(6) + (7) Sedimentary Rocks Flashcards
1
Q
Types of Sedimentary Rocks
A
- Clastic:
o Sediment composed of fragments of pre-existing rocks cemented together - Chemical:
o Sediment composed of minerals precipitated from solution (inorganic)
o Biochemical: shells or skeletons of organisms - Organic:
o Sediment composed of carbon-rich relics of dead organisms
2
Q
Clastic Rocks
A
- Fragments of pre-existing rocks cemented together
- Largest volume of sedimentary rock types
- Coarse grained
o Sedimentary breccia (angular fragments)
o Conglomerate (rounded fragments) - Medium Grained
o Sandstone - Fine Grained
o Shale or mudstone
3
Q
Types of sandstone
A
- Quartz sandstone (quartz rich)
- Arkose (feldspar rich)
- Greywacke (rich in rock fragments)
4
Q
Why is shale fissile?
A
- Lots of clay (about 2/3 of the rock is clay minerals)
- Clay is a sheet silicate mineral
- Breaks into thin layers
5
Q
Chemical sedimentary rocks
A
- Carbonites o Limestone (calcite) o Dolomite - Chert (cryptocrystalline quartz) - Evaporites (precipitate from seawater or a saline lake)
6
Q
Inorganic Limestone
A
- Precipitated directly from solution
o Crystalline texture - Some types of inorganic limestone
o Travertine [formed in groundwater, caves, hot springs when CO2 degasses from water (changes water chemistry, includes ppt)]
o Oolitic limestone (formed when currents and/or waves roll spheres of limestone precipitated around sand grains or mud)
7
Q
Dolomite
A
- Comes from dolostone
- Limestone is altered by Mg-bearing groundwater
o When?: in lagoons soon after limestone formed and long after burial - Often recrystallized
8
Q
Chert
A
- Inorganic
o Lumpy nodules
o Underground water replaces original rock with silica
o Also associates with hydrothermal systems
o High silica in hot water
o Bedded - SiO2 (fine grained)
- Biochemical and inorganic varieties
- Biochemical: accumulated siliceous organisms on the sea floor
9
Q
Biochemical: derived from organisms
A
- Shells, skeletons, algae, bacteria, plankton
- Mostly limestone
o Carbonate shells > silica shells
10
Q
Biochemical limestone
A
- Biochemical: Precipitated through actions of organisms
- Contains fossil remains (corals, algae, other shell-forming organisms)
o Shells made from ions extracted from seawater
o Creatures die
11
Q
Biochemical limestone: Creatures die..
A
- Shells become sediment
- Skeletons in place (reef builders: coral)
- Settle out of water
- Moved by currents, waves to another location where they settle out
• Shells break during transport
• Bioclastic limestone: type of biochemical limestone formed from wave-broken fragments of algae, corals, and shells
12
Q
Not all biochemical limestones retain fossiliferous character
A
- Post-deposition fluids and compactions after shell material
- Results: massive, blocky, (usually) light coloured rock
13
Q
Examples of biochemical limestone
A
- Chalk: fine grained bioclastic limestone
- Manitoba’s Tyndall stone: dolomitic limestone
14
Q
Organic sedimentary rocks
A
- Coal: formed from compaction of incompletely decayed plant material
15
Q
Varieties of coal
A
- (Peat)
- Lignite
- Subbituminous coal
- Bituminous coal
- Anthracite
- (high BTU’s and Pressure descending) (more pure coal)
