David J. Tyler on 2/2/98 7:07 AM wrote:
>The marks of uniformitarian thinking are clearly seen in the
>literature on carbonate sedimentology. Traditional ideas are
>well-established and remarkably resistant to revision. Yet,
>as Braithwaite has shown, these ideas have been positively
>harmful to science. Interpretations have not followed careful
>descriptions, and modern analogues have been assumed rather
>than tested. As a consequence, structures exist in the rock
>record which have yet to be properly studied and identified.
>
I have to disagree with David about this. Uniformitarian ideas have not
been "positively harmful" to science in general, but on the contrary
highly beneficial. And Braithwaite, in particular, was not challenging
uniformitarianism, but rather the careless or imprecise use of scientific
terminology leading to misinterpretation and misunderstanding. Indeed,
scientific interpretations of ancient carbonate buildups _have_ followed
careful descriptions, and modern analogues have _not_ been assumed rather
than tested, and this was as true in 1972 when Braithwaite wrote as it is
today. Of course, _some_ geologists may have been guilty of this, but
their example does not represent the history of carbonate research as I
know it.
>Non-uniformitarian thinking has proved to be quite fruitful in
>other areas of geology. There is no reason to think that
>carbonate sedimentology will be any different. However,
>resistance to non-uniformitarian ideas is very strong, as the
>in situ accumulation of carbonate sediments is almost
>unquestioned.
A rigid adherence to a certain type of mythological uniformitarianism (as
in the geological resistence to a giant flood creating the channeled
scablands, or a giant meteorite impact causing the terminal Cretaceous
mass extinction) has indeed put up roadblocks to progress, but in general
uniformitarian thinking finally allowed geology to become a modern
science. I don't know what you imply by "non-uniformitarian thinking,"
but if you mean catastrophism, then I must disagree. The recognition, in
the early nineteenth century, that geological processes have been
generally (not exactly) uniform through time led to widespread acceptance
of the view that modern geological processes could be used to explain
past geological events without invoking various semi-mystical,
supernatural, and fantastic global cataclysms. This is still the view
that geologists have today; giant local floods and giant meteorite
impacts have now been fully incorporated into our planet's uniformitarian
framework (i.e. there are different degrees or intensities of flooding
and meteorite impact--some small, some big, some really big). As I'm sure
you will agree, the undoubted occurrence of geological catastrophes, both
local and global, does not validate adopting a doctrine of catastrophism;
such an explanation would require much more justification than that.
Geologists do indeed think that carbonate sediments are produced in their
environment of deposition (in situ). There are many good reasons for
this, not just a uniformitarian worldview. Furthermore, some
allochthonous (transported) carbonate deposits have been recognized in
the statigraphic record--they form under specific circumstances, such as
fore-reef talus deposits.
>CHANGING PERSPECTIVES ON FOSSIL REEFS
>
>David J. Tyler
>
>Modern carbonate reefs have distinctive morphologies and
>ecologies which can be described and understood. Their
>distinctive characteristics are not difficult to identify.
>However, these characteristics are frequently lacking in
>ancient facies assemblies which have been regarded as reefs.
>[much snipped]
>Despite this commendable, although not entirely satisfactory,
>attempt to introduce descriptive, rather than generic
>terminology, a large number of geologists happily use
>"bioherm" and "reef" as synonyms. Forty years after Cummings,
>Braithwaite could write:
> "Dissention and, indeed, confusion have been the
> hallmarks of studies of fossil reefs almost since their
> inception." (p.1104)
>
>"Carbonate mound-like features or bioherms are well-known in
>the ancient record. Many of them contain abundant organic
>remains. Closer inspection of many of these ancient carbonate
>"reefs" reveals that they are composed largely of carbonate
>mud with the larger skeletal particles "floating" within the
>mud matrix.. . . .Conclusive evidence for a rigid organic framework does not
>exist in most of the ancient carbonate mounds. In this sense
>they are remarkably different from modern coral-algal reefs."
>Blatt, H., G. Middlton and R. Murray. Origin of Sedimentary
>Rocks. Englewood Cliffs: Prentice-Hall. 1972. (p.410,412).
>
>Four characteristics of modern reefs may be identified.
>
>(i) RELIEF.
>
>(ii) RIGID FRAMEWORK.
>
>(iii) VARIATION IN PHYSICOCHEMICAL ENVIRONMENT.
>
>(iv) ZONATION OF ORGANISMS.
>
>These four characteristics are all found in the different
>types of modern reef. If the word is to retain its meaning,
>it must not be used indiscriminately.
>
All this is true. Organic carbonate buildups prior to the Cenozoic are
quite different from the coral-coralline algae framework reefs such as
those that exist today. They are composed of a variety of different
marine invertebrates, consisting of either carbonate mud with skeletal
fragments as a minor constitutent or of a huge accumulation of cemented
bioclasts. In most cases, however, these buildups had topographic relief,
showed organic zonation, and undoubtedly modified the physicochemical
environment--that is, they met three of the four requirements, all except
the rigid framework provided by the coralgal constituents.
Many geologists call any organic carbonate buildup that has some
topographic expression a "reef." This was especially true in the
petroleum industry and still is today. As long as everyone knows that by
"reef" one means only an organic topographic buildup, there is no
problem. But some geologists in the petroleum industry also inferred the
presence of original framework porosity in these "reefs" for petroleum
exploration purposes, where none ever existed (most porosity in
subsurface organic buildups is due to secondary leaching during subaerial
exposure). So in the late 1960s and early 70s, geologists--such as
Braithwaite--who specialized in reefs and carbonate buildups, began to
emphasize that geologists should make interpretations of ancient "reefs"
only after a reliable description, something that has always been a good
idea. These specialists recommended that the word "reef" be restricted to
buildups similar to Cenozoic tropical framework reefs, and that other
"reefs" be called organic buildups, bioherms, or something similar.
