Heritage Trust Program; Land, Water, and Conservation Division; South Carolina Department of Natural Resources, PO
Box 167, Columbia, SC 29202. 1-919-218-0755, USA; 3Center of Excellence in Remote Sensing Education and Research, Elizabeth City
State University, Elizabeth City, NC 27921, USA; 4Department of Earth Science and Marine Science Institute, University of California
Santa Barbara, Santa Barbara, CA, USA; 5Lawrence Berkeley National Laboratory (ret.), Berkeley, CA, USA; 6Department of Geosciences,
University of West Georgia, 1601 Maple Street, Carrollton, GA 30118, USA; 7Department of Environmental Studies, Wofford College (ret.),
Spartanburg, SC, USA; 8Department of Earth and Ocean Sciences, University of North Carolina Wilmington, NC 28411, USA; 9Center for
Marine Science, University of North Carolina Wilmington, NC 28411, USA; 10University of Washington, Luminescence Dating Laboratory,
125 Raitt Hall, Seattle, WA 98195-3412, USA; 11Analytical Instrumentation Facility, North Carolina State University, Raleigh, NC 27695, USA;
12Department of Natural Sciences, Elizabeth City State University, Elizabeth City, NC 2792, USA; 13EAG Laboratories, Eurofins Materials
Science, Raleigh, NC 27606, USA; 14 CAMCOR, University of Oregon, 1443 E 13th Ave, Eugene, Oregon 97403, USA; 15Electron Microscopy
and Surface Analysis Lab, Nanofab, University of Utah, Salt Lake City, UT 84112, USA; 16School of the Environment, Florida A&M University,
FSH Science Research Center, 1515 South MLK Blvd, Tallahassee, FL 32307, USA; 17Institute for the Study of Earth, Oceans, and Space,
University of New Hampshire, Durham, NH, USA; 18College of Humanities, Arts and Social Sciences, Flinders University, Bedford Park, South
Australia; 19Geophysical Institute, University of Alaska Fairbanks, 903 N Koyukuk Drive, Fairbanks, AK, USA; 20Institute of Hydrogeology,
Engineering Geology and Applied Geophysics, Charles University, Alber tov 6, Prague, Czechia; 21Geology Program, School of Earth and
Sustainability, Northern Arizona University, Flagstaff, AZ 86011, USA; 22Comet Research Group, Prescott, AZ, USA
aDr. Bunch passed away during research for this article.
*Correspondence to: Christopher R. Moore, E-mail: MOORECR@mailbox.sc.edu
Received: 19 April 2024; Revised: 19 April 2024; Accepted: 19 April 2024; Published online: 8 May 2024
How to cite: Moore C.R., et al. Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA at the Young-
er Dryas onset (12.8 ka). Airbursts and Cratering Impacts. 2024 | Volume 2 | Issue 1 | Pages: 1–31 | DOI: 10.14293/ACI.2024.0003
ABSTRACT
Sediment sequences spanning the 12,800-year-old lower Younger Dryas boundary (YDB) were investigated
at three widely separated sites in eastern North America (Parsons Island, Maryland, a Newtonville sandpit in
southern New Jersey, and Flamingo Bay, South Carolina). All sequences examined exhibit peak abundances
in platinum (Pt), microspherules, and meltglass representing the YDB cosmic impact layer resulting from the
airbursts/impacts of a fragmented comet ∼12,800 years ago. The evidence is consistent with the Younger Dryas
impact hypothesis (YDIH) recorded at ∼50 other sites across North and South America, Europe, Asia, and the
Greenland ice sheet. These sequences were also examined for shock-fractured quartz, based on a recent study
suggesting that low-shock metamorphism may result from low-altitude bolide airbursts similar to that observed

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
2
during near-surface atomic detonations. Now, for the first time in a suite of well-separated sites in North America,
we report in the YDB the presence of quartz grains exhibiting shock fractures containing amorphous silica. We
also find in the YDB high-temperature melted chromferide, zircon, quartz, titanomagnetite, ulvöspinel, magnetite,
native iron, and PGEs with equilibrium melting points (∼1,250° to 3,053°C) that rule out anthropogenic origins
for YDB microspherules. The collective evidence meets the criteria for classification as an “impact spherule
datum.”
KEYWORDS
Younger Dryas, airbursts, shock-fractured quartz, microspherules, platinum, meltglass, Clovis
Introduction and background
Previous studies have found evidence consistent with global
extraterrestrial airbursts/impacts at the Younger Dryas
onset (modeled age: 12,835–12,735 cal yr BP at 95% con-
fidence interval) [1]. This estimated age range was deter-
mined using IntCal13, a previous calibration curve, rather
than IntCal20, the current curve. However, that range dif-
fers only by ±0.4%, so it is retained here. This evidence
includes elevated concentrations of multiple materials,
including platinum [2–10], iridium [5, 7, 11–13], magnetic
microspherules [5, 7, 12–15], meltglass [5, 13, 16], nanodi-
amonds [5, 13, 17–19], combustion aerosols and soot [5, 13,
20, 21]. These proxies have been found in sediment dated
to the YDB in virtually every geomorphic setting, includ-
ing multiple lithics-rich 12,800-year-old Paleoamerican
archaeological sites across North America [12], as well as
other sites in central Mexico [22], South America [23, 24],
South Africa [25], Europe [12, 26–29], Greenland [11], the
Middle East [5, 6, 13, 30, 31] and lacustrine, marine, and ice
core records globally [20, 21].
In this study, sedimentary sequences from three widely
separated Younger Dryas Boundary (YDB) sites in the
eastern USA are sampled and analyzed in search of
peak abundance anomalies of microspherules and plati-
num reported elsewhere in sequences dating to the YD
onset (Figure 1). Spherule candidates were identified
optically and verified using scanning electron micros-
copy (SEM) and energy dispersive x-ray spectroscopy
(EDS). Platinum abundance was determined using fire
assay (FA) and ICP-MS with a lower detection limit of
0.1 parts per billion (ppb). In addition, samples were ana-
lyzed for shock-fractured quartz grains indicative of high-
temperature and high-pressure atmospheric detonations
that could result from low-altitude bolide airbursts where
the impact plume reaches the ground [32]. To investigate
potential shock-fractured quartz candidates, we used mul-
tiple techniques, including scanning electron microscopy
(SEM), cathodoluminescence (CL), energy-dispersive
x-ray spectroscopy (EDS), electron backscatter detection
(EBSD), ion beam milling (FIB), and transmission elec-
tron microscopy (TEM).
Shock metamorphism in quartz grains
Multiple studies have described and compared the charac-
teristics of geologic and impact-related metamorphic fea-
tures observed in sedimentary quartz grains. Planar defor-
mation features (PDFs) [33–44] display lamellae that are
typically planar, parallel, crystallographically controlled,
closely spaced at less than a few microns, form at >10 GPa,
and often display amorphous silica. Planar fractures (PFs)
[42, 45] are also typically planar, parallel, crystallographi-
cally controlled, and sometimes display amorphous silica,
but form at <10 GPA and are usually spaced more than ∼10
μm apart. Tectonic deformation lamellae (DLs) [35, 36, 38,
41, 42, 46–50] are nearly always sub-planar, sub-parallel,
rarely crystallographically controlled, and are not reported
to contain amorphous silica. For more details, see Table 1 in
Hermes et al. [32].
Previous studies of cosmic impact structures have
described an additional type of shock metamorphism in
quartz, variously called shock extension fractures [51–54],
sub-planar shock fractures [48, 55], and vermicular (i.e.,
wormlike) microfractures [52, 54, 56]. Following previ-
ous studies [32, 57], we adopt “shock fractures” to denote
microfractures in quartz produced by thermal and mechan-
ical shock.
In contrast to PDFs, PFs, and tectonic lamellae, glass-filled
shock fractures in quartz grains are intragranular cracks that
are sub-parallel, sub-planar, a few microns wide, and filled
with amorphous silica [6, 32, 44, 58–63]. Although some
apparent shock fractures contain no detectable glass, this
study focuses on fractures that are discontinuously filled with
amorphous silica, a term we use interchangeably with “glass.”
It is crucial to note that, by definition, vermicular or
wormlike shock microfractures are sub-planar and curvilin-
ear in three dimensions. Thus, it is impossible to properly
index their crystallographic orientations using a universal
stage, a procedure typically used for investigating impact-
shocked quartz grains.
Shock metamorphism in airbursts
Hermes et al. [32] investigated shock metamorphism in
nuclear airbursts and summarized reports that key shocked

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
3
minerals (e.g., feldspar [64], quartz [65, 66], and zircon [67])
display evidence of pressures from 60 to 5 GPa, sufficient to
create shock metamorphism [32]. Several previous studies
also report that the Trinity nuclear airburst produced shocked
quartz [65, 66]. West et al. [57] used hydrocode modeling to
show that hypervelocity fragments from a nuclear detona-
tion and three types of low-altitude airburst events (called
“touchdown” or Type 2 airbursts [68–70]) could strike the
ground with sufficient energy to produce shocked quartz, as
well as glass-filled, shock-fractured quartz.
