HR: 13:40h
AN: P23D-01 INVITED    [Abstracts]
TI: Impact and Aqueous Strata in Holden Crater, Mars
AU: * Grant, J A
EM: grantj@si.edu
AF: Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 6th at Independence SW, Washington, DC 20560, United States
AU: Irwin, R P
EM: irwinr@si.edu
AF: Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 6th at Independence SW, Washington, DC 20560, United States
AU: Grotzinger, J P
EM: grotz@gps.caltech.edu
AF: Division of Geological Sciences, Califronia Institute of Technology, Pasadena, CA 91125, United States
AU: Milliken, R E
EM: Ralph.Milliken@jpl.nasa.gov
AF: Division of Geological Sciences, Califronia Institute of Technology, Pasadena, CA 91125, United States
AU: Tornabene, L L
EM: livio@pirl.lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721,
AU: McEwen, A S
EM: mcewen@pirl.lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721,
AU: Team, t S
AB: Images from the High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) at 2652 cm/pixel scales reveal a sequence of exposed impact megabreccia and sedimentary units in the Noachian-aged Holden crater in Margaritifer Terra, Mars (26S, 326E, 154 km diameter). Formation of Holden crater interrupted the previously through-flowing Uzboi-Ladon-Margaritifer (ULM) outflow channel system and excavated sediments deposited by ULM within the pre-existing (Early Noachian) Holden impact basin. Crater walls display variably rounded, poorly sorted, chaotically arranged, and variably bright blocks up to 50 m across residing within a finer matrix. These characteristics suggest a possible origin for many blocks as sedimentary materials excavated from the pre-impact Holden basin and these materials are interpreted as coarse, impact- fragmented megabreccia. At least 150 m of sedimentary facies partially fill the crater and were emplaced during two wet phases during the Noachian. Early prolonged erosion of crater walls and basin deposition in a quiescent distal alluvial or lacustrine setting resulted in a lower light-toned unit displaying meter- to submeter-scale bedding traceable for up to kilometers and containing phyllosilicates, but with few resolvable blocks. The lower unit is topographically restricted and capped by a thin, dark-toned layer commonly exhibiting 4–5-m-diameter polygonal fractures that may record a terminal playa phase. Later-Noachian high-magnitude flooding of the crater occurred as an impounded Uzboi Vallis lake overtopped the crater rim and rapidly emplaced a topographically restricted darker- toned, more crudely bedded deposit that drapes unconformably over antecedent relief and envelops large blocks (up to 100 m across) of material eroded from the lower unit. The upper unit exhibits alluvial morphology near the crater rim breach, but grades distally an upwards into more continuously bedded, possible lacustrine facies that were deposited during a relatively short second wet phase. The aqueous strata in Holden crater indicates a more clement, wet climate characterized some of the Noachian Period and provide the first clear context for phyllosilicates in an alluvial/lacustrine environment. Emplacement of the beds comprising the lower unit likely requires stable wet conditions and a setting likely to preserve geochemical or lithological signatures related to habitability. Hence, the possibility of evaluating the changing potential for habitability over part of Noachian Mars makes Holden crater a priority for future landed missions.
DE: 5400 PLANETARY SCIENCES: SOLID SURFACE PLANETS
DE: 5415 Erosion and weathering
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting