Late Cenozoic Geology

Neogene Period/Pleistocene Epoch

Defining the Pleistocene:

Lyell: 90-100% extant molluscs

Presence of glaciation (*Miocene)

1.6-10,000 y.b.p.

Evidence of Glaciation

The phenomenon had to be proven!Louis Agassiz, James Hutton

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Hutton’s native Scotland

Physical characteristics of glacial sediments

drift/till: texturally & mineralogically immature

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fossil till = tillite

Permian,

Gondwana

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Pleistocene till

ProterozoicGowgandaFm., Canada

outwash: well-sorted, stratified, but associated with till

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Glacial landforms:U-shaped valleys, cirques, horns, aretes (alpine)

Moraines, drumlins, eskers, outwash plains, poor drainage (continental)

Geologic Record of Glaciations

Cenozoic (0-20 mybp; Miocene-Pleistocene)

Late Paleozoic (230-350 mybp) Gondwana

Siluro-Devonian (S. America)

Ordovician (North Africa)

Ediacarian (700 mybp)-Snowball Earth??

Late Archean/Early Proterozoic (2.7-2.3 bybp) Gowganda Fm., Canada

Causes of Glaciation

Explanations must account for:

relative rarity of this phenomenon

alternating glacial/interglacial episodes (cyclicity)

Precession of Earth’s orbit

I. Astronomical hypotheses (Milankovitch)

Tilt of Earth’s axis

Eccentricity (shape of Earth’s orbit)

II. Atmospheric Hypotheses

Carbon dioxide greenhouse effect

“Impact winter” dust cloud from impact/volcanism

III. Oceanic circulation

IV. Plate tectonics

Ultimate control? Combination of astronomical parameters and position of plates?

North American Glacial centers

Ohio River is southern extent

Pleistocene history of the Great Lakes

Note: 4 glacial advances is probably an oversimplification! There are 16 recorded in Europe for the same time interval!

Glacial moraines dominate Great Lakes region topography

Compare glacial (surficial) map of Michigan to bedrock map:

Rise and Fall of the Great Lakes (themes in the movie)

Glacial/interglacials

Effects of a mile-thick glacier: subsidence/rebound changes to drainage Great Lakes carved out along pre-glacial drainageGlacial features: Scoured bedrock Erratics DrumlinsHuman impact (Lake Erie then & now)

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Proglacial, e.g., Lake Agassiz

Pluvial, e.g., Lake Bonneville (ancient Salt Lake)

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Other North American Glacial Phenomena: large fossil lakes

“Scablands” flood from release of glacial Lake Missoula

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The importance of moraines

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pubs.usgs.gov/gip/ capecod/glacial.html

Biological Effects of ice ages….