Sedimentary Rock Processes

Question 1

Define Sedimentary rock
(example x2)

Answer 1

Rock formed through the deposition and solidification of sediments
E.g - sandstone and chalk

Question 2

What are Proterozoic marine sediments

Answer 2

They are iron oxide deposits produced by the reaction of dissolved iron minerals in the ocean with oxygen produced by photosynthesis

Question 3

How are Proterozoic marine sediments formed ?

Answer 3

• Dissolved oxygen levels increased in the oceans
• Dissolved iron ions present in oceans become oxidised by the oxygen
• Iron oxides come out of solution and the solid iron forms deposits on the ocean floor

Question 4

What are proterozoic marine sediments also known as

Answer 4

Proterozoic marine sediments are also known as banded iron formations

Question 5

What are alluvial deposits

Answer 5

The minerals and metals that are deposited in riverbeds

Question 6

What is the deposition of a river based on ?

Answer 6

It is based on the mass and density of the objects and velocity and energy of the river.

Question 7

Describe how alluvial deposits can separate valuable minerals and metals

Answer 7

• 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

Question 8

What is secondary enrichment

Answer 8

when metals are leached from surface rocks and precipitated just below the water table

Question 9

What is the process of secondary enrichment
(Example Copper)

Answer 9

• 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

Question 10

How are evaporites formed

Answer 10

• 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

Question 11

What are two examples of evaporites

Answer 11

The most common marine evaporites are calcite and gypsum

Question 12

What are biological deposits formed from

Answer 12

Biological deposits are formed from the remains of living organisms