Lect 6

Question 1

Orbital forcing challenges

Answer 1

-identification of events like TI / TII is quite sketchy because the proxies they’re derived from are: a) wiggle matched b) have their own Limitations I.e
VOSTOK Ice: resolution gets worse with depth and subsequently time
SPECMAP d18O: wiggle matched to Insolation
Loess: wiggle matched to SPECMAP

Question 2

U-Series dating of Calcites

Concept

Answer 2

Th = insoluble
U6+ = soluble
-water drips onto stalagmite. Because Th is insoluble, there will be no Th and only U6+. U decays to Th by daughter deficiency and ends up at secular equilibrium.

Pros: date in calendar year so no calibration curve needed
Cons: •can’t date older than 600kyrs (activity stuck at 1) •detrital Th contamination of samples

Question 3

Devils Hole

Case Study

Answer 3

-Extensional fissure (Unknown depth) in Basin and Range, Nevada, US.
- V clean calcite precipitated= 500kyrs of terrestrial climate recorded
—> d18O proportional to local temp therefore low d18O = low Temp

Problems:

• water residence time
• isolated record; only regional recorded?
• d13C problem

Implication of Palaeo:
-mis5e and TII don’t align with insolation rise—>effects preceded the cause = causality problem
Causality problem sparked new interpretations of old data to support devils hole.
L