Fall 2006 Colloquia

Monday, October 30
Jim Brophy, Indiana University
"Is fractional crystallization an elegant but obsolete notion? On-going studies into the fractionation question."

Wednesday, November 1 - 12:00 to 1:30 PM Patton Room S201
Jeannette Forsén, Classical Archaeologist
Introductory Notes: Jim Brophy, Indiana University
Brownbag: "Archaeological and Geological Methods: A Case Study from the Greek Early Bronze Age."

This is an informal talk about Jeannette Forsén's dissertation, "The Twilight of the Early Helladics". In her research Forsén notes the large gap between archaeological data and theory. She suggests the development of more cultural hypotheses that stress continuity versus discontinutity in the archaeological record. She stresses rigorous methodology. Her discussion will be linked with Shriner's and Brophy's geological fieldwork on the South Aegean Volcanic Arc, and Aegina Island in particular. The development of appropriate raw material reference standards is advocated as the most efficient manner in which to theoretically bridge the artifactual material and cultural problems. Introducing: The South Aegean Volcanic Arc (SAVA) database and website.

Wednesday, November 1 - 4:00 to 5:30 PM Patton Room S201
Jeannette Forsén, Classical Archaeologist, and Björn Forsén, Ancient Historian
Welcome: John Steinmetz, Director of the Indiana Geological Survey
Introduction of Speakers: Nicholas Toth, Co-Director of Stone Age Institute
Special Lecture: "Recent Developments and Challenges in Greek Landscape Archaeology: Reflections on Two Projects in Arcadia and Thesprotia"

This lecture is divided between Jeannette and Björn Forsén. They will discuss their surface surveys in the Asea Valley, Arcadia, Greece and Thesprotia, Epirus, Greece. The researchers will stress the interdisciplinary aspects of modern Greek Landscape Archaeology. There will be a natural interplay between different disciplines such as archaeology, history, and geology. I think the audience would be interested in how they built their survey methodology -- after whom it was modeled -- the extent and nature of geological interaction.

Monday, November 6
Lisa Pratt, Indiana University

Thursday, November 9
Steve Wells, Desert Research Institute - 4PM in Indiana Geological Survey Room S201
Owen Award Lecture "Evolution of Desert (Stone) Pavements: Interactions of Surface and Soil Processes"

Desert pavements are a ubiquitous gravel armor mantling many landforms in arid regions of the world. Because desert pavements may exist for hundreds of thousands of years, they provide one of the longest-term records of shallow subsurface hydrologic processes and ecologic responses. These armor mantles occur as a one- to two-particle-thick layer of closely packed, angular-to-subrounded gravels and develop above a relatively gravel-free layer in which weak to moderately developed soil has formed. Previously, desert pavement formation was attributed primarily to erosion/deflation by wind and water, alternating shrinking and swelling of soil horizons, or a combination of these processes. This implies that gravel is concentrated at the land surface in a time-transgressive manner. McFadden and Wells proposed a different model of desert pavement evolution in which pavement clasts are continuously maintained at the land surface in response to deposition and pedogenic modification of windblown (eolian) dust. In this model, pavements are maintained at the surface as cumulic soils develop in response to the incorporation of eolian silts and clays deposited on the land surface and subsequently transported vertically and laterally into soil horizons and the interior of peds. The resulting increase in thickness and volume of soils underlying desert pavements provides the primary, vertical-lifting mechanism for maintaining clasts at the surface.

In situ cosmogenic exposure ages on selected volcanic landforms in the western U.S. advance the understanding of desert pavement evolution over geologic time scales. The "born at the surface" model was tested for the formation of desert pavements by comparing in-situ cosmogenic exposure ages of cobbles from desert pavements with exposure ages of their underlying source rock (in this case, constructional topographic highs on late Quaternary basaltic flows). Cosmogenic 3He surface exposure ages show stratigraphic and internal consistency at each site, supporting the hypothesis that desert pavements are born at the surface above complexly evolving soils developed within an eolian accretionary mantle.

