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The autobrecciated chalk ball. I discovered this clast while it was still in the process of being exhumed
directly from the bed of the rivulet. It is shown in the upper part of Figure 10B in its as-recovered
condition. The friable orange-brown crust on the bottom of the object (spontaneously crumbling after
desiccation) may have originally been present on its presently “bald” top surface as well – in which case it
might have been stripped by the flowing water before I dug it out. The clasts internal to the illustrated
sawed slab appear slightly darker than the pale yellowish-white matrix (a difference that I digitally enhanced
in the figure). However, this effect appears to be due to higher specular reflection of light from the clasts
due owing to their lower porosity, thus causing the matrix to appear lighter when the sawed face is viewed
at a small angle to the illuminating light. Conversely, when illuminated and viewed at complementary acute
angles, reflection from the matrix becomes equally specular and no color difference is perceived. Inspected
with a hand lens, the matrix appears fossil free, whereas the a few of the clasts display one or two split
ovoid objects ~1 mm, which to my amateur’s eye best match expectation for benthic forams cut parallel to
semi-major axes. (I would be happy to make samples of this clast available to any paleontologist willing to
render an expert judgment.)
This rock certainly could not have been emplaced by rivers because (1) it wouldn’t have survived fluvial
transport for as far as 100 m and (2) there are no chalk outcrops upriver to the north or west, nor would
any be expected anywhere in the Appalachians. On the other hand, with the eustatic sea level having been as
high as 300 m during much of the Cretaceous and remaining as high a 140 m throughout the Paleogene up
to the time of the Chesapeake Bay impact (Hallam, 1984), some pelagic limestones were almost certain to
have been present in the target area. Therefore, the clast of Figure 10B is surely a Chesapeake Bay crater
impactite.
The palagonite “cinder.” The 8.5-cm-tall object illustrated in Figure 10C matches the Glossary of Geology
definition of palagonite. However, I strongly doubt that it is of volcanic origin given its composition (vide
infra) and its incorporation of quartz clasts in sizes up to 1 cm. In Figure 10C, one of the larger quartz-
crystal inclusions protrudes from the left hand side of the object, and another one is seen in the interior of
the saw-cut slab (their locations are indicated by black outlines). This object’s grooved and pitted surface
was densely packed with the same whitish-gray quartz silt in which it was found embedded. The coherency
of this silt matrix cannot be overstated; even with a strong stream of water from a garden hose I failed to
completely dislodge it from some of the pits. More significantly, the slice sawed from the bottom revealed
that clods of the same quartz silt are encased in the interior of this “cinder.”
The only crystalline minerals identified by X-ray diffraction of a powdered sample of the orange-brown
material selected to be as free as possible of quartz inclusions were goethite ...and quartz. Both sets of
diffraction lines were relatively weak, suggesting that much of the orange-brown material may be X-ray
amorphous. Careful inspection of the sawed surface reveals that the object solidified from a sol comprising
at least two immiscible melts. The darker orange-brown material making up the continuous phase is
substantially harder than the captive yellow-brown material.
I interpret this object as a blob of impactoclastic glass – possible melted clays – which accreted quartz
during its jetting-launched flight toward Hollin Hills, 190 km distant from the crater center.
The melt-encrusted greenstone fragment. At first I believed this object to be another chalk ball. It had a
similar “toasted” orange-brown exterior surface, which was underlain by what seemed to be the same chalk
when I picked through the brittle outer rind and found a friable whitish material inside, which fizzed (briefly)
when treated with HCl. However, when I finally got around to sawing it in half, a wholly different story
emerged (Fig. 10D). The core rock turns out to be dense, hard, massive (overlooking the fine network of
well cemented fractures), and crystalloblastic. My amateur interpretation is that it is greenstone, a common
local basement rock – which in the present case (having become part of the jetting-phase ejecta) must have
been transported prior to 35.5 Ma from the Blue Ridge to a location near the top of the ~500 m of sediments
in the target area of the Chesapeake Bay impactor.
