1 / 42

Quaternary Dating Methods

Quaternary Dating Methods. Four General Categories. Numerical age, Calibrated age, Relative age, Stratigraphic correlation. Radioisotopic (atomic disintegration). Paleomagnetic Correlation. Organic/Inorganic Chemical. Biological. Radioisotopic Method.

bessie
Download Presentation

Quaternary Dating Methods

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Quaternary Dating Methods Four General Categories Numerical age, Calibrated age, Relative age, Stratigraphic correlation • Radioisotopic (atomic disintegration) • Paleomagnetic Correlation • Organic/Inorganic Chemical • Biological

  2. Radioisotopic Method

  3. Parent Daughter Half-Life Samarium-147 Neodymium-143 106 billion yrs Rubidium-87 Strontium-87 48.8 billion yrs Thorium-232 Lead-208 14 billion yrs Uranium-238 Lead-206 4.5 billion yrs Potassium-40 Argon-40 1.26 billion yrs Uranium-235 Lead-207 0.7 billion yrs Beryllium-10 Boron-10 1.52 million yrs Chlorine-36 Argon-36 300,000 yrs Carbon-14 Nitrogen-14 5730 yrs Uranium-234 Thorium-230 248,000 yrs Thorium-230 Radium-226 75,400 yrs What is half-life?

  4. Decay is often complicated by production of a radioactive daughter that must decay. The daughter then becomes a parent

  5. -Radiocarbon- Oceans, groundwater, surface water Atmosphere has 42x1012 tons of 12C 47x1010 tons of 13C 62 tons of 14C CO2 respiration, photosynthesis, tissue, aqueous, organic, inorganic states 14N + 1n – 14C + 1H ~constant global amount (not really) Plants, animals 14C 14N + B + neutrinos • Radiocarbon formed by cosmic • flux neutron • ~15 km altitude • Polar concentration greater • Related to geomagnetic field • Problems • Variations in cosmic ray flux • Variations in geomagnetic field • Lag exchange between global reservoirs • Knowledge of original amount in organism • Counting errors in lab • Sample contamination, modern 14C is worst source • Sample age relative to event age

  6. Tree ring calibration Difference due to past variations in C14 production and possibly CO2 exchange between ocean and atmosphere

  7. Calibrating a date 3000+/- 30 BP Tree ring ages at same period (+/-1 std. dev.) Possible ages

  8. Contaminated by older carbon Contaminated by modern carbon

  9. “By God's will, after a long voyage from the island of Greenland to the south toward the most distant remaining parts of the western ocean sea, sailing southward amidst the ice, the companions Bjarni and Leif Eiriksson discovered a new land, extremely fertile and even having vines, ... which island they named Vinland.” The oldest map showing North America. 1434 A.D. plus or minus 11 years.

  10. Paleomagnetism

  11. Paleomagnetism • Major reversals in geomagnetic field are well-known and well-dated from independent locations • These reversals are useful as time markers • But you must know approximate age to get proper reversal • Inclination – field lines • ~0 deg. at equator • 90 deg. at poles • Declination – angle between true N. and a needle pointing toward mag. N

  12. Dipole is stable but reverses through time Nondipole (declination and inclination) is Unstable and oscillates through time as secular excursions • The main part of Earth’s magnetic field is the dipole field (like a bar magnet centered • on the core. Lines of force represent direction in which a magnetized needle tries • to point. Concentration of these lines represents field strength. • b) Declination: departure of field from true north. Inclination: measure of dip from • Horizontal (where field lines enter surface).

  13. Paleomagnetic Records • Thermoremnant magnetization (TRM) – lavas etc. • Depositional remnant magnetization (DRM) – sediments, smoothed by bioturbation and water content that dilates grains • Chemical remnant magnetization (CRM) – remineralization, recrystallization

  14. Dipole component Normal polarity in black, dating based on K/Ar dates of lavas

  15. Secular Variation – regional in extent (1000-3000 km)

  16. Amino Acid Racemization • All organic materials carry amino acids in their proteins (20 types of AA) • Amino acids alter with time and temperature (form of weathering) • Typically found in two molecular forms (isomeres), “D” and “L” • Only L type exist in living proteins • D type exist in free state or in collagen as result of diagenesis • D/L ratio result of time and/or temperature

  17. Amino Acid Racemization EDT-estimated diagenetic temperature

  18. Biological Methods • Lichenometry • Largest lichen is oldest • Maximum lichen age is minimum substrate age • Maximum age is time substrate stabilized (boulder stopped moving) • Clusters of ages indicate boulder movement events – glacial advances or retreats

  19. Lichenometry

More Related