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Reader Comments
Dr. Peter Vogt is a marine geophysicist retired from the Naval Research Laboratory's Marine Geosciences Division,
who has been recognized by the University of Bergen, Norway, for his "international scientific role based on wide-
ranging and innovative research in the fields of marine geology and geophysics, in particular in the Norwegian-
Greenland Sea and the Arctic Ocean" and awarded an Honorary Doctorate degree by that university on August 25,
2000.
Back about that time, when we were both still working at NRL, it was Peter who first pointed out to me that the
rocks I had been studying in my neighborhood of Hollin Hills, Virginia, belong to the extensive “upland deposits” of
Maryland, Virginia, and the District of Columbia, and it was he who specifically directed me to the work of Schlee
(1957). Peter has continued to doubt my conclusions regarding their origins, but recently he agreed to discuss the
matter by e-mail:
Peter: As far as I know, not being a land geologist, not much new has been discovered in recent years--the Upland
Deposits, or whatever you want to call this unit or these units, sit stratigraphically and for the most part physically (e.
g. in Southern MD) on top of well-dated and generally pretty fossiliferous Middle and Upper Miocene shallow marine
to subtidal strata. The only way I could possibly see depositing impact breccia pebbles of ca. 35Ma age on 10-20Ma
marine sediments is for the breccia to have been FIRST deposited on the Piedmont and only THEN, much later (about
in the interval 10 to 2.75 Ma in my opinion) washed out on the Coastal Plain by the Potomac and perhaps other rivers,
to form the Upland Deposits. The Law of Stratigraphic Superposition or whatever it was called was one of the first
basic principles appreciated in the early years of modern Geology, probably by Hutton himself in late 18th century I
think.
Dave: I have been aware of, and obedient to, the stratigraphic superposition principle for 37 or 38 years – ever since
I bought and devoured Thomas Mutch’s book Geology of the Moon, which was inferring relative ages of lunar
features from sequences of overlapping crater ejecta blankets. All units underlying a given crater’s ejecta blanket are
per force older than the crater itself. So my position is that, if the “upland deposits” comprise largely pristine, un-
reworked CB-crater ejecta, then the fossils in the underlying formations are older than 35.5 Ma. And in my web-
published manuscript I present a multiplicity of reasons for why the upland deposits are almost certainly primary CB-
crater ejecta.
Peter: There are not many dates from the Upland Deposits, but there ARE some. Occasional land mammal teeth, for
example. Also, in the 1990s some time a bulldozer was alert enough to tell geologists about a black lens he was
digging into in Prince Georges County. This lens was mostly organic matter, the Oxygen having been kept off by very
tight clay above and below the lens. There were as I recall no animal fossils, but plenty of flora, including leaves of
trees. These were Pliocene. The paper was published in Geology at the time, by Lucy McCartan and others. The
Pliocene age was consistent with what was expected from these deposits. I am sure the forests of the Eocene-
Oligocene were sufficiently different from Pliocene so as not to have fooled the paleobotanists who study this kind of
thing.
Dave (replying to the above): With regard to the dates of plant and animal fossils in pits on top of the upland deposits,
I take the position that these accumulated in local topographic lows on the undulating surface of the CB-crater ejecta
blanket (as altered by erosion) as existed long before these species were living. A captive low (like a small secondary
crater) could account for burial of an organic lens by colluvial loam.
Please understand that I understand that such arguments are hand waving – that is, they would be hand waving
were it not for all the evidence I’ve amassed that the upland deposits can’t have been emplaced by rivers, the
ubiquitous ferric oxyhydroxides that weld and penetrate the gravels have to be impact products, and three separate
facies of the upland deposits can be quantitatively and stratigraphically accounted for as jetting, interference-zone, and
excavation-flow ejecta, as per Jay Melosh’s (1989) monograph on the physics and geology of major impacts.
