MISSION UPDATES | September 28, 2020

Sols 2897-2898: Marker Bed in Focus

Written by Roger Wiens, Geochemist at Los Alamos National Laboratory
Image of distant rock outcrop on Mars

This image was taken by Chemistry & Camera onboard NASA's Mars rover Curiosity on Sol 2893. Credits: NASA/JPL-Caltech/LANL. Download image

A “marker bed” is an important concept in sedimentary geology. It is a bed of rock strata that are easily distinguished and are traceable over a long horizontal distance. A marker bed is very useful in determining the chronological order of geological events and correlating them from one location to another. Rock strata that lie above the marker bed in one location are assumed to have been deposited later than rock strata that are seen below the marker bed, even if the two sets of strata are many kilometers distant from each other, as long as the marker bed is seen in both locations. One particular bed on the lower part of Mt. Sharp is visible in orbital images over a significant fraction of the circumference of the mountain. It had been noted in the scientific literature already several years ago. Ultimately, this marker bed could be used to tie the chronology of strata observed up close by the Curiosity rover to other parts of Gale Crater, for example, regions many kilometers to the south along the slopes of Mt. Sharp.

Nearly a month ago the team started taking RMI images to study the stratigraphy of some sedimentary benches about 100-200 meters from the rover’s current location. The pointing was a little high on the first set of images and ChemCam’s telescope, which is programmed to focus automatically on whatever is at the center of the image, ended up focusing on the marker bed in the background several kilometers away. We eventually got the appropriate images of the benches, but in the meantime, the team decided to take more images of the marker bed. Curiosity is not expected to explore the region around the marker bed for another couple of years, and so in the meantime, these images will provide interesting data for interpretation. The RMI image displayed above, taken on Sol 2893, is part of a large mosaic. It clearly shows Mt. Sharp’s notable marker bed as the broad dark band stretching across the lower third of the image.

Today the team planned rover operations for two Sols. The Remote Sensing Mast encountered a minor issue over the weekend, precluding a few activities from the previous Sol, including ChemCam AEGIS observations and ChemCam and Mastcam observations of a float rock, “Darvaig.” The latter observations are replanned for the current uplink. ChemCam is continuing its large “Housedon Hill” RMI mosaic, mentioned above, adding fifteen new images. Mastcam will image previous ChemCam targets “Duachy” and “Duntulm.” It will also perform some deck imaging and observe its calibration targets. Some arm diagnostic activities are being commanded; stereo slip assessment will be performed by the Hazcam imagers, both front and rear; the Sample Analysis at Mars instrument (SAM) will analyze a sample of the atmosphere with its mass spectrometers and study the carbon dioxide isotopic ratios in the atmosphere with its tunable laser spectrometer. Weather observations include a Navcam zenith movie, a suprahorizon movie, a dust devil movie, a crater rim extinction Mastcam image, and a Mastcam sun tau measurement. RAD and REMS will collect data.