Exploring Earth Science at the Frontiers of Discovery: Redhill Ridge’s Dakota Sandstones Contain Trace Fossils

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Exploring Earth Science at the Frontiers of Discovery:

Redhill Ridge’s Dakota Sandstones Contain Trace Fossils

by Chris Retzlaff (13), Colorado Springs Mineralogical Society

From: Pick & Pack, 4/2010

(2nd Place – AFMS Junior Articles, 12-17)

The Redhill Ridge area in Park County, Colorado is a hogback composed of Dakota Sandstone. This fine-grained, Cretaceous-age sandstone—near the town of Fairplay—contains trace fossils (Figures 1 and 2) that help paleontologists understand what the environment was like there more than 65 million years ago. Trace fossils, also called ichnofossils, are like fossils of any kind—they are traces of organisms preserved in the Earth's crust from prehistoric times (Hantula, 2002). Trace fossils can be important to paleontologists for

many reasons. Trace fossils capture paleo behavior of prehistoric creatures revealed through the traces they left behind, such as burrows, tracks, trails, coprolites (excrement), and boreholes (Pannell, 2004). Trace fossils also provide information on the climate and the environment they were formed in. When examined, trace fossils may reveal many important facts about the rock they are embedded in, such as the sedimentary environment, the rate of deposition, and if water flowed on or near the rock (Kusky, 2005).

Generally, if the maker of the trace is not found in direct involvement with its trace, it is difficult or impossible to know what organism made the trace. For instance, an entirely different organism may produce identical traces. Because of this problem, trace fossils are classified into either genus or specie groups—ichnogenera and ichnospecies respectively—and do not relate to the organisms that created them. For the most part, the only way to truly determine what organism created a trace fossil is to find the actual fossilized remains, or body fossils, of the organism that made the traces in direct association with those traces.

The Redhill Ridge trace fossils hold some interesting clues as to what organisms lived there. First, during the Cretaceous Period, the area near present day Fairplay was near the shore of a huge inland sea—the Western Interior Seaway (Chronic and Williams, 2002). This shows that whatever creature made these fossils in the Redhill Ridge area lived in shallow water near the shore. Using these clues it is possible to hypothesize that the organisms that made these traces were worms or similar animals. Next, the trace fossils show that the maker could dig a system of burrows and tunnels in the sand. Furthermore, it is possible to assume that the organism's habitat was wet because of its ability to burrow in sand. Finally, from measurements of the actual trace fossil specimens it is easy to tell their widths range from 3 to 5 millimeters.
The Redhill Ridge area is rich in trace fossils, and these fossils continue to aid paleontologists to better understand the local environment as it was during the Cretaceous.

Chronic, H., and Williams, F., 2002. Roadside Geology of Colorado. Missoula, Montana: Mountain Publishing Company.

Hantula, R., 2002, "FOSSIL." Funk & Wagnalls New World Encyclopedia. New York: World Almanac Education Group, Inc.
Pannell, M., 2004. "Fossil and Fossilization." The Gale Encyclopedia of Science. Detroit: Gale Virtual Reference Library.
Kusky, Timothy, 2005. "Biogenic Sediment." Encyclopedia of Earth Science. New York: Facts On File, Inc.
About the author:

Chris Retzlaff is 13 years old and in the eighth grade. He is interested in many subjects in school, especially science. He enjoys the outdoors and likes to hike, ski, and run. Also, he plays the piano and enjoys all types of music. Retzlaff lives in the Denver metro area.

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