the rock cycle. sedimentary processes 1 2) & 3) sediments are transported and deposited 4
TRANSCRIPT
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The Rock Cycle
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Sedimentary Processes1
2) & 3) Sediments are transported and deposited
4
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Products of weathering
Primary Residual DissolvedMinerals Minerals Ions
Feldspar Clay minerals K+, Ca+2, Na+
Aluminum hydroxide
Fe-Mg minerals Hematite & Mg+2
Limonite
Quartz Quartz Silica
Primary Solids that Ions that are carriedMinerals remain in soil away in water
----------Detrital sediments------------------ Chemical & biochemicalsediments
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Types of sediment
Detrital – mineral & rock fragments Chemical – halite (NaCl) crystals that precipitate from water
Biochemical – shells made of calcite (CaCO3) by organisms that extract the ions from water
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Detrital sedimentary rocks- classified by grain size differences
Conglomerate
Breccia
Sandstone
Shale
All these rocks have clastic textures – the rocks are composed of particles (fragments) that are cemented together
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Detrital sediments are sorted by the processes of transportation and deposition
Well sorted Poorly sorted
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Sands and sandstones can be used to interpret the erosional history of an area and the kinds of rocks that were eroded
Well-sorted
Poorly sorted
“Mature” sediments have little feldspar. This means that the sediment was derived from weathered rocks or that the feldspar decomposed during transportation in water.
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The same diagram is used to interpret the provenance (source rocks) of sediments
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Placer deposit– accumulation of sand or gravel containing minerals that are highly resistant to chemical attack and economically valuable - gold, platinum, ilmenite, rutile, zircon, diamond, garnet, magnetite, corundum, monazite.
These and other chemically resistant minerals are widely used to indicate the provenance of sediments, e.g. kyanite, sillimanite, staurolite
indicate that metamorphic rocks were eroded. Diamonds indicate kimberlite; gold indicates hydrothermal veins, etc.
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Chemical and biochemical sedimentary rocks
Limestones – composed of calcite
Travertine Coquina
Chalk
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Deep ocean sediments are mainly fine-grained biochemical sediment called oozes, with some hydrogenous (chemical) and terrigenous (wind or water borne) detrital sediment
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Calcareous & siliceous ooze
Manganese nodules are hydrogenous - they precipitate from deep ocean water when the Mn oxidizes:Mn+2 (dissolved) + O2 + 2e- = MnO2 (pyrolusite)
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Banded Iron Formations – ancient (>2.5 billion year old) sedimentary deposits of iron-bearing minerals. These indicate that Earth’s early atmosphere was too poor in oxygen to oxidize iron at the site of weathering. Dissolved iron was transported in water: 4Fe+2 (dissolved) + 3O2 = 2Fe2O3 (hematite)
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Phosphates form in shallow marine environments where dissolved PO4-3
is carried by upwelling of deep ocean water. These areas are biologically productive - many fossils are found, especially bone material.
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Phosphate Mining of the Bone Valley Formation in Florida
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Shallow basin with high rate of evaporation – Gulf of Mexico, Persian Gulf, ancient Mediterranean Sea, Red SeaSequence is: calcite, gypsum, halite with increasing evaporation
Evaporite minerals
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Evaporites
Gypsum
Halite
Seawater evaporation:
1) Calcite 2) Gypsum3) Anhydrite4) Halite (95% evaporation)5) Sylvite 6) Other rare minerals
Dolomite may form afterward by reaction of Mg+2 with calcite
Continental waters:Borax & boratesNitrates
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Saltdome
Sulfur is produced by sulfate reducing bacteria which consume the oxygen in gypsum or anhydrite