Chapter 5

Chapter 5 - Chapter5 18:41 Thesedimentaryarchive

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Chapter 5 18:41 The sedimentary archive The characteristics of sediment deposited in an area depend on: Tectonic setting (mountains) Physical, chemical, and biological processes in the depositional environment  (where the rock lays) Method of sediment transport Rocks in the source area from which the sediment is derived Climate (and its effect on weathering) o Certain climates rock weather very rapidly Post-depositional processes of lithification (cementation, compaction) Time Tectonics The forces controlling deformation or structural behavior of a large area of the  Earth’s curst over a long period of time Influence the grain size and thickness of sedimentary deposits An area could be: Tectonically stable-Midwestern US o No changing of rocks for hundreds of millions of years Subsiding (sinking)- new Orleans or Mexico city o Slowly sinking
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Rising gently- new England and parts of Canada after glacial retreat o Rebound of the surface Rising actively-parts of Oregon in the cascade mountains o  to produce mountains and plateaus recent uplift- of the source area leads to rapid erosion of coarse grained  sediment subsidence- in the depositional basin leads to the accumulation of great  thickness of sediment Principle of tectonic elements of a continent Craton- stable interior of a continent; undisturbed by mountain building events  since the Precambrian. o Has two parts Shields-large areas of exposed crystalline rocks (metamorphic rocks).  Are the oldest rocks of a continent Platforms- ancient crystalline rocks covered by flat-lying or gently  warped sedimentary rocks Orogenic belts- elongated regions bordering the craton which have been  deformed by compression since the Precambrian (have mountains) Depositional Environment All of the physical chemical biological conditions under which sediments are  deposited By comparing modern sedimentary deposits with ancient sedimentary rocks,  the depositional conditions can be interpreted Extrabasinal in origin o Formed from the weathering of pre-existing rocks outside the basin, and  transported to the environment of deposition Intrabasinal in origin o Formed inside the basin; includes chemical precipitates, most carbonate  rocks, and coal. Three types of broad categories of depositional environments
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Marine environments (ocean) o Continental shelf- where water is very shallow The flooded edge of the continent. Flooding occurred when the  glaciers melted about 10,000 years ago.
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Chapter 5 - Chapter5 18:41 Thesedimentaryarchive

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