Dave (starting different tack): The obvious way of putting down my “heresy” would be to obtain a Miocene-or-
thereabouts radiometric age for some horizon within the Calvert, Choptank, Saint Marys, or other underlying
formation. However, to my knowledge no suitable volcanic ash or impact layers have been, or are likely to be, found
therein.
Peter: These Miocene formations are abundantly fossiliferous, and the fossil assemblages place them rock-fast in the
middle Miocene period. The fossil ages then can be converted to absolute ages by reference to the stratigraphic time
scale, which is of course always under revision, but RE the middle Miocene, the errors in the calibration via
radiometric dates of other Miocene formations where there ARE datable ash layers gives ages of the various strata that
are within a half million or a million years (due to the age range of the fossils--one would like to find microfossils with
shorter existence times but in these shallow water marine sediments, foraminifera and nanoplankton are rare.
Dave: Regarding the fossil datings in the absence of radiometrically datable ash layers in situ, I remark that as soon as
the worldwide debris layer of the Chicxulub impact was recognized, together with the evidence of Alvarez et al.
(1980) suggesting that the impact caused extinctions, geologists got real busy looking for extinctions at the boundary.
It wasn’t very long before they began to find out that, even in well preserved pelagic limestones, the existing fossil
record wasn’t of sufficiently high resolution to the determine first and last appearances needed to be sure of which
species really went extinct at the boundary and which species truly originated above the boundary. Whence the
Signor-Lipps effect. And as you yourself have alluded, the problem is immensely compounded in the matter of
shallow-water marine species in terrigenous deposits. So I contend that if one were to demand the same rigor as was
ultimately demanded of the KT-boundary community to refine/verify first and last appearances of neritic species of
the Neogene, I think it safe to say that the current data relevant to the Calvert Cliffs fossils would be found to be
lightyears from passing muster.
Peter: As for DIRECT radiometric dating of marine sediments without ash layers or lava flows etc, there IS one
way--glauconite is an authigenic mineral in the clay family (it's often grayish green) which sucks some K out of the
ambient sea water. There is room for the big Potassium ions in the holes inside the hexagonal rings or sandwiches of
Si tetrahedra. It's the K-40 that is used to get radiometric ages for the glauconite.
There is not much glauconite in the Miocene formations here (tons in the Eocene formations at depth). However,
there is a scattering of glauconite dates from our Miocene formations (I can find the refs) and they are not off by
more than 1 Ma at most from the stratigraphically correlated ages.
Dave: Regarding the radiometrically dated authigenic glauconites: By definition of authigenesis, these were formed in
place some time after the deposition of the units in which they are presently found. How would anyone know for
sure when, why, or how these glauconites crystallized in their present context? So my speculation should be as good
as anyone else’s, and I suggest that their occurrence might relate in some way to lateral seawater permeation of pre-
existing upland-deposits-capped sea cliffs during the Miocene high stand. If so, the “correct” correlation of the
glauconite age with the fossil dating could be fortuitous
Peter: I don't know what else to say. To make the observations fit your hypothesis, you are forced to add more and
more unlikely ad hoc coincidences etc, e.g. that the glauconite K40 dates only 'happen' to fit the stratigraphic ages.
Glauconite as far as I know is ONLY precipitated (if at all) from seawater on the bottom of the sea=ocean. You would
have to dig into GEOREF and find a study that shows how this clay mineral can be precipitated in the groundwater
pore space of older sediment.
Dave: I recognize full well that it would be outrageous to challenge the glauconite K40 dates in such a way if I didn’t
have exceedingly hard evidence that some of the most common clasts in the upland deposits can only have been
produced in an impact AND that the upland deposits could not have been emplaced by rivers. In any event, my model
also invokes sea water at depth (not groundwater).
Peter: As for that peat layer, it was found within, not on top of the Upland Deposits.
