------=_NextPart_000_01BEADBF.A5EA3120
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
From: Jonathan Clarke <jdac@alphalink.com.au>
To: Allen Roy <allen@infomagic.com>
Allen Roy wrote:
It seems to me that it can be said like this:
1. A Sedimentary Deposition implies a unique Sedimentary Environment,
or SD --> SE.
2. We are able to find Sedimentary Depositions which have similar
lithofacies to Sedimentary Rocks,
or SD ~ SR.
3. We assume that a Sedimentary Rock implies a unique Sedimentary
Environment prior to litification,
or SR --> SRE.
4. Thus we conclude that there existed a Sedimentary Rock Environment that
was similar to a Sedimentary Environment of today,
or SRE ~ SE.
I would say that 1 and 3 are givens, and that 2 is an observation. When 2
is observed then 4 applies. Two is not always observed however, see my
comments below.
I prefer to leave 3 as an assumption rather than a given. We weren't there
to observe that for sure.
Often there is very good correspondence with what we see in modern
sediments and what we find in ancient ones. However as Paul Wright so aptly
said (Wright, V P 1994. Early Carboniferous carbonate systems: an
alternative to the Cainozoic paradigm. Sedimentary Geology 93: 1-5.),
rather than an exact guide to the past, the present is a yardstick with
which we compare the past, so see the ways in which past processes
conformed and differed to the present. I certainly think that the yarstick
is a much better metaphor than that of the key in how we should use the
present to understand the past.
I don't really care for the yardstick metaphor either. It implies that the
present is the standard by which the past must be measured. I prefer the
idea the present may present us with clues to the past. I'm not sure what
kind of metaphor to use.
In addition there are many present processes which are difficult to study
but which are inferred to have formed ancient deposits. It is very
difficult to study what is going on underneath a continental ice sheet, or
in a major pyroclastic eruption. Other processes could happen today but
are so rare that we have not observed them, such as asteroid impacts,
large scale cauldron subsidence, or major collapse of a carbonate
continental margin. Perhaps it is just as well.....
I am glad you made this statement and not I. I would include the Flood
catastrophe in this list.
There are also many ancient sediments which have no direct counterpart.
Examples included banded ironstones, early mimetic dolostones of the
Proterozoic, and widespread cementstones of the Proterozoic, the muddy
limestones of the Palaeozoic, etc. In your terminology then
5. SR =/= modern SD (mSD)
therefore
6. ancient SD (aSD) =/= mSD
and thus
7. aSE =/= mSE
Yeah, I agree. (it took me awhile to understand that =/= meant not equal.
:)
For these cases we need to rely of theoretical studies, laboratory
experiments, and more general analogues, often from very spatially
restricted environments.
This is just what I have been doing in trying to develop and explain my
Flood catastrophe model based on Asteroid impacts.
I have not read the early turbidite literature, so I am not familiar with
previous understandings on the depositional environments of successions
that were considered to be turbidites. However I suspect that they were
thought to have been laid down in relatively deep water. Since thick
turbidite successions are also thought to be formed and preserved only in
deep water (below fair weather wave base), the overall environments did not
change. What the turbidite model did do was provide a process for the
deposition of the sediments, a process which previously had not been
recognised.
It seems to me that the differences in process is quite significant. One
is slow the other is catastrophic.
The vast majority of sedimentary environments studied today and applied to
sedimentary rocks also apply the same rates of deposition to the rocks.
Thus, by extension, the shear quantity of sedimentary rocks implies a
record of long ages.
I would agree. This is especially the case where the sediments have to be
grown by organisms, such as fossil reefs, or sediments composed of
organisms that have grown elsewhere and transported in. Other examples are
thick acculations of fine-grained laminated shales, varves, units such as
the Green River Formation, thick cyclic evaporite deposits..... the list
goes on
These, of course, are being studied by Flood catastrophists to find other
explanations for formations interpreted as fossil reefs and such.
In addition there are the cases where there is good evidence of time breaks
in between sedimentary or volcanic strata, such as unconformities, ancient
soil horizons, buried karst surfaces, hardgrounds with borings,
encrustations of iron oxides, phosphate, glaucony, etc.
All these are also being studied to find interpretations from a
catastrophic viewpoint.
However, we must be careful not to exaggerate the recentness of acceptance
of catastrophic processes. Thick pyroclastic deposits have always been
recognised as indicating large eruptions, meteorite impacts have been
generally recognised from the 60's. The catastrophic flooding explanation
for the Channelled Scablands I think was widely accepted from the early
70's. The catastrophic model for the KT boundary was recognised as
conceptually possible from the early 80's, and so forth.
When I mentioned recent, I meant within the last 50 years or so.
