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Lecture 30

GEO 330 Lecture Notes - Lecture 30: Groundwater Sapping, Valley Network, Clay Minerals


Department
Geosciences
Course Code
GEO 330
Professor
Timothy Glotch
Lecture
30

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Valley networks, lakes, oceans, deltas, hydrated minerals water-lain sediments, evaporites,
glacial deposits, ice-rich veneers, low-latitude ice
Multiple features on the Martian surface imply climatic conditions were different in the past than
today:
Valley networks, high erosion rates, other features
Features in Noachian terrains provide best evidence for dramatically warmer climate conditions
Post-Noachian features suggest cold conditions, perhaps punctuated with occasional short warm
periods
Recent climate change caused by variations in obliquity
Climate Change
Obliquity variations
Groundwater seepage
Hydrothermal activity
Do younger examples of densely dissected terrain indicate major temporary climate change or do
they result from other effects?
What might have caused post-Noachian climate change?
What were the climate effects of catastrophic floods?
Major Questions
Strong evidence for warm Noachian climate is dense valley networks
U-shaped or rectangular cross-sections would indicate formation by groundwater sapping,
which could occur even with a thick cryosphere
Valley networks with distal, V-shaped tributaries indicate formation by surface runoff
Many valleys also start at topographic highs such as crater rim crests, making groundwater
sapping unlikely
High erosion rates during the Noachian
Water-lain sediments at Meridiani Planum
Dissolution and deposition of soluble minerals in Meridiani sediments
Clay minerals in Noachian terrains
Delta deposits in Eberswalde and other craters
Additional evidence for warm Noachian conditions includes:
Noachian Climate
Highly eroded delta
Former watercourses are left as flat-topped ridges, likely due to the fact that the stream carried
coarse debris that were more resistant to erosion
Positive curvilinear features mark former watercourses
Former watercourses show evidence of superposition of successive streams, meander migration,
and meander cutoffs
Eberswalde fan
A warm early Mars requires a very effective greenhouse
3.8Gy ago, solar luminosity was 75% of its current value -- mean Mars surface temperature would
have been 196 K with no greenhouse
To warm surface temperatures above freezing, atmosphere must intercept 85% of surface
radiance
Greenhouse Warming
Atmosphere and Climate Change
Wednesday, May 9, 2018
6:12 PM
GEO 330 Page 1
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