Origin of sediments Flashcards
What is the driving force of siliciclastic sediment creation?
The water cycle
Water is the main eroder and transport of rock
What is erosion and weathering?
Weathering (Breakdown or dissolution of rock)
Erosion (regolith being removed from it’s genesis)
Weathering -> physical, chemical and biological
What is the Goldich series?
A measure of the stability of minerals from weathering
Bowens series is related
What does incongruent mean in relation to the weathering of silicate minerals?
The amount of dissolved material is less than the original rock, due to clay minerals not dissolving.
Incongurent ex. feldspat (ions + kaolin)
Congurent ex. limestone (only i
What is the main mode of transport for sediments?
In a continental setting
Rivers
How does the size and roundedness of grains relate to the depositional environment?
In siliciclastic sediments
Rounder -> Longer transport
Smaller -> Less energy in river
Well sorted -> Stable energy in river
How are >90% of marine carbonates created?
By biological processes
How is weathering of rocks related to the Earth’s climate?
Weathering dissolves ions in the water. These ions can combine with CO2 from the atmosphere to form carbonates, storing the carbon in rocks.
What are the three most common carbonates?
Calcite>Dolomite>Aragonite
Aragonite is metastable -> Slowly turns to calcite
What does the abbreviation ‘DIC’ stand for?
Dissolved Inorganic Carbon
Inorganic compounds with carbon, such as carbonates, dissolved in oceans
Which ions are most common in sea water?
In order of most abundant to least
Cations: Na +, Mg 2+, Ca 2+, K +
Anions: Cl -, SO4 2-, HCO3 -
What is Henry’s law?
Solubility of gases decreases as temperature increses
More CO2 in cold water
How is the precipitation of carbonates related to the pH of water?
Acidic (low pH): Less precipitation
Alkaline (high pH): More precipitation
Ligevægtsforhold ifm. surheden af opløsningen
Why is cooler water more acidic than warm water?
More carbonic acid in solution due to Henry’s law
How are ooids formed?
Precipitation of Carbonate around non carbonate particles.
Partly of nonbiogenic origin
In which order do evaporites precipitate?
In relation to a start volume of water (1)
Calcite 1/2 -> Gypsum 1/3 -> Halite 1/10 -> Potassium and magnesium salts 1/20
Least soluble -> most soluble
Which two evaporite patterns are most common?
Bulls-eye patterns
Teardrop patterns
How are bulls-eye patterns formed?
Closed basin with saline water, slowly evaporating.
Least soluble ->Outer rings
fx. calcite, gypsum
Most soluble ->Inner rings
fx. halite, K/Mg salts
How are teardrop patterns formed?
Basin, with some influx of water from the ocean. Water closest to inlet is less concentrated in salts than further away.
Closer to inlet -> Least soluble
Further from inlet -> Most soluble
Which organisms form biogenic silica?
Diatoms and Radiolaria
Lavet af silica, dvs. SiO2
What is a sedimentary basin?
Sections, where the shape of the crust changes and makes room for deposits.
Which kinds of sedimentary basins occur?
Foreland basin - At the foot of mountains
Rift basin - Downwards faulting makes troughs
Intracontinental basin
Passive margin basin - At the edge of a continental plate (shelf)
