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A Tale Of Two Craters: Coriolis-Aware Trajectory Analysis CorrelatesTwo Pleistocene Impact Strewn Fields And Gives Michigan A Thumb
Abstract and Figures
Pleistocene Epoch cosmic impacts have been implicated in the geomorphology of two enigmatic events. Remarkably, in both cases spirited debates remain unsettled after nearly 100 years of extensive research. Consensus opinion holds that the Australasian (AA) tektites are of terrestrial origin despite a failure to locate the causal astroblem, while a cosmic link to the Carolina bays is considered soundly falsified by the identical lack of a related crater. Likely >100 km in diameter, such impacts during geologically recent times should be readily visible on the Earth’s surface. The improbability that two craters have eluded detection informs a hypothesis that a single impact at ~786 ka generated AA tektites as distal ejecta and Carolina bays as progeny of proximal ejecta. The AA astroblem search is focused on SE Asia despite a strewn field encompassing >30% of the Earth’s surface. This spatial scope implies to us that interhemispheric transits should be considered, as does findings that AA tektites were solidified in a vacuum, then ablated on reentry at ~10 km sec-1. A Coriolis-aware triangulation network operating on the orientations of 44,000 Carolina bays indicates a focus near 43ºN, 84ºW. Using the work of Urey and Lin, we propose that a near-tangential strike to the Earth’s limb generated the 150 km by 300 km oval depression that excises Saginaw Bay and opens Michigan’s Thumb. That region was likely encased in MIS 20 Laurentide ice at 786 ka. Schultz has shown that shallow impacts into thick continental ice yield non-traditional astroblems, and multiple glaciations have since reworked this site, making identification challenging. Hypervelocity gun tests show that low-angle impacts produce a vertical plume of ejecta, biased slightly down-range. Ballistic trajectories reflecting such a plume deliver tektites to all AA finds when lofted at ~10 km sec-1 and parameterized with the proposed depression’s location and 222º azimuth. Chemical and isotopic characteristics of AA tektites suggest they were sourced from sandstone and greywacke of Mesozoic age, which is congruent with Michigan Basin strata lost when The Thumb developed. The distribution of proximal ejecta may explain anomalously high pulses of regolith in moraines and sediment loading in regional drainage basins recently dated ~800 ka using 10Be/26Al methods.
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... The KML files can be directly imported into Google Earth to align the images on a virtual globe from which it is possible to capture geospatial metrics. The Carolina Bay survey now contains data for approximately 45,000 bays (Davias and Harris, 2015). ...
... Using great circle trajectories adjusted for the Coriolis Effect, Davias and Gilbride identified Saginaw Bay in Michigan as the intersection point of the projections of the major axes of the bays. In a subsequent paper, Davias and Harris (2015) provided a trigonometric equation that can predict the azimuthal orientation of 45,000 bays in Nebraska and the East Coast of the USA based only on their geographical coordinates. Davias and Harris (2015) also noted that the equidistance between the Carolina Bays and the Nebraska Rainwater Basins from the proposed impact point in Saginaw Bay suggests that an extraterrestrial impact at a low angle created an oval-shaped crater and a butterfly ejecta pattern. ...
... In a subsequent paper, Davias and Harris (2015) provided a trigonometric equation that can predict the azimuthal orientation of 45,000 bays in Nebraska and the East Coast of the USA based only on their geographical coordinates. Davias and Harris (2015) also noted that the equidistance between the Carolina Bays and the Nebraska Rainwater Basins from the proposed impact point in Saginaw Bay suggests that an extraterrestrial impact at a low angle created an oval-shaped crater and a butterfly ejecta pattern. This butterfly pattern could merely be a peculiarity due to the lack of terrain suitable for the formation of elliptical bays between Nebraska and the East Coast. ...