To explain the formation of glass-filled, shock-fractured
quartz, Kieffer [58, 59] proposed a process called “jetting,” in
which molten quartz is injected under high pressure and high
temperatures into shock-generated fractures in the grains.
Wakita et al. [71] observed that during the early stages of an
impact, molten material might be jetted when the impactor
contacts target rocks. Hermes et al. [32] showed that nuclear
airbursts can create a lower-pressure variety of glass-filled,
shock-fractured quartz that does not require a typical cra-
ter-forming impact event.
Thus, evidence shows that glass-filled, shock- fractured
quartz possibly was produced during YDB airbursts
through the two processes discussed above: (i) ground
surface impacts by hypervelocity fragments of the
airburst bolide and (ii) jetting that filled grain fractures
with molten material.
Shocked quartz in other YDB layers
Potential shocked quartz grains have been previously
reported in YDB-age sediments from five sites, including
one further analyzed here from Newtonville/Unexpected Pit
(UP), New Jersey [72]. The other four sites are the MUM
7B site in Venezuela [24, 73], a site in Ossendrecht, the
Netherlands [26], one in Aalsterhut, the Netherlands [74],
and Abu Hureyra in Syria [6]. For the three sites in Venezuela
and the Netherlands, the scope of the studies was limited and
lacked a robust characterization of potential shocked quartz.
For Aalsterhut, Van Hoesel [74] identified only one shocked
quartz grain, and the authors speculated that this YDB-age
grain had resulted from reworking (secondary deposition)
from an older impact event. At Abu Hureyra, Moore et al. [6]
identified multiple YDB glass-filled shock-fractured quartz
grains using a comprehensive suite of analytical techniques.
These results were attributed to low-altitude airbursts.
These investigations encouraged searching for shocked
quartz in YDB sequences. We chose these three sites because
the previously identified YDB cosmic impact layer allowed
us to test the hypothesis that shock-fractured quartz grains,
Figure 1: Locations of study sites along the Eastern Seaboard of the USA: Flamingo Bay (South Carolina), Parsons Island (Maryland), and
Newtonville (New Jersey), a range of nearly 1000 km. The image was created using Google Earth, ArcGIS (v.10.4.1), and Canvas 11 (Build
1252) software.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
4
Table 1: Radiocarbon and OSL dates for study sites.
Site name Method Material Context Depth1
Radiocarbon
age (BP) Cal BP2Range 95% CI
OSL age
(ka) Basis for age (OSL) Number
Newtonville AMS GLC Microstrat 11–13 cmbd 10,858 ± 34 12,783 ± 29 12,833–12,738 — — D-AMS 043966
Newtonville AMS GLC Microstrat 11–13 cmbd 10,185 ± 25 11,852 ± 53 11,939–11,751 — — UCI-250410
Newtonville AMS GLC Microstrat 11–13 cmbd 960 ± 20 853 ± 37 923–793 — — UGA-65780
Newtonville AMS CS Microstrat 11–13 cmbd 960 ± 20 853 ± 37 923–793 — — UGA-65781
Parsons Island AMS Sediment Profile 40–45 cmbs 10,753 ± 37 12,731 ± 14 12,757–12,702 — — D-AMS 043965
Parsons Island OSL Sediment Profile 65 cmbs — — 17.4 ± 2.27
2nd Component
(60% of grains) UW-3800
Parsons Island OSL Sediment Profile 100 cmbs — — 19.3 ± 1.56
2nd& 3rd components
(90% of grains) UW-3801
Parsons Island OSL Sediment Profile 130 cmbs — — 21.2 ± 1.78
1st Component
(98% of grains) UW-3802
Parsons Island OSL Sediment Profile 160 cmbs — — 24.2 ± 1.64
3rd component
(74% of grains) UW-3803
Parsons Island OSL Sediment Profile 180 cmbs — — 24.6 ± 2.4
3rd components
(43% of grains) UW-3804
1cmbd=centimeters below datum; cmbs=centimeters below surface.
2INTCAL20.14 calibration.
Note. GLC=Glass Like Carbon, and CS=Carbon Spherules.
microspherules, platinum, and meltglass are widely distrib-
uted in the YDB layer along the Atlantic Coastal Plain of the
United States.
Study sites
Newtonville site
The Newtonville site is located in southern New Jersey in
an abandoned commercial sand pit (39° 34′ 4.6 N; 74° 54′
36.5 W) within the New Jersey Pinelands National Reserve
(PNR) (Figures 1 and 2). The PNR encompasses more
than 1.1 million acres (4,500 square kilometers) of diverse
habitats, including forests, wetlands, rivers, and estuaries.
Established in 1978, PNR was the first National Reserve in
the United States, designated by the U.S. Congress under the
National Parks and Recreation Act.
The profiles sampled from the Newtonville sand pit
sequence include those from a buried A-horizon beneath
historic pit tailings (click on Supplementary Information
Figure 1). Since the original land surface was scalped during
historic mining activities, the depth below the original sur-
face can only be estimated at ∼30–40 cm. Sediment samples
for this study are from an intact microstratigraphic sediment
block (herein called the “microstrat”) containing an organ-
ic-rich fluvially laminated soil layer with underlying yellow
colluvial sand. Additional samples (COA-1 and COA-2;
click on Supplementary Information Figure 1) are from the
same stratigraphic layer collected from an exposed sandpit
profile ∼130 m from the microstrat location.
Parsons Island site
Parsons Island is located within the northernmost waters
of Chesapeake Bay in Queen Anne’s County, Maryland
(38°54′31.24″N; 76°14′47.27″ W) (Figures 1 and 3; click
on Supplementary Information Figure 2). The island is 6.5
km south of Kent Narrows and 15.7 km southeast of the
Chesapeake Bay Bridge. The island includes forests, agricul-
tural fields, marsh, tidal wetlands, mudflats, oyster bars, and
submerged aquatic vegetation. Prior to the 1850s, Parsons
Island was connected to the much larger Kent Island to the
north. Due to continued and extensive coastal erosion, the
landform dwindled from a 1.8 km2 peninsula of Kent Island
in 1685 to its ∼0.3 km2 as an isolated island [75].
The underlying sequence at Parsons Island is of late
Pleistocene age and part of the Kent Island Formation that
ranges in age from ∼60 to 29 kya (Marine Isotopic Stage 3).
Shallow Holocene deposits of variable thickness overlay the
Late Pleistocene sediments at Parsons Island and elsewhere
in the Delmarva Peninsula and immediately overlie the Paw
Paw Loess of Younger Dryas age discussed below. See Fig.
2.8 in Lowery [75].
Surficial aeolian deposits in the area are dominated by a
terminal Pleistocene deposit known as the Paw Paw Loess
[76] that was deposited during the cooler Younger Dryas

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
5
climate episode dating from ∼12,800 to 11,600 years BP [75,
77, 78]. As discussed below, vitrified or ‘glasslike carbon’
(GLC) found at the base of the Paw Paw Loess at Parsons
Island suggests upland loess deposition began at the Younger
Dryas onset ∼12,731 ± 14 cal BP (D-AMS 043965; 95%
range: 12,757–12,702 cal BP; 10,753 ± 37 radiocarbon years
before present (rcybp, 1950). The median calibrated date,
acquired for the stratum immediately above the YDB level,
is, as expected, slightly younger than the established YDB
age range and yet statistically isochronous with the YDB
age of 12,835–12,735 cal BP (95% probability) reported by
Kennett et al. [1].
The thickness of the Paw Paw Loess is regionally varia-
ble across the Delmarva Peninsula, ranging from ∼40 to 110
centimeters thick [79–81]. Prior to European contact, the
Paw Paw Loess may have been much thicker in places but
has been eroded due to agricultural development over the
past 300 years [75].
Lowery [75] notes that: “… the surface contact between
the Younger Dryas Paw Paw Loess and any underlying strata
is represented by an unconformity. The erosional event that
produced this unconformity may have had a duration of
less than half a century.” This inference is based on Clovis
artifacts from many sites along the Delmarva Peninsula in
unconformable sediments immediately below the base of
the Paw Paw Loess and the presence of sediments as old
as 18kya [78]. Lowery [75] also notes that “…the initial
onset of the Younger Dryas circa 12,800 years ago seems to
have markedly destabilized the region’s upland landscape. It
is unclear what caused this significant upland erosion across
such an extensive area. It is assumed that the destabiliza-
tion and upland erosion are the result of marked climatic
changes coupled with upland vegetation stress, as well as
biota overgrazing.”
A portion of the Paw Paw Loess in a well-exposed bluff
on a southwestern-facing shoreline at Parsons Island was
sampled for sediment geochemistry, granulometry, and
OSL dating in 2018 (Figure 3; click on Supplementary
Information Figure 2). Sediment samples were collected at
5-cm intervals from the surface to greater than 180 cm below
the surface (cmbs).
