2399

46th Lunar and Planetary Science Conference (2015)
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MAPPING THE PAHRUMP HILLS OUTCROP USING MARDI SIDEWALK MOSAICS. M.E. Minitti1, J.
Van Beek2, J.B. Garvin3, W. Goetz4, J.P. Grotzinger5, D. Harker2, K.E. Herkenhoff6, L.C. Kah7, M.R. Kennedy2,
G.M. Krezoski2, L. Lipkaman2, S.K. Rowland8, J. Schieber9, K.M. Stack10, and R.A. Yingst1. 1Planetary Science
Institute (1700 E. Fort Lowell, Tucson, AZ 85719, [email protected]), 2Malin Space Science Systems, San Diego,
CA; 3Goddard Space Flight Center, Greenbelt, MD; 4Max Planck Institute for Solar System Research, Göttingen,
Germany; 5California Institute of Technology, Pasadena, CA; 6USGS, Flagstaff, AZ; 7University of Tennessee,
Knoxville, TN; 8University of Hawai‘i at Mānoa, Honolulu, HI, 9Indiana University, Bloomington, IN. 10Jet Propulsion Laboratory, Pasadena, CA.
Introduction: With her arrival at the base of the
Pahrump Hills outcrop on Sol 753, the Mars Science
Laboratory Curiosity rover began her exploration of
the foothills of Aeolis Mons (i.e., Mt. Sharp). The
Pahrump Hills, which encompass ~15 meters of vertical section, are a part of the Murray formation, which
represents the basal layer of Mt. Sharp. The science
team chose to interrogate the geology and chemistry of
Pahrump with a series of campaigns, including a reconnaissance imaging survey of the outcrop to identify
and characterize the lithologies present (Fig. 1). The
findings from the reconnaissance campaign guided the
subsequent contact science campaign to study the sedimentary structures, grain size distributions, diagenetic
textures and chemistry of a subset of the identified
lithologies [1]. These findings have in turn informed
current sampling activities at Pahrump.
During the reconnaissance campaign, the most continuous record of the outcrop was acquired by the Mars
Descent Imager (MARDI) operating in “sidewalk”
video imaging mode. Images collected in sidewalk
mode during each drive of the campaign enabled the
creation of a mosaic of the ~152 meter drive path. The
goal of this work is to create a geologic map of the
sedimentary structures with the Pahrump Hills outcrop
from the MARDI sidewalk mosaic, document the lateral variability of structures both across and along
strike, and gain insight into the depositional and diage-
Light toned recessive unit
Figure 1: Reconnaissance campaign (yellow line) across
the light toned recessive unit [5] of the Pahrump Hills
outcrop. Red spots mark locations of end-of-drive imaging or sampling. White spots mark locations of mid-drive
imaging. Labels mark prominent outcrops that were the
focus of further study. Image PIA19039
(NASA/JPL/MSSS).
netic processes represented by the observed sedimentary structures and diagenetic textures.
MARDI and Sidewalk Background: MARDI is a
fixed-focus, nadir-pointing color camera attached to
the bottom of the rover chassis above the left front
wheel. MARDI’s chief mission task was to record Curiosity’s descent and landing, but since landing,
MARDI has acquired images on the surface that enable
systematic study of clast size, spacing and distribution
[2], and elements of surface roughness and texture that
support the geotechnical analysis of terrains traversed
by the rover [3]. MARDI achieves ~1 mm/pixel resolution over a ~92 x 64 cm patch of ground underneath
the rover.
In sidewalk mode, MARDI acquires images at a
constant pace (one image/three seconds) during a
drive, but onboard software only saves an image if it is
significantly different than the previously saved image.
This technique yields MARDI images with at least
75% overlap. All MARDI images saved during a sidewalk video activity are located in MARDI’s internal
flash memory, and review of the image thumbnails
allows us to select which frames from a given sidewalk
are returned to Earth. A result of the significant overlap of the sidewalk images is that a complete mosaic of
the drive path can be created using only every third
frame of a sidewalk, thus reducing the downlink data
volume necessary to create the mosaic. However, to
produce digital elevation models with mm-scale error
levels, consecutive frames must be downlinked [3,4].
