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I had a thin section prepared from a chip taken from the raised lip on the nearly flat posterior surface of the
object of Figure 11A. Figure 11B shows an eruption of amorphous material (the colors and “flow” textures
were insensitive to stage rotation when viewed between crossed polarizers) protruding just beyond the outer
surface of the rock. By process of elimination, this must be melted biotite quenched to an amorphous state.
I therefore propose that this extraordinary granitic rock was blasted deeply into space – perhaps at about 10
km/s and an elevation angle of about 80° to the northeast (see, Alvarez, 1996) from the interference zone of
the Chesapeake Bay impact (Fig. 4) and that, upon reentering the Earth’s atmosphere, it achieved an
aerodynamically stable attitude with its quasi-dome-shaped surface forward. During its descent toward our
front-yard-to-be, aerodynamic-shock-induced melting of the biotite took place in a near-surface region of
the anterior dome. Some of this melt was extruded and aerodynamically-driven backward to form the
observed streamlines following their respective paths of least resistance back up the sides. More
importantly, thicker molten-biotite-solid-crystallite slurries (clearly observed in one small patch of “naked”
feldspar and quartz crystallites) also moved backward, albeit more slowly, thus accounting for the observed
raised lip around the posterior surface (Fig. 11A) – as well as frozen flow fronts on the anterior dome
perceptible under grazing illumination.
I hope to drill a front-to-back core through the center of this rock and to cut documented samples from it
for examination by any interested researchers. (I propose to hold the rest of this object for possible future
display by the Smithsonian Institution.) Indeed, I would like to be a part of a paleothermometry study based
on electron spin resonance of paramagnetic E ´ center defects induced in α quartz by naturally occurring
radioactive impurities, given that these defects are known to anneal out at around 400° C (e.g., Jani et al.,
1983).
Of course, the prime objective of most other studies would be to determine if the object of Figure 11 is
petrologically related to the Langley Granite (Horton et al., 2005). How exciting that would be if the answer
should turn out to be, yes!
THE ANSWER, MY FRIEND, IS BLOWIN’ IN THE WIND
In fairness, I recognize that back in the time of Hack (1955) and Schlee (1957) uniformitarian geology had
long since ascended to the status of a quasi-religion. Loren Eiseley (1960) wrote eloquently on how Biblical
catastrophism had been justly supplanted by the concept of slow processes operating in deep time, thanks to
the genius and persuasion of Hutton and Lyell. Conceivably, Eiseley (1960) caught a whiff of what was yet
to come as he penned his remark on Lyell’s “insist[ence] upon his principle of preoccupancy” ...which if
taken to the limit would have required the dinosaurs to still be here instead of us. I’m sorry that Eiseley didn’
t live long enough to exhilarate in the catagory-4 wind of catastrophe by bolide impact (Alvarez et al., 1980)
...which back then was but a zephyr in what Eiseley (1961) repeatedly referred to as “the wind of the
oncoming future.” We who presently live in that future cannot be the least bit smug in our new knowledge,
given that the onrushing future will soon enough invalidate a fair share of our own philosophies. Still, as
scientists we are now obliged to use the newest revelations to mop up the errors that inevitably infest the
geological literature traceable to the absence of impact-stratigraphy chapters in the text books of the recent
past. Apropos of that, I lament too that Thomas Mutch’s life was cut so short, since I owe my appreciation
of stratigraphy to Mutch (1970).
Therefore, it is with the deepest respect for all of the geologists who in the past held firm to their
“uniformitarian faith” that I here make bold to posit that the well-rounded (though oft fractured) pebbles and
cobbles of Devonian-age quartzites ubiquitous to the gravel member of the upland deposits rested peacefully
in the target area of the Chesapeake Bay impactor one fateful day 35.5 m.y. ago. More specifically, I argue
that these upland gravels must have been present in the interference zone (Melosh, 1989) of the Chesapeake
Bay impactor, else they would have been thoroughly pulverized to Grady-Kipp fragments by the
downwardly moving tensile waves (Melosh, 1989). Indeed, I propose that the gravels that experienced that
fate were sucked into the streamlines of the excavation-flow ejecta (including a lot of erosion resistant glass)
that were re-deposited as the Bacons Castle formation in an annulus closer to the crater. I further propose
that the upland gravels were size-sorted in ballistic flight by atmospheric drag (Schultz and Gault, 1979;
Schultz, 1992), thus resulting in the radial gravel-size gradient so meticulously exposed by Schlee (1957).