Dave: I have come to realize in the course of fitting the Midlothian upland deposits into my model that secondary
craters can actually be excavated in pre-emplaced interference-zone ejecta by the later-arriving excavation flow ejecta
(timing formulae right out of Melosh’s monograph). Since I interpret all of the upland gravels and at least part of the
overlying loam as interference-zone ejecta, the pristine hours-after-impact ejecta blanket would have been heavily
pocked with “Carolina bays” (exactly as is the case for the Midlothian uplands). Throughout the Oligocene and early
Miocene, these pits would have become lakes and bogs, some of which might later have been covered over with
colluvium due to wave action during the Miocene transgressions and recessions. This is not entirely hand waving,
since you have to grant me my model at least for the sake of argument (not to mention that my model is viable so far
as cratering physics is concerned). Crucial to this argument is the fact that the Carolina bays in the Midlothian
uplands are found at much higher elevations than the highest Miocene high stand and so, unlike the peat lens in PG
County, these secondary craters would never have been backfilled with silt due to action of ocean waves (thus
accounting for their present day raised-rim-crater morphology).
Peter: The Chesapeake Impact horizon in our area falls within a major hiatus between the Calvert Formation
Fairhaven Member (ca 22 Ma, containing abundant MIOCENE AGED diatoms (in fact diatomite was mined in our
county until purer deposits were found in California in 1930s), and the underlying Eocene Aquia (56 Ma at top) or in
our area younger also Eocene Nanjemoy or Piney Point (40 Ma at top) formation. The disconformity at the base of the
Miocene is exposed in some areas, e.g. on the banks of Potomac near the Rte 301 Bridge (I have visited it on a field
trip) and does have a lag deposit or mainly reworked Miocene marine vertebrate bone. If coarse ejecta from the
Chesapeake impact had been dropped in that area, they would be part of the lag deposit. The disconformity might be
in part due to the impact tsunami having stripped off older sediments, but the absence post-impact i.e. post 36-37Ma
but pre-22 Ma sediments cannot be so explained. However, the Oligocene is scarcely represented along the Atlantic
coastal plain except in offshore drillholes, where as you know impact generated glass etc has been recovered.
Dave: As for the “Chesapeake Impact horizon” in your area falling within a major hiatus, I have two observations:
(1) I do not believe that anything at all at this horizon to the landward side of the crater (e.g., near the Rte 301 bridge)
has ever been identified as ejecta, and (2) the “canonical” model tacitly assumes that all landward traces of the ejecta
blanket have been removed by erosion. So in fact, the canonical model hangs on a “dog ate my homework” excuse
for not having established the extent, nature, and stratigraphic position of the landward ejecta.
The fact is, I’ve unearthed clasts of highly diverse lithologies among the upland deposits, many of which can be
explained as impact ejecta and in no other way. In particular, I’ve shown that the ubiquitous ferric oxyhydroxides of
the upland deposits commonly comprise the matrix material of a matrix-supported breccia (which can only be of
impact origin) and penetrate quartzite pebbles and cobbles in a way contrary to prediction of the diffusion equation
(eliminating their explanation as liesegang). I and my colleagues have done an unprecedented materials-science study
of these materials. However, I’ve gotten the impression that because it wasn’t reviewed by geologists, the defenders
of the canonical model feel no need read or respond to this elaborate 20-page article. Thus, I am left as “the voice
crying in the wilderness” that the reason no ejecta is found in this tens-of-million-year hiatus is that it has been
misplaced on the stratigraphic time scale (“which is of course always under revision”)!
But there is much more reason to reject the canonical model: The Chesapeake Bay crater ejecta blanket, which I
calculated to have been originally ~50-60 m deep at the southern end of the Potomac-Patuxent peninsula and as high
as 300 m at the rim (and similarly at corresponding radii all the way into North Carolina), was in the canonical view
totally erased as the result of just ~2 Myrs sea-level regression in the latest Eocene, possibly aided by fluvial erosion
during the Oligocene low stand. But, while it appears to be true that the resurge, or tsunami, following the impact
washed much of the seaward rim back into the crater, it surely had orders of magnitude too little energy to do more
than dent the landward rim. And during the Oligocene, the rivers would have been deflected circumferentially, as I've
discussed in my manuscript, leaving the landward rim largely intact until the Neogene transgressions and regressions.
