Hi Allen
I believe we progress in understanding out positions.
Allen Roy wrote:
> 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.
Perhaps I did not make myself clear. It is technically an assumption,
but it is such a fundamental assumption common to all science that when
interpreting geological environments it can taken as a given. A
statement like "different rocks have different formative environments"
is no different to saying that "organisms with different characteristics
belong to different taxa". In the same way the converse of these
statements is also true "organisms with the same characteristics belong
to the same taxon" and sedimentary rocks with the same characteristics
were formed in the same formative environment". If you do not hold
this to be true then you will have to give some very strong reasons why
it is not.
> 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.
Metaphors are always misleading of course, and keys and yardsticks may
be as misleading as any others. However, understanding present
geological processes does give as clues to the past, whether ancient
deposits are similar to, or different from, modern deposits. The degree
to which ancient deposits resemble modern ones gives us an idea of the
degree to which ancient processes to similar to present processes.
> 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.....
>
>
> This is just what I have been doing in trying to develop and explain
> my Flood catastrophe model based on Asteroid impacts.
>
You can't ascribe the entire geological record to impact processes - at
least not on this planet - unless you discount all the rock evidence for
non impact processes and the criteria we have discussed for recognising
depositional processes. If you do discount them, then you have no
evidence to say that there were impact processes, because the evidence
you cite in favour of would be meaningless.
We know quite a bit about impact deposits. The impact in Mexico at the
end of the Cretaceous had world wide results, but the deposits are only
cm thick globally, where [preserved. They are only a few metres thick
even quite close to ground zero. The same with the Acraman impact in
South Australia. It's deposits (which I have seen) are widespread
(across at least a quarter of the continent) but are only cm thick.
Then there are the various tektite fields. Impact deposits have some
specific characteristics, which are relatively easy to recognise. The
geological record does contain evidence of impact related deposits, but
they are very thin and do not comprise more than a tiny fraction of the
record.
> 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 processes are different, but the environment (deep water) remains
the same. Incidentally turbidite deposits typically consists of two
components. The actual turbidite deposit itself, deposited in minutes
(coarse grained) to days (fine-grained), and the muds in between them ,
that were deposited very slowly by hemipelagic fallout.
God Bless
Jonathan
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Hi Allen
I believe we progress in understanding out positions.
Allen Roy wrote:
From: Jonathan Clarke <jdac@alphalink.com.au>Perhaps I did not make myself clear. It is technically an assumption, but it is such a fundamental assumption common to all science that when interpreting geological environments it can taken as a given. A statement like "different rocks have different formative environments" is no different to saying that "organisms with different characteristics belong to different taxa". In the same way the converse of these statements is also true "organisms with the same characteristics belong to the same taxon" and sedimentary rocks with the same characteristics were formed in the same formative environment". If you do not hold this to be true then you will have to give some very strong reasons why it is not.
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.Metaphors are always misleading of course, and keys and yardsticks may be as misleading as any others. However, understanding present geological processes does give as clues to the past, whether ancient deposits are similar to, or different from, modern deposits. The degree to which ancient deposits resemble modern ones gives us an idea of the degree to which ancient processes to similar to present processes.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.....You can't ascribe the entire geological record to impact processes - at least not on this planet - unless you discount all the rock evidence for non impact processes and the criteria we have discussed for recognising depositional processes. If you do discount them, then you have no evidence to say that there were impact processes, because the evidence you cite in favour of would be meaningless.
This is just what I have been doing in trying to develop and explain my Flood catastrophe model based on Asteroid impacts.
We know quite a bit about impact deposits. The impact in Mexico at the end of the Cretaceous had world wide results, but the deposits are only cm thick globally, where [preserved. They are only a few metres thick even quite close to ground zero. The same with the Acraman impact in South Australia. It's deposits (which I have seen) are widespread (across at least a quarter of the continent) but are only cm thick. Then there are the various tektite fields. Impact deposits have some specific characteristics, which are relatively easy to recognise. The geological record does contain evidence of impact related deposits, but they are very thin and do not comprise more than a tiny fraction of the record.
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.The processes are different, but the environment (deep water) remains the same. Incidentally turbidite deposits typically consists of two components. The actual turbidite deposit itself, deposited in minutes (coarse grained) to days (fine-grained), and the muds in between them , that were deposited very slowly by hemipelagic fallout.It seems to me that the differences in process is quite significant. One is slow the other is catastrophic.
God Bless
Jonathan
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