W5L2 Biochemicla chemcial organic rocks

Question 1

stabke vs unstable

Answer 1

unstable minerals weather/break up/dissolve quickly

stable minerals dissolve after very long transport and/or a rise in pressure

Question 2

ions carried

Answer 2

ions carried in solution in surface water, subsurface water and ocean water
ions can be biomineralised by organisms as shells & skeletons deposited after death
or concentrated by evaporation & precipitated directly from water
or react with other chemical species (eg iron and oxygen) and precipitated

Question 3

Biomineralised minerals form

Answer 3

Biomineralised sediments, form anywhere that suitable organisms exist -
lakes
marine inshore: coral reefs, lagoons, bioclastic limestones
marine offshore (shelf, continental slope, sedimentary basins): oozes (shells)

Question 4

Chemically precipitated sediment form

Answer 4

Chemically precipitated sediment, formed as a byproduct of evaporation -
lake marls – clays and precipitated calcium carbonate (calcite mud/micrite)
pelagic marls – clays and precipitated calcium carbonate (calcite mud/micrite)

Question 5

Biochemical rocks coral, prerequisites

Answer 5

warm, clear, normal salinity, shallow water
no debris from the land but plenty of nutrients
tropical/subtropical environments are ideal
sunlight - corals have photosynthetic symbionts

Question 6

Coral polyps

Answer 6

Coral polyps make skeletons from dissolved mineral ions -
biomineralised calcium and carbonate ions combine to make calcite
Ca+ + HCO32- → CaCO3

Question 7

Coral reefs

Answer 7

Reefs typically build on the outer shelf, fronting the open ocean
Coral polyps are sensitive to changes in -
sea level , suspended sediment, salinity/water temperature
daily growth rings record changes in these parameters and are registers of climate change

Question 8

chemically precipitated rocks

Answer 8

evaporites

Question 9

the more precipitation

Answer 9

the less evaporites

evaporation has to be higher than precipitation levels

Question 10

evaporation concentrates ions

Answer 10

to the point of supersaturation

Question 11

Evaporite Environments

Answer 11

Playa lake or wadi: fed by desert flashfloods, water evaporates and salts are concentrated
Sabkha: low lying coast in arid environment periodically flooded by seawater
Restricted basin in arid environment, periodically flooded by seawater

Question 12

Organic (Carbonaceaous rocks)

Answer 12

Coal is the diagenetically altered remains of swamp material (peat) where low-oxygen conditions prevent organic decay
Organic-rich marine shales (oil shales) are largely composed of marine algae and terrestrial plant material deposited in low-oxygen conditions
diagenetically altered by heat & pressure
oil, with associated gas & water, migrates to a porous reservoir rock