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| Titel |
Widespread Surface Weathering on Early Mars |
| VerfasserIn |
Damien Loizeau, John Carter, Nicolas Mangold, François Poulet, Angelo Rossi, Pascal Allemand, Cathy Quantin, Jean-Pierre Bibring |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090416
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| Publikation (Nr.) |
 EGU/EGU2014-4651.pdf |
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| Zusammenfassung |
| The recent discovery of widespread hydrous clays on Mars indicates that diverse and
widespread aqueous environments existed on Mars, from the surface to kilometric depths
[1,2]. The study of the past habitability and past climates of the planet requires
assessing the importance of sustained surface water vs. subsurface water in its aqueous
history.
Using remote sensing data, we propose that surface weathering existed on Mars,
suggesting that Mars experienced durable episodes of sustained liquid water on its surface.
Weathering profiles are identified as vertical sequences of Al-rich clays and Fe/Mg-rich clays
in the top tens of meters of the surface, similar to cases of pedogenesis on Earth (e.g. [3,4]).
Such localized clay sequences have been reported by other works in 3 regions of
Mars [5-8] and a similar origin was also proposed. Their frequency is however
likely underestimated due to limitations of orbital investigations and re-surfacing
processes.
A large survey of the CRISM dataset leaded to a down-selection of ~100 deposits
with clear vertical sequences, widely distributed over the southern highlands and
grouped in regional clusters [9]. These putative weathering sequences are found
either on inter-crater plateaus, on the floor of craters and large basins, or on crater
ejectas. We investigated the thickness of the altered sequences, the age of the altered
units and the different geological contexts to further understand the weathering
process(es).
Using few HiRISE DEMs where possible, and CTX DEMs, we find that the thickness of
the exposed Al clays is on average of the order of several meters to few tens of
meters. The clay sequences reported here are consistent with terrestrial weathering
sequences which form under wet climates over geological timescales (>105-107
years).
The combined age assessment of the altered unit and the unaltered capping (where
present) provides constraints on the age of the weathering itself. All investigated cases point
to an active weathering limited to the late Noachian to early Hesperian.
The widespread distribution of weathering sequences in different geologic contexts, and
the consistency in their estimated ages are best explained if Mars experienced a
period/periods between the middle Noachian and the early Hesperian during which climatic
conditions allowed sustained liquid water flow on its surface, while the high degree of
degradation of older terrains does not allow affirming nor infirming earlier surface weathering
on Mars. Only the in-situ exploration of Phyllosian/Noachian terrains may provide an answer
to this fundamental question.
Some of the authors have received funding from the ERC (FP7/2007-2013)/ERC Grant
agreement n° 280168.
[1] Ehlmann B., et al. Nature, 479, 53-60 (2011). [2] Carter J., et al. JGR, 118, 831-858
(2013) [3] Velde B., et al. Ed. Springer, Berlin, (1995). [4] Wilson M. Clay Minerals, 39,
233-266 (2004). [5] Gaudin A., et al. Icarus, 216(1), 257-268 (2011). [6] Loizeau D., et al.
Icarus, 205, 396-418 (2010). [7] Noe Dobrea E., et al. JGR, 115, E00D19 (2010). [8] Le
Deit L., et al. JGR, 117, E00J05 (2012). [9] Carter J., et al. LPSC 2012, p.1755 |
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