Other Dating Methods

LUMINESCENCE


Materials Dated: pottery, hearths, tephra, radiolaria, speliothems, sediments
  1. measure native TL (OSL)
  2. measure sensitivity TL/rad (OSL/rad) (radiation absorbed dose)
  3. determine dose rate at site (rad/yr)
native TL / sensitivity (TL/rad) rad
age (yr) = ----------------------------- = ---------
site dose rate (rad/yr) (rad/yr)

wwwrses.anu.edu.au/environment/eePages/eeDating/QuaternaryGeochronology/ Trapped Charge Dating
http://www.uic.edu/labs/ldrl/osl.html OSL


ELECTRON-SPIN RESONANCE

PRINCIPAL: energy trapped in crystal imperfections depends on dose rate and time. Used particularly for tooth enamel.
  1. measure TD Total Dose with spectrometer
  2. measure ED External Dose rate in field
  3. age (Te) = TD/ED
http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/esr.html ESR
Luminescence Readings


FISSION TRACK DATING

Fission (radioactive decay) of 238Uranium atom produces high energy particles which leave straight "tracks" (10 - 20 µm) in glassy material

U-series decay

90 a.m.u & 135 a.m.u particles, 200 MeV

VS.


PRINCIPAL: 238U produces nearly all "tracks", 238U decays at known rate, number of tracks related to age of sample

SET TO 0 when sampled heated (annealing the old tracks)

METHOD
  1. etch with acid, count the "native" tracks (microscope 200 - 500 X)
  2. heat sample to remove tracks
  3. calculate amount of 238U by irradiating sample with neutron beam to produce artificial fission tracks from 235U
  4. calculate age from native tracks and decay rate of 238U
1 ps g ld σ I φ
Age = --- ln[ 1 + ------------------------]
LD pi lf

ps = native track density d = total 238U decay constant
pi = induced track density f = spontaneous fission 238U
φ = irradiation (neutrons cm-2) σ = cross-section area
I = isotopic ratio 235U/238U g = geometry factor
LD = decay rate for 238U (1.551 X 10-10 yr-1)




Dating Range: (30,000) 100,000 - 20,000,000 yr
Materials Dated: apatite, mica, sphene, zircon, volcanic glass
examples Fission Track Readings



AMINO ACID RACEMIZATION & EPIMERIZATION

Based on the rate of a chemical process effected both by time and temperature

Dating Range: 2000 - 2,000,000 ± 15%



Materials Dated: organic, exchangeability very important

PRINCIPLE:


METHOD: http://www.york.ac.uk/depts/arch/Research/ArchSci/Bioarch/AAR.html AA
Amino Acid Readings



OBSIDIAN HYDRATION DATING: volcanic glass


PRINCIPLE:

METHOD:
Example: Ken Pierce et al. (1976) date Rocky Mountain glacial chronology

http://www.ornl.gov/info/reporter/no7/clock.htm SIMS

Obsidian Hydration Readings


SURFACE DATING
Cosmogenic Nuclide Exposure Dating

Cosmic Rays: high-energy charged particles from outside solar system

Solar Modulation: (flares produce) solar wind deflects

Geological Modulation: magnetic field, Van Allen Belts, Geography

Surface Dating Readings
Uranium Series Readings

Assigned Reading

HOMEWORK