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A. Introduction

Traditional Ice Age Chronology

North America		Alps		Northern Europe
Glacial	Interglacial	Glacial	Interglacial	Glacial	Interglacial
Wisconsin		Wurm		Weichsel
	Sangamon		R-W		Eem
Illinoian		Riss		Saale
	Yarmouth		M-R		Holstein
Kansan		Mindel		Elster
	Aftonian		G-M		Cromer
Nebraskan		Gunz		Menap

Revised chronology based on marine oxygen isotope stages (MIS)

• even numbers generally refer to glacials

• odd numbers generally refer to interglacials

• Wisconsin, Sangamon, and Illinoian are only names still in use

B. Stratigraphic Sequencing

Law of Superposition younger beds overlie older beds younger beds truncate older beds Law of Ascendancy and Descendancy exoposed beds at higher elevations are older than exposed beds at lower elevations
Limiting Age Estimates maximum: event (unit) must be younger than the dated material outwash must be younger than the stump minimum: event (unit) must be older than the dated material moraine must be older than the tree

C. Paleomagnetism

D. Radiometric Dating

Introduction

• isotope: same number of protons, different number of neutrons

• radioactive isotopes disinegrate & radiate particles at a fixed rate

• half life: time it takes to disintegrate half of original amount

Radiocarbon Dating

• 3 carbon isotopes: ¹²C, ¹³C, and ¹⁴C

• ratio of ¹⁴C/¹²C shifts as ¹⁴C disintegrates

• half life (by international agreement) is 5568 +- 30 years; all ages are YPB; present is year 1950

• age range: 100-70,000 years

• limitations

Other Radiometric Dating Techniques

• K/Ar Dating - age range: older than 500,000 years

• Uranium Series Dating - age range: 1000-350,000 years

• Thermoluminescence Dating

• Fission Track Dating

E. Oxygen Isotopes

3 Oxygen Isotopes: ¹⁶O and ¹⁸O most common

Fractionation

ratio at which these isotopes enter chemical compounds is temperature dependent 16O lighter so evaporates preferentially; 18O heavier so condenses preferentially during interglacials 18O/16O ratio in oceans stays constant measure how much 18O/16O ratio deviates from isotope proportions found in modern oceans d18O%o   is zero for standard marine ocean water

during glacials: 16O preferentially evaporated from oceans; 18O concentrated in oceans ocean 18O/16O ratio is higher than in non-glacial seawater; d18O is positive marine shells enriched in 18O during glacials 16O deposited on ice sheets; 16O concentrated in ice ice sheet 18O/16O ratio is lower than in non-glacial seawater; d18O is negative d18O is most widely used proxy for: changes in global ice sheet volume changes in global temperatures

Challenges

• ice core interpretation

• marine core interpretation