GEO 316P Test 3

What is the difference between terrigenous, chemical and biogenic sediment?

Terrigenous - anything weathered/eroded from pre-existing rocks

Chemical - sediment that comes from chemical precipitation

Biogenic - sediment precipitated by a biologic agent like bacteria

What does "clastic" mean?

Any grains that are transported before final deposition

How much dissolved salts are present in average seawater? What are the most abundant elements/compounds present? Why does seawater have some much dissolved salt? Why is this amount largely constant over time?

85 different elements, 3.5% of the ocean is salts (by weight)

Most popular in order:

Calcite

Anhydrite

Halite

Sylvinite, Carnalite

All these salts come from rivers, and concentrate in the sea

It's constant beacuse of "salt sinks", one of which is simply the evaporation of water

How much seawater has to be evaporated to get calcium carbonate, gypsum and halite to precipitate?

81% Calcium Carbonate

90.5% Gypsum

96% Halite

How does the pH of water control carbonate precipitation/dissolution? Why does adding CO2 to water decrease the pH? How should carbonate precipitation/dissolution respond to increased/decreased CO2 in water?

Increase in CO2 lowers pH and causes CaCO3 dissolution

Decrease in CO2 raises pH and causes CaCO3 precipitation

CO2 in water creates H+ ions, making the water acidic

What controls the level of CO2 in sea water?

The water temperature and the pressure

Cold and high pressure: CO2 stuck in water

Hot and low pressure: CO2 escapes

Why are carbonates typically of warm, shallow marine settings?

In hot and low pressure water (depth is proportional to fluid pressure), carbon dioxide escapes from the water, raising the pH and causing carbonate precipitation

What are examples of inorganic and biogenic carbonate precipitation?

Inorganic: ooids lakes and whitings

Biogenic: absorbtion of CO2 by animals

What are the 3 basic ways that biogenic carbonates are made?

Photosynthesis by marine plants/bacteria

Direct extraction of CaCO3 from water to form skeletons (like shells)

Fecal Pellets - "re-packaging" of sediment + organics

What is chert?

Inorganic bilogical rock

amorphous Silica-SiO2

Precipitated abiotically or as biotic hard parts

Marine and Freshwater occurrences

What are the compositions of Gypsum and Anhydrite? How/when does conversion occur? What is Selenite?

Gypsum: (CaSO4 with H2O)

precipitated from marine bodies or saline lakes, used in cement, fertilizer...

Anhydrite: (CaSO4)

comes from gypsum when it dries in arid/high temp environments

Selenite is a bladed variety of gypsum

What is the composition of Halite? Crystal form?

NaCl

Cubic

What are the 2 most common Bitter Salts?

KCl and MgCl

What is the correlation between ocean temperature, latitude, and carbonate precipitation?

as latitude increases, temp decreases and carbonate precipitation decreases

What is the correlation between ocean temperature, latitude, and calcium carbonate saturation?

as latitude increases, temp decreases and carbonate saturation increases (closer to equator, warmer and higher saturation)

What is the influence of siliciclastic input to the ocean on carbonate precipitation?

Little clastic input: reefs form, organisms live there and precipitate CaCO3

What is the vadose zone?

Part of the soil that water travels through before saturating it

aka no water here, bottom of the zone is the water table

What is the phreatic zone?

part of the soil where the water resides

top of the zone is the water table

What is karst?

Landscape mainly caused by the dissolution of limestone

What are speleothems?

Features caused by precipitation

What properties control the degree of carbonate precipitation at groundwater springs?

Fluctuations in temperature,water chemistry, or flowrates can cause carbonate precipitation

Where and how do geodes form?

Slowly form in phreatic (water saturated) zone

What is travertine?

Layered rock made from the dissolution and precipitation of carbonates

Often in thin lamina with detrital mud

What is the chemical formula and crystalline structure of Aragonite?

CaCO3

Commonly has orthorhombic crystals

What is the chemical formula and crystalline structure of Calcite?

CaCO3

Commonly has rhombohedral crystals

What is the chemical formula and crystalline structure of Dolomite?

CaMg(CO3)2

Commonly has rhombohedral crystals

What are the cations that commonly substitute into Calcite, Aragonite,and Dolomite?

Mg, Fe, & Sr

What is the definition of Limestone?

a sedimentary rock made of calcium carbonate (CaCO3)

What is the definition of Dolostone?

a sedimentary rock made of calcium and magnesium carbonate (CaMg(CO3)2)

What is the definition of High-Mg Calcite (HMC)?

when there's a lot CaMg(CO3)2

What are the relative abundances of Aragonite, High-Mg Calcite and Calcite in modern carbonate environments?

Aragonite: most common

High-Mg Calcite: common

Calcite: least common

Is Aragonite a stable or metastable mineral? What does Aragonite alter to? Is the original grain fabric retained during recrystallization?

Metastable: alters to Low- Mg Calcite. Typically recrystallizes to coarse crystalline calcite with little fabric retention.

Is High-Mg Calcite a stable or metastable mineral? What does High-MgCalcite alter to? Is the original grain fabric retained during recrystallization?