Flamingo Bay site (38AK469)
This site is located on the rim of Flamingo Bay, a Carolina
Bay. This bay is on the U.S. Department of Energy’s (DOE)
Savannah River Site (SRS) in the Upper Coastal Plain of
South Carolina (33°20′14.13″N; 81°40′42.33″ W) (Figures
1 and 4).
Carolina bays are shallow, elliptically shaped wet-
land depressions (ponds or lakes) oriented (NW-SE in
Figure 2: Areas sampled (microstrat and COA-1/COB-1) at Newtonville Sandpit in the New Jersey Pinelands National Reserve (PNR). The
image was created using Google Earth and Canvas 11 (Build 1252) software.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
6
the Carolinas) and occur in large numbers throughout the
Coastal Plain portion of the South Atlantic Slope [82–86].
Several hundred thousand bays exist between Maryland
and northern Florida, with the greatest concentrations in
the Carolinas and Georgia [87]. Carolina bays often exhibit
elevated rims represented by fine sand to gravel-sized sedi-
ments. Although there are multiple hypotheses about bay ori-
gins, the preferred hypothesis proposes that these sediments
were deposited by high-energy, lacustrine (lake) processes
involving shoreface (water-lain) and eolian (wind-blown)
sedimentation [83, 88–91].
Optically stimulated luminescence (OSL) dates from
Flamingo Bay [92] suggest initial formation at 108.7 ± 10.9
ka BP followed by rejuvenation at 40.3 ± 4.0 ka BP (click
on Supplementary Information Figure 3). The shallow bur-
ial of in-situ archaeological assemblages on the sand rim at
Flamingo Bay and other Carolina Bays indicate continued
low rates of eolian deposition into the Holocene and/or the
small-scale reworking of existing eolian sediments through
slope-wash [88].
The eastern sand rim of Flamingo Bay contains a shallowly
stratified multicomponent archaeological site (38AK469).
Paleoamerican artifacts, including Clovis points and tools,
have been excavated below more recent Archaic, Woodland,
and Mississippian occupations. Dating at Flamingo Bay has
been difficult due to the acidic and heavily leached sandy
sediments. No radiocarbon dates of Paleoamerican age have
been obtained from the site, and OSL age estimates have
provided ages with large uncertainties; however, the strati-
graphic level for Early Paleoindian (i.e., Clovis technocom-
plex), dating to ∼13,050 to 12,750 cal BP [93], occurs at
∼50–55 cmbs in the area of the block excavation where sed-
iment samples were collected.
In a previous study [3], a large Pt peak anomaly and
smaller Pt/Pd anomaly at Flamingo Bay coincide with the
uppermost range of Clovis artifacts at ∼50–55 cmbs. Based
on abundance anomalies of Pt in well-dated western and
Midwestern YDB sites, the abundance anomaly depth at
Flamingo Bay is consistent with the onset of the Younger
Dryas.
Sediment samples were collected at Flamingo Bay
(38AK469) in continuous 2.5-cm intervals to a depth of
90 cmbs. These samples were previously tested for Pt and
shown to have significant Pt and Pt/Pd peaks in one sample
at ∼50–55 cmbs, consistent with the age of YD onset [3].
This study examined samples bracketing the YDB layer (and
Pt anomaly) (40–60 cmbs) for microspherules, meltglass,
and shock-fractured quartz presence.
Figure 3: Area sampled at Parsons Island in the Chesapeake Bay, Maryland. The image was created using Google Earth and Canvas 11
(Build 1252) software. The yellow rectangle indicates the area of the bluff sampled.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
7
Results
Newtonville
Multiple analyses were conducted on a fluvially laminated
microstratigraphic sedimentary block (microstrat; size
of ∼25 × 30 × 30 cm) removed from the sequence and on
samples collected from a sandpit profile exposure called
COA-1 and COB-1, which were ∼130 m apart (Figures 1
and 2). From the microstrat block, sediments were sampled
in contiguous 2-cm intervals. Analysis of these samples
revealed a large microspherule abundance peak (∼4500/kg;
click on Supplementary Information Table 1; Figures 5–7
and Supplementary Information Figures 4–18), including a
titanomagnetite spherule (Supplementary Information Figure
19) and a rare zircon spherule that has not been previously
reported for the YDB layer (Supplementary Information
Figure 20). The second sample location, called COA-1 and
COB-1 (see Figure 2), produced ∼10,000 microspherules/
kg in COA-1 (Supplementary Information Table 1). Sample
COB-1 is stratigraphically deeper than COA-1 and contains
significantly fewer microspherules (∼2,000/kg) and no other
proxies (Supplementary Information Figure 1). Other than in
COB-1, few microspherules were observed above or below
this peak. Microspherules ranged from <1 to over 100 μm in
diameter, with most between 10 and 25 μm. For this site, we
use this stratigraphic reference level system rather than cm
below surface (cmbs) because the original surface has been
scalped during mining activities. In the microstrat block, a
microspherule peak at 11–13 cm below datum (cmbd) repre-
sents the YDB layer (age range of 12,835–12,735 cal BP), as
supported by an AMS date on glasslike carbon (GLC) from
the microspherule peak layer (12,783 ± 29 cal BP; 95% range
12,833–12,738 cal BP) (Table 1). There are anomalously
young AMS dates on GLC and carbon spherules that were
Figure 4: Aerial image showing the area sampled at Flamingo Bay at site 38AK469 on the Savannah River Site (SRS), Aiken County, South
Carolina. The image was produced using historic aerial imagery with Canvas 11 (Build 1252) software.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
8
measured from this YDB-aged sample. These likely result
from the downward redeposition of charcoal from recent fire
events (click on Supplementary Information Figure 1).
The YDB layers in the microstrat block and COA-1 are
marked by other criteria indicative of high pressures and
temperatures. These include the following:
1. Anomalously high Pt peaks.
2. Meltglass fragments in COA-1 (Figure 6b) and
microstrat layers (click on Supplementary Information
Figures 21, 22).
3. A fractured zircon grain (click on Supplementary
Information Figures 23–25), displaying fracture infill-
ing likely produced by abrupt high-temperature melting
and quenching.
4. Abundant carbon spherules (mostly >50 μm) embed-
ded with n-diamonds, a variant of cubic nanodiamonds
[17] (Figure 8).
5. Melted ulvöspinel, an iron-titanium oxide mineral
(TiFe2O4; click on Supplementary Information Figure
26) that forms at very high temperatures. Harris and
Schultz [95, 96] concluded that this melted mineral
Figure 5: Newtonville microstratigraphic block distribution of cosmic-impact-related proxies. Pt (ppb = ±0.1); YDB-aged microspherules
(peak=4,483/kg); shock-fractured quartz and meltglass in the Newtonville, New Jersey sedimentary section across the onset of the YD. This
level marks the boundary (12,783 cal BP) between late Pleistocene colluvium (brown) and the YD gray sediments in the microstratigraphic block
sampled at 2-cm intervals. The stratigraphic level of shock-fractured quartz is from sample COA-1 at the base of the gray sediment layer (click
on Supplementary Information Figure 1), a YDB AMS date (12,783 ± 29 cal BP; 95% range: 12,833–12,738 cal BP on glasslike carbon (GLC)
and the level of the microspherule peak. The dendritic microspherule image (a) was produced using SEM, and the shock-fractured quartz grain
image (b) is an optical image using transmitted light (click on Supplementary Information Table 1). Meltglass fragments (click on Supplementary
Information Figures 21–22), indicated by the symbol, peaked in the YDB layer, with a few above the YDB likely due to redeposition. The back-
ground image shows the intact sedimentary block (∼25x 30x20 cm) surrounded by loose sediment from the sandpit profile where it was
detached. Since sandpit mining operations scalped the original surface, sample depths are shown as centimeters below datum (cmbd). The
base of gray sediment is estimated to have been 30–40 cm below the current surface (cmbs) [94].

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
9
is consistent with the anomalously high temperatures
and pressures associated with airbursts or impact
events. This interpretation is consistent with the asso-
ciated high-temperature mineral assemblages at the
Newtonville site.
6. Multiple anomalous elemental peak abundances (click
on Supplementary Information Figure 27) with sidero-
phile and rare earth elements, including chromium,
samarium, cobalt, cadmium, neodymium, gadolinium,
and scandium (click on Supplementary Information
Figure 27a).
7. Anomalously enriched potassium, silicon, aluminum,
calcium, and sulfur values are also enriched in the YDB
layer containing abundant spherules and meltglass but
depleted relative to non-adjacent samples (click on
Supplementary Information Figure 27b–d).
8. Phosphorus also exhibits an abundance peak in a
microstrat sample immediately above the base of the
YD (click on Supplementary Information Figure
27b–d).
9. Quartz grains with potential planar deformation fea-
tures (PDFs) were previously identified [17] based
on optical transmission microscope images in COA-1
(click on Supplementary Information Figure 28).
Furthermore, based on advanced techniques, we
have confirmed the presence of such shock-fractured
quartz grains in this layer, which is discussed in detail
below (click on Supplementary Information Figures
29–30).