However, there is another interesting story yet to be told in the five-layer rind on the outside of this rock.
In general, I interpret this rind to be the end result a glass layer created by an external temperature rise of
“tens of thousands of degrees (Melosh, 1989)” during the jetting phase of the impact. Its present-day multi-
layer complexity sure relates at least in part to diagenetic alterations, although the innermost layer could be a
relict zone of partial melting.
We have seen that this surface-melted greenstone object and the chalk ball – both found in the Hollin Hills
diamicton – both display “toasted” orange-brown crusts ...as did also a Chicxulub-impact-related carbonate
spheroid from southern Mexico that I have studied (Griscom et al., 2003b). This coloration is certainly due
to iron oxide, but how did it come to appear on the surfaces of these objects? Extrapolation of existing
binary phase diagrams for the system Fe-Fe2O3 (Schneider, 1969) from their presently established high
temperature of 1,600° C suggests that liquid oxide and liquid metal could coexist at temperatures above ~2,
300° C, even in air at one-atmosphere pressure. The reasons why smelted iron would transport to the
surface under those conditions are undoubtedly complex and dependent on ambient conditions thus far
unknown. However, it is clear that any such metallic component would have re-oxidized soon after
reimpact.
The rock of Figure 10D is actually surfaced by a brittle bilayer comprising a pale whitish orange-brown
outer surface and slightly thicker (~0.5 mm) black layer below it. The black layer is unlikely to be
magnetite, since it didn’t respond to a magnet. The volume of this black material seems rather large
compared to the small amount of light-colored (low-iron) melted rock represented by the existing rind.
However, it seems likely that a large amount of the original rock actually evaporated in the jet that launched
it. If so, given that iron has a lower volatility than most other constituent elements, iron would have
naturally concentrated at or near the surface. Thus, a future determination of the compositions of both the
core rock and the black layer might give an idea of how much of this rock was vaporized under differing
model jetting scenarios...
Interestingly, this rock was shaped vaguely like an Apollo command module, with a gently convex “front”
surface and a tent-shaped “superstructure.” And, lo, the (now crumbling) iron-oxide surface exhibited flow
textures leading from the front surface around the periphery and starting to climb part of the way up the side
of the “module.”
The doubly-fractured quartzite cobble emplaced in one piece. I found the three objects of Figure 10E
partially exposed in the Hollin Hills diamicton tightly meshed together. So without a doubt, this quartzite
cobble was subjected to three planar fractures before deposition, and yet it was deposited with three of its
presumed four original parts still joined. It is probable that these three fragments resulted from a cobble
deposited with a pair of partial fractures which completely split apart later due to freeze thaw cycles in a
moist environment, since nothing else could have affected them while they remained entombed in their
massive quartz-silt sarcophagus. This finding strongly supports the notion that the fractured rocks of
Figure 3 were also “fatally,” if not completely, fractured prior to deposition – implying that their current
condition was neither the work of rivers nor of any Indians or colonial farmers who might have dug them
up.
On the origin of the Hollin Hills diamicton. I propose that the whitish-gray diamict stratum of Figure
10A comprises jetting-phase ejecta possibly correlative with the basal pebble-and-“clay” bilayer in the
Midlothian uplands (vide supra). However, the location of this stratum is topographically lower by ~30 m
than the base of the local upland deposits, which overlie what in this context I will call the “Springfield-
Hollin Hills plateau.” Therefore, the temporal separation in the stratigraphic column of the Hollin Hills
diamicton from Schlee’s (1957) upland deposits is yet to be established. That is, it cannot be ruled out that
the former was deposited long before the latter and that cobbles from the latter now immediately overly a
recently exhumed ancient diamicton due to mass erosion of younger deposits on the heights.
