Misc. Non-Quiz Content Flashcards
Lithification
Transforms loose sediment into solid rock
Processes that lithification includes:
Burial: more sediment added to previous layer
Compaction: overburden weight reduces pore space
Cement: minerals from groundwater “glue” sediment together. Common cements include calcite, silica, and iron oxide
Orange/red sedimentary rock indicates that
Iron oxide is present
Biochemical/carbonate rocks
Sedimentary rocks that come from living organisms
Limestone deposition environment
“Think of the Bahamas”: warm (tropical/subtropical), normal-salinity marine water, wave-agitated, lots of oxygen, shallow and clear water
Organic rocks
Rocks made from organic carbon (like coal, the altered remains of fossil vegetation, and oil shale, shale with heat-altered organic matter)
Accumulates in lush, tropical wetland settings (ancient swamps)
Requires deposition in the absence of oxygen
Chemical/evaporative sedimentary rocks
Come from minerals precipitated from water solution
What are evaporites?
Sedimentary rocks created from evaporated seawater – evaporation triggers the deposition of chemical precipitates.
Examples: halite and gypsum
Depositional environments
Locations where sediment accumulates. They differ in energy regime, sediment delivery/transport/depositional conditions, and chemical/physical/biological characteristics
Terrestrial depositional environments (deposited above sea level)
River: channelized flow transports sediment. Sand and gravel fill concave-up channels, and fine sand, silt, and clay is deposited on flood plains
Sand dune: wind-blown piles of well-sorted sand, with dunes moving according to prevailing winds. Results in uniform sandstones with gigantic cross-beds (looks like layers in different directions)
Lakes: gravels and sands are trapped near shore, and well-sorted muds are deposited in deeper water. These sediments are preserved as finely-laminated shales which may contain fish fossils and may fill in with wetland muds
Marine depositional environments (deposited at/below sea level)
Deltas: sediments dropped where an ocean meets the sea. Sediment carried by the river is dumped when velocity drops, and deltas grow over time, building out into the basin.
Shallow water carbonates: tropical, contain skeletons of marine invertibrates, and has warm, shallow, clear, normal-salinity water.
Deep marine: skeletons of planktonic organisms make chalk or chert. Fine silts and clays turn into shale.
Strata
A series of beds
Formation
A sequence of strata that is sufficiently unique to be recognized on a regional scale
Graded beds
Bedding layers that fine(?) upward. Happen from repeated pulses of high-energy sediment transport, with sediment added as a pulse of turbid water. As the pulse wanes, the water loses velocity and the sediments settle, coursest to finest.
Turbidites
Multiple graded-bed sequences
Bed surface markings and what they may indicate
Mudcracks: alternating wet/dry conditions and necessitate deposition in a terrestrial setting
Scour marks: troughs eroded in soft mud by current flow
Fossils: evidence of past life
Regression
Retreat of seas due to sea level dropping. It’s tied to erosion and makes sediments less likely to be preserved.
Note that the sea level rises and falls in a predictable pattern
Compressive strength (in context of material strength)
Force a stone can withstand without rupturing
Characteristics to consider in building stone
Compressive strength, porosity, density, and abrasive resistance
Where does the water for hydrothermal metamorphism come from?
Magmas (“juvenile” fluids), seawater (important at oceanic ridges and subduction zones), “devolatilization” reactions (at subduction zones or during regional metamorphism; H2O and CO2 are products) surface and groundwater (“meteoric” fluids), and formation pore fluids (“connate” fluids, in pores or trapped in crystals)
What types of rocks are the ore minerals deposited at Yellowstone?
Sedimentary. The hydrothermal fluids carrying the metallic minerals came from igneous rocks, but they deposited the minerals within sedimentary rock.
List of fossil fuels
Coal, oil/petroleum, natural gas, and other nontraditional fossil fuels (oil shale, oil/tar sands, shale gas, methane hydrate)
Oil/petroleum
Liquid hydrocarbons that are present in certain layers of sedimentary rock (the geosphere)
Some petroleum products include:
Kerosene, lubricants, waxes, asphault, and chemicals
Natural gas
Major component is methane; also includes methane, propane, and butane
Process of oil/gas production (13 steps)
- Planktonic organisms live in oceans/lakes
- Zooplankton eat phytoplankton (algae) that use the sun’s energy to produce organic matter and energy through photosynthesis
- Planktonic organisms die, their remains settle to the bottom of the seafloor with anoxic conditions
- Sediments accumulate over time, containing the remains of planktonic organisms
- Thick sequences of sediments are deposited and the planktonic organisms buried in them are heated and compressed until the organic matter begins to change into kerogen
- High temperature and pressures from greater depth of burial changes the kerogen to hydrocarbons
- More heat and pressure breaks the hydrocarbons down into oil/petroleum and natural gas
- Petroleum and natural gas migrate into porous and permeable sedimentary rocks like sandstone, serving as a petroleum reservoir rock
- Oil floats on water, with gas being even lighter, so the petroleum and natural gas move up within the reservoir rock until stopped y an impermeable sedimentary layer like shale, which forms a trap
- An oil field is formed as more petroleum and natural gas accumulate in the trap
- Geologists use tools to locate oil fields
- Wells are drilled into the ground in the oil field to extract the petroleum (crude oil)
- The crude oil is transported to a refinery into gasoline, butane, kerosene, liquid petroleum gas, jet fuel, diesel fuel, fuel oil, chemicals used to manufacture plastics, et cetera
Kerogen
A solid, waxy organic material
Source rock
The unit where oil and gas formed
Tar sands
Form when oil is moving upward within a reservoir of porous, permeable sand and is not sopped by an impermeable sedimentary layer
Bitumen
Highly viscous asphalt/tar that’s formed when oil escapes the sand at the surface and is biodegraded by an “oil-eating bacteria”
Oil shale
Sedimentary rock containing kerogen that hasn’t been heated enough within the Earth to change the kerogen into hydrocarbons
Shale gas
Forms in organic-rich black shales where extremely deep burial and extremely high temperatures have broken petroleum down into natural gas/methane
Primary cause of recent increase in earthquakes in central US
Wastewater disposal (NOT fracking itself).
Fracking
Creates artificial fractures to extract the oil/methane gas from low-permeability shales. Wells are drilled to thousands of feet deep and then drilled horizontally along the shale bed. Then, high-pressure fluids and sands are injected to hydraulically fracture the shale and release the trapped resources.