>  there are molluscs (gastropods, 'monoplacophorans',  bivalves and
>smaller groups) in the Cincinatian limestones, but because they had
>aragonitic shells, the preservation is very poor compared to the
>calcitic brachiopods, corals, echinoderms and bryozoa.

Actually, I believe corals (true modern hexacorals) are aragonitic.
Like the majority of molluscs, they are diagenetically removed
(dissolved) in our regional Oligocene greensand/limestone formation,
though occasionally phosphatic ghosts of the interseptal spaces are
present.

Octocorals ("soft" corals, sea pens etc) are however calcitic, and
remain in these rocks. Graphularia, supposedly a pinnatulid (sea
pen), is very common here, but large & small solitary corals
(caryophyllia, Flabellum circulare, Stephanocyatthus etc) are absent
except in spots in which preservation is unusual (aragonitic molluscs
also occur in these very few spots).

As to Paleozoic "horn" corals (Rugosa), I have no idea as to their makeup.
--
Andrew Grebneff
Dunedin, New Zealand
64 (3) 473-8863
<[log in to unmask]>
Fossil preparator
Seashell, Macintosh & VW/Toyota van nut
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I want your sinistral gastropods!
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Opinions in this e-mail are my own, not those of my institution
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Q: Because it reverses the logical flow of conversation.
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