[Coral-List] Darwin was WRONG about reef formation

[David Blakeway]

Hi Rupert,

I don't think there would be enough direct evidence (coring, seismic) to
evaluate the multi-scale origin of the Maldives. Others might know more,
Paul Kench or Chris Perry maybe. Yes it is a reasonable assumption (not a
certainty) that the smallest-scale structures are the youngest. Given the
lagoon depths of 40-60 m and more it's likely that even the smallest faroes
developed over multiple sea-level cycles, but it is feasible that some are
entirely Holocene. If they are multi-cycle then their morphology *may *be
karst-induced, as Droxler & Jorry suggest (their Figure 3). But I think
it's more likely a growth pattern, like scaled-up Porites microatolls.

Perhaps we should be more careful about the 'Darwinian atoll' terminology,
since Darwin, did recognize alternative pathways to atollhood. In fact his
New Caledonia model for the Maldives is actually very similar to the
Droxler & Jorry model. The main difference I guess being Droxler & Jorry's
'flat-topped banks'. Regarding that though, what do those who've read the
article think about their Figures 7a and 8a seismic profiles? Seems to me
the Pliocene beneath Male atoll is not so flat??



On Wed, Oct 28, 2020 at 8:33 PM Rupert Ormond <rupert.ormond.mci at gmail.com>
wrote:

> Thanks David,
>
> This sounds like the interpretation I was trying to re-call after Doug et
> al asked about when I mentioned that decades ago I was teaching students
> that the Maldives atolls were not atolls - at least in the Darwinian sense.
>
> I still struggle to understand however how exactly the Maldives manages to
> get mini-atolls within ring reefs within atolls. As a non-geologist I could
> only guess that this was the result of eustatic fluctuations in sea-level,
> with the largest scale atolls being formed when sea level was lowest and
> conditions within unfavourable to coral growth, and smaller ring-reefs
> being able to form inside them once sea level was higher again, and so on.
>
> It would be nice to know if the evidence supports this?
>
> Thanks
>
> Rupert
>
>
> *Prof. Rupert Ormond *Co-Director, Marine Conservation International
> Hon. Professor, Centre for Marine Biodiversity & Biotechnology,
> Heriot-Watt University, Edinburgh
>