Limestone and Salt Flashcards
What are biochemcial sedimentary rocks?
minerals precipitated with assistance of organisms
What are chemical sedimentary rocks?
minerals precipitated inorganically, usually from seawater (evaporites)
What are the main elements in sea water?
chloride, sodium, sulfate, magnesium, calcium, potassium
How does calcite form?
marine organisms in normal sedimentary environments precipitate it
Why is there a lot of calcite precipitated, even though it’s not very abundant in water?
it’s near its solubility, and marine organisms are efficient ad precipitating it
What two processes are involved in the formation of biochemcial sedimentary rocks?
in situ precipitation and transport by currents
What are two common biochemical minerals?
calcite and dolomite (calcite + Mg)
What are some common biochemcial sedimentary environments?
carbonate platforms, atolls, and barrier reefs; tidal flats; deep marine; springs; freshwater lakes
What characteristics are shared by carbonate platforms, atolls, and barrier reefs; AND HOW DO THEY RELATE TO CACO3 PPTING?
shallow marine water at low latitudes
How do filter feeders on barrier reefs make use of their ability to precipitate calcite?
build structures to place them in the perfect area to catch food - where there’s some energy in the water to bring food to them, but not enough to wash them away
How are atolls formed?
when a volcano starts subsiding, CaCO3 precipitating organisms precipitate CaCO3 to build structures to keep up with subsiding volcano, so that they can stay at surface of sea
How are barrier reefs formed…?
?
What are the characteristics of tidal flats and HOW DO THEY RELATE TO CACO3 PPTING?
algal environment (algae and the bacteria on it are important CaCO3 producers), carbonate precipitation in intertidal zone, + current transportation
When a CaCO3-precipitating organism dies and its shell lands less than 4000 m deep, what happens to its shell?
shell adds to calcereous ooze
What is calcareous ooze?
shells of planktonic foraminifera and calcereous nanofossils
What happens when a CaCO3 shell descends deeper than 4000-7000 m?
it dissovles (due to high pressure)
What is a characteristic of deep marine sediment?
lacks CaCO3 sediment
How does an increase in pressure affect calcite solubility, and how does this relate to ocean depth?
increase in pressure (as depth increases) increases calcite solubility
How does an increase in CO2 affect calcite solubility, and how does this relate to ocean depth?
increased CO2 increases calcite solubility; (????)
What is the CaCO3 compensation depth (CCD)?
depth in the oceans below the rate of solvation of calcite exceeds the rate of supply, leavning no calcite sediment
How much of the deep ocean floor does calcareous ooze cover?
1/3 (floor not deeper than 4000 to 7000 m)
What are the characteristics of springs?
many solutes in water, lots of microbial growth
How does calcite precipitate in springs?
with pressure release when groundwater reaches surface
How is travertine formed and what rock does it relate to?
precipitation of calcite from GROUNDWATER, like limestone
What are the characteristics of travertine?
dense and usually banded (bands correspond to changes in groundwater composition)
What type of travertine contains large pores?
tufa
What structures are often seen in springs?
tall columns of travertine/tufa
What form of precipitation forms tufa?
algal precipitation
Where does algal precipitation occur?
where spring vents underwater (lake bottom)
What aids calcite precipitation in springs?
bacteria
What form of precipitation occurs in lakes?
algal mainly, and some inorganic precipitationa nd pellits
What kinds of lakes are more productive, and why?
saline lakes; due to lack of predators
How can lithification of biochemical sediment occur?
marine cementation, exposure to air, compaction/recrystallization
How does marine cementation work to lithify biochemical sediment?
recrystallization of CaCO3 (?)
How does exposure to air lithify biochemical sediment?
hardens rock
What characterstic to biochemical rocks that were lithified by exposure to air often have?
porosity (air preserves porosity)
What is required for compaction/recrystallization of biochemical sediment?
10s of metres of burial
What are some forms of carbonate sediment?
skeletal particles, ooliths, pellets, mud, spar
What do skeletal particles contain?
shells, shell fragments, spines, internal skeletons
What are ooliths?
spherical sand-sized carbonate particles - concentric rings of calcite
What do ooliths represent?
bacterial growth (since they surround a nucleus of something else)
Where do ooliths form?
areas of strong bottom currents
What are pellets?
fecal pellets of carbonate mud ingesting oraganisms (glue poop together and drop it discretely to bottom, to prevent predators from hunting them down by poop)
What is the most common sand type?
pellets
What does mud contain?
mostly broken fecal pellets
What is spar?
crystallized calcite cement
What are evaporites?
inorganic precipitation from brine after evaporation of seawater
What common minerals can be evaporites?
calcite, gypsum, halite, sylvite
When 1L of seawater is evaporated, what evaporites are left and in what relative proportions?
small proportion of CaCO3, very large proportion of salt halite, smallish proportions of gypsum, etc.
What is the order of precipitation from seawater, from first to last?
calcite, gypsum, halite, others
When does gypsum begin to precipitate?
at 1/3 water volume
When does halite begin to precipitate?
at 1/10 water volume
What does the order and composition of the column of evaporites left from seawater depend on?
solubility and abundance
How is salt made from seawater?
1) build ponds at different elevations
2) let sun evaporate water from top pond until CaCO3 and gypsum have precipitated out
3) drain water into lower pool, leaving behind ppts
4) let sun evaporate water until NaCl comes out
5) drain water into lower pool (where poisonous stuff ppts upon further evaporation)
What does the process of salt making take advantage of?
the order in which chemicals precipitate from water
Why is salt found in the rock record?
dry arid environments/restricted bays are occasionally filled with seawater; water evaporates and leaves salt; can repeat to make large layers of salt
What are some non-carbonate chemical sedimentary rocks?
chert, phosphorite, iron oxide sediment
How does chert form?
precipitates below CCD, where there is low clastic sedimentation
What is chert sometimes precipitated for?
internal skeletons (radiolarians, diatoms, siliceous sponge spicules)
What is phosphorite?
phosphate-rich sediment (apatite mineral - CaPO4)
Where is phosphorite formed?
areas of upwelling, with high organic productivity and low oxygen
What chemical sedimentary rock is an important source of macronutrients for plants?
phosphorite (used as fertilizer)
What is iron oxide sedimentary rock?
fine-grained marine sedimentary rock of all iron minerals
Where does most of the world’s ore come from?
iron oxide sedimentary rock
How is banded iron formation (BIF) (iron oxide sed rock) formed, and in which rocks?
only in preCambrian rocks; precipitation from ocean water during change from anoxic to oxygenated water
Why is BIF only seen in precambrian rocks?
Fe was more soluble when there was little oxygen in the oceans
What ores come from oolitic hematite sandstones (iron oxide sed rock)?
clinton iron ores, wabana iron ores, torbrook iron ores
