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Late Cenozoic 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. Hutton’s native Scotland.

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Late Cenozoic Geology

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  1. 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.

  2. Evidence of Glaciation The phenomenon had to be proven! Louis Agassiz, James Hutton Hutton’s native Scotland

  3. Physical characteristics of glacial sediments drift/till: texturally & mineralogically immature fossil till = tillite Pleistocene till Permian, Gondwana Proterozoic Gowganda Fm., Canada

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

  5. Glacial landforms: U-shaped valleys, cirques, horns, aretes (alpine) Moraines, drumlins, eskers, outwash plains, poor drainage (continental)

  6. 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

  7. Causes of Glaciation Explanations must account for: relative rarity of this phenomenon alternating glacial/interglacial episodes (cyclicity)

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

  9. 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?

  10. North American Glacial centers Ohio River is southern extent

  11. 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!

  12. Glacial moraines dominate Great Lakes region topography Compare glacial (surficial) map of Michigan to bedrock map:

  13. 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)

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

  15. “Scablands” flood from release of glacial Lake Missoula

  16. The importance of moraines

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

  18. Biological Effects of ice ages….

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