by Tim Farnham
A primary focus
of the Denver Basin Project is to understand the sediments deposited
by the uplift of the Rocky Mountains. This helps us create an accurate
timeline that helps us better date fossil plant and animal localities
throughout the Denver Basin. The Denver Basin paleosol is crucial
to our understanding of the timing of the uplift of the Rockies
as well as to our understanding of the environment of the Denver
area millions of years ago. Analysis of the paleosol is ongoing,
including both field and lab work.
The focus of
my paleosol research is to understand what kind of environment is
represented by the paleosol and its age. There are several components
of a paleosol that provide clues to its environment.
of clay mineralogy and micromorphology, or small-scale features,
are the two primary areas of research when attempting to reconstruct
an environment. Both of these techniques require extensive fieldwork
and sampling of the paleosol. Fieldwork on the paleosol has proceeded
with the help of an undergraduate intern, Adam Soldinger, from the
University of Colorado at Boulder.
With the help
of Bob Raynolds, I identified seven outcrops of the paleosol around
the Denver Basin. The outcrops are spread out, giving us as much
variation as possible. This ensures that we analyze the paleosol
throughout the basin instead of only a small portion of the Denver
Basin. Fieldwork consists of stratigraphic-section measuring and
sampling of every identifiable unit or horizon in the paleosol.
Samples are then brought to the labs at the University of Colorado.
Once in the labs, some portions of the samples are made into thin
sections for microscopic analysis, and other portions are ground
up and run through an X-ray diffraction (XRD) machine in order to
identify types of clay minerals.
Adam and I
have already made an excursion to a paleosol outcrop slightly north
of Kiowa called the Navajo Pit and have run samples through the
XRD machine at the University of Colorado. Preliminary results showed
the presence of the clay mineral kaolinite in every sample, as well
as smectite and vermiculite in one sample. Kaolinite is indicative
of a highly weathered environment, like a tropical soil, and smectite
and vermiculite are associated with seasonality in soils.
Based on fieldwork
completed so far, the general appearance of the paleosol is tropical.
The paleosol at the Navajo Pit is dark red with very large white
mottles caused by root traces or the migration of water through
the soil. In fact, several of the layers at the Navajo Pit have
the fossil roots still intact with white mottles around them. In
addition to the red beds, there are four separate horizons that
are bright purple with white and yellow mottles, which creates a