Scientist at Work: Juergen Schieber
The majority of Earth's geologic record is composed of sedimentary rocks, such as limestone, sandstone and shale. These rocks form when weathering detritus accumulates in lakes, oceans or river valleys, and also when chemical processes cause precipitation of minerals such as calcite, gypsum or quartz. Once deposited, these materials compact and turn into solid rock.
Chris Meyer
Professor of Geological Sciences Juergen Schieber at work on his mud flume
The Grand Canyon in northern Arizona may be the world's most familiar "open book" of 1.7 billion-year's worth of sedimentary rocks, but new research by Indiana University sedimentary geologist Juergen Schieber casts doubt on whether we've accurately translated the book's words.
"Two-thirds of the rock record consists of very fine grained shales and mudstones, and these have barely been touched," Schieber said. "Because the grains are so tiny, they are difficult to interpret, and thus have mystified geologists for many years. There are many unanswered questions about how these rocks form."
In 2007, Schieber published a paper in the journal Science that showed, among other things, that tiny particles in swiftly moving water can still accumulate and form muds. The particles flocculate and form muddy ripples that merge and form mud beds. This was opposite to the conventional wisdom at the time, that in swiftly moving turbulent streams, rivers and seas these particles remain suspended and require a quiet environment (quiescent deeper water) to eventually settle out and accumulate.
Schieber's research may seem small on the surface, but it's the sort of foundational work that potentially has major impact. His research is likely to influence everything from the interpretation of the sedimentary rock record and the search for oil and gas, to the undertaking of big civil engineering projects, like harbors and canals.
Schieber accomplished the research with the help of a "racetrack flume" he built in the basement of IU Bloomington's Geology building. The large, oval device pushes water around at a pre-determined velocity and allows for the infusion and removal of particulates that, with water, can form muds on the base of the track. Schieber and his collaborators can then observe the behavior of these muds, such as the migration of mud ripples.
Schieber's geologist colleagues are so enthused about the work he reported in Science that they subsequently awarded him the Best Oral Presentation at the Society for Sedimentary Geology annual meeting in 2007, as well as the Energy Minerals Divison President's Certificate for Excellence in Presentation at the American Association of Petroleum Geologists annual meeting in 2008.
Chris Meyer
Heart-shaped ripples form at the base of the mud flume, even when the water velocity is high.
Schieber's discoveries tell geologists that they cannot necessarily assume that the fine grained sedimentary rocks they are looking at were formed at the base of lazy streams and halcyon seas, and that the tiny particles that compose shales and mudstones may have traveled long distances over the bottom of ocean basins, rather than simply settling through the water column.
"You need to understand how things ended up where they are," Schieber said. "You need to know how fast they got there, and how quickly or slowly the particles accumulate where they come to rest. If you make uninformed models of how mud accumulates in a given case, any assessment of related variables, such as rate of accumulation, efficiency of carbon burial, etc., are bound to be off-target as well."
Earlier this year, Schieber published related papers in Geology and The Sedimentary Record demonstrating the physics of mud ripple formation and the relevance of his findings outside the laboratory. The latter aspect was aided by finding exact replicas of his flume-produced mud ripples in Indiana sedimentary rocks that were as much as 500 million years old.
He's also received a $2 million grant from the National Science Foundation to show how particle flow and ripple formation may influence the way in which sedimentary organic matter (forming near the sea surface) is buried and preserved in ocean sediments. Schieber and his colleagues will build a new mud flume that can simulate fine grained sediment movement at the bottom of the oceans (no light, low temperatures, low oxygen). Because carbon burial in the oceans is directly linked to the greenhouse effect, results from the project could influence scientists' understanding of Earth's ancient climate and projections for the future.
"Climate models depend on assumptions of how quickly carbon is buried, which in turn affects how we understand the global carbon budget, and how much CO2 is in the atmosphere," Schieber said.
Another image of Schieber is located at: http://newsinfo.iu.edu/asset/page/normal/4180.html.
This is an original article for the Sept. 15 issue of IU Discoveries.
