Pleistocene 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 Evidence of Glaciation The phenomenon had to be proven! Louis Agassiz, James Hutton QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture Hutton’s native Scotland Physical characteristics of glacial sediments drift/till: texturally & mineralogically immature Pleistocene till fossil till = tillite QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture Permian, Gondwana QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture Proterozoic Gowganda Fm., Canada outwash: well-sorted, stratified, but associated with till QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture 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: 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) QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture Proglacial, e.g., Lake Agassiz “Scablands” flood from release of glacial Lake Missoula The importance of moraines QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture pubs.usgs.gov/gip/ capecod/glacial.html Biological Effects of ice ages… [...].. .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
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