Abstract:

¶    Discrete boulder fields attributed to the last glacial maximum (LGM) are suggested here to have had a catastrophic origin similar to that of the 500,000 Carolina bays distributed along the Atlantic seaboard and Gulf Coasts of the continental United States.  Carolina bays are suggested by others to be secondary impact basins from the ejecta curtain of Laurentide ice-sheet fragments from a primary bolide impact on or airburst above the Laurentide ice sheet in the Great Lakes region, 12,800 B.P.  Ballistic trajectories that fell short of the coastal regions and landed on thin soil may have fractured the underlying bedrock, in some cases creating discrete boulder fields that are still devoid of vegetative cover almost 13 thousand years later.
¶    YD impact boulder fields appear to come in two varieties; in situ (or predominantly in situ), and debris-flow boulder fields.  Large boulder fields and boulder fields on steep terrain are more likely to have experienced catastrophic downhill movement, presumably in the form of a debris flow.  Hickory Run boulder field and Blue Rocks boulder field are examples of debris-flow boulder fields. , while Ringing Rocks boulder fields are examples of (mostly) in situ boulder fields.
¶    Some LGM boulder field boulders exhibit unusual properties uncommon outside of the boulder fields, such as deeply-incised surface features, such as cup marks and striations.  Additionally, “Ringing Rocks” diabase boulder fields variably exhibit an ability to ring when sharply struck, a property not exhibited by diabase boulders outside these discrete boulder fields.  Finally, smaller cobbles in the Hickory Run boulder field exhibit 2 unusual forms of rock scale.
¶    ‘YD impact boulder fields’ formed by the percussive impact of massive chunks of ice-sheet fragments in ballistic trajectories above the atmosphere, with ice-sheet fragments traveling thousands of kilometers at speeds of several kilometers per second.  Gradual melting during reentry and flash-melting at impact created super-high-velocity slurries that abrasively scoured the surfaces of impact brecciated boulders, like sandblasting, cutting cup marks (pits) and striations (grooves).
¶    Some Ringing Rocks diabase boulders exhibit the ability to ring when struck, which appears to be caused by surface stresses, since breaking or cutting “live” boulders creates “dead” rocks that don’t ring.  Thus the ability to ring is not due to bulk rock properties imparted during intrusive cooling, miles underground at tremendous pressure.  Super-high-velocity impacts creating super-high shock-wave pressures, are the suggested surficial stressing mechanism for creating the ringing attribute.
¶    Finally, cobbles tumbled in Hickory run in the Hickory Run boulder field, exhibit 2 kinds of rock scale, both commensurate with a catastrophic super-high-energy phenomenon.  Black rock scale is suggested to be condensed ‘smoke’, baked at high temperature, and brown nodular rock scale is suggested to be high-velocity impact spatter, largely comprised of extraterrestrial material with a high iron content.
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Introduction:

¶    Evidence of a Younger Dryas (YD) impact or airburst is revealed in Greenland ice sheet cores in the form of a platinum spike, circa 12,800 BP (Petaev et al., 2013).  Additionally, a thin layer of magnetic grains, microspherules, nanodiamonds, and glass-like carbon have been unearthed at various locations across North America, Europe and beyond, generally overlain by a ‘black mat’ with a high carbon content.  The black mat is nearly coincident with megafauna extinction in North America and the disappearance of the Clovis civilization (Firestone et al., 2007; Firestone, 2011), and “extinct megafauna and Clovis tools occur only beneath this black layer and not within or above it” (Firestone, 2009).

