Sedimentary Rock Processes Flashcards
Define Sedimentary rock
(example x2)
Rock formed through the deposition and solidification of sediments
E.g - sandstone and chalk
What are Proterozoic marine sediments
They are iron oxide deposits produced by the reaction of dissolved iron minerals in the ocean with oxygen produced by photosynthesis
How are Proterozoic marine sediments formed ?
What are alluvial deposits
The minerals and metals that are deposited in riverbeds
What is the deposition of a river based on ?
It is based on the mass and density of the objects and velocity and energy of the river.
Describe how alluvial deposits can separate valuable minerals and metals
- Sorted and deposited by flowing water/ river
- Rivers with high energy and high velocity carry lots of sediments
- As energy reduces some sediments drop out of suspension. Which causes the heaviest and densest to drop first
What is secondary enrichment
when metals are leached from surface rocks and precipitated just below the water table
What is the process of secondary enrichment
(Example Copper)
- Metal ore exposed at the surface E.g Copper
- Exposed to oxygen and water
- When metal ore is exposed to oxygen and water it oxides and goes into solution
- Water containing the solution percolates downwards until it reaches the water table
- Copper loses oxygen and reduces when it loses oxygen it precipitates (comes out of solution)
- Copper is now concentrated just below the water table
How are evaporites formed
- If sea levels drop some oceans become land locked (or a temporary lake)
- Water may contain salt NaCl or halite
- As water evaporates the salt is precipitated (this can be 100s meters thick that may become buried)
- Later can be mined
What are two examples of evaporites
The most common marine evaporites are calcite and gypsum
What are biological deposits formed from
Biological deposits are formed from the remains of living organisms
