Gibbsite Quantification with DSC – An Approach to Determine Relative Soil Development on a Moraine Chronosequence.

Gibbsite presence and quantity was assessed in nine soil profiles (57 genetic horizons) on glacial moraines from a developmental chronosequence on the west side of Lake Tahoe, California. Total gibbsite quantities were determined using differential scanning calorimetry – thermogravimetry (DSC-TG) of bulk soil samples and clay fractions with and without H₂O₂ pretreatment. Gibbsite was quantified by sample weight loss between 220 and 320 (region of gibbsite thermal decomposition (dehydroxilization) measured with TG and compared to standard reference materials.  XRD analysis supports TG analysis with correlation between increasing crystallinity and sample weight loss. The minimum ages of the different deposits was obtained by geomorphic correlation to previously cosmogenically dated (¹⁰Be) boulders with preliminary results showing a positive correlation between the presence of TG-Gibbsite quantity and the age of parent material deposits. In addition correlation between bulk soils and clay size fractions were strong with slightly higher quantities measured in bulk samples. Based on these results, we feel this approach holds promise as a tool to determine gibbsite quantity in bulk soil samples without particle size fractionation. A fully function method would reduce sample preparation time and potentially increase the accuracy of soil Gibbsite quantification by including coatings and other non-‘clay size’ particles. This method can support investigation at greater spatial extents with increased sample throughput at lower time commitments to better understand the stage of development of soils on glacial deposits.