¶    An impact hypothesis for large, shallow oval depressions known as Carolina bays originated in the 1940s.  Then a more-plausible secondary impact theory was advanced in the 21st century, suggesting a primary impact on or over the Laurentide ice sheet that showered North America and likely beyond with an ejecta curtain of secondary ice-sheet fragments (Firestone, West and Warwick-Smith, 2006).
¶     Carolina bays are a series of 500,000 oval depressions that range in size from 50 m to 10 km in length that are concentrated along the Atlantic seaboard and the coastal plain of the Gulf of Mexico.  The long axes of the Carolina bays point back to one or more primary bolide impacts on the former Laurentide ice sheet in the Great Lakes region, and perhaps over Hudson Bay, that lofted massive ice sheet fragments into ballistic trajectories of 1000s of kilometers to form elongated secondary-impact depressions, presumably when they landed on soft waterlogged soil along the coastal plains.

¶    If the YD-impact ejecta curtain was at all isotropic, then the rest of the North American continent was similarly showered with secondary impacts, but the harder inland terrain typically experienced less physical damage, and/or has been largely obscured by subsequent erosion and infill from subsequent flooding, whereas coastal Carolina bays presumably exist in areas that have not experienced repeated flooding.  When secondary ice-sheet fragments traveling several kilometers per second slammed into exposed bedrock or bedrock under a thin cover of soil, the impulse may have brecciated the bedrock to a depth of several meters, but without sufficient energy to eject the boulders into an excavated crater or sculpt them into raised rims like the elliptical-shaped Carolina bays.

¶    Isolated boulder fields in Pennsylvania are classically attributed to a periglacial freeze-thaw process during the Last Glacial Maximum (LGM), where frost action fractured bedrock by ‘frost wedging’.  Then boulders were transported downhill, either gradually by ‘solifluction’, or suddenly by ‘gellifluction’.  The frozen subsurface acted as a barrier to the percolation of water, trapping the water in the thawed soil at the surface, creating slick greasy soil over a solid, icy subsurface during seasonal thaw cycles.  Solifluction suggests gradual creep of boulders downhill, whereas gellifluction suggests catastrophic liquefaction of waterlogged soil, presumably causing a mudslide/rockslide.

Wikipedia entry on “Ringing rocks”:
¶    The Wikipedia entry on Ringing rocks is the most comprehensive summary on the subject at this time; however, the most significant sections, pertaining to boulder composition, bolder field formation, and origin of the ringing quality, provide no footnote citations, partly relying the long list of references at the end, and partly expressing the opinions of its author.
¶    Curiously, the two boulder fields in Bucks County; Ringing Rocks County Park, and Stony Garden, are stated to have formed from a basal olivine unit, presumably formed from olivine cumulates of the intrusive Jurassic diabase sills.  The basal olivine unit is stated to be harder, denser and more resistant to weathering than diabase that crystallized higher in the sill.  According to the included figures, the boulder fields formed mostly in situ over top of the olivine seams, not downhill of the seams from which they are derived, although a portion of the Ringing Rocks County Park boulder field apparently extends below the olivine seam, indicating a modest degree of boulder movement.  This in situ evidence would seem to rule out downhill accumulation by solifluction or gellifluction for these particular boulder fields, conventionally requiring the improbable outcome of in situ formation by periglacial frost wedging, creating boulder fields many boulders deep that are subsequently jumbled by frost heave, or similar mechanism.
¶    The pitting/cup marks, pot holes, and grooves/striations surface features are suggested in the Wikipedia entry to be chemical weathering along the joint surfaces prior to being broken out by frost heave, followed by the mechanical removal of chemically-softened material to reveal the deeply-incised surface indentations.  This despite the fact that the Ringing Rocks boulders have barely reached a sufficient state of oxidative weathering to create a rust-colored patina, which is the first stage in developing a oxidized rind that exfoliates.  Additionally, this unsupported hypothesis does not attempt to identify or suggest the origin of the presumed periglacial acids involved in the chemical weathering, nor why this form of weathering creates these peculiar surface features, nor why this process is not apparently occurring today under similar conditions closer Earth’s North Pole.
¶    The ringing quality of boulders is attributed by the author to internal stress formed by compression at a depth of 2-3 km during igneous cooling.  This stress can be relieved by fragmenting a ringing (“live”) boulder, in which case the broken fragments do not ring (“dead” boulder).  In the 1960s, a Rutgers University professor compared sawn slabs of live boulders to slabs of dead boulders from the same boulder field.  By means of strain gauges, he discovered that the live boulder slabs exhibited a distinctive expansion or relaxation within 24 hours of being cut, compared to the dead boulder slabs.  The Wikipedia author concludes that the bulk rock is loaded at the time of crystallization, due to the head pressure of 2-3 km of overlying rock, and that the slow weathering rate of the boulders keeps the stresses from dissipating (by some unspecified mechanism).
¶    Alternatively, the weather-resistant basal olivine unit causes it to stand out in relief above softer country rock and less weather-resistant upper portions of the diabase sill, such that an ice-sheet fragment impact could only create a boulder field from weather-resistant rock exposed at the surface.  The apparent in situ brecciation of the basal olivine layer of the Jurassic diabase sill dismisses one of the chief arguments supporting periglacial frost wedging, which is downhill concentration of boulders by solifluction or gellifluction.  An impact theory is particularly suited to the exquisite discreteness of boulder fields dating to the last glacial maximum, particularly in situ boulder fields not concentrated by downhill boulder movement.
¶    Secondly, super-high-velocity ice/supercritical fluids capable of brecciating bedrock would be expected to scour the exposed surfaces of brecciated boulders, resulting in incised surface features, whereas suggested chemical weathering along joint surfaces is an ad hoc explanation for an observed phenomenon not predicted by periglacial frost wedging.
¶    Thirdly, the ringing property is clearly the result of surface stresses, rather than bulk stresses, otherwise breaking a live boulder would create two smaller live boulders, due to the bulk stresses of the broken pieces.  Super-high pressure blast waves, by comparison, would only stress the exposed surfaces of boulders, since the internal portions would be protected by the low compressibility of silicates, as indeed appears to be the case.  The 1960s slab study demonstrates that dead boulders are unstressed, which also argues against an inherent formational bulk stress.