Indeed, Pope et al. (1999) have already invoked atmospheric size sorting to explain features of the Chicxulub
impact deposits in Belize.
Answers to some protestations
There is no evidence of Devonian quartzite in the target zone
It has been argued that my model is contradicted by the fact that drilling has not revealed the slightest sign
of Devonian quartzites in the target area. My response follows:
It is relevant to mention that Attal and Lavé (2006) have established quartzite to be the most abrasion-
resistant Himalayan rock in the Marsyandi River in Nepal, both by field observations and experimental
measurements in a circular flume. Their experimental mass loss per kilometer for quartzite (resulting from
an emulation of the Marsyandi River during annual peak discharge across the Lesser Himalaya) of 0.15 %
per km translates to a line that plots between the pair of curves for the Rhine and Mur Rivers illustrated in
Figure 2B. This is more bad news for Hack’s (1955) model (if any more were needed). Additionally, Attal
and Lavé (2006) found Himalayan granite and schists to abrade at rates ~3 and ~100 times faster than
quartzite, respectively. This is good news for my implicit assumption that the largest clasts eroded from the
“Proto-Appalachians-East” that were likely to have been transported the farthest eastward by rivers would
have been quartzite. And, if these Proto-Appalachians were as high as the Himalayas, landslides might have
delivered quartzite directly into the rivers as debris in diamict sizes (Attal and Lavé, 2006: dashed curves in
Fig. 12).
In the latter regard, it is worth emphasizing that Schlee’s (1957) data for the upland deposits shown in
Figure 12 pertain to the gravel member only, whereas the overlying loam member is comparable in thickness
and 90% comprised of quartz silt (Hack, 1955). Thus, if the gravel and loam members – which I argue
were atmospherically separated in ballistic flight – were to be reunited, their combined particle-size
distribution might well recapitulate one of Attal and Lavé’s (2006) quartzite landslide diamictons.
object of Figure 11A. Figure 11B shows an eruption of amorphous material (the colors and “flow” textures
were insensitive to stage rotation when viewed between crossed polarizers) protruding just beyond the outer
surface of the rock. By process of elimination, this must be melted biotite quenched to an amorphous state.
I therefore propose that this extraordinary granitic rock was blasted deeply into space – perhaps at about 10
km/s and an elevation angle of about 80° to the northeast (see, Alvarez, 1996) from the interference zone of
the Chesapeake Bay impact (Fig. 4) and that, upon reentering the Earth’s atmosphere, it achieved an
aerodynamically stable attitude with its quasi-dome-shaped surface forward. During its descent toward our
front-yard-to-be, aerodynamic-shock-induced melting of the biotite took place in a near-surface region of
the anterior dome. Some of this melt was extruded and aerodynamically-driven backward to form the
observed streamlines following their respective paths of least resistance back up the sides. More
importantly, thicker molten-biotite-solid-crystallite slurries (clearly observed in one small patch of “naked”
feldspar and quartz crystallites) also moved backward, albeit more slowly, thus accounting for the observed
raised lip around the posterior surface (Fig. 11A) – as well as frozen flow fronts on the anterior dome
perceptible under grazing illumination.
I hope to drill a front-to-back core through the center of this rock and to cut documented samples from it
for examination by any interested researchers. (I propose to hold the rest of this object for possible future
display by the Smithsonian Institution.) Indeed, I would like to be a part of a paleothermometry study based
on electron spin resonance of paramagnetic E ´ center defects induced in α quartz by naturally occurring
radioactive impurities, given that these defects are known to anneal out at around 400° C (e.g., Jani et al.,
1983).
Of course, the prime objective of most other studies would be to determine if the object of Figure 11 is
petrologically related to the Langley Granite (Horton et al., 2005). How exciting that would be if the answer
should turn out to be, yes!