Finally, the canonical view also holds that millions of years after total removal of the ejecta blanket, the Potomac,
Rappahannock, York, and, James Rivers, by an amazingly choreographed side-cutting dance over soft sediments
never once managed to cut channels to down to bed rock while grinding up quartzite cobbles 15 times more rapidly
than the modern Rhine and Mur rivers, yet transported and deposited stupendous bed loads of coarse gravel >100 km
from the Shenandoah Valley without leaving a trail of ever-larger boulders behind—and in so doing these rivers
managed to accidentally reproduce what the Chesapeake Bay crater ejecta blanket might reasonably be supposed to
look like after partial erosion—particularly the thickening of the Bacons Castle formation as the crater rim is
approached from the outside and its draping downward just inside the rim.
In the canonical view the crater is completely buried. How then does it appear to exert structural control over
fluvial deposits supposedly emplaced tens of millions of years later? Apropos, I’ve looked at the Shirley formation as
mapped in Frye’s book and find that it too appears to be structurally controlled by the crater, both above the Suffolk
scarp and on the Delmarva Peninsula. I’d love to know more about the Shirley formation. Frye (1986) wrote: “It’s
lowest strata contain pebbles and boulders which geologists recognize as having come all the way from the Blue
Ridge.” Boulders all the way from the Blue Ridge are piled up just above the rim of a buried crater? First, rivers
don’t transport boulders. And, second, the only reason to have ever believed that they were from the Blue Ridge is
because that is the nearest location of surface outcrops of such rocks (hypothetically) transportable to their current
locations by uniformitarian processes. In fact, the Blue Ridge is partially comprised of basement rocks that might well
be similar to the basement rocks that underlaid the Mesozoic sediments in the target zone of the CB impactor. So is it
not much more plausible that the Shirley formation comprises crater ejecta including a basement-rock component?
who has been recognized by the University of Bergen, Norway, for his "international scientific role based on wide-
ranging and innovative research in the fields of marine geology and geophysics, in particular in the Norwegian-
Greenland Sea and the Arctic Ocean" and awarded an Honorary Doctorate degree by that university on August 25,
2000.
Back about that time, when we were both still working at NRL, it was Peter who first pointed out to me that the
rocks I had been studying in my neighborhood of Hollin Hills, Virginia, belong to the extensive “upland deposits” of
Maryland, Virginia, and the District of Columbia, and it was he who specifically directed me to the work of Schlee
(1957). Peter has continued to doubt my conclusions regarding their origins, but recently he agreed to discuss the
matter by e-mail:
Peter: As far as I know, not being a land geologist, not much new has been discovered in recent years--the Upland
Deposits, or whatever you want to call this unit or these units, sit stratigraphically and for the most part physically (e.
g. in Southern MD) on top of well-dated and generally pretty fossiliferous Middle and Upper Miocene shallow marine
to subtidal strata. The only way I could possibly see depositing impact breccia pebbles of ca. 35Ma age on 10-20Ma
marine sediments is for the breccia to have been FIRST deposited on the Piedmont and only THEN, much later (about
in the interval 10 to 2.75 Ma in my opinion) washed out on the Coastal Plain by the Potomac and perhaps other rivers,
to form the Upland Deposits. The Law of Stratigraphic Superposition or whatever it was called was one of the first
basic principles appreciated in the early years of modern Geology, probably by Hutton himself in late 18th century I
think.
Dave: I have been aware of, and obedient to, the stratigraphic superposition principle for 37 or 38 years – ever since
I bought and devoured Thomas Mutch’s book Geology of the Moon, which was inferring relative ages of lunar
features from sequences of overlapping crater ejecta blankets. All units underlying a given crater’s ejecta blanket are
per force older than the crater itself. So my position is that, if the “upland deposits” comprise largely pristine, un-
reworked CB-crater ejecta, then the fossils in the underlying formations are older than 35.5 Ma. And in my web-
published manuscript I present a multiplicity of reasons for why the upland deposits are almost certainly primary CB-
crater ejecta.
