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Re: mammals over dinosaurs in continuous sequence
email@example.com (John Bois) retorted:
On Wed, 14 Apr 1999, Mickey P. Rowe wrote:
> > I suspect this is a long shot, but does anybody know of a single
> > location that includes the K-T boundary and has Tertiary mammal
> > fossils near Cretaceous dinosaur fossils?
> Jepsen, G.L. 1931 Dinosaur Egg Shell Fragments From Montana. Science
> I don't know if the boundary is present in this locality (east of Red
> Lodge, Montana--Dry Creek).
> Also, the location (or presence) of the boundary is not mentioned in:
> Demberelyin Dashzeveg et al (including Novacek Chiappe and Dingus)
> _Extraordinary preservation in a new vertebrate assemblage from the
> Cretaceous of Mongolia Nature_ 374:446-449
I do not believe that the boundary is preserved anywhere near that site,
(The K/T boundary is found in a surprising number of terrestrial
Lancian-correlative units around the world, but the problem is that the
areal extent is usually quite limited.)
In the Hell Creek Fm., the K/T boundary is discontinuously preserved at
the top of a highly leached paleosol zone (see papers by Greg Retallack)
that is anywhere from one meter to 3 meters thick. The zone is
conspicuously devoid of vertebrate fossils of any kind (although plant
fossils are present). The presence of plant fossils and the
rarity/absence of hydroxyfluorapatite-containing fossils could be
explained as a result of acid leaching in the boundary zone ("Barren
Zone" of Archibald, 1982). Retallack suspects that the leached paleosol
is direct evidence of acid rain that was produced from the vaporization
of sulfate targe rocks from the impact bolide.
Throughout the Hell Creek Formation, particularly at sites where seiving
has been done, mammal fossils are usually found with dinosaur fossils
(albeit in small numbers). But within the 1-3 meter-thick leached
boundary zone near the top of the formation, little can be said about
the association of the two fauna as both are commonly absent.
The Lance Formation also has a leached zone at the K/T boundary,
although I don't know if it too is almost devoid of vertebrate fossils.
The Raton Basin has many nice sites where the K/T boundary is preserved,
but I know little about those areas.
Archibald, J. D. 1982. A study of Mammalia and Geology across the
Cretaceous-Tertiary Boundary in Garfield County, Montana. University of
California Publications in Geological Sciences, volume 122, pages