Seth Kadish
Geo 292
April 6th, 2009
Meridiani Planum and the global hydrology of Mars
Jeffery Andrews-Hanna et al.
Main Points:
 How did Meridiani evaporites form where there is no enclosed basin?
 Arid conditions beginning in late Noachian let to formation of layered sediments
containing evaporitic sulphates and diagenetic haematite at Meridiani Planum. Meridiani
formed shortly after or near the end of the formation of Tharsis.
 Contemporaneous formation of valley networks and sapping valleys, with quick
infiltration of water to recharge aquifers.
 Aquifer stability is dictated by the brittle-plastic transition (BPT):
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Put simply, growth of Tharsis would have led to an upward water flux, making it a net
hydrologic sink. After completion of its formation, it would have become a source of
water.
Three scenarios considered for global hydrologic evolution. (a) Meridiani predates
Tharsis, (b) Tharsis predates Meridiani, (c) Steady rate of Tharsis formation:
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Scenario (a): Water table intersects surface across much of northern lowlands. Evaporite
groundwater loss from major impact basins. Significant groundwater upwelling and
evaporation in Meridiani.
Scenario (b): Similar to (a), but deeper groundwater at Tharsis, and more groundwater
upwelling in the southern highlands.
Scenario (c): Water table lowered at Tharsis, and groundwater upwelling inhibited in
southern highlands.
In all three scenarios, Meridiani is one of the few regions of currently exposed Noachianaged crust with predicted groundwater upwelling and evaporation.
Over 500 Myr (duration of model run), integrated flux would have been a 2.5-km column
of water over the broad area. The column can be increased by assuming a higher
hydraulic conductivity. This is necessary to account for thickness of evaporite deposits.
Morphology of the deposits results from interaction between regional upwelling and local
topography, which led to runoff, ponding, cementation, or diagenesis.
Groundwater upwelling at Meridiani may be due to the shallow slope of Arabia Terra at
the dichotomy boundary:
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Simple model: Lower slope → decrease groundwater flow velocity → increase water
table height above aquifer base → water table reaches surface → groundwater
upwelling balanced by evaporation.
Concluding remark: “…Meridiani evaporites formed as a result of sustained
groundwater upwelling over a broad region driven by global-scale flow. This
groundwater would have leached the solutes from large volumes of aquifer material
over a range of depths, before reaching Meridiani and concentrating the solutes at the
surface to produce thick deposits of evaporites in the absence of a topographic basin.”
Discussion Questions:
 Is the model overly simplistic? Can we distinguish between the three scenarios given our
current knowledge of the regional and global mineralogy and geomorphology?
 Do we see large evaporite deposits in the other regions predicted to have high amounts of
evaporation (Figure 3)?
 What does this tell us about the timing of the change in climate regime from wet to arid
conditions?
 What constraints does this place on the formation/evolution of the global cryosphere?