Geo101.15.SedimentaryRxs[1]

Geo101.15.SedimentaryRxs[1] - Earths thin skin Major Types...

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1 Earth’s thin skin… Introduction to Sedimentary Rocks Major Types of Rocks: Igneous * Sedimentary * Metamorphic What are sedimentary rocks? Consolidated sediment formed at or near the Earth’s surface… 1) by cementing together of loose grains derived from pre-existing rock or fossil fragments, 2) from precipitation of minerals from aqueous solutions, Sedimentary rocks are composed of sediment What is sediment? loose rock fragments, grains, mineral crystals, and fossil materials, derived from the erosion of pre- existing rock, or from precipitates out of water …that remain unconsolidated (loose and unattached) -…so sedimentary rocks are formed by weathering, mechanical sorting, and cementing together of pieces of pre-existing rocks and/or organic materials - or by precipitation of minerals from Fuid solutions ) …a few things we should know about sedimentary rocks 1) sedimentary rocks occur in the upper part of the crust… as a surface veneer or cover on older igneous and metamorphic rocks
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2 2) sedimentary rocks range in thickness from non-existent to almost 20km thick on continental margins / shelves 3) sedimentary rocks constitute over 80% of the Earth’s surface, …yet they make up less than 1% of the Earth’s total mass 4) sedimentary rocks form layers as they are deposited, normally parallel or subparallel to the surface of the Earth, …much like pages of book they record evidence of ancient events, past life and environments Strata A layer of sedimentary rock with a discernable base and top is called a bed or stratum .. Several beds combine form strata The boundary between two beds is a bedding plane or contact The overall arrangement of the beds is its bedding or stratiFcation Bedding is a result of changes in depositional style or environment Sedimentary beds or strata that can be traced or mapped… constitute the fundamental unit of stratigraphy called formation
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3 Why are sedimentary rocks preserved? Erosion, accumulation and preservation of sedimentary rocks depends on a tectonic interplay of uplift and subsidence…a relative change in base level Thick sequences of sedimentary rocks accumulate in basins , regions where lithosphere sinks creating a depression at the earth’s surface Why are sedimentary rocks preserved? Basins form where the lithosphere has been loaded by weight or where it has undergone folding or stretching Without subsidence, sedimentary rocks on continents would be washed out to sea!!! Where do basins exist?
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This note was uploaded on 04/03/2011 for the course GEOLOGY 939 taught by Professor Swisher during the Spring '11 term at Rutgers.

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Geo101.15.SedimentaryRxs[1] - Earths thin skin Major Types...

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