2-5 - Unsorted and unlayered conglomerate, Sierra Nevada...

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Unsorted and unlayered conglomerate, Sierra Nevada Mts., California
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Unsorted and unlayered gravels in the southern Rockies.
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U-shaped valleys in mountains Canadian Rockies?
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Large “erratic” boulders in the middle of the northern plains!
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Unsorted & unlayered conglomerate on hillsides throughout the Midwest and Northeastern US
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Also see rock surfaces with striations formed as ice slide over it.
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Glacial features Southern limit of glacial features Distribution of glacial tills, striations, U- shaped valleys, and other glacial features over North America
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Reconstruction of the extent of the European and North American ice sheets based on glacial deposits, ice striations, and other glacial features
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More detailed map of the features left by the North American ice sheets. The zone of scouring would be were the sheet was the thickest; zone of deposition is where it flowed to.
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Pollen in soils, lakes, and bogs, and microscopic animals that live near the sea-surface tell us about climate across the globe. 100 um
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Mid latitudes were cold and drier (more grasslands, less forests . Tropical ecosystems were far less extensive Deserts and dry lands were far more extensive Globally drier!
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And globally , temperatures were much cooler. •~2 ° to 6 ° C in the oceans •~2 ° to 9 ° C over land (greater difference with increasing latitude)
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http://www.ncdc.noaa.gov/cgi-bin/paleo/hsstplot.pl Color-coded differences between sea-surface temperature today and 18,000 years ago. Greens, blues and purples mean colder temperatures 18,000 years ago
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All that ice meant sea level was a lot lower than today (water was in the ice, not the oceans!) Acquire C-14 age dates on corals found at varied depths on the seafloor, but are known to grow only within a few meters of sea level 20,000 years ago, corals that grew at sea level were 110 m below present sea level
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Questions that Arise Are we sure all those glacial features and deposits are all the same age? (e.g., maybe the conglomerates are from different (smaller) glaciers in different places at different times) • If more than one, how many? • And why does climate cool and ice sheets advance; why does climate warm and those sheets retreat?
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Ridges (moraines) of unsorted, unlayered gravels mark maximum advances of glaciers.
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1 st terminus Retreat to 2nd terminus Retreat to 3rd terminus Advance to 4th terminus destroys 1 st , 2 nd and 3rd terminal moraines (tills) Only tills from the most farthest advance and any subsequent retreats are likely to be preserved.
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Map of terminal moraines (ridges of glacial till) in upper Midwest indicates maximum advance and retreats.
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small stream. Upper till
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2-5 - Unsorted and unlayered conglomerate, Sierra Nevada...

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