Award Date

1-1-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geoscience

First Committee Member

Brenda J. Buck

Number of Pages

148

Abstract

Highly indurated petrocalcic soil horizons are records of paleoclimate, and past geomorphic and pedogenic processes that have occurred in arid and semi-arid regions. This research used geomorphic mapping, profile descriptions and sampling, and micromorphological and chemical analyses to identify the geomorphic and pedogenic processes that contributed to the development of stage II-VI petrocalcic horizons at Mormon Mesa, Nevada. Soil pisoliths are described as stage II soil pendants and nodules incorporated into the indurated horizons as rotated soil pendants with pendant lamina on their undersides and as fragments of petrocalcic materials with pendant lamina on their undersides. These soil features record pedogenic responses to oscillations in climate from the early Pliocene to Holocene. The events that created pisolith features at Mormon Mesa include the exposure of the upper portions of the horizons, erosion, fragmentation, and incorporation of these fragments into eolian deposits at the surface. Chemical and mineralogical processes that occur within these highly indurated horizons include the dissolution of grains and formation of pedogenic minerals such as sepiolite, palygorskite, and barite. Pedogenic barite precipitated in areas of increased microporosity that include root pores, cracks, and amid fibers of fibrous silicate clays. Barium from dust leached into the profile during precipitation events and combined with sulfate to precipitate barite in the areas of microporosity. The chemical and mineralogical processes that have occurred in the Mormon Mesa soil are evidence that it is not a closed system. In western Arizona, strong stage V-VI petrocalcic horizons cap Neogene sediments of the Colorado River. Geomorphic mapping was used to examine the sediments that record the pre- and post-inception of the river system. Interpretation of these sediments and the soils that cap them is important for our understanding of the timing of river incision in the region. The work detailed in this dissertation is important for the overall understanding of geomorphic and climatic factors that affect the development of late-stage petrocalcic horizons. This research provides the necessary groundwork for future dating applications and contributes to our knowledge of the physical and chemical processes taking place within these unique soils.

Keywords

Arizona; Barite; Characterization; Horizons Nevada; Petrocalcic; Petrocalcic Horizons; Pisoliths; Pisoliths Stage; Vi

Controlled Subject

Geology

File Format

pdf

File Size

5918.72 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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