Reef madness (was RE: K/T revisited, was: Re: DINOSAUR digest 3382)

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> David Marjanovic
>
> Didn't the corals (which also have planktonic
> larvae) need the entire Paleocene or so to form the first full-size Cenozoic
> reefs?

True, but that may in part be due to longer-term changes in ocean chemistry. 
Here's the condensed version: the oceans have two main
phases as far as which form of CaCO3 is easier to produce. These are calcite 
oceans vs. aragonite oceans. Calcite oceans (which tend
to be associated with both higher mid-ocean ridge activity and higher sea 
levels) favor organisms that put down massive amounts of
calcite; aragonite oceans (with lower mid-ocean ridges and generally lower sea 
levels) favor aragonite.

During the Jurassic and Early Cretaceous we had aragonite oceans, and 
scleractinian corals flourished. In the later Early K and the
Late K, there was a shift to calcite seas, the scleractinians did worse, but 
the rudists (and inoceramids) bloomed. Even after the
K/T extinction, the oceans were still in the calcite phase, but the main 
calcitic reef formers present (rudists) had been clobbered.
The scleractinians had to wait for the oceans to shift back to aragonitic mode 
before they could put down lots of reef material
again.

Hope this helps,

                Thomas R. Holtz, Jr.
        Senior Lecturer, Vertebrate Paleontology
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

http://www.geol.umd.edu/~tholtz/
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