Parsons Island site
The Parsons Island site is represented by a sequence of con-
tiguous 5-cm samples from the Paw Paw Loess. This layer
sits above significantly older sediments below and under-
lies a sequence of disturbed sediments of the Ap horizon/
plowzone (Figures 3, 9, and Supplementary Information
Figure 2). The base of the Paw Paw Loess (45–50 cm at this
site) is the YDB layer based on the following criteria:
1. A large peak in microspherules (500/kg) (click on
Supplementary Information Table 2, Figures 9, 10, and
Supplementary Information Figures 31–40).
2. A peak in Pt.
3. Meltglass fragments (click on Supplementary
Information Figure 41).
4. Shock-fractured quartz grains, as discussed in detail
below. No glass-filled fractures in quartz grains were
observed immediately above or below the YDB layer.
The results of the granulometry and sediment geo-
chemistry (δ13C, δ15N, and C/N ratios are shown in
Supplementary Information Figures 42 and 43) and
discussed in the Supplementary Information, “Parsons
Island Bulk Sedimentary Organic Geochemistry.”
A YD onset age for the level containing these abundant
proxies is supported by a high-precision AMS date on GLC
(12,731 ± 14 cal BP; 95% range: 12,757–12,702 cal BP;
D-AMS 043965: 10,753 ± 37 rcybp) from near the base of
the Paw Paw Loess and immediately above the level contain-
ing YDB impact proxies.
Flamingo Bay
An analysis of contiguous sediment samples from Flamingo
Bay at site 38AK469 (Figure 1) previously revealed a dis-
tinct Pt peak in a single 2.5-cm sample at a depth of 52.5–55
cmbs. This anomaly was associated with a Clovis point. The
age of the layer is considered the YD onset based on similar
Pt abundance peaks at sites across North America in well-
dated YDB strata [3, 4]. Further analyses of these samples
revealed a peak in iron-rich microspherules in the same
sample at a depth of 52.5–55 cmbs (click on Supplementary
Information Table 3, Figures 11 and 12, and Supplementary
Information Figures 44, 45). A few such microspherules
Figure 6: SEM images of (a) dendritic iron (Fe) microspherules and (b) vesicular aluminosilicate meltglass fragment from YDB-aged COA-1
sample, Newtonville sand pit (click on Supplementary Information Figure 1). Arrows in (a) call attention to multiple spherules and a secondary
spherule with a dimple caused by impact momentum.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
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Figure 7: Examples of magnetic microspherules from Newtonville recovered from the microstratigraphic sediment block samples (a-r) taken
at 2-cm intervals (see Figures 5, 6, click on Supplementary Information Table 1, and Supplementary Information Figures 4–20). Microspherule
abundances (e.g., 13/kg) are much lower above and below the YDB peak (4483/kg) (click on Supplementary Information Table 1), and their
presence likely results from redeposition. Microspherule surface features are variable, with most exhibiting dendritic patterns.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
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were found above this Pt anomaly (click on Supplementary
Information Table 3) and likely resulted from vertical
reworking, which is common in sandy sites. In addition to
microspherules and Pt, shock-fractured quartz grains were
identified in this sample and were absent in the samples
examined higher and lower in the sequence.
Age depth models for the three sites
We produced Bayesian age-depth models for the three
sites based on radiocarbon and OSL dates, age ranges of
culturally datable lithic artifacts, and age of the Pt peak
of 12,785 ± 50 cal BP (12,835–12,735 cal BP) [1–3]. We
performed Bayesian analysis for each site using OxCal
v4.4.4, r:5 [98] using the InCal20 calibration curve [99]
(Figures 13–15). The OSL dates have high uncertainties,
typically ranging from 1000–2000 years, making for low
precision and accuracy for the age-depth models pro-
duced using OSL alone. In contrast, the Bayesian analy-
ses incorporating the Pt anomaly and designated ages of
lithics displayed much higher statistical certainty, typi-
cally of ±50–200 years.
An agreement Index of ∼100 or greater for the three sites
(the lower acceptable limit is ≥60) confirms the utility of the
peak levels of Pt and microspherule as a chronostratigraphic
marker for the YD onset. For the data tables and coding used in
the Bayesian modeling, click on Supplementary Information
“Bayesian Data” and Supplementary Information Tables 4–6.
Key additional proxies in support of a cosmic
impact
High-temperature melted minerals
Previous studies [5, 7, 13, 16] reported blebs of melted
high-temperature minerals on YDB-age spherules and melt-
glass surfaces from Abu Hureyra, Syria, the Melrose site,
Pennsylvania, and the Blackville site, South Carolina. The
last two sites are in the eastern United States, as are the
three sites in this paper. Given this earlier YDB evidence
of high-temperature, highly reduced, melted minerals, we
investigated their presence in the YDB at the three sites.
Our investigations identified the presence of minerals that
are known to wholly or partially melt at given temperatures:
mineral oxides including magnetic and titano-magnetite
quartz and zircon from ∼1700 to 2000°C and chromite and
chromferide from ∼2000 to 2600°C. Some minerals show
evidence of formation at varying temperatures under reduc-
ing conditions, thus producing oxygen-deficient minerals
(see Table 2). Using SEM to examine particles, we identified
22 minerals known to melt at high temperatures. Equilibrium
temperatures ranged from ∼1250°C for bulk sediment to
3053°C for osmium (Table 2). These are described for the
YDB at the following three sites.
Newtonville
Thirteen melted objects included a mineralized carbon
spherule embedded with melted blebs enriched in PGEs,
including osmium (1.26 wt%; melting point = 3053°C), irid-
ium (1.16 wt%; melting point = 2466°C), and platinum (2.05
wt%; melting point = 1768°C). Click on Supplementary
Information Figure 46.
We analyzed seven spherules and melted objects that
were Fe-rich but highly depleted in oxygen (FeO; melting
point = 1538°C), suggesting that they formed under highly
reducing conditions that are rare on the Earth but common in
impact-related material. The Fe content averaged 87.0 wt%
(range: 75.7 to 93.8 wt%), with O2 content that averaged 6.7
wt% (range: 0.54 to 14.83 wt%). Click on Supplementary
Information Figures 47 through 53.
We also investigated one melted, aerodynamically-
shaped titanomagnetite spherule (click on Supplementary
Information Figure 54). One melted titanomagnetite bleb
Figure 8: TEM image (a) and selected area diffraction pattern (SAD) (b) of an n-diamond from COA-1 sample at Newtonville sand pit (click on
Supplementary Information Figure 1).

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
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Figure 9: Parsons Island Sequence. Lithology, ages (radiocarbon & OSL), the abundance distribution of microspherules, Pt, shock-fractured
quartz, and meltglass. The AMS date (12,731 ± 14 cal BP; 95% range: 12,757–12,702 cal BP; on glasslike carbon (GLC) collected from sample
40–45 cmbs, and (a) the Bayesian modeled median age of the Pt abundance anomaly (12,835–12,735 cal BP; 12,785 ± 50 cal BP at 95%
confidence interval) documented at YDB sites across North America [1]. (b) SEM image of a dendritic microspherule; (c) cathodoluminescence
(CL) image of shock-fractured quartz grain. Blue represents natural quartz that has not been melted; orange represents quartz that has been
melted and then annealed; black represents fractures filled with amorphous silica.
Table 2: High-temperature melted minerals and materials were observed in the YDB at the three sites.
Phase Formula ∼Melt T (°C) Phase Formula ∼Melt T (°C)
Cerium CeO22400 Paladium Pd 1555
Chromferide Fe1.5 Cr0.2 1900 Platinum Pt 1768
Chromite (Fe)Cr2O42190 Quartz SiO21713
Iridium Ir 2466 Rhodium Rh 1964
Iron oxide (hematite) Fe2O31565 Ruthenium Ru 2334
Iron oxide (magnetite) Fe3O41590 Sediment Si-Ca-rich 1250
Iron, native Fe 1538 Spherules, Fe-rich Fe + Fe oxides 1420
Lanthanum La2O32315 Spherules, Si-rich Si, Ca, Al, Fe oxides 1250
Nickel Ni 1455 Titanomagnetite TiFe2O41625
Nickel iron NiFe 1430 Ulvöspinel TiFe2+2O41625
Osmium Os 3053 Zircon ZrSiO41775
Shown are mineral names, chemical formulae, and melting points, ranging from 1250°C to 3053°C.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
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Figure 10: Magnetic microspherules from Parsons Island. They were extracted from 5-cm interval samples between 40 and 60 cm, as shown.
Peak abundances occur at 45–50 cm. (click on Supplementary Information Table 2, Figure 9, and Supplementary Information Figures 31–41).

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
14
(click on Supplementary Information Figure 55) and one
broken spherule (click on Supplementary Information
Figure 56) composed of ulvöspinel, a form of titanomag-
netite with a melting point of ∼1625°C. One spherule
was composed of zircon with a melting point of ∼1775°C
(click on Supplementary Information Figures 57, 58).
