[Coral-List] Darwin was WRONG about reef formation

[Dennis Hubbard]

To some extent, this is probably a matter of semantics. The term "atoll" is
a geomorphic one - an emergent annular feature built by the accumulation of
coral and related materials (algae, sediment, etc.). I don't think there is
any resistance to this. However, from a process standpoint, features with
this generic shape can result from one of (at least) two very different
processes. The one we most often acknowledge is a subsiding volcano that is
cooling and sinking as it moves away from its initial hotspot location. As
long as reef accretion offsets subsidence, the feature will remain at or
near to sea level (read Ricky Grigg's paper in an old issue of Coral Reefs
on his "Darwin Point". .Another alternative is related to wave refraction
behind an exposed or nearly exposed high on a larger shallow bank. The
resulting wave pattern will create two sedimentary spits on either side of
(and just downdrift from) the high; this leads to a roughly circular or
oblate feature resembling its more-common cousins with a volcanic origin.

Dennis

On Mon, Oct 19, 2020 at 9:13 AM Rupert Ormond via Coral-List <
coral-list at coral.aoml.noaa.gov> wrote:

> Yes I pretty much agree with Doug.
>
> As usual Darwin had the key insight, and unfortunately headlines
> claiming that he was wrong risk inciting conspiracists and
> fundamentalists. Even a hundred years ago we realised from Daly's work
> on Glacial Control Theory that the results of Darwin's geological
> upheavals were likely greatly amended by shorter eustatic processes.
>
> As a result, 50 years ago, I was teaching in classes that ironically The
> Australian Great Barrier Reef is not a Barrier Reef, and that the huge
> Atolls of the Maldives are not atolls (despite atoll being a Maldivian
> word in origin) - AT LEAST in the "Darwinian Sense".
>
> Despite this, in the last decade or so I keep seeing people mentioning
> the Great Barrier Reef as the best example of a Barrier Reef, and the
> Maldives as providing the best examples of atolls - perhaps in writing
> by authors whose expertise in newer branches of bioscience left no time
> for reading in basic reef biology. Was I wrong all those years??
>
> I guess it all depends what you mean by a barrier reef or an atoll?
>
> cheers,
>
> Rupert
>
> --
> *Prof. Rupert Ormond***
> **
>
> **Co-Director, Marine Conservation International
> Hon. Professor, Centre for Marine Biodiversity & Biotechnology,
> Heriot-Watt University, Edinburgh
>
>
> On 16/10/2020 23:51, Douglas Fenner via Coral-List wrote:
> > or so says a new article:
> >
> > Popular piece:
> >
> > Study: Darwin's theory about coral reef atolls is fatally flawed
> >
> >
> http://news.rice.edu/2020/10/12/study-darwins-theory-about-coral-reef-atolls-is-fatally-flawed-2/
> >
> > Original review:
> >
> > The origin of Modern Atolls: Challenging Darwin's Deeply Ingrained Theory
> >
> > https://www.annualreviews.org/doi/10.1146/annurev-marine-122414-034137
> >
> > My thoughts, based on reading the popular article and the abstract for
> the
> > review:
> >
> > Yes, if you define an "atoll" as a ring of coral at the surface, and you
> > carefully ignore that it is on top of an accumulation of up to a mile of
> > coral reef carbonate, which is in turn on top of a two mile tall volcano
> > which all the evidence shows has indeed subsided with the ocean floor
> plate
> > as it moves across the ocean, then yes, sea level fluctuations with the
> > glaciation cycle are widely acknowledged to affect the coral reef
> > structure.  It appears that maybe the new thing in this review is that
> the
> > present ring is relatively young and built on top of the raised ring left
> > from low sea level stands when rainwater was dissolving the carbonate in
> > the center of the ring.  Actually, I don't think even that is new, though
> > their being a flat topped bank in between time may be new.  This is a
> > further embellishment on top of the Darwin theory, NOT a disproof of his
> > theory, which is heavily documented.  The argument back then was whether
> > there was a volcano under the carbonate, which drilling proved was
> correct
> > and is no longer in doubt.
> >       Perhaps by reading the entire review it will be clear that the
> review
> > isn't saying that Darwin was wrong about subsidence and a volcano being
> > under the carbonate, or that there was a sequence from fringing to
> barrier,
> > to atoll, but even the title of the review implies it is.  But of course
> > you attract a lot more attention saying that "Darwin was wrong."
> >        What do geologists think?
> > Cheers, Doug
> >
> >
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-- 
Dennis Hubbard - Emeritus Professor: Dept of Geology-Oberlin College
Oberlin OH 44074
(440) 935-4014

* "When you get on the wrong train.... every stop is the wrong stop"*
 Benjamin Stein: "*Ludes, A Ballad of the Drug and the Dream*"