DATING THE GLACIATION OF

SOUTHERN PART OF NORTH CASCADE

RANGE

by: James Leask

Main Drift Sheets

• Lakedale (youngest; 11,050-16,000 years ago)– Hyak– Domerie– Ronald– Bullfrog

• Kittitas (intermediate; over 120,000 years ago)– Indian John– Swauk Prairie

• Thorp (oldest; over 700,000 years ago)

Dating Criteria

• Upper limit of erratics• Moraine size/position• Outwash terrace position• Estimated glacial limit position• Thickness of weathering rinds• Soil Profile

Soil Measurements

• % Clay • Silt to Clay ratio• pH Levels• % Magnetic Minerals• Moist Color

Thermoluminescence Dating

Procedure1.Once buried, rock accumulates energy at the

atomic level.2.Rock samples are taken to lab and exposed to

various doses of radiation.3.Photons emitted are recorded.

Intro to OSL

OSL – Optically stimulated luminescense

According to Berger, OSL has the potential to produce more accurate dates than TL.