Such spherules are highly unusual because zircon tends to
dissociate rather than melt. In addition, one zircon grain
displaying fractures filled with melted zircon appears to
have undergone shock metamorphism at temperatures
Figure 11: Flamingo Bay Sequence, South Carolina (38AK469) showing the abundance distribution of Pt (error = ± 0.1 ppb) and microspher-
ules, shock-fractured quartz, and temporally diagnostic hafted bifaces. Peaks in Pt and microspherules and the presence of shock-fractured
quartz mark the YDB. a) SEM image of dendritic microspherule. b) Shocked -fractured quartz grain image is optical using epi-illumination.
Hafted bifaces silhouettes represent a generalized archaeostratigraphy for the downslope portion of the main excavation block at Flamingo
Bay. The accepted age range for Clovis tools is ∼13,050–12,750 cal BP [97] and overlaps with the YDB at ∼50–55 cmbs. This figure is modified
from Moore et al. [3]. Note that Pt abundance on the graph is an average of two measurements from the same sample (click on Supplementary
Information Table 3).

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
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≥1775°C (click on Supplementary Information Figures
59–62).
Parsons Island
Using SEM-EDS, we investigated 12 objects from the YDB
at this site that contained detectable levels of PGEs and other
elements commonly found in meteoritic material. Ru aver-
aged 250 ppm with a range up to 900 ppm (melting point =
2334°C), Rh averaged 192 ppm with a range up to 900 ppm
(melting point = 1964°C), Pd averaged 567 ppm with a range
up to 2300 ppm (melting point = 1555°C), Os averaged 0.3
wt% with a range up to 2.07 wt% (melting point = 3053°C),
Ir averaged 0.52 wt% with a range up to 1.58 wt% (melting
point = 2466°C), and Pt averaged 0.28 wt% with a range up
to 0.86 wt% (melting point = 1768°C). Cr averaged 1.09 wt%
with a range up to 12.51 wt% (melting point = 1907°C), Co
averaged 42 ppm with a range up to 300 ppm (melting point
= 1495°C), and Ni averaged 48 wt% with a range up to 4.94
Figure 12: Representative examples of magnetic microspherules from Flamingo Bay (38AK469) (a and e) (see Figure 11, click on
Supplementary Information Table 3, and Supplementary Information Figures 44 and 45).

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
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Figure 13: Bayesian age/depth model for Newtonville. The age-depth model uses one OSL date (black text), two radiocarbon dates, and
the age of the Pt peak (YDB layer) (green text). The OxCal program rejected two radiocarbon dates as being anomalously young. The age of
the Pt peak, as previously determined, is 12,785 ± 50 cal BP (12,835–12,735 cal BP) [1–3], and its chronostratigraphic position is statistically
supported with an Agreement Index of 113 (well above the lower acceptable limit of 60), confirming its utility as a chronostratigraphic marker.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
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Figure 14: Bayesian age/depth model for Parsons Island. The age-depth model uses 5 OSL dates (black text), 1 radiocarbon date, and the
age of the Pt peak (green text). The age of the Pt peak, as previously determined, is 12,785 ± 50 cal BP (12,835–12,735 cal BP) [1–3]. The Pt
peak (YDB layer) is given the previously determined datum age range of 12,785 ± 50 cal BP (12,835–12,735 cal BP) [1–3] and its chronostrati-
graphic position is statistically supported with an Agreement Index of 113 (well above the lower acceptable limit of 60), confirming its utility as
a chronostratigraphic marker.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
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Figure 15: Bayesian age/depth model for Flamingo Bay. This age-depth model uses age ranges of 6 culturally identifiable lithic artifacts
(orange-brown) and the age range of the Pt peak (YDB layer) (green text). The Pt peak (YDB layer) is given the previously determined datum
age range of 12,785 ± 50 cal BP (12,835–12,735 cal BP) [1–3], and its chronostratigraphic position is statistically supported with an Agreement
Index of 113 (well above the lower acceptable limit of 60), confirming its utility as a chronostratigraphic marker.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
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wt% (melting point = 1455°C). Click on Supplementary
Information Figures 63–74. One melted PGE-enriched object
was composed of chromferide (Fe1.5Cr0.2) with a melting point
of ∼1900°C (clickn on Supplementary Information Figure
74). Gurov et al. [100] reported finding melted chromferide
associated with the El’gygytgyn crater in Russia.
Flamingo Bay
In the YDB layer at this site, we identified one carbon spher-
ule embedded with melted PGE-rich blebs. The Pd abundance
was 300 ppm (melting point = 2334°C), Ir averaged 800 ppm
(melting point = 2466°C), and Pt was 500 ppm (melting point
= 1768°C). Cr averaged 100 ppm (melting point = 1907°C).
Click on Supplementary Information Figure 75.
Shock-fractured quartz
The results of our shock-fractured quartz investigations
are new and, thus, require a separate integrated section for
the three study sites. The solid identification of glass-filled
shock-fractured quartz requires multiple observations using
a variety of analytical approaches. Thus, we employed a
comprehensive suite of analytical techniques and instru-
ments to study these grains. These included optical trans-
mission microscopy (OPT), epi-illumination microscopy
(EPI), scanning electron microscopy (SEM), energy dis-
persive spectroscopy (EDS), focused ion beam milling
(FIB), transmission electron microscopy (TEM), scanning
transmission electron microscopy (STEM), fast-Fourier
transform (FFT), cathodoluminescence (CL), and elec-
tron backscatter diffraction (EBSD). All procedures and
instruments are discussed in detail in the Supplementary
Information, “Instrumentation and Analytical Details.”
For all three sites, the YDB layer had been previously
identified by the presence of multiple materials known to
be produced during cosmic impacts and airbursts. One or
more 26 × 46-mm (8 cm2) thin sections were prepared and
investigated for each layer at each site. For Newtonville
sample UP-COA1, ∼8,700 sand grains, representing quartz,
feldspar, and other minerals, were examined and found to
contain 8 shock-fractured quartz grains on one 8-cm2 slide.
For Newtonville sample UP-11–13, of ∼9,300 examined sand
grains, 6 were identified as shock-fractured quartz grains.
For Parsons Island, 22 shocked quartz grains were identified
amongst ∼56,000 sand grains from the Pars-45 sample. For
Flamingo Bay, 5 shocked quartz grains out of ∼7400 sand
grains were found in the Flam-52.5 sample (Figures 16–19).
The stratigraphic distribution of the shock-fractured quartz
grain is summarized in Figure 20. The YDB layer was sam-
pled at each of the three sites and is marked by peak abun-
dances. In addition, one to two other layers outside the YDB
were likewise investigated.
Initial candidate quartz grains were selected using light
microscopy based on the presence of closely-spaced, paral-
lel to sub-parallel, open fractures, often with material fill-
ing the fractures. For details, see Methods: Instrumentation
and Analytical Details. These candidate grains were then
carefully analyzed by SEM, TEM, and EBSD to confirm
the glass-filled fractures. We observed no candidates for
shock-fractured quartz in >8,000 sand grains from each layer
examined above and below the YDB layer for each of the
three sites. Notably, naturally fractured and quartz grains
displaying tectonic lamellae (closed and non-fractured) were
prevalent, although none analyzed contained amorphous
silica.
Summary of geochemical and other proxies
For the three sites, we report abundance peaks in Pt, micro-
spherules, meltglass, nanodiamonds, high- temperature
melted minerals, and glass-filled fractured quartz. At
Flamingo Bay, the Pt peak is chronostratigraphically associ-
ated with Clovis cultural artifacts (Figure 21).
Discussion
Many studies have documented a broadly multi-continental
distribution of YDB glass or iron-enriched and glassy micro-
spherules [e.g., [7, 12, 14–16, 23] and platinum [e.g., [2–4,
7, 25]. This study’s three widely separated sites along the
North America Eastern Seaboard are consistent with this by
exhibiting YDB peaks in microspherules and Pt. For the first
time, the impact origin of the YDB is further strengthened
by documentation of shock-fractured quartz (Figure 20) in
the three sites. Furthermore, aluminosilicate meltglass was
identified at two sites (Newtonville and Parsons Island), and
nanodiamonds were identified at Newtonville [72].
Site dating
The Parsons Island YDB layer is solidly radiocarbon-dated.
Although the shallow surficial stratigraphy at Newtonville
produced mixed radiocarbon ages, likely because of biotur-
bation, a YD-onset AMS date on GLC is consistent with
multiple impact proxies of YDB age. Similarly, although
the Flamingo Bay profile is not well radiometrically dated,
the stratified presence of Clovis artifacts (∼13,050 to
12,750 cal BP) [93] provides a chronostratigraphic datum
for the YDB.
