Dr. Rebecca M. E. Williams

Research Report 2007

 

 

Summary of Research Projects

 

  1. For the 2001 Odyssey Participating Scientist program, Williams is targeting THEMIS VIS (18 m/pix) images of Martian fluvial landforms to augment coverage of these regions.  Through an imaging campaign, the investigation seeks to a) document the orientation of mid-latitude gullies, b) search for seasonal changes of mid-latitude gullies, c) map the distribution of bifurcating ridge networks, interpreted to be inverted streams preserved in the Martian stratigraphy, and d) search for sub-kilometer fan-shaped landforms that have morphologic characteristics similar to terrestrial alluvial fan.  As a result of region of interest (ROI) targeting requests, THEMIS VIS images of 93 new southern hemisphere gully sites in craters were obtained during the second year of the study.  With data for over one third of southern hemisphere crater gully sites, a latitudinal dependence on gully orientation is evident.  There is a pole-facing preference at the lower mid-latitudes that transitions to a more uniform gully distribution at higher mid-latitudes.  This result reinforces the contention that multiple factors impact gully formation and that these are likely polygenetic landforms.    

Histogram of gully locations categorized for

each crater site.  Pole-facing gullies are more

prevalent at lower mid-latitudes.

 

  1. Recently, it has been recognized that martian valley networks exhibit various preservation states including inverted relief.  Williams’ Mars Fundamental Research Program (MFRP) project focuses on terrestrial analogs of inverted paleochannels.  She has conducted field work on several sites in Utah.  An overview of this work and relevance in studying martian landforms is presented in a volume published by the Utah Geological Association.    Differential Global Positioning System (DGPS) elevation survey and grain size distribution data collected in the field are being used to evaluate multiple models for estimating paleodischarge based on hydraulic-sediment relations and empirically-derived equations relating channel morphological measures to discharge.  The results of this investigation will enable a more informed approach to determining the magnitude and duration of fluvial activity in Martian raised curvilinear features (RCFs), some of which have been interpreted to be inverted paloechannels.

 

 

 

  1. As a participating scientist for the Context Camera (CTX) instrument aboard Mars Reconnaissance Orbiter (MRO), Williams is conducting multiple investigations on fluvial landforms.  One aspect of this research is cataloging raised curvilinear features (RCF) on Mars, many of which have attributes consistent with interpretation as inverted paleochannels.  The database presently has nearly 200 entries.  RCFs are found on a variety of terrains and have ages that span the entire history of Mars and expand the record of the martian fluvial history. 

Frequency histogram of martian fluvial landforms.  At left is the age distribution of 827 valley networks as mapped by Carr (1995).  At right is the age distribution of 175 raised curvilinear features (RCF), nearly half of which are post-Noachian in age.  RCFs are inferred to be inverted paleochannels and study of them can yield insight into the fluvial environment and climatic conditions in the Hesperian and Amazonian.

 

 

  1. Williams continues to study Mojave Crater, a site of sub-kilometer alluvial fans.  HIRISE data is revealing new details about the fans including showing the fan structure, clast size, and post-formation modification.  On-going mapping efforts at the site has identified two classes of fan-shaped landforms that appear to have different formation ages. 

 

Subscene of HiRISE PSP_002167_1880 image with superposing fan lobes illustrating a multi-phase formation.  Illumination is from the left. 

 

 

 

 

 

 

 

Publications

 

Papers

 

Williams, R. M. E., Chidsey, T. C., and Eby, D. E. 2007) Exhumed paleochanncels in central Utah - Analogs for raised curvilinear features on Mars.  In: Willis, G. C., Hylland, M. D.,  Clark, D. L. and Chidsey, T. C. (Eds) Central Utah – diverse geology of a dynamic landscape,  Utah Geological Association Publication 36, Salt Lake City, pp. 220-235. [PDF]

 

Abstracts

 

Williams, R. M. E., 2007. Exhumed Paleochannels in Utah:  Insight for Investigation of Raised Curvilinear Features on Mars. GSA

     Abstracts with Programs, vol. 39, p. 282.

 

Tornabene, L. L., McEwen, A. S., Osinski, G. R., Mouginis-Mark, P. J., Boyce, J. M.,Williams, R. M. E., Grant, J. A. and the

     HiRISE Team, 2007. Impact melting and the Role of Subsurface Volatiles:  Implications for the Formation of Valley Networks

     and Phyllosilicate-rich Lithologies on Early Mars. 7th International Mars Conference, Pasadena, CA, July 9-13.

 

Williams, R. M. E., 2007. Raised Curvilinear Features on Mars: Inverted Paleochannels in the Martian Stratigraphy. American

      Association of Petroleum Geologists Annual Meeting, Long Beach, CA. April 2.

 

Williams, R. M. E., 2007. Global Spatial Distribution of Raised Curvilinear Features on Mars. LPSC  XXVIII, Lunar and Planetary

     Institute, Houston (CD-ROM), Abstract #1821.

 

Williams, R. M. E., 2007, A Reassessment of the Spatial Orientation of Gullies on Mars, LPSC XXVIII. Lunar and Planetary

      Institute, Houston (CD-ROM), Abstract #1739.