sedimentary rocks. a. formation: compaction & cementation 1. sedimentary rocks form from the...
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sedimentarsedimentary rocksy rocks
A. Formation:A. Formation:1. Sedimentary rocks form from the COMPACTION & COMPACTION & CEMENTATIONCEMENTATION of rock fragments/sediments2. Lithification: the changing of sediments into sedimentary rock
3. Sedimentary rocks are similar to the sediments from which they form (ie. Sandstone is made up of sand)
B. CLASTICB. CLASTIC1. Form when rock fragments & sediment are carried & deposited by GRAVITY, WIND, GLACIERS, & RUNNING WATERRUNNING WATER
Clastic Rock Formation
Most sediment is carried byMost sediment is carried byRunning WaterRunning Water
2. The further water carries sediment, the ROUNDER & ROUNDER & SMOOTHERSMOOTHER the sediment becomes3. When a stream slows down, it drops the LARGESTLARGEST particles first, & the SMALLESTSMALLEST last (HORIZONTAL SORTING)(HORIZONTAL SORTING)
Observe how sediments are deposited
So….
• If you are far out from shore, would you expect the grain size of the rocks to be large or small?
• What about if you are close to the shore?
That means….
4. Rocks formed closer to shore will be made up of bigger fragments than rocks formed farther away from the shore
BrecciaBreccia – very large sediments that are angular,
most likely deposited by gravity
ConglomerateConglomerate – large
sediments that are rounded (have been
transported by a stream!)
C. CRYSTALLINEC. CRYSTALLINE
1. Formed when dissolved minerals in seawater are deposited (seawater evaporates,seawater evaporates, leaving the minerals behind to crystalize)2. Also known as CHEMICAL
Salt “Mines”Salt “Mines” - Rock Salt is being formed as the salt water evaporates
from the sea.
““Devil’s Golf Devil’s Golf Course”Course” – millions of years ago this was a sea of salt water. It has been
evaporating over time…
…and has formed
“pockets” of chemical
limestone, rock salt, and rock gypsum!
D. BIOCLASTICD. BIOCLASTIC
1. Formed from the remains of plants & animals that are compacted
– Fossil LimestoneFossil Limestone – formed when shell remains of marine organisms are cemented in fragments•Shells are made of CALCITE which reacts with acid
2. Coal Formation
a. Long ago, huge trees grew in the warm, humid
swamps.
b. Trees died and decomposed into what is
called PEAT
c. Peat was buried under layers of mud.
d. Pressure increased, slowly changing the plant
remains into coal.
Coal – Coal – note note
distinct distinct layering layering of peatof peat
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STRATIFICATIONSTRATIFICATION
1. STRATIFICATION1. STRATIFICATION (layering): Layers of sediments that have SIMILARLYSIMILARLY colored minerals and are typically sandstones or siltstones
2. Fossils2. Fossils – actual remains, imprints from plants or animals, or preserved traces from living things
bells & whistles for bells & whistles for sedimentary rock sedimentary rock
identification!identification!• Stratification• Fossils• Fragments of
materials cemented together
• Ripple marks• Mud cracks
Angel’s Landing, Zion Angel’s Landing, Zion Nat’l Park, UtahNat’l Park, Utah – note
rock layers
Red Sandstone, UtahRed Sandstone, Utah – note distinct LAYERING of sediments (sand)
Horseshoe Bend, Utah
Grand Canyon Nat’l Park, ArizonaGrand Canyon Nat’l Park, Arizona – sedimentary rock formation at its best! The canyons were formed by the Colorado River
cutting into the rock layers over time!
Fossils
•The remains, impression or any other evidence of a plant or animal preserved in rock.
• Fossilization
Brachiopod fossils in limestone Imprint
of a leaf
Trilobite fossils – over 250 MILLION years old!!!
Mud Cracks and Ripples
• Ripple Marks: A sand pattern formed by the action of winds, streams, waves or currents; preserved when sand becomes sandstone
• Mud Cracks: Develop when deposits of wet clay dry and contract. The cracks are filled with sediments and fossilize when the clay becomes shale
Ripple Marks in the Shale from
running water as the
rock was forming