Geometrical analysis of the Carolina Bays using Google Earth in combination with LiDAR data makes it possible to postulate that the bays formed as the result of impacts, rather than from eolian and lacustrine processes. The Carolina Bays are elliptical conic sections with width-to-length ratios averaging 0.58 that are radially oriented toward the Great Lakes region. The radial distribution of ejecta is one characteristic of impacts, and the width-to-length ratios of the ellipses correspond to cones inclined at approximately 35°, which is consistent with ballistic trajectories from the point of convergence. These observations, and the fact that these geomorphological features occur only on unconsolidated soil close to the water table, make it plausible to propose that the Carolina Bays are the remodeled remains of oblique conical craters formed on ground liquefied by the seismic shock waves of secondary impacts of glacier ice boulders ejected by an extraterrestrial impact on the Laurentide Ice Sheet. Mathematical analysis using ballistic equations and scaling laws relating yield energy to crater size provide clues about the magnitude of the extraterrestrial event. An experimental model elucidates the remodeling mechanisms and provides an explanation for the morphology and the diverse dates of the bays.
... The question even is whether this area, which lies south of the Mason-Quimby line, was not ice free at the time of the proposed YDIH (see discussion below). Davias and Harris (2015), among others, correlate the YD impact with Carolina Bays, oval features which have an unresolved origin. Wolbach and et al. (2018) support the YDIH with existing evidence that the YD impact event caused an anomalously large episode of biomass burning, resulting in extensive atmospheric soot/dust loading that triggered an "impact winter." ...
... The combed strike angles θ [−] for the studied area of the Great Lakes specifically in the Saginaw Bay, using EIGEN 6C4, with the Comb statistics (0.76). Superposed over a figure fromDavias and Harris (2015). ...
The hypothetical impact structure in the Saginaw Bay (Michigan, USA, Lake Huron) has been tested by the gravity data derived from the recent gravity field model EIGEN 6C4 (expanded to degree and order 2190, with ground resolution of ~9 km). The following gravity field aspects were used: the gravity disturbances/anomalies, second derivatives of the disturbing potential (Marussi tensor), two of three gravity invariants, their specific ratio (known as 2D factor), the strike angles, and the virtual deformations. These gravity aspects are sensitive in various ways to the underground density contrasts. For the Saginaw Bay area, we confirm that we do not see any typical impact crater in terms of gravity disturbance or the radial second order derivative, possibly because of the thick layer of the ice located at the place and time of the impact. But the “combed” strike angles (one type of the gravity aspects we use) disclose a trace of high pressure to the SE/S/SW of the Bay and may be due to an impacting body. Thus, we provide circumstantial evidence of the Younger Dryas impact hypothesis.
... Many of these features pre-date (or formed during) the YD, the time when the putative impact would have occurred. Indeed, none of the diagnostic features and conditions listed as requisite for the identification of a meteorite impact structure by French and Koerberl (2010), Klokočník et al. (2019) and Davias and Harris (2015), along with Davias' self-published web site cited in their paper, can be found in the Saginaw Lowlands (Table 1). In short, unlike almost all other studies of meteorite impacts, Klokočník et al. (2019) fail to present any field evidence for a clear, circular depression or rim and associated subsurface deformationnormally taken as necessary evidence for an impact structure. ...
Although we support the notion that, sometimes, bold and even outrageous hypotheses can challenge existing science and add to it, e.g., Alvarez et al., 1980, because this is good for science, we feel this
paper presents an “outrageous hypothesis” without the necessary physical evidence to support it.
This unusual book, published to honor the late iconoclast and geologist extraordinaire Warren Bell Hamilton, comprises a diverse, cross-disciplinary collection of bold new ideas in Earth and planetary science. Some chapters audaciously point out all-too-obvious deficits in prevailing theories. Other ideas are embryonic and in need of testing and still others are downright outrageous. Some are doubtless right and others likely wrong. See if you can tell which is which. See if your students can tell which is which. This unique book is a rich resource for researchers at all levels looking for interesting, unusual, and off-beat ideas to investigate or set as student projects.
