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Exhumed Fluvial Deposits: New Paleohydrological Tools Indicate Long-Duration Fluvial Activity on Early Mars

Citation

Hayden, Alistair Thompson (2020) Exhumed Fluvial Deposits: New Paleohydrological Tools Indicate Long-Duration Fluvial Activity on Early Mars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/68ft-xm49. https://resolver.caltech.edu/CaltechTHESIS:09072020-172907018

Abstract

Fluvial sinuous ridges are common landforms on Mars that have been used for interpreting the history of ancient martian rivers. They are typically interpreted as eroded casts of an ancient river at a snapshot in time. However, some ridges might instead be channel belts that preserve river history, leading to significant differences in interpretation of paleohydrology, including flow direction, duration, and discharge. In this thesis, I used analog sites on Earth and techniques from fluvial sedimentology and fluvial geomorphology to determine that many ridges are exhumed channel belts, and to create and apply new tools for measuring bankfull discharge and duration of river flow from remote-sensing observations of these sedimentary deposits. I found evidence that rivers on ancient Mars were comparable in size to those on Earth today, and that they flowed for at least millions of years.

I examined sinuous ridges in three terrestrial sites to better understand ridges on Mars: the Cretaceous Cedar Mountain Formation and Jurassic Morrison Formation of Eastern Utah, and the Miocene Caspe Formation of Northeast Spain. Ridges at all sites are capped with sandy units rich with dune and bar strata atop a mudstone pedestal and they cross each other at different stratigraphic levels, observations that together indicate that ridges are channel belts exhumed from floodplain sediments — the most common arrangement of fluvial stratigraphy. By compiling measurements of hundreds of terrestrial channel belts and their associated channels, I found that the best methods to reconstruct paleochannel bankfull geometry from such deposits are to use thickness of channel belts (1-4 times paleochannel depth) or radius of curvature of lateral accretion sets (half the channel width). Ridge width and planview wavelength, common proxies for paleochannel width, are significantly more uncertain due to channel amalgamation and ridge erosion by scarp retreat, which I quantified with geometry and a new erosion model. Intermittency factor converts bankfull discharge to average discharge, enabling measurement of duration of river flow. I calculated the intermittency factor for 206 fluvial deposits and USGS streamgages, and found that it ranges between 0.003-0.7 with a median of 0.10, with values depending on the ratio of catchment-averaged erosion rate to average precipitation but independent of timescale, river size, climate, or grainsize.

Throughout the work, I applied the methods to sinuous ridges on Mars to demonstrate their applicability. I found that many ridges are likely channel belts, and that the ancient rivers they represent are likely smaller but longer than previously studies have indicated. Altogether, this contribution enables new quantitative analyses of ancient rivers on Earth and Mars, and provides evidence that ancient Martian climate was capable of supporting liquid water at many locations across the surface for at least millions of years.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Fluvial geomorphology; planetary science; Mars; sedimentology; rivers; river deposits
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Lamb, Michael P.
Thesis Committee:
  • Fischer, Woodward W. (chair)
  • Ehlmann, Bethany L.
  • Grotzinger, John P.
  • Lamb, Michael P.
Defense Date:3 June 2020
Additional Information:"This special [October 2020] conferral also marks another noteworthy moment in the Institute's history: the granting of Caltech's 10,000th doctoral degree. The recipient, Alistair Hayden, earned his PhD in geology as part of the Division of Geological and Planetary Sciences." -- Caltech Media Relations, Nov. 13, 2020.
Funders:
Funding AgencyGrant Number
NASA Earth and Space Science Fellowship80NSSC17K0492
NSF Graduate Research Fellowship1144469
National Geographic SocietyCP-021ER-17
Record Number:CaltechTHESIS:09072020-172907018
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:09072020-172907018
DOI:10.7907/68ft-xm49
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.icarus.2019.04.019DOIArticle adapted for Chapter 3.
https://doi.org/10.1029/2020JE006470DOIArticle adapted for Chapter 4.
ORCID:
AuthorORCID
Hayden, Alistair Thompson0000-0003-3540-7807
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13869
Collection:CaltechTHESIS
Deposited By: Alistair Hayden
Deposited On:15 Sep 2020 15:34
Last Modified:17 Nov 2020 19:25

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