by R. Farley Fleming
One goal of
the Denver basin project is to locate the Cretaceous-Tertiary (K-T)
boundary. This boundary marks a mass extinction event in earth history
that includes the extinction of dinosaurs. In many places in western
North America, the boundary is also marked by the presence of an
unusual concentration of iridium, which is thought to have been
deposited after an asteroid hit the earth 65 million years ago.
Many scientists attribute the mass extinctions at the K-T boundary
to this asteroid impact.
As we were
drilling at Kiowa, I collected a suite of samples for palynologythe
study of fossil pollen and spores. Some species of fossil pollen
disappear precisely at the K-T boundary and these microscopic fossils
have proven very valuable in locating the K-T boundary. Because
of the importance of the K-T boundary in our project, I focused
primarily on locating this boundary during the drilling at Kiowa.
an on-site sampling protocol for locating the K-T boundary. Samples
were collected every 25 feet throughout most of the core, and every
10 feet when we were drilling through the interval where Bob Raynolds
predicted the K-T boundary would be found. These samples were shipped
by express courier to a laboratory in Canada for processing and
then shipped back to me for analysis. None of the samples from the
upper part of the core contained Cretaceous pollen, but they did
contain pollen typical of the early Tertiary. The first sample with
Cretaceous pollen came from a depth of 881 feet below the surface.
Detailed sampling then revealed that the K-T boundary was located
below 878.38 feet and above 880.17 feet. Thus, the K-T boundary
is located somewhere in this short interval.
position of this boundary in the core provides the Denver Basin
Project with an important time horizon that can be used to support
other studies in the Denver Basin Project. It helps place the core
in stratigraphic context, which is critical for developing the stratigraphic
framework for our hydrogeologic studies. It also gives us important
information that can be used in locating the K-T boundary in other
places in the Denver Basin and could lead to the discovery of sites
with the K-T boundary claystone, which contains the iridium from
the asteroid impact 65 million years ago.
The Kiowa core
still holds much potential for palynological studies. Ongoing work
focuses on constraining the age of the paleosol that was recovered
as well as developing an overall biostratigraphic framework for
the core. This framework will be extended throughout the Denver
Basin and will provide a foundation for understanding the geologic
evolution of the Denver area. In addition, the fossil pollen and
spores will help us construct a picture of the vegetation that was
growing in the Denver area millions of years ago.