49 Geochemistry (Posters)

Tuesday, 20 March 2012
8:00 AM - 12:00 PM
Ballrooms A, B & C and Ballroom Pre-function Area

ADIRONDACK TILL TO SOIL: GEOCHEMISTRY AND MINERAL TRANSFORMATIONS

Paper number: 49-1
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

We are studying the mineralogy and geochemistry of Adirondack till and soil as part of a larger study to better understand chemical weathering and soil formation in the Critical Zone (the thin veneer of surface material on our planet which sustains all terrestrial life - www.czen.org). Four sites were chosen for study in the town of Webb, near Old Forge, in the west-central Adirondack Mountains of New York State. Using x-ray diffraction (XRD) analyses and RockJock, a quantitative modeling program, we determined that quartz, K-spar, plagioclase (average ~An30), and hornblende were the most abundant minerals in these soil profiles, with clay minerals illite and vermiculite present at approximately 2-3%. The percentage of quartz drops substantially with depth, decreasing in concentration from 68.5 wt.% in the E horizon (of pit 10-01, for example) to 36.9 wt.% in the C-horizon. The B-horizons of all four pits contain vermiculite that takes the form of an hydroxy-interlayered clay, as determined by XRD patterns that show the gradual collapse of the clay interlayer structure with K-saturation and heat treatments.

Concentrations of exchangeable calcium, potassium, sodium, and magnesium were determined on soil leachates extracted with 1N NH4Cl and analyzed by atomic absorption spectrophotometry. Extractable calcium and potassium values are highest in the O and A horizons, and decrease with depth. High calcium and potassium values in these upper horizons result from the decomposition of litter-layer material releasing these base cations back to the soil. Tau plots show depletion of base cations and the accumulation of Fe and Al in B-horizons as a result of chemical weathering and pedogenic processes.