On 23 Jan 98 at 20:21, Glenn Morton wrote:
> I moved this first thing to the top of the response because of its importance.
>
> At 04:58 PM 1/23/98 GMT, David J. Tyler wrote:
> >I could mention at this point one contribution I would recommend
> >on the depositional environment of chalk:
> >Tyler, D.J. 1996. A post-Flood solution to the Chalk Problem.
> >EN Tech. Journal, 10(1), pp.[page numbers not to hand - sorry]
>
> Considering that Dallas is built on chalk of the same age as the Dover
> Chalk, I would be very interested in your explanation. ....
> I would be interested in an outline of
> your theory and how it applies to St. Bernard Ph. Louisiana.
Glenn, although I have spent three days in Kansas looking at the Niobrara
chalk, I did not see the overlying sediments. The model developed in the
cited paper is that all these overlying sediments are also post-Flood.
[snip]
> I guess that makes us even. I would think ANY explanation for all the data
> is superior to NO explanation of major portions of the geological data. What
> you have said is that actualism is successful but I don't want to believe in
> it. Why would we want to tie the Bible to a view which is unsuccessful at
> explaining so many features of the world? By doing this, we make the Bible
> have nothing to do with the real world.
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:
> 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....
OK. We appear to agree on this.
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.
>
> If you find them I would be interested in hearing them. Clyde Moore lead my
> first carbonate field trip and he seemed quite happy with actualism. This
> was in 1983 and I was very depressed after seeing all the evidence for life
> in the carbonate rocks of Texas. I stood on the Caprinid reef at Pipe Creek
> south of Austin. One could see about 2 acres of connected animals and
> moldic porosity. It was an awesome site for someone (like me in 1983) who
> believed that there were no connected reefs in the geologic column.
The delay in responding is because I knew I had written a short essay on
this over a decade ago. I could not find it! It has now turned up, and
I'm including it below. It does not address your observations of the
Caprinid reef, but it does claim to address the main characteristics of
the geologic record.
----------------------------
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.
In this article, factors relevant to this state of affairs are
identified, and suggestions are made concerning future
studies.
1. INTRODUCTION.
Around the coasts of the UK, "reefs" are rocky prominences on
the sea floor which threaten to wreck any ship which strays
too close. The word derives from the Old Norse "rif" which
described a protruding rib. A dictionary provides some
lesser-used applications: "a lode of auriferous rock" and "the
outcrop of a lode or vein". In tropical waters, corals are
responsible for building hard prominences which provide
navigational hazards and, as a result, the word "reef" has
become particularly associated with wave-resistant topographic
features built by corals. These diverse uses of the word
"reef" should not lead to confusion when read or spoken in
context, but they do set the scene for the imprecision and
ambiguity concerning fossil reefs that has become widespread
among geologists. The discussion that follows is based
largely on Braithwaite's 1973 article on the subject (1),
which continues to be relevant to students of carbonate
sediments and palaeoenvironments.
2. SEDIMENTOLOGY OF CARBONATE ROCKS.
The literature on the sedimentology of clastic rocks is vast.
Intensive theoretical and experimental studies have been made
of the hydrodynamics of sedimentary processes and their
associated sedimentary structures. Modern depositional
environments have been rigorously investigated so that they
can be used as analogues for the formation of ancient rocks.
By comparison, sedimentary processes involving carbonate rocks
have received much less attention. Braithwaite states:
"With some exceptions, carbonate workers have not
followed such lines of investigation. This is partly
because the distribution of the skeletal fragments
forming the sediments is not controlled in the same ways
by the physical conditions. Grains originate within the
transport system and their sizes, measured in bulk, are
not a simple reflection of the speed or duration of the
current." (p.1100)
Thus, the conviction that carbonate sediments are formed in
situ has made physically oriented studies largely superfluous.
Furthermore, the research interests of carbonate workers has
directed their attention away from depositional processes.
According to Braithwaite (1), their main interests have been
in the fossils found in carbonate rocks, or in
biostratigraphy.
"The lack of physically oriented studies also is a
product of the interests of the workers who have been,
for the most part, palaeontologists only recently
concerned with ecology, or stratigraphers." (p.1100)
The danger, therefore, has been that of uncritically accepting
familiar models to describe rocks under investigation. It
would appear that deductive reasoning is prominent in the
literature on carbonate sediments - which has led to an
unsatisfactory state of affairs. Thus, Braithwaite writes:
"Studies equivalent to those of Jopling and Walker (2)
are not available for reef systems, and there is a
regrettable tendency to interpret these environments less
stringently. One major difficulty is that, by saying
that a structure is a reef, an author immediately has a
familiar model to which he can relate sediments. Without
this model he has the more difficult task of finding
suitable descriptions and a convenient analogy." (p.1100)
A particular criticism that can be made is that terminology
has become loose and confusing. Braithwaite puts his finger
firmly on the problem:
"Any primary description which uses terms such as "reef
limestone" or "intrareef debris" (e.g. in Terry and
Williams (3)) as descriptive terms seems to the writer to
be lacking in scientific method. It is prejudging an
interpretation which may later be placed on a system and
using this as a substitute for a description of the
specimen as, for example, a boundstone, grainstone
(Dunham (4)), biomicrite, or biolithite (Folk (5)). Only
by the use of some nongenetic term can the facts of
observation be understood and stand apart from the
delusions of interpretation." (p.1100-1101)
There is no doubt that during the last 10 years, many have
taken these comments to heart. At the same time,
palaeoecology has provided a framework for renewed interests
in depositional environments. However, from personal
observation, it is clear to the writer that the traditions of
many years are resistant to change! Despite being written in
1972, Braithwaite's critique should be required reading for
all geology students setting out to study carbonate rocks.
