Origin of sediments

Question 1

What is the driving force of siliciclastic sediment creation?

Answer 1

The water cycle

Water is the main eroder and transport of rock

Question 2

What is erosion and weathering?

Answer 2

Weathering (Breakdown or dissolution of rock)
Erosion (regolith being removed from it’s genesis)

Weathering -> physical, chemical and biological

Question 3

What is the Goldich series?

Answer 3

A measure of the stability of minerals from weathering

Bowens series is related

Question 4

What does incongruent mean in relation to the weathering of silicate minerals?

Answer 4

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

Question 5

What is the main mode of transport for sediments?

In a continental setting

Answer 5

Rivers

Question 6

How does the size and roundedness of grains relate to the depositional environment?

In siliciclastic sediments

Answer 6

Rounder -> Longer transport
Smaller -> Less energy in river
Well sorted -> Stable energy in river

Question 7

How are >90% of marine carbonates created?

Answer 7

By biological processes

Question 8

How is weathering of rocks related to the Earth’s climate?

Answer 8

Weathering dissolves ions in the water. These ions can combine with CO2 from the atmosphere to form carbonates, storing the carbon in rocks.

Question 9

What are the three most common carbonates?

Answer 9

Calcite>Dolomite>Aragonite

Aragonite is metastable -> Slowly turns to calcite

Question 10

What does the abbreviation ‘DIC’ stand for?

Answer 10

Dissolved Inorganic Carbon

Inorganic compounds with carbon, such as carbonates, dissolved in oceans

Question 11

Which ions are most common in sea water?

In order of most abundant to least

Answer 11

Cations: Na +, Mg 2+, Ca 2+, K +
Anions: Cl -, SO4 2-, HCO3 -

Question 12

What is Henry’s law?

Answer 12

Solubility of gases decreases as temperature increses

More CO2 in cold water

Question 13

How is the precipitation of carbonates related to the pH of water?

Answer 13

Acidic (low pH): Less precipitation
Alkaline (high pH): More precipitation

Ligevægtsforhold ifm. surheden af opløsningen

Question 14

Why is cooler water more acidic than warm water?

Answer 14

More carbonic acid in solution due to Henry’s law

Question 15

How are ooids formed?

Answer 15

Precipitation of Carbonate around non carbonate particles.

Partly of nonbiogenic origin

Question 16

In which order do evaporites precipitate?

In relation to a start volume of water (1)

Answer 16

Calcite 1/2 -> Gypsum 1/3 -> Halite 1/10 -> Potassium and magnesium salts 1/20

Least soluble -> most soluble

Question 17

Which two evaporite patterns are most common?

Answer 17

Bulls-eye patterns
Teardrop patterns

Question 18

How are bulls-eye patterns formed?

Answer 18

Closed basin with saline water, slowly evaporating.
Least soluble ->Outer rings
fx. calcite, gypsum
Most soluble ->Inner rings
fx. halite, K/Mg salts

Question 19

How are teardrop patterns formed?

Answer 19

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

Question 20

Which organisms form biogenic silica?

Answer 20

Diatoms and Radiolaria

Lavet af silica, dvs. SiO2

Question 21

What is a sedimentary basin?

Answer 21

Sections, where the shape of the crust changes and makes room for deposits.

Question 22

Which kinds of sedimentary basins occur?

Answer 22

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)