Late Cenozoic Geology

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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.
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Evidence of Glaciation
The phenomenon had to be proven! Louis Agassiz,
James Hutton
Huttons native Scotland
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Physical characteristics of glacial sediments
drift/till texturally mineralogically
immature
fossil till tillite
Pleistocene till
Permian, Gondwana
Proterozoic Gowganda Fm., Canada
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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)
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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
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Causes of Glaciation
Explanations must account for relative rarity
of this phenomenon alternating
glacial/interglacial episodes (cyclicity)
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I. Astronomical hypotheses (Milankovitch)
Eccentricity (shape of Earths orbit)
Tilt of Earths axis
Precession of Earths orbit
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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?
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North American Glacial centers
Ohio River is southern extent
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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!
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Glacial moraines dominate Great Lakes region
topography Compare glacial (surficial) map of
Michigan to bedrock map
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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 drainage Glacial features
Scoured bedrock Erratics Drumlins Human
impact (Lake Erie then now)
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Other North American Glacial Phenomena large
fossil lakes
Pluvial, e.g., Lake Bonneville (ancient Salt Lake)
Proglacial, e.g., Lake Agassiz
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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
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Biological Effects of ice ages.
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