Peter: There are not many dates from the Upland Deposits, but there ARE some. Occasional land mammal teeth, for
example. Also, in the 1990s some time a bulldozer was alert enough to tell geologists about a black lens he was
digging into in Prince Georges County. This lens was mostly organic matter, the Oxygen having been kept off by very
tight clay above and below the lens. There were as I recall no animal fossils, but plenty of flora, including leaves of
trees. These were Pliocene. The paper was published in Geology at the time, by Lucy McCartan and others. The
Pliocene age was consistent with what was expected from these deposits. I am sure the forests of the Eocene-
Oligocene were sufficiently different from Pliocene so as not to have fooled the paleobotanists who study this kind of
thing.
Dave (replying to the above): With regard to the dates of plant and animal fossils in pits on top of the upland deposits,
I take the position that these accumulated in local topographic lows on the undulating surface of the CB-crater ejecta
blanket (as altered by erosion) as existed long before these species were living. A captive low (like a small secondary
crater) could account for burial of an organic lens by colluvial loam.
Please understand that I understand that such arguments are hand waving – that is, they would be hand waving
were it not for all the evidence I’ve amassed that the upland deposits can’t have been emplaced by rivers, the
ubiquitous ferric oxyhydroxides that weld and penetrate the gravels have to be impact products, and three separate
facies of the upland deposits can be quantitatively and stratigraphically accounted for as jetting, interference-zone, and
excavation-flow ejecta, as per Jay Melosh’s (1989) monograph on the physics and geology of major impacts.
Dave (starting different tack): The obvious way of putting down my “heresy” would be to obtain a Miocene-or-
thereabouts radiometric age for some horizon within the Calvert, Choptank, Saint Marys, or other underlying
formation. However, to my knowledge no suitable volcanic ash or impact layers have been, or are likely to be, found
therein.
Peter: These Miocene formations are abundantly fossiliferous, and the fossil assemblages place them rock-fast in the
middle Miocene period. The fossil ages then can be converted to absolute ages by reference to the stratigraphic time
scale, which is of course always under revision, but RE the middle Miocene, the errors in the calibration via
radiometric dates of other Miocene formations where there ARE datable ash layers gives ages of the various strata that
are within a half million or a million years (due to the age range of the fossils--one would like to find microfossils with
shorter existence times but in these shallow water marine sediments, foraminifera and nanoplankton are rare.
Dave: Regarding the fossil datings in the absence of radiometrically datable ash layers in situ, I remark that as soon as
the worldwide debris layer of the Chicxulub impact was recognized, together with the evidence of Alvarez et al.
(1980) suggesting that the impact caused extinctions, geologists got real busy looking for extinctions at the boundary.
It wasn’t very long before they began to find out that, even in well preserved pelagic limestones, the existing fossil
record wasn’t of sufficiently high resolution to the determine first and last appearances needed to be sure of which
species really went extinct at the boundary and which species truly originated above the boundary. Whence the
Signor-Lipps effect. And as you yourself have alluded, the problem is immensely compounded in the matter of
shallow-water marine species in terrigenous deposits. So I contend that if one were to demand the same rigor as was
ultimately demanded of the KT-boundary community to refine/verify first and last appearances of neritic species of
the Neogene, I think it safe to say that the current data relevant to the Calvert Cliffs fossils would be found to be
lightyears from passing muster.
Peter: As for DIRECT radiometric dating of marine sediments without ash layers or lava flows etc, there IS one
way--glauconite is an authigenic mineral in the clay family (it's often grayish green) which sucks some K out of the
ambient sea water. There is room for the big Potassium ions in the holes inside the hexagonal rings or sandwiches of
Si tetrahedra. It's the K-40 that is used to get radiometric ages for the glauconite.