Previous studies [3, 4] proposed that the platinum abun-
dance anomaly in YDB sediments across North America is
a reliable chrono- and litho-stratigraphic datum for the YD
onset constrained to 12,835 to 12,735 cal BP (at 95% proba-
bility) [1]. The age of the Pt anomaly is consistent with that
of the GISP2 Greenland ice core [2]. Notably, the GISP2
Pt anomaly occurs precisely in the same ice core sample as
the oxygen isotope excursion and an increase in dust con-
tent that marks the onset of the Younger Dryas cooling epi-
sode ∼12,800 years ago. This interpretation was based on a
detailed analysis of multiple climate proxies from a single
ice core, GISP2 [20] (click on Supplementary Information
Figure 76). However, this conclusion was disputed by

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
20
Holliday et al. [104], who claimed the YD onset occurred 30
years before the Pt peak. Holliday et al. based that conclu-
sion on comparing climate proxies from multiple ice cores
using the multi-core GICC05 timescale, and they neglected
to consider the GICC05 uncertainties of ± 140 years. Thus,
we consider the exact correspondence of the Pt anomaly
with the YD onset climate proxies in a single ice core with
one timescale in Wolbach et al. [20, 21] to be more reliable
than the conclusion of Holliday et al., based on a compari-
son of multiple cores with a composite age scale having an
uncertainty of ± 140 years. For the three sites in this paper,
we accept that the age of the Pt anomaly is ∼12,835–12,735
cal BP and conclude that the layer marked by the peaks of
Pt and other inferred impact proxies is more predictive in
identifying the YDB layer and especially when radiocarbon
or OSL dating is limited or problematic.
Shock-fractured quartz
Glass-filled shock-fractured quartz grains were observed at
the three sites, based on TEM-FFT and TEM-SAD, demon-
strating a lack of crystallinity, i.e., that the filling material
is amorphous (glass). SEM-EDS analysis confirmed that
this glass filling is quartz. In some cases, EBSD analyses
revealed black, non-luminescent quartz filling, consist-
ent with previous independent observations that the non-
luminescent material is amorphous [38, 101–103].
A previous study [32] demonstrated that both near-sur-
face nuclear detonations and nuclear airbursts produce very
Figure 16: Shock-fractured quartz grains from Newtonville Site (a-c), Parsons Island Site (d-f), and Flamingo Bay (g-i). Images were acquired
using optical microscopy and SEM. Yellow arrows identify selected shock fractures. Visible fractures were subsequently determined by EBSD
and TEM to contain amorphous silica. In panels e and h, the red bars mark selected areas of undulose extinction that occur under crossed
polarizers when different parts of the grain reach extinction at different polarities. This optical phenomenon commonly results from heterogene-
ous distortion of the crystal’s lattice by mechanical or thermal stress. (a) Newtonville (UP-11–13 cmbd) 23x13; epi-illuminated microscope (EPI)
image. (b) Newtonville (UP-11–13 cmbd) quartz grain 23x13; transmitted-light optical microscope (OPT) image. (c) Newtonville (UP-11–13 cmbd)
23x13; secondary electron scanning electron microscope (SEM) image. (d) Pars-45 quartz grain 22x12; EPI image. (e) Pars-45 quartz grain
22x12; OPT image under crossed polars, rotated slightly off maximum for greater visibility. (f) Pars-45 quartz grain 22x12; backscatter electron
scanning electron microscope (SEM-BSE) image. (g) Flam-52.5 quartz grain 33x-07; EPI image. (h) Flam-52.5 quartz grain 33x-07; OPT image
under crossed polars, rotated slightly off maximum for better visibility. (i) Flam-52.5 quartz grain 20x12; SEM-BSE image.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
21
high temperatures and pressures capable of melting quartz
and producing shock metamorphism. The most important
similarity is that, in both events, the shockwaves from the
ground impacts or near-surface airbursts are coupled with
the Earth’s surface, thus producing extreme temperatures
and pressures that fracture quartz grains, melt or vapor-
ize surficial quartz-rich sediments, and force molten silica
into the fractures. These conditions are unlike high-altitude
nuclear detonations or cosmic airbursts in which the fireball
does not intersect the Earth’s surface. This surface-coupling
Figure 17: Shock-fractured quartz grains from Newtonville Site (a-c), Parsons Island Site (d-f), and Flamingo Bay (g-i). Images were acquired
using scanning-transmission electron microscopy (STEM), transmission electron microscopy (TEM), fast-Fourier transform (FFT), and selected
area diffraction (SAD). Yellow arrows identify selected shock fractures. Green arrows labeled “G” mark amorphous silica (glass) areas filling
most fractures. Blue arrows labeled “V” mark voids or vesicles typically associated with fractures. All three sites display quartz grains with shock
fractures intermittently filled with amorphous silica, as confirmed using FFT and SAD. (a) Newtonville (UP-COA1) quartz grain 08x03B. STEM
image. (b-c) Newtonville (UP-COA1) quartz grain 08x03B. TEM image. (d) Newtonville (UP-COA1) quartz grain 08x03B. FFT image confirms
non-crystallinity, i.e., the filling is amorphous quartz. (e) Pars-45 quartz grain 22x-07. STEM image. (f-g) Pars-45 quartz grain 22x-07. TEM image.
(h) Pars-45 quartz grain 22x12. The SAD image confirms non-crystallinity, i.e., the filling is amorphous quartz. (i) Flam-52.5 quartz grain 20x13.
STEM image. (j-k) Flam-52.5 quartz grain 20x13. TEM image. (l) Flam-52.5 quartz grain 20x13. FFT image confirms non-crystallinity, i.e., the
filling is amorphous quartz.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
22
appears essential to produce shock-generated fractures filled
with amorphous silica. Potential formation mechanisms for
shock fracturing include compression, tensioning, and ther-
mal metamorphism. Our investigation confirms the presence
of glass-filled shock-fractured quartz at each site in the YDB
layer, but not above or below.
We concur with the jetting hypothesis suggested by earlier
studies [58, 59, 63] that high temperatures appear to vaporize
Figure 18: Shock-fractured quartz grains from Newtonville Site (a-b), and Parsons Island Site (d-f), and Flamingo Bay (g-i). Images were
acquired using SEM-based cathodoluminescence (CL). Yellow arrows mark linear, non-luminescent black bands, commonly accepted to indi-
cate open fractures or, in this case, amorphous material [38, 101–10 3]. (a) Newtonville (UP-11–13 cmbd) quartz grain 35x03. Panchromatic
CL image. (b)Newtonville (UP-COA1) quartz grain 08x-03. Panchromatic CL image. (c) Pars-45 quartz grain 09x-12. Composite color (RGB)
CL image. Blue represents unmelted quartz; orange represents melted quartz that has been annealed; black represents fractures filled with
amorphous silica. Note that the fractures in this grain radiate from the area at the upper right, potentially resulting from a high-pressure collision
with another grain. (d) Pars-45 quartz grain 07x06. Composite color (RGB) CL image. (e-f) Pars-45 quartz grain 22x12. Panchromatic CL image.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
23
Figure 19: Shock-fractured quartz grains from Newtonville Site (a-c), Parsons Island Site (d-f), and Flamingo Bay (g-i). Images were acquired
by electron backscatter diffraction (EBSD). The yellow arrows mark fractures. The inset legend at the lower right for each image except panel c
shows the color-coded Miller-Bravais crystalline axes. For a detailed description of the EBSD analytical techniques used in this Figure, click on
Supplementary Information, “Methods: Instrumentation and Analytical Details.” (a) Newtonville (UP-COA1) quartz grain 18x14. The wide range
and variation of colors indicate thermal or mechanical damage to this grain’s lattice. (b) Newtonville (UP-COA1) quartz grain 13x06. The green
and red colors represent the two Dauphine twin domains rotated 60° around the c-axis. The twinning is minimally associated with the fractures.
(c) Pars-45 quartz grain 22x-07. A multi-colored misorientation scale is inset at the lower right. The colors represent the degrees of misorientation
(i.e., damage) of the crystalline structure, ranging from 0 degrees (blue) to ∼5 degrees (red). The largest misorientations (red) are concentrated
along the fractures. (d) Pars-45 quartz grain 22x-07. Reddish colors represent the quartz matrix, and orange-tan colors indicate Dauphine twin-
ning rotated 60° around the c-axis. The twinning is closely associated with the fractures. (e) Flam-52.5 quartz grain 19x13. The wide range of
colors and their extent indicate that this grain has sustained substantial lattice damage. (f) Flam-52.5 quartz grain 19x13. Green colors represent
the quartz matrix, and purple indicates Dauphine twinning rotated 60° around the c-axis. The twinning is minimally associated with the fractures.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
24
quartz grains and sediment, after which high pressures inject
molten silica or vapor into the fractures and any other zones
of weakness in exposed quartz grains [59, 63]. We also
concur with two more recent studies [6, 32] that molten sil-
ica may enter quartz grains along multiple possible zones
of weakness: (i) fractures produced by the shockwaves,
Figure 20: The number of shock-fractured quartz grains observed by depth at (a) Newtonville, microstrat, (b) Parsons Island, and (c) Flamingo
Bay. Shock-fractured quartz grains were observed only in the YDB layer, co-occurring with the peaks in microspherules, Pt, and anomalously
high values in various other elements. Also shown is generalized archaeostratigraphic data for Flamingo Bay (38AK469) (i.e., Paleoindian
through Woodland hafted biface silhouettes), radiocarbon dates (cal BP), and YDB layer (blue bar) each sample for the Flamingo Bay sequence
is plotted in the middle of the sample interval. The accepted date range for the Clovis culture is ∼13,050–12,750 cal BP [93], and the YDB proxy
layer overlaps with the base of the Younger Dryas episode estimated at ∼50–55 cmbs. In Kennett et al. [1], a Bayesian analysis of dates from
YDB sites across North America shows synchronous deposition of the YDB proxy layer at ∼12,785 ± 50 years (range 12,735 to 12,835) cal BP
[3]. Note that Pt abundance on the graph is an average of two measurements from the same sample.