But there is another possibility – and I think the correct one – namely, that the Hollin Hills diamicton is
indeed jetting-phase ejecta of the Chesapeake Bay crater, which is fortuitously preserved in its present
location by virtue of this debris flow having reached zero velocity at just the right moment to settle into a
well-shielded topographic low existing at the time of the impact (currently a 66-m/km reverse slope relative
to the direction of ejecta arriving from the Chesapeake Bay impact). This “good fortune” could have
prevented it from being ripped up and incorporated into the later-arriving, interference-zone-launched upland
gravels. Indeed, the relative rarity of such shielded locations could be the reason why Schlee (1957) did not
report similar whitish-gray-quartz silt strata at the base of the upland deposits in any of the 98 sites he
sampled.
So why didn’t the “rip up” effect happen at the Midlothian sites? I think the answer is that, in that case, the
ejecta landed on solid bedrock of the Piedmont, so there was no soft substrate to rip up. Indeed, I propose
that the concave upward unconformity of Figure 9A was originally scoured out of this Petersburg granite
outcrop by the first arriving, highest energy materials jetted in that direction during the contact phase of the
Chesapeake Bay impact. I want to emphasize that, while the Hollin Hills diamicton is technically not lithified,
it is definitely not soft! I think this ultra-dense-packed stratum could easily have withstood being caught
“between a rock and a hard place” at Midlothian Stop #4 (Fig. 9A). Obviously, this notion should be a
sufficient justification for careful studies of the Midlothian “pebble-and-clay” bilayer to find out whether the
Hollin Hills diamicton is a one-off fluke ...or is the stratotype of a vast (and highly information laden!)
impactoclastic formation. N.B. Melosh (1989) states that the jetted mass should comprise “comparable
quantities of both target and projectile material,” so the probability of finding intact fragments of the
impactor should be large if my interpretation is correct.
A SPALL OF LANGLEY GRANITE IN PLAIN SIGHT?
For the first 20 years or so that we lived in Hollin Hills I would sometimes balance myself on a half-buried
dome-shaped rock while contemplating Nature from the top of our driveway. When eventually this rock
had to be removed to make room for an herb garden, I placed it above ground as an ornamental. Then one
day my eye caught the streaks on its side. Going for closer look, I happened to turn the domed side down,
revealing for the first time that the other side was nearly flat and had a raised rim around its circumference
and that the streaks ran from the domed side “backwards” in wind-tunnel-like fashion (Fig. 11A). Being
familiar with button tektites (e.g., Glass, 1984), it took me only seconds to conclude that this rock must be a
meteorite. But its color was all wrong for a chondrite; in fact, it looked to me like granite. I knew then that
I possibly had in my lap a meteorite from a terrestrial planet (Gladman et al., 1996), maybe even our own! I
became so excited that I spread the story far and wide to scientists I thought surely would be professionally
interested. But, perhaps not surprisingly (Mitroff, 1975; Griscom, 1994), my story was universally met by
disinterest or outright disbelief, even after some looked closely at my objects. So for the past 9 years I have
been the sole researcher of this 27-kg rock. However, no one has been paying me to do this, and I’ve had
much else on my platter ...so I must make these excuses for the paucity of results I have to report below.
The anterior (domed) surface differs from the rest of the rock by showing a faint orange coloration
reminiscent of the orange or orange-brown outer crusts on the objects found in the Hollin Hills diamicton –
and probably for the same reason. From inspection with a hand lens, it appeared to me that the sub-parallel
streaks on its sides might be melted biotite. So, I tried and succeeded in replicating such an effect by
applying a well-tuned H2-O2 torch (2,800° C) tangentially to a freshly fractured sample of biotite granite.
By sheer coincidence, it turns out that the temperature of the Apollo command-module heat shields rose to
2,800° C on reentry (Allday, 2000). And, if any further proof of my conclusions were needed, Deer et al.
