Hi Bill
Bill Payne wrote:
> On Tue, 09 Jan 2001 16:22:51 +1100 Jonathan Clarke
> <jdac@alphalink.com.au> writes:
>
> Having fought through the coal-origin issue and realizing that obvious
> empirical data is being unintentionally overlooked because it doesn't
> allow conformance with the reigning uniformatarian paradigm, I would have
> to say that your conclusion of subaerial dissolution is suspect (by
> analogy with conclusions about the origin of coal ). I would have to
> study the outcrops and literature for myself, but just at this distance I
> am thinking that "extremely planar" is incompatible with "subaerial
> dissolution." I am not saying that you are not right, just that I am
> skeptical.
Sigh. Bill, you shouldn't just dismiss other people's views that you don't
like by saying "empirical data is being unintentionally overlooked because it
doesn't allow conformance with the reigning uniformitarian paradigm".
Paradigms are important, but they are not all powerful. Otherwise nobody
would ever change their mind. And nobody would argue! No present day
geologist I know is a uniformitarian senso Lyell. There is far more kudos
for a scientist who overthrows an existing paradigm than one who simply
reinforces an old one. So don't accuse people willy nilly of conforming to an
existing paradigm, especially when it is you who denies very strong empirical
evidence, which I have outlined previously and again below, that subaerial
exposure surfaces are a real part of the geological record.
Personally, I have no vested interested in the issue except where the data
leads. I have interpreted other people's karst deposits in the Cambrian of
South Australia as submarine cements, and the other way roundel, like in the
Miocene of Victoria. In other cases I have agreed completely with previous
interpretations, for instance in the Eocene of Western Australia or the
Miocene of South Australia. A hardground is just as interesting
scientifically as a karst surface, a marine erosion surface as important as a
subaerial one.
These features are common. I have seen personally convincing palaeo karst
horizons in rocks of Early Proterozoic, Cambrian, Silurian, Devonian, Miocene
and Pliocene age. So convincing that to say otherwise is to argue that black
is white, just to be bloody minded. I have also seen other surfaces which
are much more equivocal. This is to be expected.
"Extremely planar" is not incompatible with "subaerial dissolution". Just
three examples: the Nullarbor plain in southern Australia is extremely flat -
just a few m of relief over almost a 1000 km E-W, but is developed on Miocene
limestones. The land of the onshore Canarvon Basin in Western Australia is
almost as flat, and developed on Cretaceous limestones. The upper surface of
the Late Pliocene Roe Calcarenite west of Eucla has a relief of 1-2 m for
100's of km.
You can be as sceptical as you like but if you want advance our discussion
you need to demonstrate how the palaeokarst explanation does not adequately
explain these features. Then you should come up with an interpretation for
the palaeokarst which:
1) Explains the morphological features better than the palaeo karst model.
These include a wide range of large, medium, small and microscopic scale
morphologies that are identical to those found on modern exposed karst
surfaces. Examples include caves, cavities and vugs, towers, pinnacles, and
dolines, klints and grikes, rillenkarren, rundkarren, trittenkarren, and
kamenitzas, calcretes, bauxites, palaeosols, and surficial megabreccias.
2) Explains the stratigraphic features better than the palaeokarst model.
These features are developed only on stratigraphic breaks. The karst
features die out downwards away from the surface. They are associated with
palaeo-topographic highs, rather than lows. Typically, they terminate upward
shallowing successions and are buried by deeper water sediments. If marine,
the burying sediments often contain evidence of encrusting organisms.
3) Explains the geochemical and mineralological features better than the
palaeokarst model. These include evidence of oxidation of organic matter and
sulphides, enrichment in inmobile elements, accululation of insoluble
minerals and rock components (such as chert, quartz, and dolomite) derived
from the underlying lithology. Many karst surfaces have oxygen and carbon
isotope signatures indicating exposure to rain water, not hydrothermal,
basinal, or marine water, that disappear downwards.
4) Explains the textural features better than the palaeokarst model. The
textures include meniscus and stalactitic cements, dissolution of aragonitic,
internal sediments, and speleothems in larger cavities. Soil fabrics are
sometimes preserved in the topmost part of the palaeokarst profile and in the
immediately overlying sediments. Where the appropriate geochemical signatures
are preserved, they are associated with these cements.
5) Occurrence of younger fossils within the palaeokarst features. In some
cases the fossils are the same as those found in the immediately overlying
sediment, in some cases they belong to much younger epochs. Then:
A) Use your model to make predictions as to what the geological record should
look like .
B) Demonstrate that the predictions are fulfilled, and better than by
alternatives.
If you do this and convince others you will be one of the greatest carbonate
petrologists of the century. You will join the illustrious company of
Sorby, Bathurst, James, and Folk.
I strongly urge you to read the literature on palaeokarst. Keith has given
you some references, so have I. The compilations of Bosak et al (1989) and
James and Choquette (1988) are an important place to start. They are written
from European and North American perspectives, respectively.
BOSAK, P., FORD, D. C., GLAZEK, J. and HORACEK 1989 (eds.). Paleokarst. A
systematic and regional review. Elsevier and Academia, Amsterdam.
JAMES, N. P. and CHOQUETTE, P. W. 1988 (eds.). Paleokarst.
Springer-Verlag, New York.
Respectfully, with apologies, if I have come over a bit strong,
Jon
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