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HiRISE imaging of impact megabreccia and sub-meter aqueous strata in Holden Crater, Mars

¹ Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, D.C. 20560, USA
² Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
³ Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
⁴ Planetary Science Institute, Tucson, Arizona 85719, USA
⁵ Department of Astronomy, Space Sciences Building, Cornell University, Ithaca, New York 14853, USA
⁶ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA

View larger version (117K): [in this window] [in a new window]   Figure 1. Elevation data (inset) and mosaic of Mars Global Surveyor Mars Orbiter Camera images over THEMIS (thermal emission imaging system) data of southwest Holden crater, layered sedimentary deposits, and rim breach created by Uzboi Vallis. Inset covers 19°S–32°S, 27°W–40°W and elevations from +2500 m (red) to –2500 m (purple). Contours indicating –1960 m (white) and –2060 m (black) are indicated. High Resolution Imaging Science Experiment (HiRISE) images within figure boundaries are labeled in yellow. White numbers indicate locations of Figures 2–5. North is up.

View larger version (70K): [in this window] [in a new window]   Figure 2. Example of megabreccia exposed in crater walls. Most blocks are dark toned, but some (arrows) are relatively light toned. Other impact megabreccia is revealed by High Resolution Imaging Science Experiment (HiRISE) around 12 craters to date. Portion of HiRISE image PSP_001666_1530 with image scale of 26 cm/pixel.

View larger version (67K): [in this window] [in a new window]   Figure 3. A: Upper unit and upper and middle members of the lower unit. Thin layer capping the upper unit commonly exhibits 4–5-m-diameter polygonal fractures in map view (inset), including these from 4 km to the south. B: Middle and lower members (above and below dashed line, respectively) of lower unit. C: Idealized stratigraphic section for Holden crater. Sedimentary section in C is 150 m thick, though the unknown thickness of lower unit, lower member, makes this a minimum estimate. Stratigraphic positions of units in A and B are indicated in C by connecting lines. North is up in A and down in B. High Resolution Imaging Science Experiment (HiRISE) image PSP_001468_1535_RED was used for A and B and image PSP_002154_1468 was used for inset in A (image scale of both is 26 cm/pixel).

View larger version (73K): [in this window] [in a new window]   Figure 4. Alluvial fan deposits overlying upper member, lower unit beds. Outcrop was exposed when discharge from Uzboi breach drained across the fan, highlighting steeply dipping alluvial beds (arrows) that vary across tens to hundreds of meters, in contrast to more uniform, continuous, flat-lying upper member, lower unit beds below. High Resolution Imaging Science Experiment Image PSP_003077_1530_RED with image scale of 26 cm/pixel.

View larger version (69K): [in this window] [in a new window]   Figure 5. High Resolution Imaging Science Experiment (HiRISE) data. A: Layered upper unit fan deposit containing numerous rocks larger than 1 m and capped by flat-lying beds. B: Incised upper member, lower unit unconformably overlain by upper unit; base of incision is lined with blocks (arrows) of lower unit material. C: Enormous lower unit blocks eroded and deposited in the lee of flow obstacles within matrix of upper unit sediments. Images PSP_002721_1530_RED (A) and PSP_001468_1535_RED (B and C), both with image scale of 26 cm/pixel.