Sediment-water interactions in three Holocene saline, alkaline playas, south-central Oregon: Mineralogy and geochemistry

Mineralogical, chemical, and isotopic analyses of clay minerals from outcrops and playa sediments, as well as chemical and isotopic analyses of groundwater and interstitial playa pore waters, have been used to improve understanding of the nature of sediment/water reactions in playa environments. Outcrop samples and 5 to 7 m deep playa cores were studied from three closed basins in south-central Oregon. Al-rich dioctahedral smectite dominates outcrop samples from the Alkali and Abert basins, whereas Al- and Fe-rich dioctahedral smectite is most abundant in the Alvord basin. The composition of smectite from outcrop samples reflects the composition of parent rock in each basin. In Alkali and Abert playas, randomly interstratified Mg-rich trioctahedral kerolite/smectite (Ke/Sm) formed, whereas in the Alvord playa Mg-smectite did not form, due to a lower degree of evaporative concentration. Thus, mineral authigenesis in playa sediments is controlled by the composition of pore waters. Although the pore waters from all three playas plot in the stability field for trioctahedral Mg-smectite, progressive evaporation reaction-path calculations of dilute playa pore waters predict that Mg-silicate minerals should not precipitate from Alvord pore waters until the maximum extent of evaporative concentration observed at Alvord. In contrast, calculations predict precipitation of Mg-silicates at Alkali and Abert playas after little evaporative concentration. Additional reactions in playa sediments are formation of clinoptilolite $(\pm$ searlesite) at 2 to 4 m depth in the Alkali playa, probably reflecting an influx of volcanic ash and K$\sp+$-fixation within collapsed smectite interlayers at the Alvord playa. Authigenic illite was not found.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Geology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Matthews, James Coert

Contributors dc:contributor

• Altaner, Stephen P.

• Mineralogy
• Geochemistry

Statement dc:rights

• Copyright 1992 Matthews, James Coert

Language dc:language

eng

Identifier

AAI9305616
(UMI)AAI9305616

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/22463