This unusual book, published to honor the late iconoclast and geologist extraordinaire Warren Bell Hamilton, comprises a diverse, cross-disciplinary collection of bold new ideas in Earth and planetary science. Some chapters audaciously point out all-too-obvious deficits in prevailing theories. Other ideas are embryonic and in need of testing and still others are downright outrageous.
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Chapter 24 Abstract:
This thesis embraces and expands upon a century of research into disparate geological enigmas, offering a unifying catastrophic explanation for events occurring during the enigmatic mid-Pleistocene transition. Billions of tons of “Australasian tektites” were dispatched as distal ejecta from a target mass of continental sediments during a cosmic impact occurring ca. 788 ka. The accepted signatures of a hypervelocity impact encompass an excavated astrobleme and attendant proximal, medial, and distal ejecta distributions. Enigmatically, the distal tektites remain the only accepted evidence of this impact’s reality. A protracted 50 yr search fixated on impact sites in Southeast Asia—the location of the tektites—has failed to identify the requisite additional impact signatures. We postulate the missing astrobleme and proximal/medial ejecta signatures are instead located antipodal to Southeast Asia. A review of the gradualistic theories for the genesis and age of the “Carolina bay” landforms of North America finds those models incapable of addressing all the facts we observe. Research into 57,000 of those oriented basins informs our speculation that they represent cavitation-derived ovoid basins within energetically delivered geophysical mass surge flows emanating from a cosmic impact. Those flows are seen as repaving regions of North America under blankets of hydrated impact regolith. Our precisely measured Carolina bay orientations indicate an impact site within the Laurentide ice sheet. There, we invoke a grazing regime impact into hydrated early Mesozoic to late Paleozoic continental sediments, similar in composition to the expected Australasian tektites’ parent target. We observe that continental ice shielded the target at ca. 788 ka, a scenario understood to produce anomalous astroblemes. The ensuing excavation allowed the Saginaw glacial lobe’s distinctive and unique passage through the Marshall Sandstone cuesta, which encircles and elsewhere protects the central region of the intracratonic Michigan Basin. Subsequent erosion by multiple ice-age transgressions has obfuscated impact evidence, forming Michigan’s “Thumb” as an enduring event signature. Comprehensive suborbital modeling supports the distribution of distal ejecta to the Australasian tektite strewn field from Michigan’s Lower Peninsula. The mid-Pleistocene transition impact hypothesis unifies the Carolina bays with those tektites as products of an impact into the Saginaw Bay area of Lake Huron, USA. The hypothesis will be falsified if cosmogenic nuclide burial dating of Carolina bay subjacent stratigraphic contacts disallows a coeval regolith emplacement ca. 788 ka across North America. We offer observations, interdisciplinary insights, and informed speculations fitting for an embryonic concept involving a planetary-scale extraterrestrial impact.
Regions of the Atlantic Coastal Plain are often capped by a surficial sheet of quartz sand. For example, the Pinehurst Formation sands are mapped as a separate unit, distinct from the well-provenanced terraces below. The Goldsboro Ridge sand is also distinct, resting on the Sunderland formation. From the Carolina Sandhills eastward to the coast at Wilmington, a nearly continuous and occasionally thick (up to 10m) sheet of high purity quartz sand is blanketed across the intervening terraces and scarps. While the Coastal Plain surfaces show evidence of eolian reworking, studies of the deeper extents of these sandy deposits often mention difficulties in determining their geomorphology, although deemed as gradualistic eolian, fluvial or marine. Marine deposition is appropriate at the coastline, supported by glacial-driven sea level transgressions; but they contain no shell fragments. Inland, deposition on interfluvials during flooding of is reasonable; but these are coarsely skewed, showing no sorting or channeling and minimal clays. At higher elevations, workers implicate eolian deposition on undissected terrain; but delivering coarse sand upslope from distant drainage mandates powerful winds. Oriented ovoid Carolina bay depressions have evolved in these sand sheets, seemingly without deforming or altering the antecedent strata and paleosols they rest upon. They are present in prodigious quantities and may represent diagnostic markers for these distinct sand deposits. In an attempt to identify a universal mechanism for the materialization of these sand sheets, we speculate on an aerial deposition, mobilized and delivered as a "rain" of pulverized distal ejecta emanating from a cosmic impact. The bay depressions may be artifacts of steam outgassing, frozen in time as the sand transited from liquefaction to lock-up, preserving an arrival vector in their orientation. Using data from our LiDAR-augmented geospatial survey of 30,000 Carolina bays, we note systematically varying orientations and robust adherence to archetype planforms. A triangulation network, built using bay orientations and considering the Coriolis steering of trajectories, suggests a probable source impact site. While such a catastrophic mechanism is unorthodox, our survey data and analysis suggests further research is warranted.
