Re: All kinds of odd observat...

[N.MacLeod@xxxxxxxxx (N. MacLeod)]

But dinosaurs, rudists, inoceraminds, planktonic foraminifera etc. didn't
all die out at the same stratigraphic horizon no matter where you look in
the fossil record.  That is a very well established fact.  As for Ir, it's
distribution is very curious.  There are multiple Ir anomalies in many
marine sections (e.g., Braggs, Brazos River) where the fluvial mechanism
Tom alludes to is not operable.  Even more troubling is the fact that
prominent Ir spikes show up in biostratigraphically incomplete successions
(e.g., Gubbio, Stvens Klint) whereas in some biostratigraphically complete
sections (e.g., Miller's Ferry) no Ir anomaly has been found.  I don't see
how these data can simply be ignored.  These observations, coupled with the
fact that instantaneous faunal turnovers only coincide with Ir anomalies in
the biostratigraphically incomplete sequences, should tell us that the
story is a bit more complicated than that a big rock fell out of the sky
and everything died (somehow), except for those things that didn't.

Norm MacLeod


----------------------------------------------------------------------------
Norman MacLeod
Senior Scientific Officer
N.MacLeod@nhm.ac.uk (Internet)
N.MacLeod@uk.ac.nhm (Janet)

Address: Dept. of Palaeontology, The Natural History Museum,
         Cromwell Road, London, SW7 5BD

Office Phone: 071-938-9006
Dept. FAX:  071-938-9277
----------------------------------------------------------------------------