¹Abigail A. Fraeman
Journal of Geophysical Research, Planets (in Press) Link to Article [DOI: 10.1002/2018JE005535]
¹Jet Propulsion Laboratory, California Institute of Technology
Published by arrangement with John Wiley & Sons

Mittlefehldt et al. [2018] synthesize APXS chemical measurements along more than 4.5 km of Endeavour crater’s rim. Their analyses clarify details of Endeavour’s geologic history, including evidence for three to four distinct episodes of aqueous alteration. Fracture driven aqueous systems and Mn mobility are particularly important both here and at Curiosity’s landing site on the opposite side of the planet. The detailed documentation of APXS data products within this paper will be a key reference for researchers who want to perform future work on questions related to Mars aqueous geochemistry, impact processes, and Martian crustal and atmospheric evolution.

¹David W. Mittlefehldt et al. (>10)
Journal of Geophysical Research, Planets (in Press) Link to Article [DOI: 10.1002/2017JE005474]
¹Mail code XI3, Astromaterials Research Office, NASA/Johnson Space Center, Houston, TX, USA
Published by arrangement with John Wiley & Sons

We report the results of geological studies by the Opportunity Mars rover on the Endeavour Crater rim. Four major units occur in the region (oldest to youngest): the Matijevic, Shoemaker, Grasberg and Burns formations. The Matijevic formation, consisting of fine-grained clastic sediments, is the only pre-Endeavour-impact unit and might be part of the Noachian etched units of Meridiani Planum. The Shoemaker formation is a heterogeneous polymict impact breccia; its lowermost member incorporates material eroded from the underlying Matijevic formation. The Shoemaker formation is a close analog to the Bunte Breccia of the Ries Crater, although the average clast sizes are substantially larger in the latter. The Grasberg formation is a thin, fine-grained, homogeneous sediment unconformably overlying the Shoemaker formation, and likely formed as an airfall deposit of unknown areal extent. The Burns formation sandstone overlies the Grasberg, but compositions of the two units are distinct; there is no evidence that the Grasberg formation is a fine-grained subfacies of the Burns formation. The rocks along the Endeavour Crater rim were affected by at least four episodes of alteration in the Noachian and Early Hesperian: (i) vein formation and alteration of pre-impact Matijevic formation rocks; (ii) low-water/rock alteration along the disconformity between the Matijevic and Shoemaker formations; (iii) alteration of the Shoemaker formation along fracture zones; and (iv) differential mobilization of Fe and Mn, and CaSO4-vein formation in the Grasberg and Shoemaker formations. Episodes (ii) and (iii) possibly occurred together, but (i) and (iv) are distinct from either of these.