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WMU - GEOS 1300 - Class Notes - Week 5

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WMU - GEOS 1300 - Class Notes - Week 5

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background image CHAPTER 5: The Formation of Sediment and Sedimentary Rocks  5.1 How and Why Do Rocks Disintegrate to Form Sediment? Sediment results from the disintegration of rocks exposed to weather and is then 
redistributed on Earth’s surface by wind, water, and glaciers.
It gets buried and transformed to hard rock. Weathering is the process that break down preexisting rocks at Earth’s surface, reducing 
them to loose particles, dissolving some minerals and forming new ones.
Erosion refers to the process that pick­up sediment particles. Weathering occurs when the geosphere interacts with the atmosphere, hydrosphere, and 
o Physical: Break large rocks into smaller fragments o Chemical: Reactions among minerals and water and gases that dissolve some  minerals and produce new ones Physical Weathering Water freezing into rock cracks causes the rock to break more Salt during the winter causes concrete to crack Expansion and contraction of minerals in rocks causes rock disintegration Chemical Weathering The key to understanding chemical weathering lies in figuring out how minerals 
react with oxygen and water
The reactions that take place in oxygen and water are important also in the 
shallow subsurface where ground water interacts with minerals
Dissolution: reactions break apart mineral molecules and these molecules then 
disperse in water
Hydrolysis: reactions that consume both mineral and some of the water molecules
and form new solid minerals and dissolved ions
Oxidation: the process in which substances react with oxygen to form new 
substances by exchanging electrons
Plutonic and metamorphic rocks form below Earth’s surface in the absence of 
oxygen gas, so they are especially prone to oxidation reactions on the surface
What Minerals Survive Weathering  Minerals dominated by ionic bonds most readily dissolve in water, especially if 
the water is acidic
Silicate minerals are generally more resistant to chemical weathering o Those with more silicon­oxygen bonds weather more slowly 5.2 What Is the Link Between Weathering and Sediment?
background image Recall: Weathering is the process that forms sediment Two things are produced – solid minerals and dissolved ions Making Clastic Sediment They are of solid mineral particles that are left behind as rocks weather They form by chemical weathering Quartz is the most resistant to weathering because of its covalent bonds and the 
lack of iron
Making Chemical Sediment Chemical sediment: dissolved ions precipitate as solid ionic compounds Most precipitation of chemical sediment takes place in lakes and oceans In some case, biochemical processes also cause mineral precipitation o Ex: formation of shells and bones 5.3 How Does Loose Sediment Become Sedimentary Rock? The first step in forming sedimentary rock: Compaction The first step of lithification of compaction: sediment particles are weighed down 
with previous sediment and pressure to break bonds
o Decrease the volume of pore space and packs grains Stickiness of compacted sediment is explained by the observation that natural 
broken surfaces on minerals expose atoms with unbalances charges that tent to 
attract oppositely charged atoms in adjacent grains
The second step: Cementation Cementation: Filling pore spaces with precipitated minerals to make rock hard Minerals precipitate from water in the pore spaces between sediment particles and
cement them together into rock
Cement minerals grow to fill pore spaces and surround the sediment particles  Most common cementing agents are calcite, quartz, clay minerals, and hematite Precipitation of mineral cements is caused partly by and increase in ion 
concentration in the water, but affected by temperature
Calcite precipitates and forms cement readily at depth because it relies on high 
heat to precipitate
5.4 How Are Sedimentary Rocks Classified? 1. Clastic Sedimentary Rocks are composed primarily of mineral grains remaining from or  produced by weathering of preexisting rocks and cemented by minerals that precipitated 
from pore water.
2. Chemical and biogenic sedimentary rocks composed of minerals that were precipitated  from water or that are remains of organisms.

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School: Western Michigan University
Department: Geoscience
Course: Physical Geology
Professor: Kaczmarek
Term: Winter 2016
Tags: Geology and Chemistry
Name: GEOS 1300 Week 5 Notes
Description: These notes cover the formation of different sedimentary rocks. Beginning with how the components of sedimentary rocks are broken down by different weathering. They go over how sedimentary rocks are classified, how fossil fuels are found in sedimentary rocks, and what sedimentary rocks reveal about ancient environments.
Uploaded: 02/26/2018
6 Pages 35 Views 28 Unlocks
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