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Multiple primary impacts on the Laurentide ice sheet:

¶    In a seminal work on the secondary impact theory for the formation of Carolina bays (Firestone, West and Warwick-Smith, 2006), it was noticed that a small minority of Carolina bays had a major axis orientation that pointed much further north than the bulk of the bays.  The majority of Carolina bays converge toward the Great Lakes Region, while a small minority converge over Hudson Bay.  This suggests at least 2 primary strikes or cluster of strikes on the Laurentide ice sheet—one on Hudson Bay and one on the Great Lakes Region.  Hudson Bay is further from anywhere in the contiguous United States than the Great Lakes Region, such that the ballistic speed of ice-sheet fragments from a Hudson Bay strike would have been significantly higher than the ballistic speed of ice-sheet fragments from a Great Lakes Region.  And since kinetic energy is a squared function of velocity, the kinetic energy would have been several times higher in Eastern PA.
¶    A cluster of Carolina bays with a particularly north-south orientation in the Delmarva Peninsula indicate ice-sheet fragments trajectories across Eastern Pennsylvania.  Ice-sheet fragments that fell short of Delmarva coming from the Hudson Bay region may have rained down across Eastern Pennsylvania, and these longer ballistic trajectories would have had much-greater kinetic energy than ice-sheet fragments from the Great Lakes Region.  Perhaps high-kinetic-energy trajectories from Hudon Bay Region are necessary to form impact boulder fields, with the cluster of trajectories from Hudson Bay across Eastern PA explaining the cluster of LGM boulder fields in Eastern PA.  In the following figure, ice-sheet fragment trajectories from one or more primary strikes on Hudson bay are indicated in red, showing their passage across Pennsylvania, bordered in green.