We propose that the Carolina bays are depositional artifacts in the surface of a ~10 meter-thick sheet of distal ejecta, spread differentially from a cosmic impact. The lack of a correlated impact structure in North America is challenging, however. Using the alignments of 40 fields of Carolina bays in the East and the Mid-West, we generated great circle paths for visualization in Google Earth's virtual globe. This yielded a fuzzy triangulation locus centered at 43.5 N, 89.5 W. Our analysis implies this triangulation would yield an erroneous impact location, offset to the west due to Earth rotation of .25 degrees of arc every clock minute of flight time. Adjustment of the crater eastward along the 43.5º N Parallel should direct us towards the actual impact site. We examined geological depressions found along that transit, selecting the Saginaw area of Michigan. It is generally understood that glacial activity removed vast quantities of softer strata from around the Michigan Basin’s periphery (i.e., Lakes Michigan, Huron and Erie), however the ice sheet was unsuccessful in breaching proximal cuestas encircling the basin with one major exception: Saginaw Bay. We propose a low-density hydrated silicate impactor, likely cometary, impacting the Earth on a shallow angle, nearly tangential. Remote sensing shows that approximately 5% of all craters are created during such oblique impacts, creating an oval shaped crater and a butterfly ejecta pattern. The mechanism for removal of terrestrial material is seen as shearing rather than compression, thus many of the classic impact markers (such as shocked quartz) are not expected. We note that the Saginaw region exhibits an oval shaped depression, oriented SW to NE, and correlates well with the annular distribution of Carolina bays seen across North America. Recent studies suggest that oblique impacts into solid surfaces protected by a layer of low impedance materials produces structures that differ from classic crater planforms. In our specific case, we invoke the Wisconsinan ice shield as a low-impedance layer protecting the sedimentary strata of the Michigan basin. The ice sheet offers a rationale for the relatively shallow “crater” seen in the area today. Implicating the ice sheet also provides a vehicle to re-distribute the local crater ejecta across a wide area as "glacial till".
A 1930 aerial photographic survey of Horry County, South Carolina, revealed vast fields of aligned elliptical landforms, sparking intense scientific research into their geomorphology. Today, Digital Elevation Maps (DEMs) generated using the remote sensing technology of Light Detection And Ranging (LiDAR) accentuate the visual presentation of these shallow basins by elucidating their closed circumferential rims. While the planform of these “Carolina bays” is considered to be elliptical, we document the existence of subtle, yet distinctive, regional variations in the shape of their closed planforms. Six archetypes are offered as taxonomy: bay, bayBell, bayShore, bayOval, baySouth and bayWest. To support a geospatial survey of these enigmatic landforms, 500,000 km2 of hsv-hinted (hue-saturation-value) DEMs were generated using publically accessible LiDAR data. Here, I describe the DEM image generation process, and their integration as tile sets into Google Earth for visualization. My measurement protocol involves manually placing an appropriate archetype planform template - as a PNG image "overlay" - onto the Google Earth virtual globe, then sizing and rotating it so that a satisfactory representation of a particular bay’s rim is achieved. The resulting overlay data element is programmatically processed to generate bay characteristics such as geographic location, elevation, surface area, and major axis spatial orientation. Over 40,000 distinct Carolina bays have been measured using the methodology described. Although the visual pattern matching process is to some extent subjective, the robust adherence of thousands of bays to this set of planforms supports the taxonomy's relevance. The resulting data are publically accessible from Google’s Fusion geospatial data repository facility, both in tabular form and in situ on the virtual globe. Preliminary findings from the survey are discussed, such as how the distribution of the archetypes and the spatial orientation of the bay’s major axis vary systematically by latitude and longitude across North America. The availability of this extensive spatial data set may assist in identifying the geomorphology of these enigmatic landforms. The processes demonstrated here might be applicable to the geospatial analysis of other landforms on Earth and the planets.
