Continental Groundwater Flow: Great Artesian Basin

Great Artesian Basin 2

Great Artesian Basin 3

Great Artesian Basin 4

Great Artesian Basin 5

Western edge ~1.4Ma-old water

(ages in ka)

Cl-36 Isotope dating technique36Cl made by interaction of cosmic rays with 40Ar

in atmosphere (40Ar is ~1% of atmosphere). Nuclear Reaction:

40Ar + cosmic ray energy = 36Ar + 4He

36Cl decays to 36Ar with a halflife of 310,000yr36Cl incorporated into rainwater, but not made

by nuclear reactions in Earth’s interior.Rainwater seeps into ground, where 36Cl

decays slowly away…Amount of remaining 36Cl can be used to date

time since rainfall at surface.

Great Artesian Basin 6

Water moves through basin at ~1-5m/yr, flow-through time of ~1Ma

Great Artesian Basin 7=4

Great Plains (same type of tale)

Great Plains 2

Great Plains 3

Great Plains 4

Implication: water at Boon’s Lick came from Rockies…