>I want to clarify something here in what appears to be a discrepancy between
>your response and mine. I have read Nevins/Austin's paper on the Capitan.
>He is correct that there is not this one huge framework for the thing. But
>if you look at the rock forming immediately beneath a coral reef today you
>don't have a huge framework left in place. The coral breaks and the debris
>falls to the floor of the sea where it becomes cemented. It looks often
>like the biohermal buildups of the past.
I agree with you, Glenn. Back-reef and fore-reef sediments and colonizing
deposits beneath the core of any reef or carbonate buildup, including
living reefs, will not exhibit framework carbonate fabrics. This is what
I meant when I said that modern reefs contain a lot of non-boundstone
lithologies. In fact, the major part of the carbonate sediments of any
reefal area, fossil or modern, consists of non-framework fabrics. This
depositional style is common to organic buildups throughout the
Phanerozoic, but component details will differ. The wackestone/packstone
core of the Permian Reef of West Texas is notorious for being different
than the framework boundstones of modern reefs, but the geometries,
facies patterns, and physiographic relationships of these buildups
(bioherms) are similar.
>
>Where Nevins/Austin goes wrong is that he says that there is no evidence
>that the reefs grew in place and were not deposited by Noah's flood. Nevins
>wants to show that the fossil record could be dumped into place by showing
>that nothing took time to grow big during the middle of the geologic column.
>This is the entire thrust of this argument within the young-earth position
>to explain away the evidence for long periods of time in the growth of
>coral/biohermal beings in the middle of the flood deposits.
Thanks for explaining the Nevins/Austin claim, of which I was not
previously aware. It is nonsense, of course. The Capitan limestones
contain sponges, corals, and algae in growth positions, and there is a
shallowing-upward facies change to fusulinid-grainstones at the top as
the reef built to sea-level and began to prograde. Of course, we
understand this partly from uniformitarian comparisons with living reefs,
but also because other ancient organic buildups show a similar pattern.
There are many other reasons to infer slow, gradual construction and
sedimentation, many of which you properly discussed in previous posts.
> I think this is
>what David would like to do with this also. If one can find framework's in
>situ this falsifies Nevins/Austin's claim. There ARE frameworks found in the
>fossil record and I will give you some more examples. Robert H. Dott Jr.,
>and Roger L. Batten, Evolution of the Earth, 1971 p. 605 fig AII.5 shows a
>colonial devonian Hexagonaria coral.(this same picture is found on p 310 of
>their 1988 edition) On p. 607 Figure AII.7 shows a framework tabulate coral
>colony. (This same picture is found in their 1988 edition on page 343)
>
>Thus while the remains of most modern reefs when limestone is formed is an
>amorphous bioherm, there are frameworks preserved. Similarly this occurs in
>the past.
>
I agree--but the distinction is one of relative abundance. If we ignore
back-reef deposits (usually mudstones and wackestones) and fore-reef
deposits (usually packstones and grainstones), the central part of a
modern reef forms a lime boundstone, a framework, but also containing
lots of calcite cement and recrystallized micrite matrix in the pores.
Some Cenozoic reefs retain the framework structure (I have seen excellent
Oligocene, Pliocene, and Pleistocene reefs with as fine a boundstone as
one could want), but in others it is altered and the framework must be
inferred. In Paleozoic and Mesozoic buildups, I agree that local
instances of frame-building occur, such as the ones you mentioned in your
post here and before, and others you didn't mention, but they are
volumetrically insignificant compared to the buildups as a whole, which
are primarily wackestones, packstones, and occasionally bafflestones. If
I implied in my initial post that there were none, then I apologize. If
the existence of ANY organic frameworks in the stratigraphic record
falsifies the Nevins/Austin claim, I agree with you that it's been
falsified.
Once again, the details will differ from period to period because the
organisms that build the bioherms are different and grow together,
cement, and erode in different ways, but the facies zonations, reef
geometries, physiographic relationships, etc., are remarkably similar all
through the Phanerozoic. As Braithwaite emphasized, it is important to
study the details before making an interpretation, so we must look at
each geologic period's organic buildups on their own terms. Modern reefs
offer us a guide or a pattern, not a rigid framework (sorry about the
pun) for interpretation. When geologists make comparisons using
uniformitarian or actualistic approaches, they should not, and usually do
not, abandon the uncommon sense that science demands. I know from your
many posts that this is what you believe, also.
Steve
Steven Schafersman
schafesd@muohio.edu
http://www.muohio.edu/~schafesd/