1] Layered planetary surfaces occur ubiquitously in the solar system, where sedimentary sequences or icy layers overlay crystalline bedrock. Previous experimental studies investigated how the presence of weak layer overlying a strong basement affects crater morphology, subsurface damage and soft-sediment compression. Numerical studies generally focus on the final morphology as a function of thicknesses and burial depths of weak layers. In field studies of impact craters, the shock state of minerals is a key metric. Here, we evaluate the effect of a surficial low-impedance layer on peak pressure magnitudes and consequent damage extent in the competent substrate. Laboratory experiments coupled with 3D CTH models of oblique (30 from horizontal) hypervelocity impacts at laboratory and planetary scales show that surface layers with a thickness on the order of the projectile diameter shield the underlying surface and absorb/scatter $70% of the impact energy. Numerical simulations reveal that surficial layers reduce peak pressure magnitudes within the subsurface by $60–70%, while damage in the substrate is due to shear failure. Sedimentary layers are more efficient shields than icy layers, but both reduce the extent of subsurface damage and the resulting shock levels recorded by minerals. These results indicate that a thin surficial low impedance layer mitigates the expression of shocked minerals in the substrate even when a structural response is still observed.
IN a recent communication1, Dr. Kohman suggests that tektites are meteorites which originate in interstellar space and collide with the solar system. I should like to direct attention again to the various facts that must be explained by any acceptable postulated history of these objects. (1) Tektites have chemical compositions remarkably similar to those of the more acid sedimentary rocks. This is true for the major and minor constituents. (I have been privileged to see analyses as yet unpublished on these minor constituents.) Such a chemical composition is not produced by any other naturally occurring chemical processes that we know of, except perhaps in very rare and special circumstances. (2) Tektites obviously have been melted, and this means that a temperature of some 1,500°C. or more was supplied by some means. In fact some appear to have been reheated to the melting point by passage through gas or by a blast of gas over the object. No terrestrial source of heat is known which could produce such high temperatures. (3) They are distributed thinly over areas of hundreds and thousands of kilometres in linear dimensions. (4) They are reported to contain aluminium-26 and beryllium-10. This observation is due to Dr. Kohman and Dr. Ehmann.