There is not much glauconite in the Miocene formations here (tons in the Eocene formations at depth). However,
there is a scattering of glauconite dates from our Miocene formations (I can find the refs) and they are not off by
more than 1 Ma at most from the stratigraphically correlated ages.
Dave: Regarding the radiometrically dated authigenic glauconites: By definition of authigenesis, these were formed in
place some time after the deposition of the units in which they are presently found. How would anyone know for
sure when, why, or how these glauconites crystallized in their present context? So my speculation should be as good
as anyone else’s, and I suggest that their occurrence might relate in some way to lateral seawater permeation of pre-
existing upland-deposits-capped sea cliffs during the Miocene high stand. If so, the “correct” correlation of the
glauconite age with the fossil dating could be fortuitous
Peter: I don't know what else to say. To make the observations fit your hypothesis, you are forced to add more and
more unlikely ad hoc coincidences etc, e.g. that the glauconite K40 dates only 'happen' to fit the stratigraphic ages.
Glauconite as far as I know is ONLY precipitated (if at all) from seawater on the bottom of the sea=ocean. You would
have to dig into GEOREF and find a study that shows how this clay mineral can be precipitated in the groundwater
pore space of older sediment.
Dave: I recognize full well that it would be outrageous to challenge the glauconite K40 dates in such a way if I didn’t
have exceedingly hard evidence that some of the most common clasts in the upland deposits can only have been
produced in an impact AND that the upland deposits could not have been emplaced by rivers. In any event, my model
also invokes sea water at depth (not groundwater).
Peter: As for that peat layer, it was found within, not on top of the Upland Deposits.
Dave: I have come to realize in the course of fitting the Midlothian upland deposits into my model that secondary
craters can actually be excavated in pre-emplaced interference-zone ejecta by the later-arriving excavation flow ejecta
(timing formulae right out of Melosh’s monograph). Since I interpret all of the upland gravels and at least part of the
overlying loam as interference-zone ejecta, the pristine hours-after-impact ejecta blanket would have been heavily
pocked with “Carolina bays” (exactly as is the case for the Midlothian uplands). Throughout the Oligocene and early
Miocene, these pits would have become lakes and bogs, some of which might later have been covered over with
colluvium due to wave action during the Miocene transgressions and recessions. This is not entirely hand waving,
since you have to grant me my model at least for the sake of argument (not to mention that my model is viable so far
as cratering physics is concerned). Crucial to this argument is the fact that the Carolina bays in the Midlothian
uplands are found at much higher elevations than the highest Miocene high stand and so, unlike the peat lens in PG
County, these secondary craters would never have been backfilled with silt due to action of ocean waves (thus
accounting for their present day raised-rim-crater morphology).
Peter: The Chesapeake Impact horizon in our area falls within a major hiatus between the Calvert Formation
Fairhaven Member (ca 22 Ma, containing abundant MIOCENE AGED diatoms (in fact diatomite was mined in our
county until purer deposits were found in California in 1930s), and the underlying Eocene Aquia (56 Ma at top) or in
our area younger also Eocene Nanjemoy or Piney Point (40 Ma at top) formation. The disconformity at the base of the
Miocene is exposed in some areas, e.g. on the banks of Potomac near the Rte 301 Bridge (I have visited it on a field
trip) and does have a lag deposit or mainly reworked Miocene marine vertebrate bone. If coarse ejecta from the
Chesapeake impact had been dropped in that area, they would be part of the lag deposit. The disconformity might be
in part due to the impact tsunami having stripped off older sediments, but the absence post-impact i.e. post 36-37Ma
but pre-22 Ma sediments cannot be so explained. However, the Oligocene is scarcely represented along the Atlantic
coastal plain except in offshore drillholes, where as you know impact generated glass etc has been recovered.
