Dr Helen LangDept of Geology amp Geographyp gy g p yWest Virginia University

SPRING 2012

GEOLOGY 285INTRO PETROLOGYINTRO PETROLOGY

Diagenesis of LimestonesDiagenesis of Limestones

Diagenesis begins very early in limestones right on the seafloorg

Limestone Diagenesisg

bull Compaction and Cementation (mostly calcite) similar to that in sandstones

bull Pressure solution - dissolution caused by ypressure of one grain on another

bull Replacement of Aragonite by CalciteReplacement of Aragonite by Calcitebull Local replacement of limestone by chert

R l t f li t b d l itbull Replacement of limestone by dolomite called ldquodolomitizationrdquo

Pressure Solution

bull Load pressure causes some calcite to dissolve

bull In some limestones as much as 40 of original carbonate may have dissolvedoriginal carbonate may have dissolved

bull Insoluble things (clay organic matter) get concentrated or left behind and may formconcentrated or left behind and may form black marks called stylolites

Stylolites

bull Irregular surface of interpenetrating ldquofingersrdquo marked by concentrations of g yinsoluble clay or organic matter

bull In cross section they look like the writingIn cross section they look like the writing of a stylus

bull See walls of bathroom stalls in White Hallbull See walls of bathroom stalls in White Hall (no more)

Stylolitesy

Stylolites

Bruce RailsbackU of Georgia

Calcite and Aragonite are polymorphs of CaCO3

Calcite is more stable at Earth- Aragonite)stable at Earthsurface conditions than Aragonite but

G=29

(dep

th)

some organisms make their hard-

t t f ure

Calcite

5000 atm~15 km

parts out of aragonite anyway Pr

essu Calcite

G=27

Temperature (oC)200 4000

Aragonite changes to CalciteAragonite changes to Calcite during diagenesis

bull Exposure to fresh water speeds up aragonite l i ito calcite conversion

bull Paleozoic limestones donrsquot have any aragonite left

Dolomitizationbull Dolomite is rare in modern carbonatesbull Makes up about 14 of Paleozoic limestonesbull Makes up about 34 of Precambrian

limestones

bull Whybull When and where does dolomite formbull When and where does dolomite form

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Diagenesis of LimestonesDiagenesis of Limestones

Diagenesis begins very early in limestones right on the seafloorg

Limestone Diagenesisg

bull Compaction and Cementation (mostly calcite) similar to that in sandstones

bull Pressure solution - dissolution caused by ypressure of one grain on another

bull Replacement of Aragonite by CalciteReplacement of Aragonite by Calcitebull Local replacement of limestone by chert

R l t f li t b d l itbull Replacement of limestone by dolomite called ldquodolomitizationrdquo

Pressure Solution

bull Load pressure causes some calcite to dissolve

bull In some limestones as much as 40 of original carbonate may have dissolvedoriginal carbonate may have dissolved

bull Insoluble things (clay organic matter) get concentrated or left behind and may formconcentrated or left behind and may form black marks called stylolites

Stylolites

bull Irregular surface of interpenetrating ldquofingersrdquo marked by concentrations of g yinsoluble clay or organic matter

bull In cross section they look like the writingIn cross section they look like the writing of a stylus

bull See walls of bathroom stalls in White Hallbull See walls of bathroom stalls in White Hall (no more)

Stylolitesy

Stylolites

Bruce RailsbackU of Georgia

Calcite and Aragonite are polymorphs of CaCO3

Calcite is more stable at Earth- Aragonite)stable at Earthsurface conditions than Aragonite but

G=29

(dep

th)

some organisms make their hard-

t t f ure

Calcite

5000 atm~15 km

parts out of aragonite anyway Pr

essu Calcite

G=27

Temperature (oC)200 4000

Aragonite changes to CalciteAragonite changes to Calcite during diagenesis

bull Exposure to fresh water speeds up aragonite l i ito calcite conversion

bull Paleozoic limestones donrsquot have any aragonite left

Dolomitizationbull Dolomite is rare in modern carbonatesbull Makes up about 14 of Paleozoic limestonesbull Makes up about 34 of Precambrian

limestones

bull Whybull When and where does dolomite formbull When and where does dolomite form

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Limestone Diagenesisg

bull Compaction and Cementation (mostly calcite) similar to that in sandstones

bull Pressure solution - dissolution caused by ypressure of one grain on another

bull Replacement of Aragonite by CalciteReplacement of Aragonite by Calcitebull Local replacement of limestone by chert

R l t f li t b d l itbull Replacement of limestone by dolomite called ldquodolomitizationrdquo

Pressure Solution

bull Load pressure causes some calcite to dissolve

bull In some limestones as much as 40 of original carbonate may have dissolvedoriginal carbonate may have dissolved

bull Insoluble things (clay organic matter) get concentrated or left behind and may formconcentrated or left behind and may form black marks called stylolites