¶    Coincidence can be a positive attribute, supporting a theory, or a negative attribute, steepening the odds against a theory.  An impact theory for the origin of Carolina bays and impact boulder fields that requires multiple (2 or more) impacts on the Laurentide ice sheet would appear to steepen the odds against the theory; however, the passage of Earth through a (Taurid) meteor stream of a disrupted Kuiper belt object might plausibly cause Earth to sustain multiple nearly-simultaneous hits by meteor-stream debris.  Indeed, the Taurid meteor stream has been suggested elsewhere (Wolbach et al.,1., 2018) as the likely origin of the YD bolide, from the breakup of a 100 km diameter Kuiper belt object (comet).
¶    A possible positive coincidence links Eastern PA boulder fields with suggested ‘YD impact comet crust’ meteorites.  Suggested YD impact comet crust closely resembles industrial iron furnace slag in its appearance and in its major chemical composition; however, unlike iron furnace slag, it often contains millimeter-to-centimeter-scale metallic iron inclusions that could not be suspended in an igneous melt on a high-gravity planet, and some comet-crust specimens exhibit apparent fusion crust, presumably from ablation during passage through Earth’s atmosphere.  Additionally, some large pristine specimens of suggested YD impact comet crust resonate like Ringing Rocks when sharply struck with a hammer, whereas industrial iron furnace slag is not known to possess this acoustic property.  The Eastern PA overlap between YD impact boulder fields and YD impact comet crust suggests that comet crust may originate from a primary strike in the Hudson Bay Region, rather than the Great Lakes Region, with the red trajectories suggesting other areas with possible comet crust contamination.  (See section, YD IMPACT COMET CRUST)
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Debris-flow boulder fields:

¶    The Ringing rocks Wikipedia entry provides evidence for in situ boulder fields, but the ¾ kilometer-long Blue Rocks boulder field at Hawk Mountain, PA, with ≥ 5:1 length-to-width aspect ratio, demonstrates that some boulder fields were apparently created by (catastrophic) downhill flow.  The Blue Rocks boulders are stacked high above the surrounding terrain, making in situ formation an impossibility.

¶    Classically, boulder fields attributed to the LGM are presumed to have formed by periglacial freeze-thaw cycles, with boulders cleaved from the bedrock by ’frost wedging’.  If Ringing Rocks County Park boulder field, and Stony Garden boulder field are substantially in situ boulder fields, fractured from the basal olivine unit of the Jurassic diabase sills, then classically we are asked to believe that in situ frost wedging and associated heaving can fracture, displace and stack boulders 10 feet deep, creating discrete boulder fields immediately adjacent to undisturbed bedrock of the same kind.

¶    Classical processes with no good explanation are often glossed over as self evident, such as sharp isoclinal folding in metamorphic rocks, and particularly dramatic cases of ptygmatic folding that resemble ribbon candy.  Solifluction or gelifluction for the formation of periglacial boulder fields is another example, where invoking the term itself is apparently due diligence, although modern examples of these phenomena fall many orders of magnitude short of producing boulder fields.  Solifluction occurs during seasonal surface melting over a permafrost subsurface, where the permanently-frozen subsurface acts as a barrier to downward percolation of surface water, turning the thawed surface into a greasy lubricant.  Solifluction implies a slow mass wasting, whereas gelifluction involves sudden liquefaction of thawed soil over frozen ground, as in a periglacial-induced mudslide.  Alternatively, invoking a (self evident) downhill debris flow in a secondary impact is quite another thing, when the ice-sheet fragment impact carries the punch of a small atom bomb and provides its own water for the (aqueous) debris flow.

¶    The crumbly, heavily-tumbled and heavily-weathered Tuscarora sandstone boulders of Blue Rocks boulder field do not exhibit and may not have retained deeply-incised surface features scoured into impact brecciated boulders by super-high velocity slurries, forming cup marks, pot holes and striations.  Incised surface features in boulder field boulders are suggested to be the most-reliable indicator of secondary ice-sheet fragment impacts, and without this evidence, the Blue Rocks boulder field can not be definitely attributed to a secondary YD impact.  But if Blue Rocks is indeed a YD impact boulder field, the impact elevation may have been as high as the mountain pinnacle, perhaps at ‘Pulpit Rock’, some 300 meters in elevation above the bottom of the boulder field, in which case the impact shock wave may have blown out the cliff face, which rushed downhill in a hook-shaped rockslide or debris flow.