Figure 21: Stratigraphic Distribution of analyzed proxies and placement of the YDB layer. (a) Newtonville, microstrat (b) Parsons Island, and
(c) Flamingo Bay. Graphs show platinum (Pt) abundances in ppb (error = ±0.1 ppb), the Pt peak, the microspherules peak, and the presence
of nanodiamonds and meltglass. Also shown is generalized archaeostratigraphic data for Flamingo Bay (38AK469) (i.e., Paleoindian through
Woodland hafted biface silhouettes), radiocarbon dates (cal BP), and YDB layer (blue bar) each sample for the Flamingo Bay sequence is plot-
ted in the middle of the sample interval. The accepted date range for the Clovis culture is ∼13,050–12,750 cal BP [93], and the YDB proxy layer
overlaps with the base of the Younger Dryas episode estimated at ∼50–55 cmbs. In Kennett et al. [1], a Bayesian analysis of dates from YDB
sites across North America shows synchronous deposition of the YDB proxy layer at ∼12,785 ± 50 years (range 12,735 to 12,835) cal BP [3].
Note that Pt abundance on the graph is an average of two measurements from the same sample.

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
25
(ii)fractures produced by high temperatures, (iii) pre-exist-
ing quartz fractures, (iv) new fractures that form along pre-
existing PDFs and PFs, (v) new fractures along pre-existing
tectonic lamellae, and (vi) new fractures along pre-existing
subgrain boundaries. In the cases of the pre-existing fea-
tures, the shock fracturing process overprints and modifies
the existing features. Even though these types of fractures
may form under substantially different shock and non-shock
conditions, all have one common characteristic: the impact
events inject them with amorphous silica. To support the
suggested connection to airbursts/impacts, Ernstson et al.
[105] reported extensive low-pressure, glass-filled fracturing
in multiple proposed airbursts during the Cenozoic.
Identifying glass-filled shock-fractured quartz grains at
YDB sites adds another significant proxy consistent with
an airburst or impact of a fragmented cosmic impactor, as
predicted by the Younger Dryas impact hypothesis (YDIH).
Tectonic shock metamorphism is ruled out for these three
sites because amorphous quartz that fills fractures has never
been observed under tectonic conditions, and low-pressure
tectonic lamellae with no glass filling were common at the
three sites. The glass-filled shock-fractured quartz grains
recovered from these three widely separated study sites are
significant new evidence because shock metamorphism is a
classic indicator of a cosmic impact event.
Formation of high-temperature minerals in
meltglass and microspherules
The origin of the 22 high-temperature minerals we have
identified in this study requires explanation. Several pro-
cesses can potentially form high-temperature minerals, and
so we compare and contrast them as follows:
Biomass or “haystack” fires Thy et al. [106] reported
that biomass glass or slag is sometimes found in midden
piles of African prehistoric settlements with estimated for-
mation temperatures of 1155–1290°C. These temperatures
are lower than the melting points of 20 of the 22 minerals
observed, making midden fires an unlikely source [7, 16].
Lightning-induced melting Temperatures in fulgurites
reach >1720°C, the melting point of quartz, making lightning
a potential source of the numerous high-temperature minerals
observed at these three sites. However, we found no examples
of the hollow, tubular shapes of fulgurites produced by light-
ning, thus making lightning an unlikely source [7, 16].
Anthropogenic contamination Anthropogenic activity
can produce high-temperature minerals. However, only mod-
ern arc furnaces can reach or exceed the melting points of only
about half of the high-temperature minerals observed, mak-
ing anthropogenesis an unlikely formation mechanism for all
the objects [7, 16]. Anthropogenesis appears highly unlikely
because such material reaches significant peaks in the YDB
layers with few to none of these materials above or below.
Cosmic ablation from meteorites Two types of micro-
spherules form during the typical rain of meteorites and
extraterrestrial debris. The influx of stony meteorites pro-
duces only glassy spherules that typically contain >10 wt%
MgO [7, 16]. Fe-rich microspherules produced by the influx
of iron meteorites typically contain more than a few percent
of Ni. Microspherules and meltglass from the three sites
meet neither of those conditions, indicating that they were
not ablated from meteorites.
Cosmic impact Nearly all 22 high-temperature minerals
observed at these three sites do not melt under natural ter-
restrial conditions. In particular, native iron, melted zircon,
chromferide, and melted PGEs are rare under normal terres-
trial conditions but common in cosmic impacts or airbursts
[7, 16]. We conclude that the data supports this hypothesis of
a cosmic impact. No other hypothesis supports the evidence
that is distributed synchronously across widely separated sites.
The YDB as an “impact spherule datum layer”
We suggest that the broad, collective YDB evidence meets
the criterion as an “impact spherule datum layer,” as pro-
posed by Simonson and Glass [107]. Previously, micro-
spherule peaks have been reported at each of ∼50 YDB sites
widely distributed ∼12,000 miles across four continents [5,
7, 13, 15, 16, 22, 23] (click on Supplementary Information
Figure 78). In this study, impact proxies, such as microspher-
ules (all three study sites), meltglass (two of the study sites),
and shock-fractured quartz, are widely distributed across
nearly 1000 km. Typical YDB sites average ∼1 microspher-
ule >125 microns per cm2 of the YDB surfaces. In contrast,
Glass and Simonson [108] showed that for a single 10-km
crater, sand-sized particles (>125 microns), as seen for the
Ivory Coast microtektites, can be dispersed between ∼1,000
and 3,000 km from the impact site (click on Supplementary
Information Figure 77). One possible explanation for this
wide distribution is that multiple high-energy, near-surface
YDB airbursts/impacts injected into the atmosphere via
impact plumes, multi-micron-sized melt products, including
shock-fractured quartz, meltglass, and microspherules and
dispersed them widely.
These layers typically contain a variety of impact mark-
ers, including microspherules, meltglass, and PGE anoma-
lies [107]. Impact microspherule layers are also known for
their utility as chronological datums for stratigraphic corre-
lation and age determination, even over vast distances [109].
Although most impact microspherule layers have been
linked to large impact craters, many such layers have
not been linked to any known crater. Indeed, Glass and
Simonson [Table 1 in ref. [109]] reported 21 impact micro-
spherule layers with no known associated crater, including
the Australasian tektite field spread across ∼10% of the
planet and the Libyan Desert glass field, covering 2500 km2.
Similarly, no known crater is associated with the YDB impact
microspherule layer. Thus, the discovery and identification

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
26
of a crater are not required to interpret such a widely distrib-
uted microspherule layer as of cosmic impact origin.
The ∼12.8 ka YDB layer at ∼50 broadly distributed sites
has been extensively reported to contain abundance peaks
of one or more potential impact-related proxies, including
iron-enriched or glassy microspherules, meltglass, charcoal,
aciniform carbon, soot, glasslike carbon, carbon microspher-
ules, nanodiamonds, PAHs, Pt, Ir, and Ni, among others [5,
7, 13, 15, 16, 22, 23]. Some YDIH critics consider these
YDB proxies individually in isolation, claiming they are
merely coincidentally associated, and they invoke alternative
hypotheses for each proxy’s provenance [104, 110–113].
However, no critic has identified any other non-impact layer
that coincidentally contains the broad suite of these prox-
ies found in the YDB layer. It is statistically improbable that
these dozen proxies are unrelated and only coincidentally
found in the same layer. Instead, the most parsimonious
explanation is that the same cosmic impact event produced
and deposited them. In support of that, the only known geo-
logic layers found in the Earth’s multi-billion-year strati-
graphic record that contain similar peaks in microspherules
and related materials, as reported in other studies, are widely
acknowledged to result from an extraterrestrial impact.
Conclusions
In this study of three sites along the Eastern Seaboard of
the United States, we report YDB abundance peaks in iron-
enriched microspherules, glassy microspherules, meltglass,
nanodiamonds, high-temperature melted minerals, and plat-
inum, all variably found at >50 sites on four continents,
including the Greenland ice sheet. We also investigated the
temperatures and conditions required to produce micro-
spherules and meltglass in the 12,800-year-old YDB layers.
