K-T Boundary Location Narrowed
The Denver Basin Project, a research endeavor supported by the National Science Foundation, continues to involve dozens of researchers in the intriguing process of understanding the geology beneath Denver. In 1999, the main focus of the project was the drilling of a 2,256-foot-deep cored well at the Elbert County Fairgrounds in Kiowa. In 2000, the focus was on the laborious process of analyzing the two-and-a-half-inch-round core. Early results from the core have initiated some strategic fieldwork on the plains of eastern Colorado.

A major goal of the drilling project was locating the horizon that marks the Cretaceous-Tertiary (K-T) boundary. This 1/8-inch-thick layer is made of debris from a catastrophic impact that occurred 65.5 million years ago when a giant asteroid smashed into Mexico. One of the most compelling hypotheses of the last 20 years is that this impact may have been responsible for the extinction of the dinosaurs and their world. But finding a layer this thin is more challenging than searching for a needle in a haystack. Fortunately, the layer can be located by studying tiny fossilized grains of pollen that blew off of extinct plants and landed in streams and lakes in the distant past. The highest level of the pollen in the core marks the level of the K-T boundary. Although the horizon was located 879 feet below the core’s surface, the drill bit had obliterated the very layer that contained the asteroid debris. All was not lost, however, because by using the Museum’s new geographic information systems (GIS) mapping laboratory, the team was able to narrow the search to an area 35 miles east of Denver.

Using a systematic search of the target area, Rich Barclay, a master’s student at the University of Florida, discovered a promising site on the banks of West Bijou Creek south of Strasburg. He carefully trenched and measured the horizontal rock layers that formed the slope of a 120-foot-high bluff. Near the top he found three sites yielding fossil leaves from plants that grew after the extinction of the dinosaurs. At the bottom he collected a rock sample yielding Cretaceous pollen. Realizing that Barclay had bracketed the K-T boundary, more samples were collected, reducing the span between the lowest Tertiary sample and the highest Cretaceous sample to a mere four inches! About fifteen feet below this level, the team found the bones and teeth of a duck-billed dinosaur, one of the last of its kind in the world. The team is now painstakingly searching the target layers for the rare metals and catastrophically shocked minerals that uniquely identify the K-T boundary.

It is awesome that these miniscule fragments blasted out of a crater in Mexico and rained down on the Colorado landscape some 65.5 million years ago.

-- Kirk Johnson, DMNS curator of paleontology

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