During the reconnaissance campaign, sidewalk
videos were acquired on Sols 780, 785, 787, 790, 792,
794 and 797. Only Sol 787 failed to yield a continuous
record of the drive, for reasons not fully understood,
leaving 1-6 meter gaps in the mosaic. Mosaics were
created from geometrically corrected full frame images
using
the
open
source
software
Hugin
(http://hugin.sourceforge.net).
Sedimentary Structures: There are a variety of
primary and secondary sedimentary structures observed throughout the Pahrump Hills outcrop, and their
distributions and relationships can be tracked in the
MARDI sidewalk mosaic.
46th Lunar and Planetary Science Conference (2015)
Laminae. Laminae are defined as thin (mm-scale)
parallel layers that can be traced over tens of centimeters (Fig. 2). They are restricted to the light-toned recessive unit ([5] and Fig. 1), and they are observed
Figure 2: Laminae visible in a cropped portion of one
frame of the Sol 790 sidewalk video
(0790MD0003330010102841M01). Image is radiometrically and geometrically processed, filtered and sharpened,
white balanced, gray matched and stretched. Field of
view is ~60 cm wide.
only intermittently across the traverse. They are most
prominent near the base of Pahrump (e.g., Confidence
Hills drill site) and between the Alexander Hills and
Chinle waypoints (Fig. 1). Mars Hand Lens Imager
(MAHLI) observations indicate that they consist of
laminae with abundant crystals of an as-yetundetermined evaporite mineral (in a fine-grained matrix) that alternate with fine-grained laminae. Finegrained is ≤60 µm, as constrained by the highest resolution utilized by MAHLI on these features (~20
µm/pixel).
Figure 3: Cluster of resistant material (arrow) visible in
a cropped portion of one frame of the Sol 780 sidewalk
video (0780MD0003270010102631M01). Image is processed as in Fig. 2. Field of view is ~30 cm wide.
2399.pdf
Clusters. Clusters are defined as resistant features
that are embedded in the recessive unit of Pahrump.
Clusters first observed at the Confidence Hills drilling
site at the base of the Pahrump Hills have dendritic
morphologies, but other morphologies are also observed (Fig. 3) [6]. They occur within individual bedrock slabs, or emanate from fractures or veins that cut
the bedrock. Mg and S enrichments in the clusters relative to the bedrock host material are observed by both
ChemCam LIBS and APXS [7,8]. Their structure and
chemistry suggest clusters are diagenetic in origin,
formed after lithification of the recessive unit because
the clusters do not deform laminae within the bedrock.
Veins and fracture fills. Light toned veins and fracture fills typically <5 mm in thickness (Fig. 4) are distributed throughout Pahrump. They exhibit multiple
morphologies, from straight over tens of centimeters,
to curvilinear. In some instances, they occur with clusters along the same fracture. ChemCam LIBS analyses
of veins indicate they are enriched in Ca and S relative
to the surrounding bedrock [7].
Figure 4: Thin veins and fracture fills (arrows) visible in
a cropped portion of one frame of the Sol 797 sidewalk
video (0797MD0003390010103534M01). Image is processed as in Fig. 2, but is not stretched. Field of view is
~30 cm wide.
Additional Work: The nature, distribution and relationships of laminae, clusters and veins across the
Pahrump Hills will also be cross-checked against complementary Mastcam imaging acquired during the reconnaissance campaign, and be further refined through
close-up MAHLI observations.
References: [1] McBride, M.J. et al. (2015) LPSC
XLVI, this vol. [2] Garvin J.B. et al. (2014) LPSC XLV,
Abstract #2511. [3] Minitti M.E. et al. (2014) AGU,
P43D-4016. [4] Garvin J.B. et al. (2015) LPSC XLVI,
this vol. [5] Stack, K.M. et al. (2015) LPSC XLVI, this
vol. [6] Kah, L.C. et al. (2015) LPSC XLVI, this vol.
[7] Nachon, M. (2015) LPSC XLVI, this vol. [8]
Thompson, L.M. (2015) LPSC XLVI, this vol.