Historical Geology Week 13 Notes
Historical Geology Week 13 Notes GEOL1005
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This 5 page Class Notes was uploaded by Kate Notetaker on Thursday April 14, 2016. The Class Notes belongs to GEOL1005 at George Washington University taught by Catherine A. Forster in Winter 2016. Since its upload, it has received 37 views. For similar materials see Historical Geology in Geology at George Washington University.
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Date Created: 04/14/16
April 12, 2016 Eocene o Huge evolution of animals o Ungulates hooved animals o After the PETM, there is a huge drop in temperatures Cooling off into the Eocene and into the Oligocene Oligocene o Two important events that occurred There is complete separation of Antarctica from South America and from Australia (Tasmania) Has a big effect on Antarctica Antarctic Circumpolar Current no warm water comes down to Antarctica only cold water stays around it It doesn’t warm the air around Antarctica anymore this is when it started to ice over Late Oligocene, mostly Miocene Collision of India and the Eurasian plates India moves faster than Australia o The Indian Subcontinent was much larger than India is today Leading edge was actually an oceanic plate subducted until the craton hit Indian Plate and the Eurasia Plate were both about the same density Both plates compressed India plate began to subduct beneath the Eurasian Plate Parts of both plates formed mountains Two large thrust faults formed Collision of India with Southeast Asia had a big effect on the rest of Asia as well o Himalayas are nine kilometers high and are still rising at about 1 cm per year So large because they’re still relatively young o End of the Oligocene Things are cooling down Miocene o Still warm o Minor geographic changed post-Miocene Arabian Peninsula met Eurasia Mediterranean Ocean narrowed o Biggest post-Miocene event glaciations From the pole to the equator Development of the Artic or Northern ice sheet With the rise of all these mountain chains on the west side of North America o Rain shadow effect rising air cools and condenses but only falls on one side of the mountain because they can’t go over the very tall mountains Lots of rain on the west sides of the mountains West to east wind directions made these deserts o Similar situation in the rain shadow of the rising Himalayas o Big effect on the plants and animals living there Animals adapted to the open, treeless landscape Evolution of horses in North America In order to become faster, horses (and other ungulates) made similar changes to gain a speedier lifestyle Shorten the proximal (upper) sections of their legs and lengthen the distal (lower) sections o In the plant world evolution and spread of grasses in the Miocene Oldest known grasses are from the Late Cretaceous Phytoliths in every blade of grass made of little pieces of silica Acts as a backbone Silica is a harder than tooth enamel When animals eat the grass, it will wear down their teeth Animals evolve so that they have longer teeth hypsodonty o Very tall crowns so that they can wear them down Eocene-Oligocene 1 really large mammals (ungulates) o Biggest land mammal ever to live Paraceratherium (Oligocene- Miocene) o Elephants o A lot of cat evolution o Dog evolution in the middle of the Cenozoic o “Bear dogs” but not closely related to either Big predators in the Northern hemisphere o Big predator in South America are birds o Whale evolution marine mammals At the end of the Miocene, temperatures start to go down again As we hit the Pliocene, there are big intervals of hot and cold o Then there are these rapid glacial cycles April 14, 2016 Rapid cycling of warm and cold in the Pleistocene Glacial periods o Nebraskan o Kansan o Illinoisan o Wisconsinan most recent In between each period is a period of warming o These are called interglacials o Sometimes we say that we are in an interglacial now but that implies that another glaciation is going to happen All of these periods involve o Continental ice sheets o Glaciation at high altitudes Build up of glaciers o All ice begins with snow o Accumulation during a season has to exceed how much can melt o As more and more snow accumulates going to compact Overlying pressure of the snow on top of it is going to make it recrystallize to ice o Continued build up continue the cycle o As global temperatures cool, these conditions expand Glacial ice moves o Polar ice so cold that the base of the glacier is frozen to the ground Completely non-erosional Ice near the bottom is under a lot of pressure causes the ice crystals to “shear” undergo plastic deformation Temperate continental glaciers and alpine glaciers o Entire mass of ice actually moves o Not frozen to the ground Incredibly erosional Glaciers are incredibly filthy filled with rocks, dust, dirt, etc. When these glaciers move down the mountain o Compressing climatic belts Toward the equator o Great change in river drainages Water that forms the ice comes from the ocean o Sea level drop that is associated with these glaciations o During the Wisconsinan 450 ft. Eventually the ice will hit its furthest extent o Will start a glacial retreat Ice no longer moves, it simply melts o Ice moves forward but next moves backward Forward when they are accumulating until they reach their furthest extent o Melting can happen in a couple ways Can go from a solid to a liquid Solid to a gas ablation The ice is picking up anything from clay sized material to boulders o When it comes to a stop, there will be a pile of the material all around the outside of the moving ice o Glacial till the unsorted jumble of geological materials All the material at the very end of the glacier Terminal moraine o Moraine is a general name for the till Lateral moraines the till that is alongside the ice A lot of material that gets incorporated into the ice o All of the till that is incorporated, just falls down into the ground o Ground moraine the till that covers the ground where the glacier used to be If it starts cooling down again, the glacial retreat will stop o But there is still melting going on toward the top o Accumulation of stuff, marking where the glacial retreat has stopped Temporary o Recessional moraine mark the temporary standstill of a retreating glacier When the glaciers melt there’s a lot of water coming off of them o Form rivers that flow through the ground moraines and come out to distribute their water o Wash material out along with it They can carry out the smaller materials silt and sands The silt and sands that are distributed are called outwash o Ground moraine (un-sorted till) with a layer of outwash (finer grained/sorted) above it Clay and silt wind loess o The loess gets blown there are huge loess deposits from these glaciations o Sometimes deposited hundreds and hundreds miles away o Help us reconstruct the wind patterns Gouged out spots Great Lakes o Sitting in depressions that are gouged out by glaciers moving through them Altered topography o Glaciers tend to flatten things out o A lot of striated rocks Development in a lot of lakes kettle lakes o Shed big chunks of ice o Depression from the till and the ice will fill with water o Little round lakes Change in river drainage New river drainage o A lot of water coming off the glaciers o It will develop new systems Climate zones follow
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