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Seminar -- Addressing a Dating Puzzle: How Old is Old on Mars?

Wednesday, April 20, 2016
Radu
Capitan

Abstract. Evidence that basalt sediments1 formed at the surface of Mars and wide-spread wind-driven and aqueous-related sediments at MSL location2 and elsewhere on Mars3 rise questions of when these “young” processes acted. The current Martian chrono-stratigraphic scheme offers solutions for planetary-scale geologic units and mostly the early periods of Martian evolution (e.g.~ >3.5 Gy ago)4. However, the spatial extent of many sedimentary landforms, including the MSL landing area5, and the difficulty to calibrate the ages for post- Late Heavy Bombardment period6 make difficult the applicability of Size Frequency Distribution (SFD) dating for these regional to local-scale landforms and geologic units7. Here I show that dating of Martiansurfaces can be addressed by combining morphometrical characteristics of craters and their accumulation statistics in a single age model. In the MSL area I use crater morphometry and mapping techniques to calibrate the ages of local to regional-scale landforms. Modifications of small craters morphometry that are concordant for a period less than 87 My ago within Curiosity’s landing area8 set an age of 1.626 0.068 Gy ago for the Bedded Fractured BF formation and 1.234 0.056 Gy ago for Alluvial Fan AF unit. I can thus confirm an Earth-like evolution of the Martian surface at the regional scale, and set premises to refine its geochronology.

 

References:

1. E.M. Stopler et al., The Petrochemistry of Jake_M: A Martian Mugearite, Science, 341, DOI: 10.1126/science.1239463 (2013).

2. P. Grotzinger et al., Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars, Science 350, DOI:10.1126/science.aac7575. (2015).

3. M.C. Malin and K.S. Edgett Sedimentary Rocks of Early Mars, Science, 290, 1927-1937. (2000).

4. Hartmann, W.K. & Neukum, G. Cratering chronology and the evolution of Mars, Space Sci. Rev.96, (1-4), 165-194. (2001).

5. J. A. Grant, S. A. Wilson, N. Mangold, F. Calef III, J. P. Grotzinger, The timing of alluvial activity in Gale crater, Mars. Geophys. Res. Lett. 41, 1142–1149 (2014). DOI: 10.1002/2013GL058909.

6. Daubar, I.J et al. The current martian cratering rate., Icarus, 225, 506-516 (2013).

7. Smith, M. et al., Effect of obliteration on crater-count chronologies for Martian surfaces, Geophys. Res. Lett., 35, L10202, doi:10.1029/2008GL033538 (2008).

8. K. A. Farley et al., In situ radiometric and exposure age dating of the martian surface. Science 343, 1247166(2014). DOI: 10.1126/science.1247166

 

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