L10: Sedimentary Rock Flashcards
Define sedimentary rock
Composed of compacted or cemented grains which have become lithified
Coarser material carried in from a river get deposited _________. , while finer _____ and _______ are carried into deeper waters
- First
- Silts and clays
What are clastic sedimentary rocks?
- Formed from the products of mechanical weathering of pre-existing rocks
- The grains are then transported by gravity, water, ice, or winds to accumulate as sediments in streams, lakes, oceans, soils, or deserts
- BASICALLY: The transport of existing rock from pre-existing particles
What are chemical sedimentary rocks?
- Do not form from the mechanical break-up and transport of grains. Instead, they derive from the precipitation of minerals from supersaturated solutions
- Precipitate out of sea/lakewater
Examples of chemical sedimentary rock
- Limestone = from calcite
- Chert = silica
- Evaporites = gypsum and halite
- Iron formations = iron oxides
What are biological sedimentary rocks?
- Formed biologically from the shells of plankton
- Ex.: diatoms and foraminifera
What are the 3 types of sedimentary rocks?
- Clastic
- Chemical
- Biological
What do currents reveal?
A propensity to change flow speed
What is sorting?
The tendency for variations in current velocity to segregate sediment according to size
What happens the longer transport processes are and when particles are exposed to more abrasion?
- The more rounded and the smaller the grains become
- Sedimentary rock also give clues to how far the grains have travelled from their source
Sedimentary structures include all the features that are formed at the time of __________.
depositions
What is strata
Individual beds nearly horizontal when deposited
What can be found within sedimentary rocks?
Oil and gas
What is cross-bedding?
- Consists of bedded material deposited by wind or water and inclined at angles as large as 35o from the horizontal, the angle of repose
- They form when grains are deposited on the steeper, downcurrent slopes of sand dunes on land or on sandbars in rivers and under the sea
- Common in sandstones
What is the precursor for oil and gas?
- Plankton
- Organic carbon
What is graded bedding?
- Abundant in continental slope and deep-sea sediment deposited by dnse, muddy “turbidity currents”
- Hug the bottom of topography of the oceans as they move downhill
Turbidites
Accumulations of many graded-beds in this manner
Continental shelf
Water thats 150 m deep in the ocean then drops off to BP
Bissell plank
The depth past continental shelf; drops down
What are ripples?
- Very small dunes of sand or silt whose long dimensions are at right angles to the current or wave direction
- Ripples are present in shallow water bc current is present to move the water along
- Help us identify what the environment was like at that time
What is bioturbation?
- Bedding in structures thats broken down by the burrowing activity of animals
- Appear as cylindrical tubes that represent burrowing
What occurs when pressure and temperatures change?
- Cause pre-existing sediment to dissolve, such that the water which does seep through the buried sediment carries dissolved minerals
- Common cementing agents = silica and calcite
Lithification is . . .
Turning loose sediment into rock
What is diagenesis?
Changing loose sediments (a rock) composition
What is the process of maturation?
- Process by which organic matter is transformed into various forms of petroleum
- Occurs when the temperature reaches a certain point and the element becomes unstable
Clastic rocks are . . .
- Carried from land back to the ocean
- Based on particle size
- High flowing water needs more energy to move big particles along fine particles, coarse grained
If rocks are fine grained, where can we assume they formed?
Fine grained particles are formed further offshore
How are clastic rocks formed?
Most rocks are made up of mud bc most sediments around keep getting recycled
What is biomass useful for?
Finding fossil fuels
Carbonate sediments are best examples of . . .
- Chemical and biological participates
- Form mostly from the accumulation of carbonate minerals that are directly formed by organisms
What is caused by seawater evaporation?
Causes the precipitation of an ordered sequence of minerals of increasing solubility
Evaporites
Highly soluble; easy to weather bc formed in extreme environments
Place the following in order: Limestone, halite, patash, gypsum
- Limestone
- Gypsum
- Halite
- Potash
What is banded iron formation?
- Formed during the precambrian period
- 95% of earth’s iron reserves come from this
- Precipitate out of seawater
- From BIF we know that oceans used to be full of iron, indicating the change in earth’s composition
Limestone
- Brine reaches 2x the concentration of seawater
- Calcite the first mineral to precipitate out
Gypsum
- Reaches approximately 5x the concentration of seawater
- More soluble than limestone
Halite
- 10-12x original seawater concentration
- Halite precipitates out of brine
- A highly soluble salt; will dissolve in a natural environment
Potash
- Bittern starts to precipitate
- Major potassium source
- Concentration of brine reaches the viscosity of honey
