Clastic sediments Flashcards
(27 cards)
By what processes are clastic sediments derived by?
Weathering and erosion of subaerially exposed pre-existing rock
How is rock made available to be weathered and eroded?
Uplift, exposure, tectonic, and volcanic processes
What does weathering lead to the formation of?
Regolith and soil
What factor controlled the rate of soil formation?
Climate
What affects water availability, needed to mediate chemical weathering?
Faster reactions in areas of high rainfall. In colder areas, where the water is solid, it is unavailable.
How does temperature affect the rate of chemical weathering reactions?
Higher temperatures increase the rate of chemical weathering reactions.
Give three examples of physical weathering
Frost wedging, exfoliation, action of plants
What is true of all chemical weathering processes?
They are all mediated by water
What does chemical weathering involve?
Dissolution of minerals, for example by hydrolysis, hydration, ion exchange
What does the development of thick regolith do and what is needed to prevent it?
Inhibits the access to water to fresh rock. Mechanism for its continuous removal is needed.
Name four hill slope processes
Falls, landslides, creep, surface runoff
What is the most common clast in clastic sediments?
Quartz
Why does quartz not weather easily?
It is inert at the Earth’s surface and it has a hardness of Mohs 7.
What are the breakdown products of feldspars and micas?
Clay and free ions (K, Ca, Na)
Why are clays weak?
They are sheet silicates with one perfect cleavage. Mohs 1-2.5
Why does the physical weathering of clay make different minerals difficult to identify?
Produces a fine matrix (mud) where particles cannot be discerned with the naked eye
Describe shales
Mudstones that are mostly clays, with a matrix that holds clasts.
Name the three types of processes that can erode weathered regolith and soil
Fluvial, wind, glacial
Where can short-term storage of sediment occur?
Anywhere
Where cam long-term storage of sediment occur?
Subsiding sedimentary basins
Describe the characteristics of a texturally mature grain
Decreasing: size, angularity.
Increasing: sphericity, porosity of formation.
What dictates grain sorting?
Rate of change of velocity
Describe the characteristics of a chemically mature grain
Loss of feldspar, mica, and other clasts, in favour of clay, matrix, and quartz
Define diagenesis
The conversion of a sediment into a sedimentary rock through burial
