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A. Introduction

• Ice age started in late Pliocene ~2.5-1.8 MYBP

• Continued into Pleistocene 1.8 MYBP - 10,000 YBP

B. The Pleistocene

Early Pleistocene 1.8 MYBP - 750,000 YBP (MIS 20-36)

• Matuyama-Brunhes polarity reversal 750,000 BP marks Early/Middle boundary

Middle Pleistocene 750,000-130,000 YBP (MIS 6-19)

• MIS 6 & 8; Illinoian Glacial

  • possibly more severe than Wisconsin glaciation

  • ~150 m drop in sea level; major land bridges exposed

• MIS 7; interglacial

  • warm climates & dense vegetation in North America & Europe

  • little continental erosion or marine sedimentation

  • formation of paleosols

  • sea level higher than today

Late Pleistocene 130,000-10,000 BP

• Sangamon Interglacial MIS 5e or all of MIS 5

  • MIS 5 (130,000-75,000 YBP) or just substage 5e (130,000-115,000 YBP)

  • midlatitudes slightly warmer than today

  • sea level slightly higher than today

  • widespread paleosols

• Wisconsin Glacial MIS 2, 3 & 4 (and 5 a, b, c, d)

C. Wisconsin Glaciation

Dates

• starts ~115,000 BP with isotope substages 5a, b, c, d

• or, starts ~75,000 BP with isotope stage 4

• includes MIS 4, 3 and 2 (and parts of 5)

Early Wisconsin or "Eowisconsin" 115-75 ka YBP; isotope substages 5 a, b, c, d

• MIS 5d (115,000-105,000): stadial

• MIS 5c (105,000-93,000): interstadial

• MIS 5b (93,000-85,000): stadial

• MIS 5a (85,00075,000): interstadial

Middle Wisconsin 75-25 ka YBP

• MIS 4 (75,000-60,000): stadial

• MIS 3 (60,000-25,000): interstadial

Late Wisconsin 25-10 ka YBP; MIS 2

D. Late Wisconsin 25,000-10,000 YBP

Woodfordian Substage

• ~ 22,000-12,5000 YBP

• Last glacial maximum (LGM) ~21,000-17,000 YBP

• Numerous lakes in western mountains

  • Lake Bonneville, Idaho (wetter conditions than now)  

  • Lake Missoula: western Montanna (ice-dammed lake)

• Glacial Lake Agassiz (pro-glacial lake)

  • formed about 11,700 YBP; drained southwards to Gulf of Mexico

  • 11,000-10,100 YBP drained eastwards to North Atlantic

  • 10,100-9,400 YBP drained northwest

  • 9,400-8,200 YBP drained eastwards to North Atlantic

  • numerous catastrophic outburst floods

• Evolution of the Great Lakes

Twocreekan Substage (Allerod)

• interstadial: 12,500-11,8000 YBP

• retreat of ice; most of Great Lakes region deglaciated

• followed by eventual establishment of spruce forest at Two Creeks

• corridor opened between Laurentide & Cordilleran Ice Sheets

Greatlakean Substage (Younger Dryas)

• stadial ~11,800-10,000 YBP

• glacial readvance; Two Creeks forest killed ~11,850 YBP

• possible catastrophic outflow of ice-dammed lakes to North Atlantic

Short term fluctuations in proxy records

Heinrich events massive iceberg flotillas deposited ice rafted debris (IRD) across Atlantic events associated with very cold temperatures & drops in ocean salinity evidence for 6 events H1 ~14,000 YBP H2 ~21,000 YBP H3 ~28,000 H4 ~40,000 H5 ~51,000 YBP H6 ~63,000 YBP possibly related to ice sheet instabilities & surges Dansgaard-Oeschger (D-O) events rapid temperature rise of 8-16C (interstadial) slow temperature drop back to stadial conditions Heinrich events occur after a series of declining D-O events Bond cycles methane cycles contain several D-O events slow cooling leads to more cold-based ice sudden warming causes bed to thaw & ice sheet surges producing Heinrich events

Image credit: NOAA Paleoclimatology Slide Set. Heinrich Events: Marine Record of Abrupt Climate Changes in the Late Pleistocene. http://www.ncdc.noaa.gov/paleo/slides/slideset/19/index.html Image credit: NOAA Paleoclimatology Slide Set. Heinrich Events: Marine Record of Abrupt Climate Changes in the Late Pleistocene. http://www.ncdc.noaa.gov/paleo/slides/slideset/19/index.html

E. The Holocene

• MIS 1

• Hypsithermal (Altithermal) about 9,000-6,000 YBP; climatic optimum

• Little Ice Age: ~1500s to 1800

F. Vegetation Changes

Maps from: Adams J.M. & Faure H. (1997) (ed.s), QEN members. Review and Atlas of Palaeovegetation: Preliminary land ecosystem maps of the world since the Last Glacial Maximum. Oak Ridge National Laboratory, TN, USA. http://www.esd.ornl.gov/projects/qen/adams1.html

G. Summary

• Early (1.8 MYBP - 750,000YBP), middle (750,000 YBP - 130,000 YBP) and late Pleistocene

• Late Pleistocene (130,000 YBP - 10,000 YBP): Sangamon interglacial and Wisconsin glacial

• Early (115,000 YBP - 75,000 YBP), middle (75,000 YBP - 25,000 YBP), and late Wisconsin

• Late Wisconsin (25,000 YBP - 10,000 YBP)

  • substages: Woodfordian, Twocreekan, Greatlakean

  • short term fluctuations in the proxy record: D-O events, Heinrich events