Morphology, evolution and tectonics of Valles Marineris wallslopes (Mars)

Ages of rampart craters in equatorial regions on Mars:Implications for the past and present distribution of ground ice D. REISS 1* , S. VAN Abstract-We are testing the idea of Squyres et al. (1992) that rampart craters on Mars may have formed over a significant time period and therefore the onset diameter (minimum diameter of a rampart crater) only reflects the ground ice depth at a given time. We measured crater size frequencies on the layered ejecta of rampart craters in three equatorial regions to derive absolute model ages and to constrain the regional volatile history. Nearly all rampart craters in the Xanthe Terra region arẽ 3.8 Gyr old. This corresponds to the Noachian fluvial activity that region. Rampart crater formation declines in the Hesperian, whereas onset diameters (minimum diameter) increase. No new rampart craters formed after the end of the Hesperian (~3 Gyr). This indicates a lowering of the ground ice table with time in the Xanthe Terra region. Most rampart craters in the Valles Marineris region are around 3.6 Gyr old. Only one large, probably Amazonian-aged (~2.5 Gyr), rampart crater exists. These ages indicate a volatile-rich period in the Early Hesperian and a lowering of the ground ice table with time in the Valles Marineris study region. Rampart craters in southern Chryse Planitia, which are partly eroded by fluvial activity, show ages around 3.9 Gyr. Rampart craters superposed on channels have ages between ~1.5 and ~0.6 Gyr. The onset diameter (3 km at ~1.5 Gyr) in this region may indicate a relatively shallow ground ice table. Loss of volatiles due to diffusion and sublimation might have lowered the ground ice table even in the southern Chryse Planitia region afterwards. In general, our study implies a formation of the smallest rampart craters within and/or shortly after periods of fluvial activity and a subsequent lowering of the ground ice table indicated by increasing onset diameter to the present. These results question the method to derive present equatorial ground ice depths from the onset diameter of rampart craters without information about their formation time.

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“…This scenario would also be in agreement with a slow transition from wet to dry conditions in Valles Marineris (Peulvast et al 2001).…”

Section: Discussionsupporting

confidence: 80%

Ages of rampart craters in equatorial regions on Mars: Implications for the past and present distribution of ground ice

Reiss

Gasselt²,

Hauber

et al. 2006

Meteorit & Planetary Scien

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“…The walls have a typical 'spur and gully' morphology as described by Peulvast et al (2001). Therefore, the stratigraphy is not clearly resolved in the middle and lower sections.…”

Section: Morphologic Evidence For Discontinuitiesmentioning

confidence: 97%

Pristine Noachian crust and key geologic transitions in the lower walls of Valles Marineris: Insights into early igneous processes on Mars

Flahaut

Quantin

Clénet

et al. 2012

Icarus

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“…Within the equatorial region of Mars, the extensive system of canyons (also known as troughs) that collectively comprise Valles Marineris has been the subject of much study, especially with respect to its coupled structural and geologic evolution, which spans much of the planet's history (e.g., Lucchitta and Bertolini, 1989;Peulvast and Masson, 1993;Mè ge and Masson, 1996;Peulvast et al, 2001;Lucchitta et al, 1992Lucchitta et al, , 1994Schultz, 1998;and references therein). Key issues of current interest here center on understanding the geologic history of layered sedimentary deposits that are found at the bottom of these canyons (called chasma or chasmata (plural), from the ancient Greek language and referring to a deep, elongated, steep-sided depression (according to International Astronomical Union definitions; see http://planetarynames.…”

Section: Faulting and Folding Of Layered Sedimentary Depositsmentioning

confidence: 99%