Structural mapping of the Eagle Crater outcrop on Mars: New Challenges for the Extraterrestrial Field Geologist

Declan G. De Paor, B. M. Brenton, K. F. Cox, S. R. Duplantis, P. T. Egan, D. E. Kowalewski, P. J. Lancaster, C. A. Masaric-Johnson, H. Melanson, A. J. Orlando, L. M. Sauer, and C. M. Witkowski

We report the results of a structural analysis of the outcrop at Eagle Crater, Meridiani Planum, Mars, which was carried out as an undergraduate class project at Boston University. The outcrop exposes an approximately 20-meter-diameter, semi-circular section of the crater rim in the prevailing down-wind direction. Sedimentary units dip radially outwards on the whole, consistent with an impact origin, though there is some evidence of local folding. Many rock slabs are only slightly out of place, forming a quasi-broken formation that accounts for a sizable portion of the exposure. Geometric features in and around the crater include inclined bedding, cross bedding, undeformed "blueberry" concretions, fracture cleavage, faults, fractures, undeformed crystal vugs, and striations. Observed structures are consistent with an origin by impact cratering and/or wrinkle ridge tectonics. Oblique panorama imagery presented unusual challenges which we overcame with new analytical techniques. Our approach may prove useful for professors and students aiming to understand new forms of field data using the classical techniques of structural analysis.