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Nature and properties of fragipans in Massachusetts
Abstract
A comparison of features between pans developed in the glaciated terrain of Massachusetts and those considered diagnostic to fragipans reveals numerous similarities. The overall morphology of both pan types includes high and low chroma mottles, bleached prism faces (polygons), numerous clay skins, vesicles, evidence of an eluviated horizon, and a massive to platy structure. Most pans observed have a sufficient clay accumulation to qualify as argillic horizons indicating that illuviation is occurring. The pans also have high bulk densities and low permeabilities. The Massachusetts pans exhibit micromorphology including the presence of: argillans, ferrans, skeletans, grain argillans (clay bridges), and a sepic fabric; all are common pedogenic features and typical to fragipans. Examination of the chemistry and mineral assemblages (both clay and heavy minerals) of the soils studied also suggests that pedogenic processes have altered the glacial till parent material. The pan is slightly more weathered, typically having lower pH and base saturation, more developed clay minerals, and stained and etched heavy minerals than the underlying till. Two of the soils investigated have aeolian components that are easily identified based on the heavy mineral assemblages. New England fragipans exhibit the typical brittle character and slaking in water commonly associated with all fragipans. Shear strength analysis indicates that removal of clay is primarily responsible for a decrease in strength, yet silica is also indicated as contributing to the strength of the pan. Pebble fabric analysis indicates that the fabric of the pan is consistent with that of the late Wisconsinan Upper Till whereas fabric of the till beneath the pan suggests that it is Illinoian (early Wisconsinan) Lower Till with the exception of the sandy Ridgebury soil. This determination sets the age for the material comprising the pan to approximately 18 ka. Evidence of pedogenic development is observed in the micromorphology, chemistry, mineralogy, and strength of the fragipans investigated. The similarities between the pans investigated and the taxonomic diagnostic indicators suggest that the pans have formed via similar processes as those developed elsewhere.
Subject Area
Geology|Agronomy|Environmental science|Mineralogy
Recommended Citation
Lindbo, David Lloyd, "Nature and properties of fragipans in Massachusetts" (1990). Doctoral Dissertations Available from Proquest. AAI9100522.
https://scholarworks.umass.edu/dissertations/AAI9100522