Where is the Cretaceous-Tertiary boundary? This is one of the questions that the team of researchers on the Denver Basin Project will try to answer. The Cretaceous-Tertiary boundary marks the division between the Mesozoic and Cenozoic periods in the Earth’s geologic history. It is also the time when the dinosaurs became extinct.

One science that is very useful in locating the Cretaceous-Tertiary boundary is palynology, which is the study of pollen and spores. Pollen is produced by flowering plants (including plants like aspen dandelions) and gymnosperms (including plants like pines and spruce trees). Plants such as ferns produce spores. Plants produce microscopic pollen and spores in huge numbers as part of their life cycle. After they are released from the plant, wind and water disperse pollen and spores and they can be carried great distances.

People who study pollen and spores are called palynologists. Some palynologists specialize in studying fossil pollen and spores. Because the cell wall of pollen and spores is so resistant, it is preserved in certain sedimentary rocks in huge numbers. During the Paleozoic, Mesozoic, and Cenozoic, pollen and spores were produced in huge numbers and preserved in sedimentary rocks. One small sample of shale or coal can contain billions and billions of these microscopic fossils.

Palynologists have learned that, like the plants that produced them, pollen and spores evolved over the course of geologic history. Pollen and spores from different times in Earth history are distinctive and they can be used to tell the age of the sedimentary rock.

One goal of the Denver Basin Project is to find the Cretaceous-Tertiary boundary in the core that was drilled at Kiowa. As the core is gradually removed from older and older rocks, samples will be taken for palynological analysis. These samples will be processed and analyzed to determine what kind of pollen is present. Pollen and spores are removed from sedimentary rocks by breaking up the rock and dissolving them in various acids. The microscopic fossils are mounted on a glass slide and examined under a compound microscope.

If the fossils are well preserved, we will be able to precisely locate the Cretaceous-Tertiary boundary. Some kinds of fossil pollen were produced by plants that lived only during the Cretaceous—these plants became extinct at the same time as the dinosaurs. Samples from Cretaceous rocks will have these Cretaceous pollen grains and they will be absent from Tertiary rocks. Looking for fossil Cretaceous pollen grains from the core will allow us to locate this important boundary. By using this method, we hope to precisely locate the Cretaceous-Tertiary boundary.

By studying other rocks from outcrops throughout the Denver basin, we can tell which rocks are Cretaceous and which rocks are Tertiary. By combining this information with information from other scientists on the project, we hope to reconstruct the history of the Denver basin.