Research Training Program

Smithsonian Institution
National Museum of Natural History

PROJECT SUMMARY
1996

Darren R. Locke
Norwich University
Cornfield, Vermont
William Melson, Ph.D.
Supervising Scientist
Department of Mineral Sciences
"This experience of working with a great scientist was exciting as well as being extremely informative."

Ordovician Volcanism and its Implications to the Taconic Orogeny

ABSTRACT
Altered volcanic ash beds (K-bentonites) are exposed in 450 million year old (Ordovician) rock in Strasburg, Virginia. These volcanic ashes fell into a shallow sea and were deposited upon a stable carbonate platform where marine life consisted largely of brachiopods, trilobites, and crinoids. Those beds are a record of large volcanic eruptions that ejected large amounts of ash that extended over large areas of land and sea. Some ash fall material became mixed with muds that were derived from the land. The ash beds were later altered by the process of making sediments into rocks (diagenesis). The resulting mineralogy of the layers are now different than the original mineralogy. However, it is possible to characterize K-bentonites based on their heavy mineral contents (minerals with specific gravity greater than 2.8). Using a standard petrographic microscope and electron microprobe, identification of heavy minerals is possible. The heavy minerals of K-bentonitos may include apatite, zircon, pyrite (fools gold), and hematite. Apatite and zircon are minerals that have not altered and still have their respective crystalline forms. A Scanning Electron Microscope (SEM) was used to look at the morphologies of these near perfect crystals and the grain sizes for K-bentonites and shales. An X-ray diffractometer, a machine that allows scientist to identify minerals using crushed rock samples, was used to identify quartz, albite (feldspar), calcite, and chlorite. All the equipment that was used in this study was used specifically to answer a question. The information that was received from these analyses has led to a characterization of K-bentonites and shales which can be used to correlate these layers of rock between different rock exposures. In the future, there are plans to obtain ages of these K-bentonites by radiometric dating.

This research was supported by a grant from the National Science Foundation Research Experiences for Undergraduates program, Award Number DBI-9531331.

Letter of Gratitude