Metastable: alters to Low-Mg Calcite. Conversion of HMC to LMC usually occurs with good fabric retention

Is Calcite a stable or metastable mineral at typical Earth-surface conditions?

Stable

Is Dolomite mostly a primary or secondary mineral?

Secondary. It's when water leaves limestone (it goes through diagenesis)

What rock type does Dolostone replace?

Limestone

Do the diagenetic reactions that produce Dolomite occur shortly after deposition or much later in time?

Dolomite is made when calcium is replaced by magnesium

this takes a while and happens way later in time

What happens to the primary structures and fabrics preserved in limestone when it undergoes dolomitization?

Dolomite and limestone are quite similar

However the key point is that dolomite has magnesium (and calcium) ions and limestone has calcium

Does Calcite dissolve in pH neutral water?

Yes

CaCO3 -> Ca++ and CO3-2

What is the Solubility Product and how is it determined?

Ksp = solubility product

product of ionic concentrations in an equilibrium solution

determined empirically (by experiment)

What is the Ion Activity Product?

IAP = [Ca++][CO3-2]

Essentially the product of the concentrations of Ca++ and CO3-2

How large is the Solubility Product relative to the Ion Activity Product when a solution is said to be undersaturated with regards calcium carbonate?

Ksp > IAP undersaturated, will dissolve

Ksp = IAP saturated, in equilibrium

Ksp < IAP supersaturated, will precipitate

How large is the Solubility Product relative to the Ion Activity Product when a solution is said to be saturated with regards calcium carbonate?

Ksp > IAP undersaturated, will dissolve

Ksp = IAP saturated, in equilibrium

Ksp < IAP supersaturated, will precipitate

How large is the Solubility Product relative to the Ion Activity Product when a solution is said to be supersaturated with regards calcium carbonate?

Ksp > IAP undersaturated, will dissolve

Ksp = IAP saturated, in equilibrium

Ksp < IAP supersaturated, will precipitate

Will CaCO3 dissolve or precipitate in an undersaturated, saturated, and supersaturated solution?

Ksp > IAP undersaturated, will dissolve

Ksp = IAP saturated, in equilibrium

Ksp < IAP supersaturated, will precipitate

Are the chief carbonate minerals Calcite, Aragonite, and Dolomite undersaturated or supersaturated in surface seawater?

the surface seawater is supersaturated with respect to all of the chief carbonate minerals

How does the degree of Aragonite and Calcite saturation vary as a function of water depth in the Atlantic and Pacific oceans?

The saturation gets lower the deeper you go into the ocean.

What are the two main reasons why carbonate minerals only precipitate with great difficulty in surface waters of the oceans in spite of thermodynamically favorable conditions?

1. Kinetic effects - rates of precipitation are low

2. The precipitation is stopped by other dissolved species, like Mg+2, Fe+2, PO4-3, SO4-2

What does carbon dioxide plus water form?

Water + carbon dioxide yields carbonic acid

H2O + CO2 ↔ H2CO3

Calcium carbonate plus Hydrogen ions react to produce what two ions?

Calcium carbonate + acid yields Calcium + bicarbonate

CaCO3 + H+ ↔ Ca++ + HCO3-

An increase in Hydrogen ions lead to dissolution or precipitation of calcium carbonate?

more acid -> more dissolution

A decrease in Hydrogen ions lead to dissolution or precipitation of calcium carbonate?

less acid -> more precipitation

An increase in the partial pressure of dissolved carbon dioxide in seawater leads to dissolution or precipitation of calcium carbonate?

more CO2, dissolution

A decrease in the partial pressure of dissolved carbon dioxide inseawater leads to dissolution or precipitation of calcium carbonate?

less CO2, precipitation

What changes in the pH of a solution leads to the precipitation and dissolution of calcium carbonate?

more pH, more basic, precipitation

less pH, more acidic, dissolution

What changes in pressure promote the precipitation and dissolution of calcium carbonate?

more Pressure, more CO2 in water, dissolution

less Pressure, less CO2 in water, precipitation

What changes in water temperature promote the precipitation and dissolution of calcium carbonate?

higher Temp, CO2 escapes water, precipitation

lower Temp, CO2 stuck in water, dissolution

Do cold waters hold more or less dissolved carbon dioxide than warm waters?

cold water holds more carbon dioxide than warm water

How does photosynthesis promote carbonate precipitation in surface seawater?

uses carbon dioxide and removes it from the water promoting carbonate precipitation

How does respiration promote carbonate dissolution in surface seawater?

Releases carbon dioxide adding it back into the water promoting carbonate dissolution

Why does the decay of organic material often promote the precipitation of calcium carbonate?

Decay can increase alkalinity, promoting carbonate precipitation

What are the three main pathways of carbonate precipitation in aquatic environments?

Abiotic - no biotic influence

Biotically Induced - organisms start the precipitation

Biotically controlled - organisms control all steps of the precipitation (shells)

What is an autotroph?

Organisms that make their own carbs, proteins and fats from whats around them

Think plants and photosynthesis

What is a heterotroph?