Hickory Run boulder field, PA:
¶    The main Hickory Run boulder field is accompanied by several smaller nearby boulder fields that may telegraph the location of an ice-sheet-fragment impact in Hickory Run State Park.  Alternatively, the smaller associated boulder fields may be due to separate ice-sheet fragment impacts in their own right, from a sub-fragmentation that occurred upon reentry; however, the greater specific wind resistance on smaller sub-fragmentation masses would should cause the smaller masses to fall short of the larger primary impact, whereas the ‘Southern boulder field’ would represent an overshoot of the primary impact, suggesting that the associated boulder fields were caused by secondary effects of a single primary impact.  The secondary effects were presumably caused by a trifurcated debris flow.
¶    The proposed impact site is on the relative high ground of a valley between two ridges, where the valley dips both to the east and to the west between a ridgeline to the north and a ridgeline to the south.  See following figure, A & B.  Additionally, the southern ridgeline has a pass directly south of the proposed impact site, like an enormous bite out of the southern ridgeline.  The secondary ice-sheet impact is suggested to have resulted in a trifurcated debris flow, with the east branch creating the main boulder field, the west branch creating the ‘Western boulder field’ and the south branch spilling through the southern ridgeline pass to create the ‘Southern boulder field’.
– East branch of a trifurcated debris flow.  The ‘Eastern boulder field’ appears to lie behind a slight rise in the terrain, which suggests that a hill may have stalled the debris flow, dropping the boulders on the leeward side.  The slight rise in the terrain may have shielded the trees on the leeward side from the impact blast wave, such that the stand of trees contributed to stalling the debris flow.
– West branch of a trifurcated debris flow.  The “Auxiliary boulder field” exhibits particularly-large and tabular-shaped boulders, which is located between the suggested secondary impact site and the “Main boulder field”.  Apparently the larger tabular-shaped boulders were the first boulders to fall out of debris flow suspension, forming the Auxiliary boulder field.  The rest of the boulders continued on for another 300 meters, or so, before coming to a rest to form the Main boulder field after reaching Hickory Run.
– South branch of a trifurcated debris flow.  The southern branch of the debris flow had the forward momentum of the ice-sheet fragment, but it was also slightly uphill through the pass in the southern ridgeline.  The elevation rise to the pass shielded the trees beyond the pass, such that the southern debris flow may have had to knock down trees for the distance of about 1 km trees before finally coming to rest to form the diminutive “Southern boulder field”, and a majority of the boulders in the south branch of the debris flow may have stalled along the way from the work of plowing through a dense stand of trees, shielded from the impact blast wave.
– “Unrelated talus slope(?)”.  The large boulders in the Unrelated talus slope lie at the bottom of a steep 100 meter high slope, which may have nothing to do with the suggested ice-sheet fragment impact, or a rock slide may have been triggered by impact ground tremors.
¶    Many of the smaller boulders and cobbles in the main boulder field are suspiciously rounded and smooth, as if by long-distance tumbling in Hickory Run itself, and many exhibit variable degrees of suggested secondary YD-impact rock scale, which is not apparent on larger boulders.  Suggested impact rock scale presents in two varieties; brown/orange nodular rock scale, and black rock scale.  Black rock scale can so easily be confused with black lichen that a black coating on rocks should be considered suspect, except when it exhibits a shiny graphite-like sheen.  Additionally, these smaller boulders and cobbles are composed of a smaller clast size than the larger boulders, with the cobbles composed of fine-grained sandstone or quartzite and the particularly-pink large boulders composed of coarser-grained sandstone.  A minority of the smooth cobbles appear to have indurated somewhat-glossy surfaces, which in some cases appears to be the result of a thin coating of impact rock scale.  For the smaller boulders and cobbles to have retained impact rock scale, cobble rounding and smoothing would have had to preexist the secondary impact, suggesting the cobbles were smoothed by tumbling in Hickory Run itself, although the nearest point to Hickory Run is about 1 km distant from the suggested location of ground zero.  The pink boulders of the Hickory Run boulder field are apparently Devonian sandstone from the Catskill Fm, Duncannon Member.  Upward fining suggests a smaller clast size upstream, where the well rounded and smoothed smaller boulders and cobbles presumably originated in the hills north of the boulder field.  The cobbles of Hickory Run were presumably spattered by the nearby impact, imparting YD-impact rock scale, and then bulldozed by the Western branch of the debris flow to become part of the main boulder field.

