A primary focus of the Denver Basin Project is to understand the sediments deposited by the uplift of the Rocky Mountains. This will help us create an accurate timeline, which will help 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, and field and lab work have started.
The focus of my paleosol research is to understand what kind of environment is represented by the paleosol and its age. As indicated by my discipline summary on the Web site, there are several components of a paleosol that provide clues to its environment.
Identification 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 palaeosol is proceeding 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 will consist of stratigraphic-section measuring and sampling of every identifiable unit or horizon in the paleosol. Samples will then be brought to the labs at the University of Colorado. Once in the labs, portions of the samples will be made into thin sections for microscopic analysis, and portions will be 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.
We have not yet made any thin sections, but 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 spectacular outcrop.
Field and lab work will continue for the rest of the summer and into the fall. Look for another posting about the paleosol in about nine weeks; and thanks for stopping by the Denver Basin Project Web site!