Sedimentary Rocks Flashcards
What are Siliciclastic sedimentary rocks?
Silica based
Example - Sand
Formed of fragments/grains of pre-existing rock and material.
How are siliciclastic rocks form?
- Erosion
- Transportation
- Deposition
- Burial
- Diagenesis
What is a turbidity current?
Rapid, downhill flow of water caused by increased density due to high amounts of sediment.
Give 3 examples of a sedimentary feature.
Wave ripples.
Turbidity currents.
Storm surges.
Define a rock.
A naturally occurring aggregate of minerals.
What kind of texture do igneous rocks have?
Interlocking with a preferred mineral orientation.
What texture does sedimentary rocks have?
Fragmentary.
What is the definition of a sedimentary rock?
Rocks that are formed at the earth’s surface a low temperature, <50 degrees, formed by surface processes and are the product of physical and chemical breakdown of other rocks, and biological processes.
What depth does diagenesis occur at?
10 Km depth.
What is diagenesis?
When grains are fused together by heat and pressure.
What is the average geotherm?
25 degrees C/ 1 Km
What is physical weathering?
Mechanical breakdown.
What is chemical weathering?
Breakdown through chemical means.
Give 5 examples of physical weathering.
Frost action. Movement of ice. Salt. Water. Wind.
What is frost action?
When water enters a crack, freezes and expands, breaking the rock.
What is detrital sedimentation?
Solid particles settling out of fluid. (liquid or air)
What is precipitate sedimentation?
Solid particles formed out of solution.
What group is limestone in?
Carbonate.
Ironstones are evaporates, what does this mean?
The ironstones are deposited in a rock by chemical replacement.
What do glaciers grind rocks into?
Rock-flour.
U-shaped valleys, hanging valleys, cirques, aretes, fjords and roche montonnes are created by what?
Glaciers.
How does salt erode?
Salt crystals expanded by periodic hydration and dehydration.
What makes rivers and coasts good at eroding?
The sediment they carry.
What are Aeolian processes?
Wind.
What kind of erosion makes rounded edges?
Aeolian and chemical.
What minerals are stable at the earths surface?
Muscovite, quartz, clay and calcite (sometimes unstable)
Minerals that are unstable at the earths surface are?
Olivine, pyroxene, garnet, amphibole, plagioclase, k feldspar and biotite.
When deep minerals are are brought to the surface are they stable?
They become thermodynamically unstable at the surface due to their interaction with water. Compared with shallow formed minerals that are more stable.
How does temperature and humidity effect chemical weathering?
Higher temperature and humidity increases chemical weathering.
What do feldspars weather into?
Clay and dissolved ions.
What do carbonates weather into?
Carbonic acid and calcium.
What minerals are easiest to remove from solution?
Ca, K and Na.
What minerals are next hardest to remove from solution after the 3 easiest?
Mg and Fe2 then Si.
What are the hardest minerals to remove from solution?
Al and Fe3+, they are often left as residue.
What is a regolith?
A mineral not transported after weathering.
What do minerals react with?
Temperature, humidity and pH.
Rain water is acidic, what is the pH?
pH 6.
When organic matter oxidizes what is produced?
Acidity.
What is H+
A proton.
Is a Low pH acidic or alkaline?
Acidic.
What are 5 ways weathered material can be transported?
Slumps, slides, in solution, as bedload and in suspension.
What determines the transport mechanism of weathered material?
Grain density, size and current velocity.
What does the Hjulstrom diagram show?
Velocity against grain diameter.
What is Strokes law?
This basically says that diameter is the most variable. Finer-grained material is more likely to be carried in suspension. Velocity is proportional to the diameter and density of the grain.
What is saltation?
The bouncing of grains on a riverbed.
What is the bedload?
Sediment that rolls along the riverbed.
How are sandstones in the UK formed?
Aeolian.
Where does ice transport material?
Within, above and below it.
What can ice do to material it is transporting?
It can alter it.
What kind of sorting is left by ice?
Poor sorting.
What is required for deposition?
A change in physical/chemical environment. e.g. ice melting or a river slowing.
What is required for sediments to be preserved?
Deposition rates to exceed erosion rates.
What is Flocculation?
Coming out of solution.
Do terrestrial environments have a net erosion or net deposition?
Net Erosion.
Do marine environments have a net erosion or net deposition?
Net deposition.
What is induration?
Hardening/squeezing out water.
What is cementation?
Joining of grains.
What is the process of diagenesis?
Burial with an increase of temperature, compaction, induration, recrystallization and cementation.