Planetary impacts occur indiscriminately, in all locations and materials. Varied geologic settings can have significant effects on the impact process, including the coupling between the projectile and target, the final damage patterns and modes of deformation that occur. For example, marine impact craters are not identical to impacts directly into bedrock or into sedimentary materials, though many of the same fundamental processes occur. It is therefore important, especially when considering terrestrial impacts, to understand how a low impedance sedimentary layer over bedrock affects the deformation process during and after a hypervelocity impact. As a first step, detailed comparisons between impacts and hydrocode models were performed. Experiments performed at the NASA Ames Vertical Gun Range of oblique impacts into polymethylmethacrylate (PMMA) targets with low impedance layers were performed and compared to experiments of targets without low impedance layers, as well as to hydrocode models under identical conditions. Impact velocities ranged from 5 km/s to 5.6 km/s, with trajectories from 30 degrees to 90 degrees above the horizontal. High-speed imaging provided documentation of the sequence and location of failure due to impact, which was compared to theoretical models. Plasticine and ice were used to construct the low impedance layers. The combination of experiments and models reveals the modes of failure due to a hypervelocity impact. How such failure is manifested at large scales can present a challenge for hydrocodes. CTH models tend to overestimate the amount of damage occurring within the targets and have difficulties perfectly reproducing morphologies; nevertheless, they provide significant and useful information about the failure modes and style within the material. CTH models corresponding to the experiments allow interpretation of the underlying processes involved as well as provide a benchmark for the experimental analysis. The transparency of PMMA allows a clear view of failure patterns within the target, providing a 3D picture of the final damage, as well as damage formation and propagation. Secondly, PMMA has mechanical properties similar to those of brittle rocks in the upper crust, making it an appropriate material for comparison to geologic materials. An impact into a PMMA target with a one-projectile-diameter thick plasticine layer causes damage distinct from an impact into a PMMA target without a low impedance layer. The extent of the final damage is much less in the target with the low impedance layer and begins to form at later times, there is little to no crater visible on the surface, and the formation and propagation of the damage is completely different, creating distinct subsurface damage patterns. Three-dimensional CTH hydrocode models show that the pressure history of material around and underneath the impact point is also different when a low impedance layer is present, leading to the variations in damage forming within the targets.
The U-Pb age spectrum of detrital zircons in sandstone of the fluvial Middle Jurassic Ionia Formation in the Michigan basin, United States, resembles the age spectra in Jurassic eolianites of the Colorado Plateau, except that a Neoproterozoic (725-510 Ma) subpopulation present in the eolianites is absent from the Michigan basin strata. The detrital zircon data are compatible with the hypothesis that the Ionia Formation was deposited by northern tributaries of a transcontinental Jurassic paleoriver system that transported detritus from headwaters in Atlantic rift highlands of the Appalachian region to floodplains and deltas in the present northern Rocky Mountains region. Previous detrital zircon studies have indicated that sedimented lowlands in that paleogeographic position were deflated by paleowinds to feed eolian sand southward (in present coordinates) into the Colorado Plateau ergs (sand seas).
Aerodynamic experiments with tektite glass demonstrate that, subsequent to the termination of ablation, high thermal stresses are formed within a thin outer shell. This shell spontaneously spalls, leaving a core shaped like many of the tektites found in Billiton, Java, Philippines and Australia. Certain tektite fragments from Java and Australia are shown to have the same internal stress patterns as pieces of aerothermal stress shell. The over-all evidence indicates that the Australasian tektites descended into the atmosphere as rigid objects of glass.Core shapes found in the extreme southwest part of Australia surprisingly are more like those found in the Philippines than in other areas of Australia; comparisons of chemical analyses and of specific gravity population polygons reveal the same striking circumstances. It is concluded that all Australasian tektites represent a single event.A study of tektite forms, in relation to results from laboratory experiments, indicates that the temperature of formation of primary shapes varied progressively across the Australasian strewnfield. The sculpture on certain australites provides a record of tumbling during entry into the Earth's atmosphere. The effect of turning on the determination of entry trajectories is discussed, and new evidence is presented pertaining to the deceleration which existed when ablation terminated on the australites. The trajectory determinations correspond to an origin from the Moon.Numerous trajectories from the Moon to Earth have been studied with a high-speed electronic digital computer. The relative probability of such trajectories is about for the Moon as a whole, and for certain crater locations. A comparison of the geographical spread of the Australasian tektites with the Earth landing patterns for lunar material ejected within the a zimuthal dispersion observed of lunar rays, and within the elevational dispersion measured in hypervelocity impact experiments, indicates mutual compatibility.
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Reactivation of the Archean--Proterozoic suture along the southern margin of Laurentia during the Mazatzal orogeny: Petrogenesis and tectonic implications of ca. 1.63 Ga granite in southeastern Wyoming
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Johnson,D., 1942, The Origin of the Carolina Bays, Columbia University Press, figure 27,
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Petrogenesis and tectonic implications of ca. 1.63 Ga granite in southeastern Wyoming, GSA Bulletin V. 125 no. 1--2