These materials are associated with melted chromferide, zir-
con, quartz, titanomagnetite, ulvöspinel, magnetite, native
iron, and PGEs with equilibrium melting points ranging
from ∼1250° to 3053°C. These high temperatures imply that
these materials did not form under normal terrestrial con-
ditions but likely formed during an unusual cosmic impact
event. We also report peak abundances of high-temperature,
high-pressure shock-fractured quartz in the YDB layer but
not in samples taken above or below at each site investi-
gated. These high temperatures and pressures are unlikely to
occur under normal terrestrial conditions but are often char-
acteristic of cosmic impact events.
Our observations are consistent with the hypothesis of
multiple near-surface atmospheric airburst detonations of a
fragmented cosmic impactor ∼12,800 years ago at the onset
of the Younger Dryas climate event. These airbursts pro-
duced a synchronous layer over much of the world, arguably
meeting the formal recognition criteria for classification as
an “impact microspherule datum.” The consequences of this
event, including possible global effects on environmental
ecosystems, glacial ice sheets, megafaunal extinctions, and
human populations, are yet to be fully understood but need
to be evaluated in the context of a geologically instantane-
ous and likely catastrophic event. These ramifications are
not uniform geographically and must be worked out at the
regional and sub-regional levels. Our evidence supports the
hypothesis that the abundance anomalies in platinum, micro-
spherules, meltglass, and shock-fractured quartz form a reli-
able chrono- and litho-stratigraphic datum for the YD onset
at ∼12,800 cal BP, consistent with the Younger Dryas impact
hypothesis.
Methods
Geochemistry (Pt, Pd, Au)
For geochemical analysis, sediment samples were collected
directly from cleaned archaeological unit profiles, stored in
plastic bags, and allowed to air dry over several days. Bulk
sediment samples were then dry-sieved using a 63-micron
sieve to separate the silt and clay fractions from the sand.
The silt and clay fraction were then weighed and repackaged
in a plastic bag for shipment to Activation Laboratories Inc.
(Actlabs) for “1C-Research” analysis. Sediment samples of
∼50 grams are required for the “1C-Research” analysis.
Activation Laboratories Inc. (Actlabs) followed Hoffman
and Dunn [114] and used fire assay (FA) and inductively
coupled plasma mass spectrometry (ICP-MS) to measure
elemental concentrations of the sediment samples from all
sites. Before analysis, each sample is mixed with fire assay
fluxes (borax, soda ash, silica, litharge), and silver (Ag) is
added as a collector. The mixture is placed in a crucible, pre-
heated at 850°C, heated to 950°C, and finished at 1060°C for
60 minutes. After the crucibles are removed from the assay
furnace, the molten slag is poured into a crucible, leaving a
lead button, which is then preheated to 950°C to recover the
Ag (doré bead) plus Au, Pt, and Pd.
The Ag doré bead is digested in hot (95°C) HNO3 + HCl
with a special complexing agent to prevent the Au, Pd, and Pt
from adsorbing onto the test tube. After cooling for 2 hours,
the sample solution is analyzed for Au, Pt, and Pd using a
Perkin Elmer Sciex ELAN 9000 ICP-MS. There were two
method blanks, three sample duplicates, and two certified
reference materials on each tray of 42 samples. The ICP-MS
is recalibrated every 45 samples. Smaller sample splits are
used for high chromite or sulfide samples. Measurements
are reported in parts per billion (ppb) with a lower detection
limit for Pt at 0.1 ppb.
Shock-fractured quartz
We employed a comprehensive suite of analytical techniques
and instruments to study these thin sections. These included
optical transmission microscopy (OPT), epi-illumination
microscopy (EPI), scanning electron microscopy (SEM),
energy dispersive spectroscopy (EDS), focused ion beam

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
27
milling (FIB), transmission electron microscopy (TEM),
scanning transmission electron microscopy (STEM),
fast-Fourier transform (FFT), electron backscatter diffrac-
tion (EBSD), cathodoluminescence (CL), and micro-Ra-
man. All procedures and instruments are discussed in detail
in the Supplementary Information, “Instrumentation and
Analytical Details.”
Each slide was carefully and methodically searched for
candidate grains of shocked quartz using optical and trans-
mission microscopy. Grains exhibiting closely spaced,
oriented fractures were marked as candidates for shocked
quartz, with each requiring focused investigations using
multiple techniques. Descriptions of techniques presented
below are adapted from Hermes et al. [32], which shares
ten co-authors with the current study. These descriptions are
publishable under Creative Commons, CC by 4.0 (http://cre-
ativecommons.org/licenses/by/4.0/).
Microspherules and meltglass analysis
To analyze sediment samples for magnetic microspherules,
we weighed and then ultrasonicated the samples for 30 min-
utes with a chemical dispersant (sodium metaphosphate).
Following ultrasonication, samples are wet-sieved over
a 20-micron sieve and dried under a heat lamp. Processed
samples are then size sorted, and sediment fractions between
≥63 and <125 and ≥20 and <63 microns are spread thinly
on a large sheet of paper. A neodymium magnet is placed
inside a plastic bag and slowly moved over the size-sorted
sediment fractions to extract the magnetic grains if present.
This process is repeated three times to extract most mag-
netic grains. These grains are then examined under a stereo
binocular microscope to determine if microspherule candi-
dates are present. When present, microspherule candidates
are counted, and a sample is placed on carbon SEM tape for
analysis by scanning electron microscopy (SEM) and ener-
gy-dispersive x-ray spectroscopy (EDS) analysis. Only SEM
and EDS analysis can confirm the identification of glassy or
Fe-rich microspherules [14]. The microspherule counts and
total sediment sample weights are used to estimate micro-
spherules/kg for each sample.
After extracting the magnetic fraction to investigate
iron-enriched microspherules, the remainder of the sand
fraction is examined for meltglass candidates. This aliquot
mainly includes larger sand size fractions >63 microns,
which are examined with optical microscopy to identify
meltglass. When present, meltglass candidates are placed on
carbon SEM tape for analysis by scanning electron micros-
copy (SEM) and energy-dispersive x-ray spectroscopy
(EDS) analysis.
OSL dating
Optically Stimulated Luminescence (OSL) samples were
acquired from an eroding bluff on the southwestern shore-
line of Parsons Island and submitted to the University of
Washington Luminescence Dating Laboratory for dating
using the single-grain method.
AMS radiocarbon dates were acquired on glasslike car-
bon (GLC) fragments and carbon microspherules collected
from sediment samples at Parsons Island and Newtonville.
Samples were dated at the Center for Applied Isotope Studies
at the University of Georgia, Direct AMS, and the University
of California, Irvine (UCI).
Acknowledgments
We thank the South Carolina Institute for Archaeology and
Anthropology (SCIAA), the Savannah River Archaeological
Research Program (SRARP), and the College of Arts
and Sciences at the University of South Carolina (USC),
Columbia, South Carolina. We also thank Billy P. Glass for
constructive discussions on the classification of the YDB
as an impact microspherule layer, Mark Demitroff for pro-
viding samples and consulting on the chronostratigraphy
at Newtonville, Rooney Floyd, John Kolmar, and Bob Van
Buren for assistance processing sediments, Darrin Lowery
for assistance with sampling at Parsons Island, and Eugene
Jhong for supporting this research through generous dona-
tions to the University of South Carolina and the University
of California Santa Barbara. Last, we thank seven anony-
mous reviewers for helping to improve the manuscript.
Funding
The study was funded by the Comet Research Group
(CRG), the University of South Carolina (USC), and the
South Carolina Institute for Archaeology and Anthropology
(SCIAA). G.K. was partially supported by the Czech Science
Foundation (project No. 23-06075S).
Data availability
All data generated or analyzed during this study are included
in this published article [and its Supplementary Information
files].
Sample availability
Samples from the YDB layer are mostly depleted, but limited
amounts may be available from the Corresponding Author.
Author contributions
All authors reviewed and approved the manuscript. C.R.M.,
M.A.L., and A.W. conceived and directed the project.
C.R.M., M.A.L., J.P.K., A.W., M.D.Y, and C.S.L. wrote the
manuscript. M.J.B., R.B.F., A.H.I., T.A.F., C.S.L., K.A.D.,

C.R. Moore et al.: Platinum, shock-fractured quartz, microspherules, and meltglass widely distributed in Eastern USA
28
J.K.F., C.B.M., V.A., D.B., M.S., K.A.L., J.J.R., V.B.,
B.V.D., J.P.P., R.P., M.M.C., B.N.R., M.D.Y., J.P.K., G.K.
and T.E.B contributed data and technical analysis for the
paper.
Potential conflicts of interest
All co-authors may receive reimbursements from their
respective organizations for attending symposia on the
research presented in this paper. C.R.M is an author and
co-editor of one book on southeastern archaeology and
receives royalties. A.W. and R.B.F. are co-authors of “The
Cycle of Cosmic Catastrophes,” a book related to the Younger
Dryas Impact Hypothesis; A.W. donates all proceeds to the
non-profit Comet Research Group. The authors declare no
other competing interests. M.A.L. C.R.M, and A.W. are edi-
tors of the journal but played no role in accepting, rejecting,
or reviewing the paper.
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