Year of Award

2009

Document Type

Thesis

Degree Type

Master of Science (MS)

Other Degree Name/Area of Focus

Geology

Department or School/College

Department of Geosciences

Committee Chair

Nancy Hinman

Keywords

geyserite, hydrothermal breccia, microfacies, sinter

Publisher

University of Montana

Abstract

Ertel, Bonnie, M.S., Spring 2009 Geology Microfacies and Morphology of a Fossil Hot Spring System, McGinness Hills, Nevada Chairperson or Co-Chairperson: Dr. Nancy Hinman The Miocene McGinness Hills sinters are a well-preserved, fossil hot spring system in Nevada. The sinter in McGinness Hills is comparable with the fossil hot spring system in the Drummond Basin, Queensland, Australia (Farmer and Hinman, 1998), Artist Point in Yellowstone National Park (Hinman and Walter, 2005) and with modern systems in Yellowstone. Further The purpose of this study was to further our understanding microfacies preserved in hot springs systems after diagenesis thus facilitating the identification of epithermal systems in which exposure is limited. It is possible to recognize a range of paleo-hot spring environments from near-vent stratiform geyserite, outflow channels and terraces and distal marsh facies. McGinness Hills is a ‘decapitated’ system in which hydrothermal, eruption breccia is exposed on top of the sinter mound. Based on lithology, macro-features and micro-features the sinter at McGinness Hills was divided into seven microfacies, hydrothermal breccia, massive chalcedonic sinter, flat-laminated sinter, stromatolitic sinter, palisade sinter, palisade sinter, sinter breccia and marsh sinter. The microfacies followed a general bulls-eye pattern with hydrothermal breccia and massive chalcedonic sinter in the center, grading out to the opaline, low temperature marsh facies. Hydrothermal eruption breccia is normally a subsurface feature confined within the throat of the geyser (Browne and Lawless, 2001) hence the breccia at McGinness Hills provides a glimpse into the inner workings of a geyser.

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© Copyright 2009 Bonnie Jean Ertel