Stylolites

bull Irregular surface of interpenetrating ldquofingersrdquo marked by concentrations of g yinsoluble clay or organic matter

bull In cross section they look like the writingIn cross section they look like the writing of a stylus

bull See walls of bathroom stalls in White Hallbull See walls of bathroom stalls in White Hall (no more)

Stylolitesy

Stylolites

Bruce RailsbackU of Georgia

Calcite and Aragonite are polymorphs of CaCO3

Calcite is more stable at Earth- Aragonite)stable at Earthsurface conditions than Aragonite but

G=29

(dep

th)

some organisms make their hard-

t t f ure

Calcite

5000 atm~15 km

parts out of aragonite anyway Pr

essu Calcite

G=27

Temperature (oC)200 4000

Aragonite changes to CalciteAragonite changes to Calcite during diagenesis

bull Exposure to fresh water speeds up aragonite l i ito calcite conversion

bull Paleozoic limestones donrsquot have any aragonite left

Dolomitizationbull Dolomite is rare in modern carbonatesbull Makes up about 14 of Paleozoic limestonesbull Makes up about 34 of Precambrian

limestones

bull Whybull When and where does dolomite formbull When and where does dolomite form

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Pressure Solution

bull Load pressure causes some calcite to dissolve

bull In some limestones as much as 40 of original carbonate may have dissolvedoriginal carbonate may have dissolved

bull Insoluble things (clay organic matter) get concentrated or left behind and may formconcentrated or left behind and may form black marks called stylolites

Stylolites

bull Irregular surface of interpenetrating ldquofingersrdquo marked by concentrations of g yinsoluble clay or organic matter

bull In cross section they look like the writingIn cross section they look like the writing of a stylus

bull See walls of bathroom stalls in White Hallbull See walls of bathroom stalls in White Hall (no more)

Stylolitesy

Stylolites

Bruce RailsbackU of Georgia

Calcite and Aragonite are polymorphs of CaCO3

Calcite is more stable at Earth- Aragonite)stable at Earthsurface conditions than Aragonite but

G=29

(dep

th)

some organisms make their hard-

t t f ure

Calcite

5000 atm~15 km

parts out of aragonite anyway Pr

essu Calcite

G=27

Temperature (oC)200 4000

Aragonite changes to CalciteAragonite changes to Calcite during diagenesis

bull Exposure to fresh water speeds up aragonite l i ito calcite conversion

bull Paleozoic limestones donrsquot have any aragonite left

Dolomitizationbull Dolomite is rare in modern carbonatesbull Makes up about 14 of Paleozoic limestonesbull Makes up about 34 of Precambrian

limestones

bull Whybull When and where does dolomite formbull When and where does dolomite form

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Stylolites

bull Irregular surface of interpenetrating ldquofingersrdquo marked by concentrations of g yinsoluble clay or organic matter

bull In cross section they look like the writingIn cross section they look like the writing of a stylus

bull See walls of bathroom stalls in White Hallbull See walls of bathroom stalls in White Hall (no more)

Stylolitesy

Stylolites

Bruce RailsbackU of Georgia

Calcite and Aragonite are polymorphs of CaCO3

Calcite is more stable at Earth- Aragonite)stable at Earthsurface conditions than Aragonite but

G=29

(dep

th)

some organisms make their hard-

t t f ure

Calcite

5000 atm~15 km

parts out of aragonite anyway Pr

essu Calcite

G=27

Temperature (oC)200 4000

Aragonite changes to CalciteAragonite changes to Calcite during diagenesis

bull Exposure to fresh water speeds up aragonite l i ito calcite conversion

bull Paleozoic limestones donrsquot have any aragonite left

Dolomitizationbull Dolomite is rare in modern carbonatesbull Makes up about 14 of Paleozoic limestonesbull Makes up about 34 of Precambrian

limestones

bull Whybull When and where does dolomite formbull When and where does dolomite form

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Stylolitesy

Stylolites

Bruce RailsbackU of Georgia

Calcite and Aragonite are polymorphs of CaCO3

Calcite is more stable at Earth- Aragonite)stable at Earthsurface conditions than Aragonite but

G=29

(dep

th)

some organisms make their hard-

t t f ure

Calcite

5000 atm~15 km

parts out of aragonite anyway Pr

essu Calcite

G=27

Temperature (oC)200 4000

Aragonite changes to CalciteAragonite changes to Calcite during diagenesis

bull Exposure to fresh water speeds up aragonite l i ito calcite conversion

bull Paleozoic limestones donrsquot have any aragonite left

Dolomitizationbull Dolomite is rare in modern carbonatesbull Makes up about 14 of Paleozoic limestonesbull Makes up about 34 of Precambrian

limestones

bull Whybull When and where does dolomite formbull When and where does dolomite form

