Monday, November 5, 2007 - 11:05 AM
114-5

Have Soils in Northwestern Indiana Been Influenced by Post-Glacial Acid Sulfate Weathering?.

Darrell Schulze and Phillip Owens. Purdue University-Agronomy Dept., Purdue Univ.-Agronomy Dept., 915 W State Street, West Lafayette, IN 47907-2054

Some soils formed in outwash deposited in front of the Valparaiso Moraine in northwestern Indiana appear to have undergone acid sulfate weathering since the end of the Wisconsin Ice Age. Morphological evidence includes: deep leaching of carbonates, base saturation < 50% in the lower parts of the profiles, weakly developed argillic horizons, parent materials described as "acid shale," and prominent, yellowish-brown, iron-oxide-rich masses that may be weathered pyrite nodules. Pyrite nodules, apparently inherited from the shale bedrock excavated from the Lake Michigan basin by the glacier, are occasionally described in the lower part of some profiles, and pyrite is frequently found in gravel mined in the area. As early as 1913, aluminum toxicity was identified as the cause of poor crop growth on soils in the area, and in some areas even the native vegetation grew very poorly. Although many of the soils on the outwash fan are acid and well drained, marl frequently occurs under peat in depressional areas. Bog iron ore is common in the Kankakee River Valley which drains runoff from the outwash fan. Arsenic is higher in sediments of the Kankakee River than in any other streams in the Illinois River Basin. We hypothesize that the acidity produced by the weathering pyrite resulted in a regional redistribution of elements and the minerals in which they are contained. Calcium was leached from upland positions and reprecipitated as marl in the wetlands that formed in depressions. Iron may have moved regionally as well, although probably not to the extent of Ca. Arsenic originally in the pyrite probably accounts for the high As contents of the Kankakee River sediment. Hydroxy-interlayered phyllosilicate minerals should have formed in the most acid upland positions, but this remains to be investigated. The acid, pyrite rich material was spread over a large area south of Lake Michigan by water and wind. Broader implications remain to be investigated.

Back to Symposium--Distribution of Soil Minerals in Landscapes (includes Graduate Student Competition): I
Back to S09 Soil Mineralogy

Back to The ASA-CSSA-SSSA International Annual Meetings (November 4-8, 2007)