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Chapter 8
SedimentaryRocks Part2
Types of sedimentary rock
Sedimentary structures
Types of sedimentary
rocks
• Sediment originates from mechanical and/or chemical weathering
• Rock types are based on the source of the material
• Clastic rocks – transported sediment as solid particles
• Chemical/Biochemical rocks – sediment that was once in solution
Sedimentaryrocks
Chapter 8 Sedimentary rocks
Clastic sedimentary rocks
Size of clasts (particles)
gravel bigger than 2 mm conglomerate (1/10 inch) or breccia
sand sand-sized (1/16-2) sandstone
silt, clay very fine-grained (<1/16) shale, mudstone,siltstone
common name size Detrital rock
See Table 8.3
conglomerate sandstone siltstone shale
claysiltsandgravel
sediments
sedimentaryrocks
Chapter 8 Sedimentary rocks
Clastic sedimentary rocks
Siltstone, Mudstone & Shale silt & clay-sized particles (clay, silt),
particles too small to identify w/ eye over 1/2 of all sedimentary rocks deposited in quiet (slow moving) water
- deep ocean & continental slope- lakes- floodplains (siltstone)
Shale w/plant remains
shale beds often underlay groundwater conduits
raw material for brick, tile, pottery, china
shale+limestone= Portland cement
shale may contains fossils, oily organics, breaks along bedding planes
Chapter 8 Sedimentary rocks
Clastic sedimentary rocks
Sandstone
composed of sand grains
2nd most abundant sedimentary rock
deposited by moderate currents: - rivers & deltas - beaches - wind (sand dunes)
mostly quartz (strong & chemically stable, but may also contain volcanic rock)
See Fig. 8.15 for major groups of sandstone
Chapter 8 Sedimentary rocks Clastic sedimentary rocks
Sandstone
sorting
degree of similarity in particle size
Chapter 8 Sedimentary rocksClastic sedimentary rocks
Sandstone
shapedegree of roundedness
Chapter 8 Sedimentary rocks
Clastic sedimentary rocks
Conglomerate
composed mostly of gravel pebbles to boulders
poorly sorted
deposited by strong, turbulent currents: - big flooding rivers - steep streams (near mountains) - glaciers
Chapter 8 Sedimentary rocks
Clastic sedimentary rocks
Breccia
conglomerate with angular grains
didn’t travel far
Chapter 8 Sedimentary rocks
Chemical sedimentary rocks
derived from material carried in solution to lakes/seas
2 types of precipitation - chemical - biochemical
precipitation from solution to form “chemical sediments”
See Table 8.4
Chapter 6 Sedimentary rocks
Chemical sedimentary rocks
Limestone
composed primarily of calcite (calcium carbonate CaCO3)
10% of all sedimentary rocks (by volume) most abundant chemical sedimentary rock
Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms) Inorganic limestones include travertine (caves) and oolitic limestone (tropical beach environment) Dolostone: dolomite=CaMg(CO3)2 Typically formed secondarily from limestone
Chapter 6 Sedimentary rocks
Chemical sedimentary rocks
coquina (rock of shell fragments): bioclastic
Organic rock of biochemical origin
Chapter 6 Sedimentary rocks
Chemical sedimentary rocks
Fossiliferous limestone
Coral reef Limestone cliff(Guadalupe MountainsNatl Park, TX)
• How to build a carbonate platform
See Figure story 8.16
• How to build an atoll
See Box 8.1
Darwin’s theory on atolls (1831)
Chapter 8 Sedimentary rocks
Chemical sedimentary rocks
Common chemical sedimentary rocks
•ChertMade of microcrystalline silica (SiO2)
Varieties include flint and jasper (banded form is called agate)
Agate
Chapter 8 Sedimentary rocks
Chemical sedimentary rocks
Evaporites water evaporates and triggers the deposition of salts
sequence of precipitation: calcite (calcium carbonate), gypsum (calcium sulfate), rock salt (halite, NaCl); bitter salts (potassium and magnesium salts)
(a) calcite
Chapter 8 Sedimentary rocks
Chemical sedimentary rocks
Evaporites water evaporates and triggers the deposition of salts
ancient seawater basins evaporated and deposited saltSalt flats, Utah Death valley, Calif.
sequence of precipitation: carbonate, gypsum (calcium sulfate), rock salt (halite, NaCl); bitter salts (potassium and magnesium salts)
Chapter 8 Sedimentary rocks
Chemical sedimentary rocks
Evaporites- the story of the Mediterranean
Fig. 8.19
During the Miocene, lower sea level almost shut down the inflow of Atlantic surface water into the Mediterranean over the Strait of Gibraltar. Evaporation removed vast quantities of water and left behind evaporative sediments that underlay the sediments in the Mediterranean today.
Chapter 8 Sedimentary rocks
Chemical sedimentary rocks
Coal buried and compacted plant material different kinds of coal, depending on formation process
Sedimentary structures (Physical features)
1. Layers (bedding, or “strata”)1. Layers (bedding, or “strata”)
2. Cross-bedding2. Cross-bedding
3. Graded beds3. Graded beds
4. Ripple marks4. Ripple marks
5. Mud cracks5. Mud cracks
Sedimentary structures (Physical features)
1. Layers (bedding, or “strata”)
each layer is unique
deposited horizontally
separated by bedding planes
Sedimentary structures (Physical features)
2. Cross-bedding tilted beddingtilted bedding commonly ancient sand dunescommonly ancient sand dunes
river deltas, flow channelsriver deltas, flow channels
Sedimentary structures (Physical features)
3. Graded beds
particles within a layer gradually change:
coarse at bottom fine at top
rapid deposition from water w/ varying sed. sizes
Colorado River
Sedimentary structures (Physical features)
4. Ripple marks
wavy surfaces in sand: current ripple marks
tell direction of current becausethey are perpendicular to flow
See Fig. 8.8
Sedimentary structures (Physical features)
5. Mud cracks sediment alternatively wet/dry
shallow lakes, desert basins
flood plains
Some MC questions…
Which of the following sets of processes is written in order of increasing temperature?
A. sedimentation, metamorphism, diagenesisB. diagenesis, sedimentation, metamorphismC. sedimentation, diagenesis, metamorphismD. metamorphism, diagenesis, sedimentation
Some MC questions…
What type of sediments are accumulations of solid fragments produced by weathering?
A. biochemical sedimentsB. chemical sedimentsC. clastic sedimentsD. all of the above
Some MC questions…
Which of the following statements about transportation of sediment is false?
A. Smaller particles settle faster than larger particles.B. As a current slows, the largest particles start to settle.C. Faster currents carry larger particles than slower currents.D. Rivers and ocean currents move much more material than do air currents.
Some MC questions…
In what type of environment did the ripples depicted above most likely form?
A. beach (waves)B. desert (wind)C. alluvial (stream)D. delta (river + tides)
Some MC questions…
Which of the following minerals is least likely to occur in a marine evaporite environment?
A. calciteB. gypsumC. halite D. quartz
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