THE ANSWER, MY FRIEND, IS BLOWIN’ IN THE WIND
In fairness, I recognize that back in the time of Hack (1955) and Schlee (1957) uniformitarian geology had
long since ascended to the status of a quasi-religion. Loren Eiseley (1960) wrote eloquently on how Biblical
catastrophism had been justly supplanted by the concept of slow processes operating in deep time, thanks to
the genius and persuasion of Hutton and Lyell. Conceivably, Eiseley (1960) caught a whiff of what was yet
to come as he penned his remark on Lyell’s “insist[ence] upon his principle of preoccupancy” ...which if
taken to the limit would have required the dinosaurs to still be here instead of us. I’m sorry that Eiseley didn’
t live long enough to exhilarate in the catagory-4 wind of catastrophe by bolide impact (Alvarez et al., 1980)
...which back then was but a zephyr in what Eiseley (1961) repeatedly referred to as “the wind of the
oncoming future.” We who presently live in that future cannot be the least bit smug in our new knowledge,
given that the onrushing future will soon enough invalidate a fair share of our own philosophies. Still, as
scientists we are now obliged to use the newest revelations to mop up the errors that inevitably infest the
geological literature traceable to the absence of impact-stratigraphy chapters in the text books of the recent
past. Apropos of that, I lament too that Thomas Mutch’s life was cut so short, since I owe my appreciation
of stratigraphy to Mutch (1970).
Therefore, it is with the deepest respect for all of the geologists who in the past held firm to their
“uniformitarian faith” that I here make bold to posit that the well-rounded (though oft fractured) pebbles and
cobbles of Devonian-age quartzites ubiquitous to the gravel member of the upland deposits rested peacefully
in the target area of the Chesapeake Bay impactor one fateful day 35.5 m.y. ago. More specifically, I argue
that these upland gravels must have been present in the interference zone (Melosh, 1989) of the Chesapeake
Bay impactor, else they would have been thoroughly pulverized to Grady-Kipp fragments by the
downwardly moving tensile waves (Melosh, 1989). Indeed, I propose that the gravels that experienced that
fate were sucked into the streamlines of the excavation-flow ejecta (including a lot of erosion resistant glass)
that were re-deposited as the Bacons Castle formation in an annulus closer to the crater. I further propose
that the upland gravels were size-sorted in ballistic flight by atmospheric drag (Schultz and Gault, 1979;
Schultz, 1992), thus resulting in the radial gravel-size gradient so meticulously exposed by Schlee (1957).
Indeed, Pope et al. (1999) have already invoked atmospheric size sorting to explain features of the Chicxulub
impact deposits in Belize.
Answers to some protestations
There is no evidence of Devonian quartzite in the target zone
It has been argued that my model is contradicted by the fact that drilling has not revealed the slightest sign
of Devonian quartzites in the target area. My response follows:
- (1) I am arguing that the gravel member of the upland deposits derives from the effective interference
zone of the Chesapeake Bay impact (Melosh, 1989, p. 73), that is, a volume ~12 km in radius and
~600 m in depth (minus the central footprint of the impactor which, for example, might have been a
6-km-diameter comet moving at 30 km/s and striking at a 45° angle). It follows therefore that the
immediately contiguous materials out to a radius of 45 km were completely removed by the impact
and thus all drilling into lithologies pre-existing the impact is pushed outward at least 33 km from the
putative location of the materials that the doubters would like to have verified. If, for example, a
prime source of the quartzite gravels should have been the Jurassic wedge cartooned in Fig. 4
(Koeberl et al., 1996; Poag 1997), then only ocean-side drilling down to bedrock will ever reveal
them, and this has not been done. Indeed, the sediments immediately seaward of the Chesapeake Bay
Impact Structure in its first moments of existence are likely to have transported some distance farther
easward during the past 35.5 m.y.
- (2) The sorting-coefficient data of Schlee (1955) for the upland gravels, when compared with the
data of Emery (1955), show the upland gravels to be a near perfect match for an alluvial fan (Fig.
