DEVELOPMENT OF A STAGE IV CALCIUM CARBONATE SOIL AT MORMON MESA, NEVADA

 Amy L. Brock, Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV, [email protected]

Pisoliths and brecciation have been identified in soils in many locales throughout the southwestern U.S. and world.  However, the processes by which they form are relatively unknown.  This research proposes a model of development for these features.  This study focuses on highly developed petrocalcic horizons at Mormon Mesa, Jean and Laughlin, NV and is currently testing the following three hypotheses: (1) Multiple processes result in the formation of calcic soil pisoliths.  (2) Multiple processes result in the formation of brecciation that defines stage VI petrocalcic soils and the sequence of brecciation reveals multiple cycles of landform erosion, followed by sedimentation and renewed landscape stability.  (3) The formation and development of these features is time dependant.

This study uses micromorphology to examine pisoliths and brecciation, minerals present and the relationships between these features both developmentally and chemically.  X-ray diffraction is being used to compliment micromorphology results as to what minerals are present in these soil horizons.

This study will provide a more extensive look into the genesis of highly developed petrocalcic horizons.  Applications of this research can be applied to understanding other similar soils throughout the world and regionally, results of this study will assist in characterizing previously unstudied southern Nevada soils and associated geomorphic surfaces associated with the Colorado River drainage.