Recent studies of desert pavements illustrate that they are comprised of a mosaic of spatially distinct regions, varying in physical and biological parameters that both influence and reflect surface and subsurface hydrologic processes such as infiltration/runoff and leaching. Leaching within the subsurface is least and runoff is highest in areas with the best developed pavement, including 90% clast cover. With decreasing percent of clast cover, infiltration and depth of soil leaching increase resulting in the highest values for percent of cover by vegetation. In areas of well-developed desert pavements, an increase in the content of pedogenic clay and CaC03 cause mantle permeability to decrease. Decreased mantle permeability, in turn, results in lower vegetative cover and promotes increased runoff, surface erosion, and drainage network development. In conclusion, key properties of desert pavements (e.g., clast size distribution and degree of interlocking of clasts forming the armor) can be used to predict mesoscale spatial variability of soil properties and shallow subsurface hydrologic processes.

Monday, November 20
Martin Appold, University of Missouri - Columbia
"Flow and Geochemistry of Mississippi Valley-type Ore-Forming Brines in the Western Arkoma Basin and Ozark Plateau"

Numerical groundwater modeling and laser ablation ICP-MS have been used to investigate the role of fluid flow associated with uplift of the Arkoma basin during the closing stages of the Ouachita orogeny in forming the Mississippi Valley-type Zn-Pb ores of the Tri-State district. The model hydrostratigraphy was flexurally compensated to account for the restoration of Pennsylvanian-Permian sediments removed since the close of the orogeny in estimating the regional paleotopogrpahic gradient. Estimates of the amount of Pensylvanian-Permian sediment that has been removed by erosion vary widely. A thick and a thin endmember case were considered, and in both cases topography-driven fluid flow was shown to have been an important mechanism for groundwater motion, with a lesser component contributed during the early stages of uplift by overpressuring created by compaction of the deep portion of the Arkoma basin. The Pennsylvanian-Permian sediments and underlying Western Interior Plains confining system acted as thick capping aquitards that caused slow rates of groundwater flow over much of the profile. As a result, meteoric water infiltration initiated during uplift was slow to flush saline formation waters, allowing MVT ore-forming salinities to persist at Tri-State on the order of at least 100 million years. The slow groundwater flow rates also caused heat transport to occur primarily by conduction rather than advection. Despite this, MVT ore-forming temperatures were still reached at Tri-State for both endmember cases of Pennsylvanian-Permian aquitard thickness, though much more readily in the thick aquitard case. Faults within the district served as a regional fluid focusing mechanism and probably played a much more important role in localizing mineralization than the window in the Ozark confining unit that occurs in the district. Fluids rising along these faults would have cooled by about 10° C and a further 0.2 to 0.25° C/km as they flowed laterally northward.

Laser ablation ICP-MS analyses of fluid inclusions from quartz, sparry dolomite, and sphalerite from the Tri-State and Northern Arkansas districts reveal concentrations of Zn, Pb, and Cu on the order of tenths to 1â€TMs of ppm, and Ba concentrations ranging from 10-60 ppm during most of the period of gangue mineral precipitation. These results indicate that fluids circulating through the Tri-State district during the time of gangue mineral deposition were not anomalously metal-rich compared to typical sedimentary basinal brines. During sphalerite deposition, Pb concentrations in fluid inclusions reach significantly higher concentrations (over 400 ppm in Northern Arkansas). Major element compositions of fluid inclusions in quartz and sparry dolomite also differ from those in sphalerite. Together, these data suggest that metal sulfide deposition in the Tri-State and Northern Arkansas districts may have been caused by invasion of a metal-rich fluid into the districts, perhaps mixing with another fluid there that was enriched in reduced sulfur.

Monday, November 27
Eric Roden, University of Wisconsin
"Anaerobic redox cycling of iron in sediments"

Recent studies indicate that a diversity of microorganisms are capable of oxidizing Fe(II) with nitrate as an electron acceptor. In contrast to the rapid abiotic oxidation of Fe(II) with oxygen at circumneutral pH, abiotic reaction of Fe(II) with nitrate is negligible under the temperature and aqueous geochemical conditions typical of natural soil and sedimentary environments. Thus, microbial activity is directly responsible for nitrate-driven Fe(II) oxidation, and this reaction greatly enhance the potential for coupled Fe-N redox interactions in sediments. Such interactions have the potential to lead to the development of novel microbial populations and/or communities specifically adapted to take advantage of the energy available during redox oscillations. An overview of recent experimental investigations of this possibility will be presented, including evidence for both reduction of Fe(III) and nitrate-driven oxidation of Fe(II) by the same organisms.