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37 Cards in this Set

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  • Back
Sedimentary rock
rock that forms at or near the surface of the Earth
Three ways sedimentary rock forms
cementing of pre-existing sediment (clastic), growth of skeletal material (biochemical), or precipitation of minerals (chemicals)
Explain sedimentary rocks in the crust
By volume, there are substantially more igneous and metamorphic rock, but sedimentary drapes over all of it.
What is sediment?
Loose fragments of rocks, minerals, and shells
How do we get sediment?
Weathering, either physical or chemical (reactions that destroy minerals if rock contacts air or water)
Physical weathering: Jointing
cracking due to removal of overburden or cooling
Physical weathering: Exfoliation
jointing in onion-like sheets (Characteristic of granitic plutons)
Physical weathering: frost wedging
Ice expansion during freeze / thaw cycles
Physical weathering: root wedging
Plant roots push joints apart
Physical weathering: salt wedging
salt from ground water or sea spray cause crystals to grow in porous rock and splits the rock.
How does physical weathering help chemical weathering?
It breaks it down into smaller pieces, increasing surface area substantially.
Chemical weathering: dissolution
dissolving of minerals in water (CaCO3 + H2CO3 Ca2+ + 2HCO3-)
Chemical weathering: hydrolysis
Reaction of minerals with water to produce secondary minerals. (K Feldspar makes Kaolinite / Clay)
Chemical weathering: oxidation
"Elemental loss of electrons, commonly due to oxygen. For example: 4Fe2+ + 7O2 + 4H+ => 4(Fe3+)2O3 + 2H2O
Climate controls of chemical weathering
Water (volume and movement), temperature (reaction rates), and latitute (weathering is faster in the tropics)
Rock controls of chemical weathering
Mineral resistance (highly variable), and texture (available surface area)
Mineral resistance to chemical weathering with silicates
Olivine and feldspars are the least stable, while quartz is the most. Amphiboles and pyroxene's are in the middle.
Secondary minerals (most resistance to chemical weathering)
Iron oxides, aluminum oxides, and clay
Evaporites, carbonates, sulfates (least resistent to chemical weathering)
Dolomite, calcite, pyrite, gypsum, halite
sediment produced by chemical and physical weathering that is subjected to additional processes.
Three additional processes that occur in soil
1. Addition of organic matter, ions from rainwater, dust; 2. movement of material downward by groundwater percolation; 3. bioturbation (mixing and disturbing by plants and animals)
How does soil develop (four steps)
1. Bedrock begins to disintegrate; 2. Organic materials facilitate disintegration; 3. Horizons form (layers) primitive plants like lichen and moss are degrading the surface; 4. Developed soil supports thick vegetation (so now you have both an A and B-horizon)
Soil horizons- temperate climate
O: organic layer, no minerals; A: topsoil, dark, organics; E: transition layer as iron leaches, light color; B: subsoil, clays and ions collect, orange; C: weathered rock; R: regolith, unweathered.
Soil variation will be due to:
climate, substrate composition, slope steepness, drainage, time, and vegetation type
Clastic transport rocks
transport via water, wind, and ice. The higher the velocity of the transport, the larger the sediment it moves. Also, the further, the finer the material gets sorted.
Clastic Deposition
Sediment settles out of transport medium due to velocity change
Clastic Lithification (2)
Compaction: minerals are squeezed together and the water / air in pore spaces is expelled; Cementation: circulating waters precipitate cements into the void spaces (CaCO3, silica, oxides, etc.)
pebble to boulder, clasts well-rounded, usually poorly sorted, deposted with high energy currents (flooring rivers, steep mountains, etc.)
Poorl sorted coarse grains, but with angular braings. Has a short transport
deposted by moderately active transport processes (rivers, beaches, wind / sand dunes). Ends up being mostly quartz, feldspar, micas, and rock fragments
Shale and siltstone
silt and clay-sized particles, over 1/2 of all sedimentary rocks, particles not visible, deposited in quiet water (deep ocean, lakes, floorplains)
biochemical sedimentary rocks
limestone (CaCO3 derived mostly from shells of organisms)
Formation of Sandstone
CaCO3 precipitates in warm water and biochemical formation occurs
Silica-rich marine plankton oozes (diatoms, radiolarians) deposited on deep seafloor are recrystallized.
Plant remains that are deposited in layers, along ancient rivers, swamps, over 50% carbon
Chemical rock: evaporites
water evaporates and dissolved materials precipitate, usually in arid marine shorelines, examples are: halite and gypsum.
Chemical rock: precipitates
travertine (CaCO3) and cert (SiO2)