earth history geol 2110 the ice age the pleistocene epoch the ice age
TRANSCRIPT
Earth History GEOL 2110
The Pleistocene EpochThe Ice Age
Major Concepts• The gradual cooling evident in the mid to late Cenozoic
reached a critical threshold which triggered extensive glaciation around 1.8 Ma.
• Causes for this general cool down are not generally agreed upon but seem to be related to the dispersal and enlargement of the continents (relative to ocean areas) and thermal isolation of the polar regions.
• Multiple cycles of advance and retreat (with periods of about 100,000 yrs most recently) appear to be related to earth’s orbital motions (orbital eccentricity & axial wobble.
• These glacial cycles have had a profound global effect on climate, sea level changes, land elevation, distribution of lakes and rivers, and the ecology of the land.
The Great Cenozoic Cool Down
Thermal Threshold
Recognition of Continental Glaciation
Swiss Alps
Jura Mtns
Swiss Plains
Drift, Erratics, and Moraines• Hutton (1795) suggests Alpine
glaciers more extensive than today• Esmark (1824) first to propose
continental glaciation of N Europe• Venetz-Sitten & de Charpentier
(1830) confirm Alpine glaciers extended to the Swiss Plain
Louis Agazzi – Father of Continental Glaciation Theory (1840)
The Swiss-born naturalist came to the U.S. in the mid-1800’s and founded the Museum of Comparative Zoology at Harvard. Ichthyologist, paleontologist, geologist, Agassiz mounted the first significant scientific expedition on Lake Superior in the summer of 1848, delivering 12 papers describing his findings at the first annual meeting of the American Association for the Advancement of Science that fall.
Louis Agassiz (1807-1873)
The Last Peak of Glaciation20,000ybp
Tropical Belt Shrinks, but same climate
Continental Shelves Exposed
Siberian Desert
The Last Peak of Glaciation20,000ybp
Missouri and Ohio – Pro-glacial Drainage Pathways of Glacial Meltwaters
Continental Shelves Exposed
Semi-arid desert - Loess
Effects of GlaciationIsostatic Rebound
Effects of GlaciationSea Level Change
Minimum – 140mMaximum + 65m
Effects of GlaciationSea Level Change
River Terraces Develop as Base Levels Drop in Steps
Effects of GlaciationLarge Meltwater Lakes
LavaDam
IceDam
Channeled Scablands of the Columbia PlateauCarved 18,000ybp by catastrophic outletting of Glacial Lake Missoula. Water velocities likely topped 50 mph
Potholes
Effects of GlaciationLarge Meltwater Lakes
Effects of GlaciationWind-blown Silt - Loess
Palouse Loess of Southeastern
Washington
Loess Hills of Western Iowa
Dating Glacial Episodes Techniques: C14 isotopic dating (<80,000y)Fission Track in obsidianK-Ar isotopic dating (>100,000y)Th-Pr dating of clays (<300,000)
The Current Glacial Stratigraphy
Correlating Glacial Episodes
Correlating Glacial EpisodesIce Cores from Greenland and Antarctica
Correlating Glacial EpisodesIce Cores from Greenland and Antarctica
Correlating Glacial EpisodesLake Sediment Cores
Piston Coring
Greenland ice core
warm coldIce rafted debris
North Atlantic sediment core% cold water foram species
Last 650,000 yrs of Glacial CyclesAntarctic Record
Current CO2 level
380!
Why the Cycles?
Possible Factors• Changes in Solar Radiation• Orbital Effects• Changes in Atmospheric Transparency• Changes in Reflectivity – Albedo• Paleogeographic Controls of Climate• Changes to Ocean Currents
Can’t Test
Volcanism not apparently more prevalent in Pleistocene
Why the Cycles?Orbital Effects
Milankovitch Cycles
Why the Cycles?Orbital Effects
What Brought us to the Thermal Threshold?
Thermal Threshold
What Brought us to the Threshold?Changes in Reflectivity - Albedo
•Land more reflective than Oceans
•Land area has been growing
•Land getting higher – more cloud cover
•Ice caps increase albedo - feedback
What Brought us to the Threshold? Changes in Paleogeography
The Thermohaline Conveyer BeltBrings warm waters to the Arctic
The Younger DryasSmall Scale (1,000 y) Cycles
Fresh Meltwaters Shut Down the Conveyor
CatastrophicGlacial Calving
Next Lecture
The Pleistocene EpochThe Ice Age in Minnesota
Read MN at a Glance – Quaternary Geology