Carbonate Diagenesis

What trend arises from mixing diagenetic end members

A linear trend between Sr and Mn concentrations

What would be the trace metal content of a primary, unaltered carbonate mineral

High Sr concentration and low Mn concentration

What would be the trace metal content of a fully altered carbonate mineral

Low Sr and high Mn concentrations

What does an open system refer to in diagenesis

Successive iterations of a one step reaction which mimic continuous water-rock interactions

What does the single element distribution coefficient D mean

Ratio of concentrations of an element between mineral and fluid phases at equilibrium

What is the exchange reaction distribution coefficient (Kd)

Ratio of two elements, equilibrated between solid and fluid phase (Kd = Di/Dj)

What does Coi represent

Concentration of element i in the entire fluid-rock system before any interaction occurs

Recipe for closed system diagenesis

• Put the fluid and rock into the box. Calculate Coi in whole F-R system

• React fluid with rock. Calculate concentration of element i in the rock after equilibration with the fluid by using Coi and Di

Is a carbonate rock homogeneously reflective of its diagenetic history

No! Different minerals/regions may be more susceptible to diagenesis than other regions.

What is the bulk rock composition of a carbonate rock represent

Mixing of any diagenetic end members within the structure

Why would the concentration of Mn and Sr behave differently during diagenesis

Mn increases in concentration due to the very high compatibility to the solid phase while Sr decreases due to its lesser solid phase compatibility

How do you find equilibrium concentrations of an element

Multiply the fluid concentration by the distribution coefficient

Why does it take Mn longer to reach equilibrium with the fluid during open system diagenesis

Mn has a higher distribution coefficient which means that it needs more passes of fluid to change composition. Increased D = increased rock buffer

Why is it that C and O concentrations do not change during diagenesis

Masses are conserved and concentrations wont change as long as the same mineral/polymorph are dissolved and reprecipitated (not true for trace elements like Sr and Mn whose concentrations do change)

Are d13c values in pore fluids similar to seawater

NOPE, water-rock equilibration can result in very different isotope values

What is the isotopic concentration of rock with no fractionation between solid-liquid phases (alpha = 1)

D13c of the rock will equal d13c of the whole system

Recipe for isotopic diagenesis model

• put fluid and rock in box. Calculate concentration of element i in entire system (Coi)

• Calculate isotopic composition of the rock after equilibration (d13co)

• React the fluid with the rock. Calculate the iso composition of the rock after equilibration (d13Cs)

What is the fractionation factor alpha

Distribution coefficient for isotopes (alpha = d18os + 1000 / d18o + 1000)

Is C or O more sensitive to alteration

Oxygen is extremely sensitive to alteration

Why is O extremely sensitive to diagenetic alteration

Pore fluids contain much more O than C so less interaction is needed to change the isotopes

What is closed system Rayleigh distillation

Exponential relationship that describes the partitioning of isotopes between two reservoirs as one of them decreases in size

Why does burial diagenesis mainly impact oxygen isotopes

D18O fractionation factor between the fluid and carbonate phase is large and temperature dependent. Higher temperatures lower fractionation (decrease isotope values)

Under water scenarios is covariation during diagenesis possible

• mixing of different mineral end-members (linear trend)

• Mixing of diagenetic fluids (linear or not linear relationship (arced))

Which trace element is more susceptible to diagenetic alteration

Sr (smaller distribution coefficient)