Thermal Analysis Mineral Quantification and Applications as a Relative Dating Tool in Moraine Chronosequences
2016
Aburto, Felipe A. | Southard, Randal J.
Clay mineral quantification through thermal analysis (TA) is one of the most reliable methods currently available. However, this method can be time consuming because it may require previous particle size fractionation. We evaluated the quantification of gibbsite and kaolinite with and without fractionation and the effect of organic matter (OM) removal in nine pedons distributed in two Pleistocene moraine chronosequences near Lake Tahoe, CA. We also assessed whether the quantification of these minerals in bulk samples could be useful as a relative dating tool. Gibbsite and kaolinite were quantified by differential scanning calorimetry-thermogravimetry (DSC-TG) in bulk soils (<2 mm) and in the clay and silt fractions. The effect of OM was evaluated after chemical oxidation with H₂O₂ in the bulk soils and the clay fractions. In untreated bulk samples, strong OM oxidation in the kaolinite and gibbsite dehydroxylation ranges made TA quantification unreliable. OM removal facilitates and improves mineral quantification in bulk soil materials and in the finer fractions. Gibbsite content quantified in bulk samples was highly correlated with gibbsite estimated by DSC-TG in clay plus silt fractions (adjusted R² [R²ₐdⱼ] = 0.91; p < 0.01) and by quantitative X-ray diffraction (XRD) estimates (R²ₐdⱼ = 0.96; p < 0.01). There is a strong positive correlation (R²ₐdⱼ = 0.98; p < 0.01) between gibbsite content and the relative age of the deposits. Analysis of bulk soil material was faster than analyzing separated soil fractions and proved to be as effective in discriminating the ages of glacial deposits when used in combination with other relative dating techniques and deposit ages estimated by cosmogenic nuclide methods.
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