[Coral-List] Darwin was WRONG about reef formation

[tomascik at novuscom.net]

I really enjoyed this exchange. Anyone who may be interested in 
additional information on atolls here are two links you may find 
interesting:


https://1drv.ms/b/s!Aq1K6CQCBeATgrUZzsY5CjuHCgLaoQ?e=4icCqy

https://www.researchgate.net/publication/303304939_Tomascik_T_A_J_Mah_A_Nontji_M_K_Moosa_1997_Chapter_Sixteen_Atolls_and_Raised_Islands_In_The_Ecology_of_the_Indonesia_Seas_Part_II_pp_751-788_Singapore_Periplus_Editions_HK_Ltd#fullTextFileContent

Cheers,
Tom

On 2020-10-21 13:08, Douglas Fenner via Coral-List wrote:
> I think this is a good point, if you define an atoll as a ring of
> coral at the surface of the water without an island in the center (as 
> we
> generally do), then there are ways it can form other than a sinking
> volcano, and an elevated ring left by rainwater dissolving the center 
> of a
> platform during low sea level is a way in which a ring can form, or on 
> a
> raised continental block as in the western Caribbean.  On the other 
> hand,
> Darwin was right about the sequence that happens on subsiding volcanoes 
> on
> oceanic plates, from fringing to barrier to atoll, but reefs commonly 
> also
> build on continents, which can also have vertical movements (though 
> usually
> less total vertical movement).  I just remembered that there are 
> oceanic
> volcanic islands that do not subside, namely the volcanoes in island 
> arcs
> behind trenches.  Examples being the windward Antilles in the 
> Caribbean,
> and Tonga, Vanuatu, and the Marianas in the Pacific.  Those latter 
> three
> have volcanic islands that have been raised some, with layers of reef
> limestone raised out of the water that sometimes look like layered 
> cakes
> from a distance.  The edge of the plate that they are on does not 
> subside,
> a plate moving down into the trench and going under where the volcanoes
> are, or other factors, can raise the islands at least enough to lift 
> reefs
> out of the water.     Cheers,  Doug
> 
> On Wed, Oct 21, 2020 at 8:22 AM Dennis Hubbard via Coral-List <
> coral-list at coral.aoml.noaa.gov> wrote:
> 
>> 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*"
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