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KA Farley, C Malespin, P Mahaffy, JP Grotzinger, PM Vasconcelos, RE Milliken, M Malin, KS Edgett, AA Pavlov, JA Hurowitz, JA Grant, HB Miller, R Arvidson, L Beegle, F Calef, PG Conrad, WE Dietrich, J Eigenbrode, R Gellert, S Gupta, V Hamilton, DM Hassler, KW Lewis, SM McLennan, D Ming, R Navarro-González, SP Schwenzer, A Steele, EM Stolper, DY Sumner, D Vaniman, A Vasavada, K Williford and RF Wimmer-Schweingruber
We determined radiogenic and cosmogenic noble gases in a mudstone on the floor of Gale crater. A K-Ar age of 4.21 ± 0.35 Ga represents a mixture of detrital and authigenic components, and confirms the expected antiquity of rocks comprising the crater rim. Cosmic-ray-produced (3)He, (21)Ne, and (36)Ar yield concordant surface exposure ages of 78 ± 30 Ma. Surface exposure occurred mainly in the present geomorphic setting rather than during primary erosion and transport. Our observations are consistent with mudstone deposition shortly after the Gale impact, or possibly in a later event of rapid erosion and deposition. The mudstone remained buried until recent exposure by wind-driven scarp retreat. Sedimentary rocks exposed by this mechanism may thus offer the best potential for organic biomarker preservation against destruction by cosmic radiation.
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Metamorphic rock, Time, Middle Ages, Shale, Geology, Sediment, Rock, Sedimentary rock
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