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Incised surface features in impact boulder field boulders:

¶    The seismic impulse of ballistic ice-sheet fragments traveling at several kilometers per second shattered target bedrock.  Super-high-velocity (supercritical) fluids presumably contributed to brecciation.  Additionally, these super-high-velocity fluids abrasively scoured exposed rock surfaces, like sand blasting or high-pressure water jet cutting, inscribing deeply-incised surface features in brecciated boulders.
¶    Three of four Boulder field boulders examined exhibit a high incidence of incised surface features, that typically take the form of pock marks or pits (elsewhere called ‘cup marks’), as well as linear striations and pot holes, where pot holes are defined here as deep pits, often with flat bottoms shaped like a pan, and often with associated ‘handle’ striations.  Striations are defined here as deep straight grooves, sometimes crossed.
¶    ‘Cup and ring marks’ on boulders and bedrock exposures are well known in Europe, where they’re understood to be petroglyphs.  Indeed, some cup marks are circumscribed by concentric rings that are very evidently man made, although the central cup marks could be natural, from secondary ice-fragment impacts, and subsequently decorated by concentric rings, perhaps to appease the gods who rained down fire and ice.  By comparison, incised surface features on boulder field boulders in North America are not considered to be petroglyphs, and are not decorated by concentric rings, but instead are attributed to unusual weathering.  If ballistic ice-sheet fragments reached Europe from the Laurentide ice sheet in North America, they would have had higher speeds than any secondary impacts that formed the Carolina bays and impact boulder fields in North America.  Perhaps the wind-resistance stress on ballistic speeds necessary to reach Europe and beyond exceeded bulk ice strength, causing the ice to shatter upon reentry, such that the scale of the shattered sub-fragments was insufficient to form boulder fields and Carolina bays in Europe and beyond, but sufficient to abrasively scour exposed bedrock and boulders, creating cup marks and striations.

¶    Ring art around what could be naturally-incised cup marks in this IMAGE from Fowberry Cairn, UK.

¶    Presumably only the cup-marked top portion of the rock was exposed above the soil line at the time of a local iceberg impact, in this IMAGE from Farnhill Moor, UK.

¶    Note the distinct pitting in the largest cup mark on the right side of the image below.  The total effect is more random than artistic, suggesting a natural origin.

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Secondary impact rock scale:

¶    There appear to be two types of impact rock scale; a common black rock scale, and a less-common brown/orange rock scale.  Both types of rock scale must be particularly inert and tenacious to have survived 12,800 years at the surface in such relative abundance.

