GEO 330 Lecture Notes - Lecture 30: Groundwater Sapping, Valley Network, Clay Minerals
14 May 2018
School
Department
Course
Professor
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
What caused the warmer Noachian conditions, and how were they maintained?
•
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
Document Summary
Multiple features on the martian surface imply climatic conditions were different in the past than today: Valley networks, lakes, oceans, deltas, hydrated minerals water-lain sediments, evaporites, glacial deposits, ice-rich veneers, low-latitude ice. 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. Strong evidence for warm noachian climate is dense valley networks. Valley networks with distal, v-shaped tributaries indicate formation by surface runoff. U-shaped or rectangular cross-sections would indicate formation by groundwater sapping, which could occur even with a thick cryosphere. Many valleys also start at topographic highs such as crater rim crests, making groundwater sapping unlikely. Dissolution and deposition of soluble minerals in meridiani sediments. 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.
