_10_SedRoxDeepTime

_10_SedRoxDeepTime - GEL 1: Lecture 10: Sedimentary Rocks &...

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1 GEL 1: Lecture 10: Sedimentary Rocks & Deep Time Sedimentation Rocks A great heat balance exists on Earth that continually modifies the landscape: the interior of the Earth is inexorably giving off heat that drives plate tectonics, volcanism, and the uplift of mountains - the other great heat source, the Sun, warms up the Earth’s exterior, driving weather and climate systems that act to wear down mountains and fill in low spots on Earth (like the oceans) with the loose, eroded sediment. The origin of sedimentary rocks is ultimately driven by solar energy that produces weather and climate. One of the main characteristics of sedimentary rocks , and the feature that differentiates them from igneous rocks that we've talked about, is that they are arranged in layers, called beds or strata . Sedimentary rocks are the solidified products of mud, silt, sand and other loose sediment originally deposited as laterally extensive, horizontal layers in various depositional environments - horizontally layered rocks, like those exposed in the Grand Canyon, are sedimentary rocks, and are formed near Earth’s surface by a sequence of processes: 1) weathering and erosion of previously existing rocks exposed on land to produce loose sediment 2) transport of sediment downslope by water, wind or ice (glaciers) 3) deposition of sediment in a topographic depression like a river floodplain, a lake, a delta, or an ocean basin (i.e., a depositional environment ) - deposition occurs when the energy of the transporting system (e.g., a river) decreases enough for grains to settle out by gravity along a relatively horizontal surface 4) burial , compaction and cementation : as loose sediment becomes buried by more sediment on top, it compacts, loses water from between the grains, and solidifies into rock - compaction – original water trapped between grains in pore spaces gets squeezed out, permitting a closer packing of grains - cementation of loose sediment grains occurs as ion-bearing groundwaters percolate through the sediment, precipitating ‘cement’ of calcite, iron oxide, silica or other minerals within the pores between grains and binding them together - sandy sediment solidifies over time into sandstone - silty sediment (finer grains than sand) solidifies into siltstone - clay-rich sediment solidifies into shale (or a very similar rock called mudstone )
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2 Sediment is deposited in horizontal layers within depositional environments (e.g., lakes, rivers, floodplains, deltas, deserts, beaches, reefs, shallow continental shelves, deep oceanic basins) - horizontal layers of sed rox called beds or strata In the Grand Canyon, all of the horizontal, multicolored layers represent 2 billion years of changing environments such as shallow oceans, meandering rivers and floodplains, and migrating deserts All of these interpretations of depositional environments represented by rocks are based on the principle of actualism
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This note was uploaded on 12/25/2009 for the course PLB 9876655 taught by Professor Canington during the Spring '09 term at UC Davis.

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_10_SedRoxDeepTime - GEL 1: Lecture 10: Sedimentary Rocks &...

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