(1966) state that, while biotite is often the first granitic mineral to crystallize in magmas at depth, it also has
the lowest melting point at atmospheric pressure.
directly from the bed of the rivulet. It is shown in the upper part of Figure 10B in its as-recovered
condition. The friable orange-brown crust on the bottom of the object (spontaneously crumbling after
desiccation) may have originally been present on its presently “bald” top surface as well – in which case it
might have been stripped by the flowing water before I dug it out. The clasts internal to the illustrated
sawed slab appear slightly darker than the pale yellowish-white matrix (a difference that I digitally enhanced
in the figure). However, this effect appears to be due to higher specular reflection of light from the clasts
due owing to their lower porosity, thus causing the matrix to appear lighter when the sawed face is viewed
at a small angle to the illuminating light. Conversely, when illuminated and viewed at complementary acute
angles, reflection from the matrix becomes equally specular and no color difference is perceived. Inspected
with a hand lens, the matrix appears fossil free, whereas the a few of the clasts display one or two split
ovoid objects ~1 mm, which to my amateur’s eye best match expectation for benthic forams cut parallel to
semi-major axes. (I would be happy to make samples of this clast available to any paleontologist willing to
render an expert judgment.)
This rock certainly could not have been emplaced by rivers because (1) it wouldn’t have survived fluvial
transport for as far as 100 m and (2) there are no chalk outcrops upriver to the north or west, nor would
any be expected anywhere in the Appalachians. On the other hand, with the eustatic sea level having been as
high as 300 m during much of the Cretaceous and remaining as high a 140 m throughout the Paleogene up
to the time of the Chesapeake Bay impact (Hallam, 1984), some pelagic limestones were almost certain to
have been present in the target area. Therefore, the clast of Figure 10B is surely a Chesapeake Bay crater
impactite.
The palagonite “cinder.” The 8.5-cm-tall object illustrated in Figure 10C matches the Glossary of Geology
definition of palagonite. However, I strongly doubt that it is of volcanic origin given its composition (vide
infra) and its incorporation of quartz clasts in sizes up to 1 cm. In Figure 10C, one of the larger quartz-
crystal inclusions protrudes from the left hand side of the object, and another one is seen in the interior of
the saw-cut slab (their locations are indicated by black outlines). This object’s grooved and pitted surface
was densely packed with the same whitish-gray quartz silt in which it was found embedded. The coherency
of this silt matrix cannot be overstated; even with a strong stream of water from a garden hose I failed to
completely dislodge it from some of the pits. More significantly, the slice sawed from the bottom revealed
that clods of the same quartz silt are encased in the interior of this “cinder.”
The only crystalline minerals identified by X-ray diffraction of a powdered sample of the orange-brown
material selected to be as free as possible of quartz inclusions were goethite ...and quartz. Both sets of
diffraction lines were relatively weak, suggesting that much of the orange-brown material may be X-ray
amorphous. Careful inspection of the sawed surface reveals that the object solidified from a sol comprising
at least two immiscible melts. The darker orange-brown material making up the continuous phase is
substantially harder than the captive yellow-brown material.
I interpret this object as a blob of impactoclastic glass – possible melted clays – which accreted quartz
during its jetting-launched flight toward Hollin Hills, 190 km distant from the crater center.
The melt-encrusted greenstone fragment. At first I believed this object to be another chalk ball. It had a
similar “toasted” orange-brown exterior surface, which was underlain by what seemed to be the same chalk
when I picked through the brittle outer rind and found a friable whitish material inside, which fizzed (briefly)
when treated with HCl. However, when I finally got around to sawing it in half, a wholly different story
emerged (Fig. 10D). The core rock turns out to be dense, hard, massive (overlooking the fine network of
well cemented fractures), and crystalloblastic. My amateur interpretation is that it is greenstone, a common
local basement rock – which in the present case (having become part of the jetting-phase ejecta) must have
been transported prior to 35.5 Ma from the Blue Ridge to a location near the top of the ~500 m of sediments
in the target area of the Chesapeake Bay impactor.