Allen
------=_NextPart_000_01BEADBF.A5EA3120
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
From: Jonathan Clarke <jdac@alphalink.com.au>
To: Allen Roy <allen@infomagic.com>
Allen Roy wrote:
It seems to me that it can be said like this:
1. A Sedimentary Deposition implies a =
unique Sedimentary Environment,
=
or SD --> SE.
2. We are able to find Sedimentary Depositions which have =
similar lithofacies to Sedimentary Rocks,
or SD ~ SR.
3. We assume that a Sedimentary Rock implies a unique =
Sedimentary Environment prior to litification,
or SR --> SRE. =
4. Thus we conclude that there existed a Sedimentary =
Rock Environment that was similar to a Sedimentary Environment of =
today,
or =
SRE ~ SE.
I would say that 1 and 3 are givens, and that 2 is an observation. =
When 2 is observed then 4 applies. Two is not always observed =
however, see my comments below.
I prefer to leave =
3 as an assumption rather than a given. We weren't there to =
observe that for sure.
Often there is very =
good correspondence with what we see in modern sediments and what we =
find in ancient ones. However as Paul Wright so aptly said (Wright, V P =
1994. Early Carboniferous carbonate systems: an alternative =
to the Cainozoic paradigm. Sedimentary Geology 93: 1-5.), rather =
than an exact guide to the past, the present is a yardstick with which =
we compare the past, so see the ways in which past processes conformed =
and differed to the present. I certainly think that the yarstick is a =
much better metaphor than that of the key in how we should use the =
present to understand the past.
I don't really =
care for the yardstick metaphor either. It implies that the =
present is the standard by which the past must be =
measured. I prefer the idea the present may present us with =
clues to the past. I'm not sure what kind of metaphor =
to use.
In addition there are many present =
processes which are difficult to study but which are inferred to have =
formed ancient deposits. It is very difficult to study what is =
going on underneath a continental ice sheet, or in a major pyroclastic =
eruption. Other processes could happen today but are so rare =
that we have not observed them, such as asteroid impacts, large =
scale cauldron subsidence, or major collapse of a carbonate continental =
margin. Perhaps it is just as well.....
I =
am glad you made this statement and not I. I would include the =
Flood catastrophe in this list.
There are also =
many ancient sediments which have no direct counterpart. Examples =
included banded ironstones, early mimetic dolostones of the Proterozoic, =
and widespread cementstones of the Proterozoic, the muddy limestones of =
the Palaeozoic, etc. In your terminology then
5. SR =3D/=3D =
modern SD (mSD)
therefore
6. ancient SD (aSD) =3D/=3D =
mSD
and thus
7. aSE =3D/=3D mSE
Yeah, I agree. (it took me awhile to understand that =
=3D/=3D meant not equal. :)
For =
these cases we need to rely of theoretical studies, laboratory =
experiments, and more general analogues, often from very spatially =
restricted environments.
This is just =
what I have been doing in trying to develop and explain my Flood =
catastrophe model based on Asteroid impacts.
I =
have not read the early turbidite literature, so I am not familiar with =
previous understandings on the depositional environments of successions =
that were considered to be turbidites. However I suspect that they =
were thought to have been laid down in relatively deep water. =
Since thick turbidite successions are also thought to be formed and =
preserved only in deep water (below fair weather wave base), the overall =
environments did not change. What the turbidite model did do was =
provide a process for the deposition of the sediments, a process which =
previously had not been recognised.
It seems to =
me that the differences in process is quite significant. One is =
slow the other is catastrophic.
The vast majority of sedimentary environments studied = today and applied to sedimentary rocks also apply the same rates of = deposition to the rocks. Thus, by extension, the shear quantity of = sedimentary rocks implies a record of long ages.
I would agree. This is especially the case where the sediments =
have to be grown by organisms, such as fossil reefs, or sediments =
composed of organisms that have grown elsewhere and transported in. =
Other examples are thick acculations of fine-grained laminated shales, =
varves, units such as the Green River Formation, thick cyclic evaporite =
deposits..... the list goes on
These, of course, =
are being studied by Flood catastrophists to find other explanations for =
formations interpreted as fossil reefs and such.
In addition there are the cases where there is good evidence of =
time breaks in between sedimentary or volcanic strata, such as =
unconformities, ancient soil horizons, buried karst surfaces, =
hardgrounds with borings, encrustations of iron oxides, phosphate, =
glaucony, etc.
All these are also being studied to =
find interpretations from a catastrophic viewpoint.
However, we must be careful not to exaggerate the =
recentness of acceptance of catastrophic processes. Thick pyroclastic =
deposits have always been recognised as indicating large eruptions, =
meteorite impacts have been generally recognised from the 60's. =
The catastrophic flooding explanation for the Channelled Scablands =
I think was widely accepted from the early 70's. The catastrophic model =
for the KT boundary was recognised as conceptually possible from the =
early 80's, and so forth.
When I mentioned =
recent, I meant within the last 50 years or so.
Allen