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EAIS Stability 2 (Dating Transition (Implication (Must've been sudden…
EAIS Stability 2
What happened since then?
Very dry climate since ~15 Ma in Dry Valleys
Inferred from
undisturbed nature / minimal erosion
of meltwater deposits
Ash supports cold climate
(Marchant 2002)
Volcanic ash
- collected in
tundra polygon wedges
Cold periglacial envmts
repeated freeze-thaw
forms contractional polygons
Airfall deposits dated ~ 8 Ma
Ar-Ar date = 8 - 15 Ma
Undisturbed since ! (except tilting by downslope mvmt)
Eureka Moment Beacon Valley
Sugden 1995
Found ice beneath
excavated lag deposits
Lag deposit
= deposit winnowed by physical actions
e.g. aeolian / fluvial processes remove finer portion
Beacon Valley Findings
Sugden 1995
Volcanic ashfall in wedges ~8 Ma
Glacier ice below
Regelation ice incl debris
∴ must've been warm-based
Beacon Valley Interp
Regelation ice presence suggests
Originated
during much colder period
--> in order for ice sheet to be there
Granite terraces
Suggest main ice sheet ice
Very old ~13-14 Ma
Age of till of surrounding area
Fact ice
= preserved
Shows climate has remained
very stable
Must've been v cold for long time (atleast 8 Ma ?)
Transition
warm → cold-based ice
Transition observed
One side: meltwater deposits
→ abraded & striated stones
Other side: No evidence abrasion/water action
Terminal moraine
@ foot corrie glacier in Olympus Range
Seemingly sudden ∆
Dating Transition
How old W→C transition?
Volcanic ash found beneath junction
~ 14 Ma
Implication
Must've been sudden temp drop ~14 Ma
modelling suggests ~20°C ∆ required to drive ∆ from W→C-based ice
Lake deposits
fossils suggest temp ~17°C warmer 14 Ma
Lewis & Marchant 2008
Wider implications
Dry Valleys climate past 14 Ma
=
cold, dry & stable
Unpopular finding:
EAIS = stable/unchanged past 14Ma
suggests EAIS
survived
warm Pliocene period
Testing EAIS Stability
(Barrett 2001)
How?
Drilled sediments just offshore Dry Valleys
Expect
If theory wrong - lotsa sed to present day
If correct (EAIS stable) - not much sed offshore
Findings
No sediments < 17 Ma
Supports Sugden theory
EAIS stable since 14Ma
Glaciation began ~34 Ma in Antarctica
Glacial cycles from 33 - 17 Ma
Overall cooling trend
Cape Roberts Offshore Drilling
Important publication
when public started to believe EAIS could've been stable