12). But alluvial fans develop at the base of the mountains they derive from, whereas the nearest
significant sources of Devonian (and Silurian) quartzites are the anticlines capping the Appalachians
to the west of the Blue Ridge (see Fig. 1) and the synclinorium of Massanutten Mountain in the
intervening Shenandoah Valley. Since I believe it proven beyond the shadow of a doubt that rivers
could not have dragged 50 to 100 km3 of quartzite silts, sands, and coarse gravels from the
Shenandoah Valley out to the Coastal Plain in the last 10 m.y., it seems to be a more fruitful line of
inquiry to now search for reasons why these materials were actually present in the target zone. To
that end, I propose that at the beginning of the Appalachian orogeny around 250 Ma, the very same
Paleozoic quartzite formations that are now truncated at Massanutten Mountain actually extended
eastward of what is now the Blue Ridge. In this scenario, the putative eastward extensions of these
Silurian and Devonian quartzites would have been eroded to alluvium in Mesozoic times. This
alluvium would at some point have been transported still farther eastward by rivers in order to
eventually become part of the presently ~600-m-thick, non-marine "seaward-thickening wedge of
mainly lower Cretaceous to upper Eocene, poorly lithified, and mainly siliciclastic sedimentary rocks"
(Koeberl et al., 1996; Poag et al., 2004) present in the target zone of the Chesapeake Bay crater
impactor (Fig. 4).
It is relevant to mention that Attal and Lavé (2006) have established quartzite to be the most abrasion-
resistant Himalayan rock in the Marsyandi River in Nepal, both by field observations and experimental
measurements in a circular flume. Their experimental mass loss per kilometer for quartzite (resulting from
an emulation of the Marsyandi River during annual peak discharge across the Lesser Himalaya) of 0.15 %
per km translates to a line that plots between the pair of curves for the Rhine and Mur Rivers illustrated in
Figure 2B. This is more bad news for Hack’s (1955) model (if any more were needed). Additionally, Attal
and Lavé (2006) found Himalayan granite and schists to abrade at rates ~3 and ~100 times faster than
quartzite, respectively. This is good news for my implicit assumption that the largest clasts eroded from the
“Proto-Appalachians-East” that were likely to have been transported the farthest eastward by rivers would
have been quartzite. And, if these Proto-Appalachians were as high as the Himalayas, landslides might have
delivered quartzite directly into the rivers as debris in diamict sizes (Attal and Lavé, 2006: dashed curves in
Fig. 12).
In the latter regard, it is worth emphasizing that Schlee’s (1957) data for the upland deposits shown in
Figure 12 pertain to the gravel member only, whereas the overlying loam member is comparable in thickness
and 90% comprised of quartz silt (Hack, 1955). Thus, if the gravel and loam members – which I argue
were atmospherically separated in ballistic flight – were to be reunited, their combined particle-size
distribution might well recapitulate one of Attal and Lavé’s (2006) quartzite landslide diamictons.
Figure 11. A: A 27-kg granite boulder recovered by the author in his front yard in Hollin Hills,
Fairfax County, Va. B: Thin-section photomicrograph of a chip of boulder of A showing
amorphous biotite extruded from the interior to the exterior (from the lower left to upper right).
C: Thin-section photomicrograph of a feldspar grain showing twinning (alternating yellow and
orange lines) with multiple fractures running perpendicular to these. D: Thin-section
photomicrograph of a feldspar grain showing mosaic structures. Images B, C, and D were
recorded under cross-polarized light. Object A is suspected by the author to be
interference-zone ejecta from the 35.5-Ma Chesapeake Bay impact.
Fairfax County, Va. B: Thin-section photomicrograph of a chip of boulder of A showing
amorphous biotite extruded from the interior to the exterior (from the lower left to upper right).
C: Thin-section photomicrograph of a feldspar grain showing twinning (alternating yellow and
orange lines) with multiple fractures running perpendicular to these. D: Thin-section
photomicrograph of a feldspar grain showing mosaic structures. Images B, C, and D were
recorded under cross-polarized light. Object A is suspected by the author to be
interference-zone ejecta from the 35.5-Ma Chesapeake Bay impact.
In Plain Sight
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