X-RAY DIFFRACTION ANALYSIS OF WEATHERING PATTERNS IN HIGH-ELEVATION GLACIAL, PERIGLACIAL, AND EOLIAN SEDIMENTS IN NORTHERN NEVADA AND UTAH

This study presents preliminary results from XRD analysis of the clay-size fraction of Quaternary glacial deposits from the Ruby Mountains in NE Nevada and eolian and periglacial sediments of the Uinta Mountains in N Utah. The purpose of the study is to better understand the mineralogy of tills comprising moraines in the Ruby Mtns, as well as non-glaciated, clay-rich Pleistocene (or Pliocene?) periglacial sediments on summit flats in the Uinta Mtns as a first step in exploring possible links between glacial deposition, pedogenesis, long-term weathering and eolian processes. Ruby Mtn samples consist of A-horizons and C-horizons of soils developed on a series of moraines of known relative ages (absolute ages are not yet constrained). The clay-sized mineralogy of the C-horizon of each moraine is dominated by illite (I), kaolinite (K), vermiculite (V) (all likely pedogenic), plus quartz (Q) and plagioclase (P). Other than the presence of a small amount of chlorite (Ch) in the youngest moraine, there is no appreciable difference in C-horizon mineralogy. In contrast, moraine A-horizons show little evidence of pedogenic minerals; they primarily contain I, Ch, Q and P. Dust deposited on a snowbank at high elevation in the Uinta Mtns provides a proxy for eolian inputs– these sediments contain I, K, Ch, Q, P and minor V. The similarity of this signature to that of moraine A-horizons in northern Nevada suggests that A-horizon mineralogy regardless of age is dominated by eolian deposition. The non-glaciated summit flat in the Uinta Mtns near the site of the snowbank sample is characterized by an evolved Bt-horizon with abundant pedogenic smectite and K; however, the A2-horizon contains Q, F, K, Ch and I, suggestive of a strong eolian contribution to the A-horizon. Conclusions from this preliminary stage support other studies which demonstrate that pedogenesis at high elevations is a combination of eolian deposition and in situ weathering of locally-derived parent material. Future research will target extensive sampling of soil horizons, local parent materials and eolian deposits, as well as geochemical analysis of major and trace elements. Profile development indices will also be calculated in order to better constrain contributions of glacial parent material, time, and eolian deposition on pedogenesis in these environments.