The problem here was not a rigid reliance on uniformitarianism, but the
different meanings of the word "reef." True, some geologists evaluated
fossil reefs on the basis of what they had learned about living reefs.
This error was not duplicated by research geologists who had more
extensive knowledge, and was therefore never a problem in the scientific
literature. It was a problem, however, in the petroleum industry, where
geologists expected to find abundant porosity whenever they found
subsurface reefs. Sometimes these "reefs" had porosity, sometimes not,
but the expectation of primary porosity was misguided.
>The proposal of Braithwaite, which is supported by the writer,
>is that the characteristics of modern reefs must be regarded
>as definitive for all structures described by the word "reef".
> "Unless geologists provide adequate descriptions,
> followed by interpretations, we can look forward only to
> further years of dispute. The recent "reef" is the only
> model that can be used for structures which, by the use
> of this word, are being gauged against it." (p.1113)
>The proposal is, essentially, a request for a more rigorous
>application of modern analogues, and for the rejection of
>loose terminology which promotes the illusion of familiarity
>with the calcareous body under investigation.
>
Although this proposal which you support is good, it cannot be rigorously
implemented. I once thought as you did, but eventually changed my mind. I
say let geologists use the word "reef" in whatever way they want, as long
as they have a common understanding in context. For example, as you
mentioned, mariners have used the word "reef" for centuries to refer to
underwater hazards to navigation (the Exxon Valdez hit a "reef" made of
igneous rock in Alaska). Surely you don't mean to take that usage away.
We should correctly use the phrase "organic reef" to refer to living
tropical coralgal reefs. Out of long habit and experience, I usually
refer to fossil "reefs," such as the Permian Reef of West Texas or the
Silurian reefs of Indiana and Illinois, as organic or carbonate buildups,
but when geologists call these things fossil "reefs," I know what they
mean, and it doesn't bother me.
We should, of course, define our terms if we use them formally in the
scientific literature, or if we wish to restrict their meaning. And I can
hardly deny that we should reject things which promote the illusion of
false familiarity of the carbonate body under investigation. Sometimes
the word "reef" is one of these, sometimes not, so "description, followed
by interpretation" will always be necessary. I just can't agree with you
that the lack of this has been a general problem in the geological
literature, however.
>
>[Tyler] I am happy to describe myself as an actualist. I don't think I have
>indicated that "I don't want to believe in it". What I did say was:
>> >As an aside, actualism is a word which can mean different things
>> >to different people. The neo-catastrophists regard themseles as
>> >actualists but not uniformitarianists. So, your treating these
>> >words as synonyms is not something which I endorse.
>
>You replied:
>>[Morton] I would define actualism as meaning that the laws of physics were
>> the same for all historical times is a reasonable assumption. I really did
not
>> mean to make actualism a synonym for uniformitarianism....
>
>[Tyler] OK. We appear to agree on this.
Actually, actualism and uniformitarianism are very close in meaning. The
original Huttonian concept of uniformitarianism was that natural
(geological) processes operating today also operated in the past, so that
past events and features could be explained by invoking those same
uniform natural processes (which mostly happen to operate slowly) over
millions of years. Later, Lyell extended uniformitarianism to mean that
geological processes operated in the past at exactly the same rate and
intensity as they do in the present, a mistaken exaggeration of the
concept which we of course today reject (this is the mythological version
I mentioned above). Later, the principle was generalized for all sciences
to mean that natural processes and laws operate uniformly through time
and space. This principle was termed actualism, and is an essential
working hypothesis (NOT assumption or presupposition) of modern science.
So actualism is really a generalization of uniformitarianism, not
something terribly different. It could be said that uniformitarianism is
the historical, geological principle that today we call actualism. I use
both terms depending on the context.
>
>I had written:
>> >I do not have quotations to hand, but there are a number of
>> >carbonate specialists who readily acknowledge that
>> >uniformitarianism has not delivered satisfactory depositional
>> >models for carbonates.
>
>[Morton] If you find them I would be interested in hearing them.
I presume that you answered Glen by referring to the paper by
Braithwaite. If you also mean the paper by Stuart Nevins, I confess that
I have never read it (but would like to). If his argument is the same as
yours--that understanding the formation of ancient fossil reefs by
rigidly forcing them into the modern organic reef concept is an example
of the misapplication or failure of the principle of
uniformitarianism--then I have to say it would not be convincing.
Geologists are quite aware that the constituents and construction of
organic buildups have changed through time, and they don't confuse the
different depositional models. And for the semantic problem of reef
terminology--Is the Capitan Limestone a fossil reef?--the simple answer
is yes and no. The Permian Reef (whose main body is the Capitan
Limestone) IS a reef if by that term you mean an organic buildup with
significant topographic relief. It is NOT a reef if by that term you mean
a framework structure composed of cemented lime boundstone like Cenozoic
reefs (the Permian Reef actually consists of heavily altered lime
wackestone, packstone, and grainstone).
Even modern reefs contain a lot of non-boundstone lithologies, so it is
important to look first at an organic buildup's location, shape,
components, facies, and genesis, rather than just its structure and
lithology (the latter are important, but they depend on the original
organic constituents). If you do this, then there has been a remarkable
uniformity of reef depositional models through Phanerozoic time and
space, about 540 million years on Earth. This certainly vindicates the
use of uniformitarianism or actualism when we try to understand organic
buildups and their depositional processes.
Regards,
Steven Schafersman
schafesd@muohio.edu
http://www.muohio.edu/~schafesd/