¶    Black rock scale, which can have a graphite-like sheen, is suggested here to be condensed smoke, baked on by high temperatures and pressures in the impact vicinity.  Black rock scale tends to be relatively uniform in thickness, somewhat resembling fusion crust on a meteorite, but the coverage will not be ubiquitous, since the portions of rock in contact with the ground at the time were shielded from smoke exposure.  Black rock scale can so easily be confused with black lichen or forest-fire scorching that perhaps only black rock scale with a metallic graphite-like sheen can definitely be attributed to an impact origin; however, when other attributes of a secondary impact are locally present, black rock scale that does not have a graphite-like sheen can be more confidently attributed to an impact origin.
¶    The much less common orange/brown rock scale often presents in the form of brown nodules on smooth river cobbles, since river cobbles were commonly exposed above ground 12,800 B.P. as they are today, and even small amounts of nodular rock scale stands out prominently on smooth rocks.  Thicker coatings of impact spatter show prominently on coarser rocks.  Impact-spatter rock scale is suggested here to be the result of high-velocity spattering of predominantly extraterrestrial material with a high iron content, hence the rusty brown to orange coloration.  Thin spatter coatings may be more orange in coloration, where the coating may impart an indurated surface effect on relatively-smooth rocks.  Nodular rock scale is almost invariably present on ‘one side only’ of exposed rocks, unlike black rock scale from smoke exposure that can encircle rocks, so only the side of a rock that could ‘see’ the incoming ice-sheet fragment will have been exposed to high-velocity impact spatter, and presumably only to a distance from ground zero where the spatter arrives at high speed.  The relative rarity of nodular rock scale compared to black rock scale is presumably due to the requirement for high-velocity line-of-sight exposure, such that nodular rock scale may have occurred only a modest number of impact-basin radii from ground zero, whereas black rock scale may have occurred many impact-basin radii distant, including on the leeward side of hills and etc., shielded from line-of-sight impact spatter.  Brown nodular rock scale is found on rough boulders on mountain tops as well as on river cobbles.

¶    Both kinds of rock scale are absent from brecciated target rock boulders in suggested impact boulder fields.  In debris-flow boulder fields, any rock scale was likely abraded off by debris-flow tumbling, and in diabase boulder fields, orange/brown nodular rock scale would be almost indistinguishable from the orange weathering rind that appears on diabase boulders due to oxidative exposure over time; however, black rock scale would stand out nicely on diabase.  Curiously, the sand in the southeast rims of Carolina bays has been bleached white, compared to nearby sand, and perhaps brecciated boulders are similarly bleached by exposure to super-high-temperatures and -velocities by supercritical fluids.

¶    The following two images show nodular rock scale on Devonian conglomerate and sandstone on Stony Mountain, north of Fort Indiantown Gap, PA.  Stony Mountain is covered with boulders, giving the mountain its name, suggesting the possibility of the mountain being ground zero of a large secondary impact.

¶    The greywacke ‘shoe stone’ from the Susquehanna River, Millersburg, PA exhibits millimeter-scale nodules on one side only (left side and bottom).  One small area on the sole, circled in red, exhibits apparent human modification, presumably to more closely resemble a human shoe.  If the nodular rock scale is indeed YD impact splatter, then its presence at the surface 12,800 years ago raises the probability that the sole modification was Clovis, perhaps a child-sized moccasin last, or a child’s toy.

Magnetic spherules in Pleistocene tusk and bone and in Clovis chert flakes:

¶    Firestone et al. (2006) discovered magnetic spherules embedded in Clovis chert flakes, apparently caused by high-velocity spherule impacts, with attendant particle tracks.  Similarly, magnetic spherules with entrance wounds were found in earlier Pleistocene tusk and bone, circa 33 ka.  Since early days, these claims of embedded spherules have not been pursued by the the Comet Research Group, due to the lack of a plausible origin story.  While a date long before the Younger Dryas can be defended by evoking repeated passage of Earth through the Taurid meteor stream, YD impact skeptics have dismissed the suggestion of high-velocity ground-level magnetic spherules, as in the contrarian paper, The Younger Dryas impact hypothesis: A requiem (Nicholas Pinter et al., 2011).

