Doctoral Dissertations

Date of Award

12-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geology

Major Professor

Devon M. Burr

Committee Members

Christopher M. Fedo, Anna Szynkiewicz, Liem T. Tran

Abstract

Ancient fluvial features on Mars evidence past episodes of hydrologic activity and paleoclimate conditions suitable for liquid water. The Aeolis Dorsa region preserves the most numerous and diverse assemblage of fluvial features yet observed on Mars and many of these features have experienced a history of burial, exhumation, and topographic inversion. This dissertation describes analyses of visual images and topography of Mars and complementary analyses of fluvial analogs on Earth. These analyses provide information about the styles of fluvial activity, magnitudes of paleodischarge, changes in slope, and inferences about Martian paleoclimate conditions. Results indicate that the Aeolis Dorsa deposits encapsulate a wet-to-dry hydrologic transition, characterized by decreasing geospatial extent and frequency of hydrologic events. This wet-to-dry transition mimics the history of hydrologic activity preserved in valley networks and alluvial fans elsewhere on Mars. Results from an analysis of the Quinn River, NV, a terrestrial analog fluvial channel, indicate that width-discharge relationships from hydraulic geometry yield more accurate and more precise estimates of discharge than previously applied width-discharge relationships from the Missouri River Basin. These more accurate width-discharge relationships from hydraulic geometry, when applied to Martian features, yield larger paleodischarge estimates for Noachian-Hesperian valley networks and smaller paleodischarges for Hesperian-Amazonian fluvial deposits than were previously estimated. These new paleodischarges increase the contrast between early and late episodes of hydrologic activity by an order of magnitude. Results from additional analyses of terrestrial analogs and the Aeolis Dorsa deposits reveal confounding factors associated with resistant channel banks and erosion. These factors increase the systematic uncertainty of terrestrial-based empirical relationships and increase the error associated with estimates of paleochannel width and paleodischarge. These results point to the importance of assessing the validity of applying terrestrialbased empirical relationships to Mars, and they suggest that changes in paleodischarge are equivocal explanations of major changes in fluvial geomorphology. Findings from the remote analyses presented in this dissertation, combined with results from many previous field investigations, emphasize the importance of coupling Martian and terrestrial investigations for elucidating paleohydraulic conditions and fluvial histories, both of which are important considerations in the evaluations of future rover landing sites.

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