Organisms that really on others for nutrition

literally me when

Why is the statement "Carbonates are born" largely true?

Most of them are a result of biotic precipitation

This means that organisms "gave birth" to them as their shells and skeletons, and then they are ground down into rocks

What are the major autotrophic producers of carbonate?

bacteria and algae

What are the major heterotrophic producers of carbonate?

sponges, bivalves, cephalopods and many more

Is there such a thing as autotrophic production via symbionts?

Yes and simbionts are basically organisms that work together:

Corals and certain bivalves

What is the most critical environmental factor for high rates of autotrophic carbonate sediment production?

Light penetration, basically a good amount of light for photosynthesis and other autotrophic processes

How is light penetration into seawater correlated with high nutrient levels and high organic productivity?

Think a forest, and how there is little to no sunlight in it and all the organisms are fighting for sunlight?

High nutrient levels promotes organic activity, lowering light penetration and lowering carbonate sediment production

What is the photic or euphotic zone?

Layer of the ocean that receives sunlight

How does carbonate production by autotrophs vary as a function of distance below the water surface?

The deeper you go, the less carbonate production

How does light intensity vary as a function of distance below the water surface?

the deeper you go, the less light

What is the Calcite Compensation Depth? Why does the ratio of carbonate dissolution rate to carbonate supply rate vary with distance below the water surface?

Depth at which calcite gets dissolved

fluid pressure varies with fluid depth

What is a carbonate factory?

Places with major carbonate production

What are the three important but fundamentally different carbonate factories?

Tropical factory

Cool water factory

Mud mound factory

Name at least three distinguishing characteristics of tropical and cool-water carbonate factories.

Tropical:

Biotically controlled

low nutrient levels

war and sunlight waters (within 30N and 30S)

Cool-water:

biotically controlled

a little higher nutrient levels

higher than 30N and 30S (colder waters)

What are two common types of organisms building tropical and cool-water carbonate factories?

Tropical: corals & green algae

Cool-water: red algae & bryozoan

Name at least two distinguishing characteristics of mud-mound carbonate factories.

Mostly abiotic precipitation & biotically induced precipitation

waters high in nutrients & relatively low light levels

galveston is one

What does the profile for relative production of carbonate as a function of water depth look like for the Tropical, Cool-Water, and Mud-Mound factories?

Slide 54

Tropical has the highest production but fastest dropoff (100 m water depth is the max)

Cool-water has low production but is constant for 470 meters

Mud-mound starts at close to 0 and increases to its max at 100 m depth, constant until 400m then it goes back to 0 until 500m

What is the minimum water temperature associated with the Tropical carbonate factory?

18 C

What level of water clarity, nutrients, and organic productivity is typically associated with the Tropical carbonate factory?

clear water

low organic productivity

low nutrient levels

What is an approximate maximum seawater depth associated with the euphotic zone?

110 m

Name two archipelagos constructed by the Tropical carbonate factory?

Bahamas, Maldives

In the Tropical carbonate factory rates of carbonate deposition are typically highest at what location on the platform?

The reef rim

(slow on the platform interior)

Where are coral reefs typically located on modern Tropical carbonate factories?

Their reef rims

Most modern coral reefs are found between what latitudes North and South?

30 N 30S

The Cool-Water carbonate factory typical produces a depositional profile of what form?

Ramp

A modern example of a Cool-Water factory is found off the southern shore of what continent?

apparently australia is a continent

Name two locations where deposits of the Mud-Mound factory are preserved.

Slide 68

Porcupine Mounds near Ireland

What is an allochem?

recognizable grains in carbonate rocks

What are 4 basic types of allochems?

Intraclasts - little clastic clasts that have been eroded and transported away

Ooids - carbonate accretion on nucleus, >2mm = pisoids, oncolites are even bigger

Peloids - sediment repackaged as fecal pallets

Skeletal - microfossils to shelly fragments to wholeexoskeletons. the most common

How are skeletal allochems differentiated from each other?

Faunal grouping (type of organism)

Age

Size

Shape

Skeletal microstructure

Mineralogy

What is a planktonic organism?

Organisms that float in the ocean, as they can't direct themselves

What is a benthonic organism?

Organisms that live on the bottom of the water

What are the nine dominant plus important carbonate producing faunal groups during the Cenozoic?

Cocoliths

Forams (both planktonic and benthonic)

Green algae

Coraline red algae

Bivalves

Gastropods

Corals

Echinoids

What are the ten dominant plus important carbonate producing faunal groups during the Mesozoic?

Cocoliths

Forams (both planktonic and benthonic)

Coraline red algae

Bivalves

Gastropods

Corals

Brachipods

Crinoids

Echinoids

What are the four dominant plus important carbonate producing faunal groups during the Paleozoic?

Corals

Brachiopods

Bryozoans

Crinoids

What are the three major faunal groups producing calcite skeletons during the Cenozoic?

Cocoliths

Forams

Brachiopods

What are the four major faunal groups producing high-Mg calcite skeletons during the Cenozoic?

Coraline red algae

Echinoids

Crinoids

Bryozoans