Dave: As for the “Chesapeake Impact horizon” in your area falling within a major hiatus, I have two observations:
(1) I do not believe that anything at all at this horizon to the landward side of the crater (e.g., near the Rte 301 bridge)
has ever been identified as ejecta, and (2) the “canonical” model tacitly assumes that all landward traces of the ejecta
blanket have been removed by erosion. So in fact, the canonical model hangs on a “dog ate my homework” excuse
for not having established the extent, nature, and stratigraphic position of the landward ejecta.
The fact is, I’ve unearthed clasts of highly diverse lithologies among the upland deposits, many of which can be
explained as impact ejecta and in no other way. In particular, I’ve shown that the ubiquitous ferric oxyhydroxides of
the upland deposits commonly comprise the matrix material of a matrix-supported breccia (which can only be of
impact origin) and penetrate quartzite pebbles and cobbles in a way contrary to prediction of the diffusion equation
(eliminating their explanation as liesegang). I and my colleagues have done an unprecedented materials-science study
of these materials. However, I’ve gotten the impression that because it wasn’t reviewed by geologists, the defenders
of the canonical model feel no need read or respond to this elaborate 20-page article. Thus, I am left as “the voice
crying in the wilderness” that the reason no ejecta is found in this tens-of-million-year hiatus is that it has been
misplaced on the stratigraphic time scale (“which is of course always under revision”)!
But there is much more reason to reject the canonical model: The Chesapeake Bay crater ejecta blanket, which I
calculated to have been originally ~50-60 m deep at the southern end of the Potomac-Patuxent peninsula and as high
as 300 m at the rim (and similarly at corresponding radii all the way into North Carolina), was in the canonical view
totally erased as the result of just ~2 Myrs sea-level regression in the latest Eocene, possibly aided by fluvial erosion
during the Oligocene low stand. But, while it appears to be true that the resurge, or tsunami, following the impact
washed much of the seaward rim back into the crater, it surely had orders of magnitude too little energy to do more
than dent the landward rim. And during the Oligocene, the rivers would have been deflected circumferentially, as I've
discussed in my manuscript, leaving the landward rim largely intact until the Neogene transgressions and regressions.
Finally, the canonical view also holds that millions of years after total removal of the ejecta blanket, the Potomac,
Rappahannock, York, and, James Rivers, by an amazingly choreographed side-cutting dance over soft sediments
never once managed to cut channels to down to bed rock while grinding up quartzite cobbles 15 times more rapidly
than the modern Rhine and Mur rivers, yet transported and deposited stupendous bed loads of coarse gravel >100 km
from the Shenandoah Valley without leaving a trail of ever-larger boulders behind—and in so doing these rivers
managed to accidentally reproduce what the Chesapeake Bay crater ejecta blanket might reasonably be supposed to
look like after partial erosion—particularly the thickening of the Bacons Castle formation as the crater rim is
approached from the outside and its draping downward just inside the rim.
In the canonical view the crater is completely buried. How then does it appear to exert structural control over
fluvial deposits supposedly emplaced tens of millions of years later? Apropos, I’ve looked at the Shirley formation as
mapped in Frye’s book and find that it too appears to be structurally controlled by the crater, both above the Suffolk
scarp and on the Delmarva Peninsula. I’d love to know more about the Shirley formation. Frye (1986) wrote: “It’s
lowest strata contain pebbles and boulders which geologists recognize as having come all the way from the Blue
Ridge.” Boulders all the way from the Blue Ridge are piled up just above the rim of a buried crater? First, rivers
don’t transport boulders. And, second, the only reason to have ever believed that they were from the Blue Ridge is
because that is the nearest location of surface outcrops of such rocks (hypothetically) transportable to their current
locations by uniformitarian processes. In fact, the Blue Ridge is partially comprised of basement rocks that might well
be similar to the basement rocks that underlaid the Mesozoic sediments in the target zone of the CB impactor. So is it
not much more plausible that the Shirley formation comprises crater ejecta including a basement-rock component?