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Stylolites

Bruce RailsbackU of Georgia

Calcite and Aragonite are polymorphs of CaCO3

Calcite is more stable at Earth- Aragonite)stable at Earthsurface conditions than Aragonite but

G=29

(dep

th)

some organisms make their hard-

t t f ure

Calcite

5000 atm~15 km

parts out of aragonite anyway Pr

essu Calcite

G=27

Temperature (oC)200 4000

Aragonite changes to CalciteAragonite changes to Calcite during diagenesis

bull Exposure to fresh water speeds up aragonite l i ito calcite conversion

bull Paleozoic limestones donrsquot have any aragonite left

Dolomitizationbull Dolomite is rare in modern carbonatesbull Makes up about 14 of Paleozoic limestonesbull Makes up about 34 of Precambrian

limestones

bull Whybull When and where does dolomite formbull When and where does dolomite form

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Calcite and Aragonite are polymorphs of CaCO3

Calcite is more stable at Earth- Aragonite)stable at Earthsurface conditions than Aragonite but

G=29

(dep

th)

some organisms make their hard-

t t f ure

Calcite

5000 atm~15 km

parts out of aragonite anyway Pr

essu Calcite

G=27

Temperature (oC)200 4000

Aragonite changes to CalciteAragonite changes to Calcite during diagenesis

bull Exposure to fresh water speeds up aragonite l i ito calcite conversion

bull Paleozoic limestones donrsquot have any aragonite left

Dolomitizationbull Dolomite is rare in modern carbonatesbull Makes up about 14 of Paleozoic limestonesbull Makes up about 34 of Precambrian

limestones

bull Whybull When and where does dolomite formbull When and where does dolomite form

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Aragonite changes to CalciteAragonite changes to Calcite during diagenesis

bull Exposure to fresh water speeds up aragonite l i ito calcite conversion

bull Paleozoic limestones donrsquot have any aragonite left

Dolomitizationbull Dolomite is rare in modern carbonatesbull Makes up about 14 of Paleozoic limestonesbull Makes up about 34 of Precambrian

limestones

bull Whybull When and where does dolomite formbull When and where does dolomite form

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Dolomitizationbull Dolomite is rare in modern carbonatesbull Makes up about 14 of Paleozoic limestonesbull Makes up about 34 of Precambrian

limestones

bull Whybull When and where does dolomite formbull When and where does dolomite form

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Observations about Dolomite

bull Almost all dolomite forms by replacement of pre-existing calcite and aragonite

bull Dolomite rhombs cross-cut allochemsbull Dolomite obscures fine structures in

limestoneslimestonesbull Dolomite crosscuts bedding planes

D l it i l i t d ithbull Dolomite is commonly associated with evaporites

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Dolomite Rhombs in Thin Section

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

To form dolomite by replacement of calcite or aragonite you need

bull Water of the right composition andbull A mechanism to move that water throughA mechanism to move that water through

the limestone

bull There are two proposed mechanisms

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Evaporative Reflux

bull Requires periodic flooding of an exposed tidal flat or ldquosabkhardquo over a limestone

bull Evaporation that causes evaporites (especially p p ( p ygypsum CaSO42H2O) to precipitate

bull Two effectsTwo effectsndash increased density of brine so it sinks through the

limestonelimestonendash increase in the MgCa ratio of brine

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Evaporative RefluxCa-depleted (Mg-rich) brine moves through the limestone and

Calcite (CaCO3) is replaced by Dolomite (CaMg(CO3)2)

Works for dolomites associated with evaporites

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Dolomites without EvaporitesDolomites without Evaporites require a different model

bull Mixing of fresh water and seawater called ldquoD rdquo hi h ldquo i d bl drdquo i P ildquoDoragrdquo which means ldquomixed bloodrdquo in Persian

bull A mixture with ~5 to ~70 seawater is under-saturated with Calcite (wants to dissolve Cc) and super-saturated with Dolomite (wants to precipitate Do)

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Calcite and Dolomite Saturation

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

~5 ~70

5-70 seawater Dorag works Dolomite replaces Calcite

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Dorag Dolomite

bull Landward of the shoreline there is a zone of mixing of fresh groundwater and seawater

bull It should be a dolomitizing zonegbull Zone migrates landward as sea-level rises

(during transgression)(during transgression)bull Zone migrates seaward as sea-level falls

(during regression)(during regression)bull This model is attractive for dolomites with no

id f itevidence of evaporites

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

Dolomite formation on the north side of Jamaica - Dorag model

RainwaterRainwater

Groundwater

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

edve

rsat

urat

eat

ed

saturated

ovnd

ersa

tura

seawater

un

0 50 100freshwater seawater seawaterfreshwater seawater

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D

esai

ns

vapo

rite

ux e

xpla

with

Ev

Jam

aica

ve R

eflu

ciat

ed w

el n

orth

pora

tives

ass

o

ag M

ode

Evap

Dol

omite

Dor

a

D