Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmep53f..01m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #EP53F-01
Physics
[5415] Planetary Sciences: Solid Surface Planets / Erosion And Weathering, [5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Fluvial activity on Mars is identified from well organized valley networks, which activity peaked in the Late Noachian - Early Hesperian transition. Nevertheless, a growing trend of evidence supports the presence of fluvial activity later in the Hesperian period (3 to 3.5 Gy), after the traditional period of early Mars activity ceased. Small post-noachian valleys such as those on volcanoes, could suggest that regional effects are predominant. However, more regions of post-Noachian activity are now identified, and some of them contain lacustrine deposits dated of the same epoch. In this study, we propose to examine the morphology and chronology of two types of fluvial landforms. First, in regions such as Valles Marineris, Thaumasia highlands and Nili Fossae, fluvial valleys are associated with depositional fans (sometimes being delta) that lay on Hesperian bedrock. Despite valleys are less branched than typical early Mars valleys, these landforms require sustained liquid water to form. Second, fretted channels are known as post-Noachian erosional valleys of unknown origin, rectangular in section and poorly branched. They are re-assessed using most recent orbital data. Results show that they likely consist of fluvial valleys, with local lacustrine activity and fan deposition in lows. A set of depositional fans are also identified on plateaus near these fretted channels in Deuteronilus Mensae showing that this fluvial activity was not limited to putative subsurface aquifers and sapping erosion forming rectangular valleys. Even if regional activity certainly exists and explain some landforms, these results mainly favor a role of a global climate to form these Hesperian landforms. Nevertheless, an episodic activity, rather than a continuous activity, can explain most observations. The origin of such a episodic global activity will be discussed.
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