However, there is another interesting story yet to be told in the five-layer rind on the outside of this rock.
In general, I interpret this rind to be the end result a glass layer created by an external temperature rise of
“tens of thousands of degrees (Melosh, 1989)” during the jetting phase of the impact. Its present-day multi-
layer complexity sure relates at least in part to diagenetic alterations, although the innermost layer could be a
relict zone of partial melting.
We have seen that this surface-melted greenstone object and the chalk ball – both found in the Hollin Hills
diamicton – both display “toasted” orange-brown crusts ...as did also a Chicxulub-impact-related carbonate
spheroid from southern Mexico that I have studied (Griscom et al., 2003b). This coloration is certainly due
to iron oxide, but how did it come to appear on the surfaces of these objects? Extrapolation of existing
binary phase diagrams for the system Fe-Fe2O3 (Schneider, 1969) from their presently established high
temperature of 1,600° C suggests that liquid oxide and liquid metal could coexist at temperatures above ~2,
300° C, even in air at one-atmosphere pressure. The reasons why smelted iron would transport to the
surface under those conditions are undoubtedly complex and dependent on ambient conditions thus far
unknown. However, it is clear that any such metallic component would have re-oxidized soon after
reimpact.
The rock of Figure 10D is actually surfaced by a brittle bilayer comprising a pale whitish orange-brown
outer surface and slightly thicker (~0.5 mm) black layer below it. The black layer is unlikely to be
magnetite, since it didn’t respond to a magnet. The volume of this black material seems rather large
compared to the small amount of light-colored (low-iron) melted rock represented by the existing rind.
However, it seems likely that a large amount of the original rock actually evaporated in the jet that launched
it. If so, given that iron has a lower volatility than most other constituent elements, iron would have
naturally concentrated at or near the surface. Thus, a future determination of the compositions of both the
core rock and the black layer might give an idea of how much of this rock was vaporized under differing
model jetting scenarios...
Interestingly, this rock was shaped vaguely like an Apollo command module, with a gently convex “front”
surface and a tent-shaped “superstructure.” And, lo, the (now crumbling) iron-oxide surface exhibited flow
textures leading from the front surface around the periphery and starting to climb part of the way up the side
of the “module.”
The doubly-fractured quartzite cobble emplaced in one piece. I found the three objects of Figure 10E
partially exposed in the Hollin Hills diamicton tightly meshed together. So without a doubt, this quartzite
cobble was subjected to three planar fractures before deposition, and yet it was deposited with three of its
presumed four original parts still joined. It is probable that these three fragments resulted from a cobble
deposited with a pair of partial fractures which completely split apart later due to freeze thaw cycles in a
moist environment, since nothing else could have affected them while they remained entombed in their
massive quartz-silt sarcophagus. This finding strongly supports the notion that the fractured rocks of
Figure 3 were also “fatally,” if not completely, fractured prior to deposition – implying that their current
condition was neither the work of rivers nor of any Indians or colonial farmers who might have dug them
up.
On the origin of the Hollin Hills diamicton. I propose that the whitish-gray diamict stratum of Figure
10A comprises jetting-phase ejecta possibly correlative with the basal pebble-and-“clay” bilayer in the
Midlothian uplands (vide supra). However, the location of this stratum is topographically lower by ~30 m
than the base of the local upland deposits, which overlie what in this context I will call the “Springfield-
Hollin Hills plateau.” Therefore, the temporal separation in the stratigraphic column of the Hollin Hills
diamicton from Schlee’s (1957) upland deposits is yet to be established. That is, it cannot be ruled out that
the former was deposited long before the latter and that cobbles from the latter now immediately overly a
recently exhumed ancient diamicton due to mass erosion of younger deposits on the heights.
