SS: "I hope no one minds if I jump in here."
Welcome to the debate! We don't often get much of an exchange
on things geological on this list (apart from palaeontology), and
it does help to have people like yourself contributing.
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.
SS: "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....."
We continue to disagree! There has been a long tradition of
fuzziness about "uniformitarianism", due largely to the immense
influence of Charles Lyell. Steven Gould has probably done more
than most in clarifying the issues: the distinction he makes
between substantive uniformitarianism and methodological
uniformitarianism is very important. For the Christian,
methodological uniformitarianism is merely a technical way of
talking about the providence of God (his faithfulness in
upholding and sustaining his creation), whereas what revelation
we have in the Bible points us away from substantive
uniformitarianism. It is, however, the latter which brings
controversy. Methodological uniformitarianism has, as Gould
points out, been held by catastrophists and uniformitarians
alike. It is the basis of all science. Substantive
uniformitarianism has often been used as a dogma within geology,
because this has been regarded as the only way to practice
science. This is what I continue to believe to have been
positively harmful.
SS: "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."
Insofar as Braithwaite was saying that "the present is NOT the
key to the past", I think he was challenging uniformitarianism.
Your perception of the way carbonate geologists have behaved is
not the same as mine. There have been changes since Braithwaite
wrote his paper - and people have been much more alert to
shoehorning the data to fit orthodox depositional models.
However, very often, there has been no viable alternative:
several times I've been with carbonate field geologists who have
been able to describe the carbonate buildups in their research,
but continue to find the evidence mysterious; they content
themselves with offering tentative interpretations.
I had written:
>Non-uniformitarian thinking has proved to be quite fruitful in
>other areas of geology...
SS: "A rigid adherence to a certain type of mythological
uniformitarianism (as in the geological resistance 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 point to these examples as illustrative of the uniformitarian
mind-set which has dominated geology for 150 years. The
recognition that we can be genuine scientists without holding to
the tenets of substantive uniformitarianism is what has helped
to clear away these hindrances to progress.
SS: "I don't know what you imply by "non-uniformitarian
thinking," but if you mean catastrophism, then I must disagree."
I mean the freedom to consider non-uniformitarian models and
mechanisms. I am not wanting to impose one doctrinaire system
with another! I want genuine freedom in science, which means
that we consider arguments on their merits and do not reject
interpretations because they do not fit "orthodoxy" (from
whatever quarter it comes!).
SS: "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."
Yes, and in order to do this they had to shoehorn the data to fit
their modern analogues. This is why the influence of Lyell has
been far from positive.
SS: "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."
This is a fair comment about the contemporary scene. The
question I ask, however, is: how much of this "big picture" is
a legacy from Lyell, and how much is good science? Has the
geological community retained the mindset of substantive
uniformitarianism whilst feeing itself from the straightjacket
this dogma brings? My answer is: far more than people realise!
Regarding Carbonate buildups, you write:
"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 constituent 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."
Since there are so many contrasts between modern "reefs" and
those of the Palaeozoic and Mesozoic, we need to be very careful
when interpreting data. When you say "these buildups had
topographic relief, showed organic zonation, and undoubtedly
modified the physicochemical environment", my reaction is to say
that this underplays the contribution made by the depositional
models used to interpret the data. I am not yet convinced that
we have satisfactory depositional models.
SS: "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. ...
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. ..."
I think it has been an enormous problem! It's one reason for
Braithwaite writing his paper!
>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".
> ....
SS: "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."
I'll respond by citing A. Hallam, "Facies interpretation and the
stratigraphic record". W.H. Freeman and Company, Oxford.
"Many large lensoid bodies of massive, unbedded or poorly
bedded limestone in the stratigraphic record have been
termed reefs (Laporte 1974). However, the term is open to
objection because it comes from the old Norse word rif
meaning a rib of rock and has special significance for
navigators. Detailed studies suggest that many ancient
`reefs' might not have been firmly consolidated or reached
wave base, hardly the sort of structures in fact that would
constitute a hazard to shipping. Furthermore, there may be
a conspicuous absence of organic skeletons. For these
reasons the non-committal term buildup is to be preferred
for these structures (Heckel 1974). Reef can then be
defined as a biologically produced buildup that displays
evidence of potential wave resistance or growth in
turbulent water and control over the surrounding sediment.
(page 52).
SS: "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."
It does bother me. It makes me suspect that the user of "reef"
is carrying a load of (substantive) uniformitarian
interpretations which are unconsciously imposed on the data.
SS: "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."
This illustrates the problem - you see a "uniformity of reef
depositional models through Phanerozoic time"; I see the
inappropriateness of modern day depositional models. I am happy
to concur about looking at the data. All I would add is: test
models rigorously!
Here are a few other citations I looked out relevant to this:
First, from A. Hallam, "Facies interpretation and the
stratigraphic record". W.H. Freeman and Company, Oxford.
"The two best-known areas of extensive carbonate sedimentation,
on which facies interpretation depends heavily, are the Great
Bahama Bank and the Persian Gulf." (page 47)
"Ancient carbonate platforms were enormously more extensive than
modern ones, especially in the Palaeozoic." (page 50)
Second from: Derek Ager, "The New Catastrophism". Cambridge
University Press, Cambridge, 1993.
"Another way in which today differs from yesterday is in the
extent of carbonate deposition. Apart from the poor old Bahamas
Banks, which have been worked to death by sedimentologists,
together with a few other small areas such as Sharks' Bay in
Western Australia and the south end of the Persian/Arabian Gulf,
there is nothing today to compare with the vast spreads of
limestones and dolomites which extended across the continents
repeatedly in the past." (page 167)
Comment: we study intensively a few localised carbonate
depositional environments today, and then think that they are
adequate to model origins of the vast carbonate deposits of the
past. How can we be so confident? Surely it is a matter of
methodology: despite our "official" abandonment of substantive
uniformitarianism, we still believe in it and don't see the need
to explore alternatives.
Best wishes,
David J. Tyler.