3. FOUR CHARACTERISTICS OF REEFS.
Geologists have been describing reefal limestones for over one
hundred years, and it is clear from the literature that there
has been no consensus about the distinguishing marks of a
reef. In 1932, Cummings (6) introduced two words to try and
improve the available terminology:
Bioherm: "a reef, bank, or mound; for reeflike, moundlike
or lenslike or otherwise circumscribed structures of
strictly organic origin, embedded in rocks of different
lithology." (p.333)
Biostrome: "Purely bedded structures, such as shell beds,
crinoid beds, et cetera, consisting of and built mainly
by sedentary organisms, and not swelling into a moundlike
or lenslike form . . . which means a layer or bed.
(p.334)
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)
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.
Four characteristics of modern reefs may be identified.
(i) RELIEF. The structure rises appreciably above the sea
floor.
(ii) RIGID FRAMEWORK. Not only are frame-building organisms
present, but also they can be shown to have functioned as
frame builders. There are evidences of internal structure.
(iii) VARIATION IN PHYSICOCHEMICAL ENVIRONMENT. The structure
lies within the zone of wave action, and there are major
variations in light, oxygen, temperature, salinity and
turbidity affecting different parts of the reef.
(iv) ZONATION OF ORGANISMS. Both frame-builders and their
associated vagrant organisms show a zonation consequent upon
their physicochemical environment.
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.
4. FOSSIL "REEFS".
Braithwaite discusses several well-documented examples of
fossil "reefs" to show that the situation is far from
satisfactory. He reviews data relevant to the Permian
Guadaloupe Mountain Complex, the Niagaran "reefs" of the Great
Lakes area, the Middle Devonian "reefs" of South Devon, and
several others.
"An analysis of the criteria available for the
recognition of ancient reefs shows that other structures
are present in the geologic column which pass unnoticed
beneath the blanket title of "reef"." (p.1100)
[These other kinds of structure] "undoubtedly exist, but
are commonly disguised, because of their appearance under
the misleading title of "reef", particularly where they
lack any detailed description." (p.1113)
5. COMMENT.
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.
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.
The Permian Complex of the Guadaloupe Mountains (West Texas)
has been studied by Stuart Nevins from a non-uniformitarian
diluvialist perspective (7-9). Readers following up thoughts
raised by Braithwaite are recommended to consult these
articles.
REFERENCES
1. Braithwaite, C.J.R. Reefs: just a problem of semantics?
Bulletin of the American Association of Petroleum Geologists.
1973, 57(6), 1100-1116.
2. Jopling, A.V. and R.G. Walker. Morphology and origin of
ripple-drift cross-lamination with examples from the
Pleistocene of Massachusetts.
Journal of Sedimentary Petrology. 1968, 38(4), 971-984.
3. Terry, C.E. and J.J. Williams. The Idris "A" Bioherm and
oilfields, Sirte basin, Lybia.
in Exploration for Petroleum in Europe and North Africa.
London: Institute of Petroleum. 1969, 31-48.
4. Dunham, R.J. Classification of carbonate rocks according
to depositional texture.
in: Classification of Carbonate Rocks. 108-121.
American Association of Petroleum Geologists Memoir 1. 1962.
5. Folk, R.L. Spectral subdivision of limestone types.
in: Classification of Carbonate Rocks. 62-84.
American Association of Petroleum Geologists Memoir 1. 1962.
6. Cummings, E.R. Reefs or Bioherms?
Geological Society of America Bulletin. 1932, 43(1), 331-352.
7. Nevins, S.E. Is the Capitan limestone a fossil reef?
Creation Research Society Quarterly. 1972, 8(4), 231-248.
8. Wonderly, D.E. Critique of "Is the Capitan limestone a
fossil reef?"
Creation Research Society Quarterly. 1974, 10(4), 237-241.
9. Nevins, S.E. Reply to critique by Daniel Wonderly.
Creation Research Society Quarterly. 1974, 10(4), 241-244.
Additional quotation:
"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).
----------------------
Best wishes,
David J. Tyler.