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- Title
Evolution of Escarpments, Pediments, and Plains in the Noachian Highlands of Mars.
- Authors
Cawley, Jon C.; Irwin, Rossman P.
- Abstract
Extensive Noachian‐aged intercrater planation surfaces comprise much of the southern highlands of Mars. We mapped aggradational and stable to degradational surfaces in three study areas with diverse relief elements and ages: the high and rugged relief of Libya Montes, the well‐preserved intercrater plains of Noachis Terra, and the rolling relief with more drainage development in Terra Cimmeria. Here we describe four major geomorphic features that formed in these regions: debris‐mantled escarpments, regolith pediments, sloping aggradational surfaces, and depositional plains. We interpret that with tectonic stability and an arid paleoclimate, these features supported slow pedogenesis, sediment transport, and diagenesis over hundreds of millions of years during heavy impact bombardment. Slow aqueous weathering generated primarily fine‐ or medium‐grained particles from basaltic surfaces of impact ejecta and megabreccia. These sediments were collected in local lows, reducing surface roughness, permeability, and populations of small craters. Larger crater walls and structural escarpments retreated radially or linearly as ~5–20° slopes, indicating efficient removal of fine‐ or medium‐grained debris but little downslope transport of coarse material by fluvial erosion or creep. Gently to moderately sloping, composite intercrater planation surfaces evolved as regolith pediments with tectonic stability and little fluvial dissection. Noachian impact craters degraded in place on pediments and became embayed or buried on basin floors. The concentration of aggradational surfaces in low‐lying areas, lack of coarse‐grained alluvial fans in most locations, and resistance to later eolian deflation suggest intermittent low‐magnitude (hypo‐)fluvial erosion with aqueous cementation or development of a lag in basins. Plain Language Summary: The surface of Mars at Libya Montes, Noachis Terra, and Terra Cimmeria includes steep eroded slopes, gently to moderately sloping stable surfaces, gently sloping low areas that were thinly buried, and flat‐floored basins that accumulated thick deposits of sediment. The development of these surface features suggests low‐intensity, intermittent erosion by running water and wind over hundreds of millions of years. The key elements of this landscape evolution include weathering of Martian basaltic bedrock to finer‐grained sediments rather than coarse gravel, a lack of intense rainfall or snowmelt, minimal movement of loose material downslope, and processes that concentrated sediment in basins. The blankets of material ejected from impact craters required little erosion to form stable and better sealed surfaces, which were later eroded by rivers during brief wetter epochs of Martian history. Key Points: Debris‐mantled escarpments, regolith pediments, sloping aggradational surfaces, and depositional plains developed on Martian cratered terrainNoachian arid‐zone geomorphology included aqueous weathering of basalt to fines, low‐intensity fluvial erosion, and deposition in basinsThese processes smoothed and sealed Noachian ejecta blankets, which required little geomorphic work to form stable pediments
- Subjects
MARTIAN geology; PEDIMENTS (Geology); CLIFFS; MARS (Planet); SURFACE roughness; MARTIAN craters
- Publication
Journal of Geophysical Research. Planets, 2018, Vol 123, Issue 12, p3167
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2018JE005681