But there is another possibility – and I think the correct one – namely, that the Hollin Hills diamicton is
indeed jetting-phase ejecta of the Chesapeake Bay crater, which is fortuitously preserved in its present
location by virtue of this debris flow having reached zero velocity at just the right moment to settle into a
well-shielded topographic low existing at the time of the impact (currently a 66-m/km reverse slope relative
to the direction of ejecta arriving from the Chesapeake Bay impact). This “good fortune” could have
prevented it from being ripped up and incorporated into the later-arriving, interference-zone-launched upland
gravels. Indeed, the relative rarity of such shielded locations could be the reason why Schlee (1957) did not
report similar whitish-gray-quartz silt strata at the base of the upland deposits in any of the 98 sites he
sampled.
So why didn’t the “rip up” effect happen at the Midlothian sites? I think the answer is that, in that case, the
ejecta landed on solid bedrock of the Piedmont, so there was no soft substrate to rip up. Indeed, I propose
that the concave upward unconformity of Figure 9A was originally scoured out of this Petersburg granite
outcrop by the first arriving, highest energy materials jetted in that direction during the contact phase of the
Chesapeake Bay impact. I want to emphasize that, while the Hollin Hills diamicton is technically not lithified,
it is definitely not soft! I think this ultra-dense-packed stratum could easily have withstood being caught
“between a rock and a hard place” at Midlothian Stop #4 (Fig. 9A). Obviously, this notion should be a
sufficient justification for careful studies of the Midlothian “pebble-and-clay” bilayer to find out whether the
Hollin Hills diamicton is a one-off fluke ...or is the stratotype of a vast (and highly information laden!)
impactoclastic formation. N.B. Melosh (1989) states that the jetted mass should comprise “comparable
quantities of both target and projectile material,” so the probability of finding intact fragments of the
impactor should be large if my interpretation is correct.
A SPALL OF LANGLEY GRANITE IN PLAIN SIGHT?
For the first 20 years or so that we lived in Hollin Hills I would sometimes balance myself on a half-buried
dome-shaped rock while contemplating Nature from the top of our driveway. When eventually this rock
had to be removed to make room for an herb garden, I placed it above ground as an ornamental. Then one
day my eye caught the streaks on its side. Going for closer look, I happened to turn the domed side down,
revealing for the first time that the other side was nearly flat and had a raised rim around its circumference
and that the streaks ran from the domed side “backwards” in wind-tunnel-like fashion (Fig. 11A). Being
familiar with button tektites (e.g., Glass, 1984), it took me only seconds to conclude that this rock must be a
meteorite. But its color was all wrong for a chondrite; in fact, it looked to me like granite. I knew then that
I possibly had in my lap a meteorite from a terrestrial planet (Gladman et al., 1996), maybe even our own! I
became so excited that I spread the story far and wide to scientists I thought surely would be professionally
interested. But, perhaps not surprisingly (Mitroff, 1975; Griscom, 1994), my story was universally met by
disinterest or outright disbelief, even after some looked closely at my objects. So for the past 9 years I have
been the sole researcher of this 27-kg rock. However, no one has been paying me to do this, and I’ve had
much else on my platter ...so I must make these excuses for the paucity of results I have to report below.
The anterior (domed) surface differs from the rest of the rock by showing a faint orange coloration
reminiscent of the orange or orange-brown outer crusts on the objects found in the Hollin Hills diamicton –
and probably for the same reason. From inspection with a hand lens, it appeared to me that the sub-parallel
streaks on its sides might be melted biotite. So, I tried and succeeded in replicating such an effect by
applying a well-tuned H2-O2 torch (2,800° C) tangentially to a freshly fractured sample of biotite granite.
By sheer coincidence, it turns out that the temperature of the Apollo command-module heat shields rose to
2,800° C on reentry (Allday, 2000). And, if any further proof of my conclusions were needed, Deer et al.
(1966) state that, while biotite is often the first granitic mineral to crystallize in magmas at depth, it also has
the lowest melting point at atmospheric pressure.
In Plain Sight
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