¶    Indeed, microspherules can not maintain high velocity in their passage through the atmosphere, although they might splinter off at the last second from a larger high-velocity bolide.  Alternatively, a rain of spherules falling at terminal velocity from the Taurid meteor stream might receive a high-velocity kick from the sonic boom of supersonic bolide or its explosion overhead in the upper atmosphere.  A sonic-boom shock wave would instantly accelerate particles small enough to be entrained by a shock wave compression.  So extraterrestrial microspherules from the Taurid meteor stream freefalling through the atmosphere in the immediate vicinity of a wooly mammoth could be accelerated to speeds approaching that of the Mach 1 shock wave itself, enabling locally-accelerated spherules to penetrate hide, tusk, bone, or even silicates.
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Conclusion:

¶    An impact origin for coastal Carolina bays presumes a similar density of inland impacts, which appears to fit with discrete boulder fields dating to the LGM.  Conventionally, a periglacial, freeze-thaw, frost-wedging solifluction/gelifluction model strains credibility to explain the exquisite discreteness and concentration of LGM boulder fields.

¶    Deeply-incised surface features, such as cup marks and striations are predictive in an ice-sheet fragment impact, but require ad hoc mechanisms to explain them away in a conventional periglacial frost-wedging context, particularly since there are no contemporary examples under similar freeze-thaw conditions today.

¶    The resonant quality of Ringing Rocks diabase boulders is evidently a surficial skin effect, rather than a bulk-rock effect due to cooling of igneous intrusions under high pressure, since cutting or breaking boulders relieves the stress, which it would not due if the stress were an intrinsic bulk-rock property.

¶    Rock scale associated with boulder fields and beyond fits with a high-velocity high-temperature impact of an ice sheet fragment containing traces of extraterrestrial bolide material, whereas conventional theories have thus far overlooked this phenomena.

¶    Finally, microspherules embedded in bone, tusks and Clovis chert flakes suggest a Taurid meteor stream that’s at least 33,000 years old.  It’s more probable that the Taurid meteor stream is at least that old than it is that another meteor stream appeared and disappeared since then.  Presumably, high-energy sonic booms from multiple Taurid meteor stream meteors locally accelerated meteor-stream mineral grains in freefall up to a velocity sufficient to penetrate chert, bone and tusks.
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References:

Dietz, R. S., Barring, J. P., (1973), Hudson Bay arc as an astrobleme: A negative search, Meteoritics, Vol. 8, p. 28-29

Firestone, Richard; West, Allen; Warwick-Smith, Simon, (2006), The Cycle of Cosmic Catastrophes: Flood, Fire and Famine in the History of Civilization, Bear and Company

Firestone, Richard; Allen West;, and Simon Warwick-Smith, (2006), The Cycle of Cosmic Catastrophes, Bear & Company, Rochester, Vermont

Firestone, Richard B., Analysis of the Younger Dryas Impact Layer, (2007), Lawrence Berkeley National Laboratory https://escholarship.org/uc/item/03q2r98x

Firestone, R.B.; West, A.; Kennett, J.P. et al., (2007), Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling, PNAS October 9, 2007, vol. 104, no. 41

Firestone, Richard B., (2009), The Case for the Younger Dryas Extraterrestrial Impact Event: Mammoth, Megafauna, and Clovis Extinction, 12,900 Years Ago, Journal of Cosmology, 2009, Vol 2, pages 256-285, Cosmology, October 27, 2009

Petaev, Michail I.; Huang, Shichun; Jacobsen, Stein B.; Zindler, Alan, (2013), LARGE PLATINUM ANOMALY IN THE GISP2 ICE CORE: EVIDENCE FOR A CATACLYSM AT THE BØLLING-ALLERØD/YOUNGER DRYAS BOUNDARY?, 44th Lunar and Planetary Science Conference (2013)

Pinter, Nicholas; Scott, Andrew C.; Daulton, Tyrone L.; Podoll, Andrew; Koeberl, Christian; Anderson, R. Scott; Ishman, Scott E., (2011), The Younger Dryas impact hypothesis: A requiem, Earth-Science Reviews, Volume 106, Issues 3-4, June 2011, Pages 247-264

Wolbach, Wendy S. et al, (2018), Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ~12,800 Years Ago. 1. Ice Cores and Glaciers, The Journal of Geology, Volume 126, Number 2, March 2018
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