Pleistocene geology

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
Pleistocene till

fossil till =
tillite
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Permian,
Gondwana

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Proterozoic
Gowganda
Fm., 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)


I. Astronomical hypotheses (Milankovitch)
Eccentricity
(shape of Earth’s orbit)
Tilt of Earth’s axis

Precession 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
drainage
Glacial features:
Scoured bedrock
Erratics
Drumlins
Human impact (Lake Erie
then & now)


Other North American Glacial Phenomena: large fossil lakes
Pluvial, e.g., Lake Bonneville (ancient Salt Lake)

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Proglacial, e.g., Lake Agassiz


“Scablands” flood from release of glacial Lake Missoula


The importance of moraines

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


Biological Effects of ice ages….