late cenozoic geology
DESCRIPTION
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. Hutton’s native Scotland. - PowerPoint PPT PresentationTRANSCRIPT
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?
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
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The importance of moraines
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pubs.usgs.gov/gip/ capecod/glacial.html