Introduction: Today I was able during an ATV EVA to obtain geophysical readings of radioactivity and magnetic susceptibility in an area I hadn't covered previously, to the southwest of the Hab along the ridge to the west, with its face of Mancos Formation shale and sandstone.

We were relieved to see a Bureau of Land Management sign along the track that said people can go off-road in that area as long as they are careful not to disturb the vegetation. A soil experiment is being conducted in the area, and in addition to a lot of vegetation we saw birds and a lizard. However, we kept to the road with our vehicles, dismounting to climb up the cliff to take some more readings and samples.

(Click Image for Detailed View)
Life on Shale	Geodetic Survey Benchmark

Note on Map vs. Observation Differences: Some of our crew have found on EVAs that their own observation of the terrain deviates markedly from the contour information on the USGS maps (which were printed in 1987 and therefore could be expected to be somewhat outdated). The presence of multiple National Geodetic Survey (part of NOAA) benchmarks in the area prompted me to visit the NGS Web site, where I found a page devoted entirely to letting people like us send the NGS information about such discrepancies so this agency can update its database. The NGS Web site is http://www.ngs.noaa.gov/.

Equipment and Procedures: Using the GPS unit, scintillometer, and magnetic susceptibility meter (see Geology Report for February 25 for more about the instruments), I took readings at several points.

Narrative: I got positive readings with the scintillometer along the shale and sandstone (indicating the presence of radioactivity in the area). I got readings of "0" with the magnetic susceptibility meter in all locations except one.

After we finished our EVA, we found the photojournalist who had followed us for the first part of our EVA waiting for us back at the Hab. His eagerness to take more photos gave me another opportunity to take more data readings in the area in the immediate vicinity of the Hab toward the northwest.

Tentative Conclusions and Future Work:

1. Shales commonly trap small amounts of radionuclides, so finding the positive scintillometer readings in the Mancos Formation areas was a good confirmation of my initial objective.
   
   
2. The scintillometer samples only about 1-2 cm deep at the most, so any readings obtained with this instrument indicate only the topmost layer.
   
   
3. The magnetic susceptibility meter samples about 6-10 cm below the surface, so I am surprised not to have gotten more frequent positive readings with this instrument, which generally responds to magnetite and pyrrhotite, both of which should be present in the sediments around the Hab. In this kind of sedimentary area (Morrison and Mancos formations), the magnetite has generally been oxidized and often converted to hematite and limonite, I expected higher readings. I will monitor the average low readings I get and correlate them with the sedimentary layers.
   
   
4. On my return to the MDRS, I hope to take more readings in many layers of the sedimentary environment. Then I may be able to distinguish between layers from a more oxidized (arid, dry) paleo-environment and layers from wetter and more anoxic environments, where there may be more magnetite.
   
   
5. I will do some lab work with the samples I have obtained when I return to "Earth" (home) to try to refine the characterization of the units I am mapping. Once I can develop a geophysical or chemical characterization of a particular unit, future mappers can use it as a "marker bed" or diagnostic key to the geology, allowing further reconstruction of the sedimentary history.
   
   
6. I hope to do more work toward Muddy Creek toward the northeast of the Hab, where the samples I collected on a previous EVA seemed to indicate the possibility of an older igneous intrusion. The presence of white mica in so many areas around here also indicates the possibility of hot fluids from such an intrusion.