Vol. 17, No. 14	Dec. 11, 1997

Geologists well-represented at AGU meeting

Department chairperson John F. Wehmiller, for instance, described his latest efforts to resolve conflicting data concerning the ages of fossil shells and corals collected from sites along the U.S. Atlantic coastal plain.

The samples in question formed during the Quaternary Era, a period that began approximately 2 million years ago, when continental glaciers began to expand and retreat again and again. During each ice age, Wehmiller explained, global sea levels have dropped by approximately 100 meters. Whenever the ice has retreated, however, today's interglacial conditions have prevailed, and sea levels have been similar to current levels. Dating fossils from the U.S. Atlantic coastal plain helps researchers learn more about the climate and relative position of sea level at various points during the Quaternary Era, Wehmiller noted.

Through a fossil-dating technique known as "aminostratigraphy," certain protein components can serve as a kind of "geological clock," he added. Trapped inside Quaternary fossils, amino acids may exist in "left-handed" form, or in a mirror-image, "right-handed" form. Most living organisms contain only left-handed amino acids, Wehmiller said. But, over geologic periods ranging from thousands to millions of years, these left-handed forms are converted into mirror-image versions through a process known as "racemization."

Wehmiller studies the use of this reaction for fossil dating, comparing amino-acid dates with results from other methods, such as the examination of radioactive decay of uranium to thorium. New results from the U.S. Atlantic coastal plain are "challenging and exciting," he said. "They indicate an age and sea-level position that's not consistent with records elsewhere in the world, and so they raise questions about some of the fundamental theories of aminostratigraphy." Wehmiller said his latest findings may prompt a reevaluation of basic assumptions about this method of fossil dating.

Also during the AGU meeting, UD geologist James E. Pizzuto presented a new theory to explain the mechanisms that prompt randomly shaped grains within sediment to begin sliding or rolling. Such fundamental information should help researchers better understand the behavior of rivers and river sediments, Pizzuto noted. His theory resulted from an experiment conducted in the Grand Canyon, where Pizzuto collaborated with colleagues from the U.S. Geological Survey. The research team imbedded transmitters in boulders along the Colorado River, then examined the movement of sediment grains during an experimental flood, he explained.

Geophysicist Susan McGeary participated in a special AGU session on shallow subduction zones-regions that release 90 percent of the Earth's earthquake energy, causing almost all large, damaging earthquakes. In 1994, McGeary noted, UD served as the lead institution for a multi-million dollar seismic-imaging investigation of a key shallow subduction zone within an Alaskan volcanic arc. "We received reflections from the subducting plate at depths of 20 to 40 miles beneath the ship for a distance of 560 miles, allowing us to produce a type of picture of the zone where earthquakes occur," she explained. McGeary discussed the implications of her data during the AGU session.

Alaskan geology was the subject of a presentation by one of McGeary's undergraduate students, Kristoffer T. Walker, as part of a poster presentation. Michael S. Harris, a graduate student working with Wehmiller, discussed the geomorphic evolution of the central South Carolina coastal zone, using a combination of drilling, map analysis and aminostratigraphy.

Other UD participants in the AGU meeting included faculty from the College of Marine Studies, the Department of Geography, the Department of Physics and the Bartol Research Institute.

-Ginger Pinholster