Sedimentary Rocks
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Transcript of Sedimentary Rocks
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Sedimentary Rocks
http://www.fi.edu/fellows/payton/rocks/create/sediment.htm
Sedimentary rock is formed by erosion
Sediments are moved from one place to another
Sediments are deposited in layers, with the older ones on the bottom
The layers become compacted and cemented together
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Sedimentary Rock
Sedimentary Rocks are formed at or near the Earth’s surface
No heat and pressure involved
Strata – layers of rock
Stratification – the process in which sedimentary rocks are arranged in layers
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Sediments-pieces of material left by:
*wind *ice *chemical precipitation
*water *gravityStep 1: WEATHERING
Chemical- minerals are chemically broken down
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* Physical – minerals remain chemically unchanged
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Step 2: EROSION* transporting weathered materials to another location* Wind, water, gravity and glaciers transport
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Step 3: DEPOSITION* sediments are deposited and sorted
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Step 4: BURIAL* deposited into depressions called
“sedimentary basins”* the deeper it gets, the more pressure on it
til……2 ROCK BURIAL
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Step 5 : LITHIFICATION (FYI – lithos: Greek for stone)* physical and chemical process that changes it
to sedimentary rock1st Compaction
2nd Cementation & Solidificationnew minerals precipitate more of the same type
around existing ones crystallize around
existing ones
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FEATURES OF SEDIMENTARY ROCKSBEDDING – *horizontal layers*if sorted, graded bedding
CROSS-BEDDING - *inclined layers move forward like sand dunes
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RIPPLE MARKS* when sediment is moved into small ridges by
wind or wave action* back & forth waves yield symmetrical waves* currents, (like in rivers) asymmetrical waves
Sand dune – ripple marks from wind
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Asymmetrical ripple marks
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FOSSILS*animals die, buried, lithified* some plants replaced by other minerals* shells, bones, etc. could leave impressions
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CONCRETIONS* lumps of fine grained silica* called chert*also called nodules
CHERT
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MUD CRACKS*wet clay dries and contracts* cracks later fill with sediment
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TYPES OF SEDIMENTARY ROCKS1. CLASTIC formed by lithifications
Coarse MediumFine
gravel sandsilt & mud
some rocks sandstonesiltstone
conlglomeratesmudstone
POROSITY* percent of open space between grains of sand*good reservoirs for oil, natural gas, and H2O* permeable if water can pass through
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Porous Rock
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2. CHEMICALa. rocks formed by evaporation
- called evaporites ex: calcite, halite & gypsum
S
CALCITE
DEAD SEA SALT
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b. organic sedimentary rock-formed from the remains of living things- most abundant is limestone (mostly
calcite)CaCO3 from shells
if shells are high in silica, they form siliceous ooze
- Coal – from remains of plant material…almost entirely carbon
CALCAREOUS OOZE Siliceous ooze