All of carbonate diagenesis

What is diagenesis?

• Sequence of biological physical and chemical processes at low P an dT that turns carbonates into lithified carbonates

What is the main driver of carbonate equilibrium ?

Co2

What are the key players in carbonate diagenesis

• Pressure

• Temperature

• Water composition

• Mineral composition

• Salinity

• Partial pressure of Co2

• Life

What is the difference between fabric specifc and non fabric specific dissolutiuon

• Fabric specific particles cemennt

Porosity in diagensis

• largest amount of porosity closest to the surface

• can be fabric selective or non selective

Neomorphism

• recrystallization

• orginal component was not fully dissolved

What are the two types of diagenetic systems

• Open diagenetic system

• Closed diagenetic system

What is an open diagenetic system

• Low rock and high water ratio

What is a closed diagenetic system

• High rock low water ratio

What are the major elements in a carbonate system

• Ca, C, O, Mg

At what environment is high Mg-Ca and aragonite more soluble

• At high temeperatures and high latitudes

In what environments is there abundant Sr2+

in Aragonitic allochems

• ooids corals

What are the stable isotopes of Carbon

• 12 C and 13 C radioactive is 14 C

Why does methane have such a negative 13 C ratio

• very depleted in 13 C, as 12 C is used in organic reactions meanwhile 13 C is not used and is harder to use in organisms

Oxygen isotope depletion

• Further landward more enriched in light isotope depletion of heavy

• aka the rain out effect

• Depleted in 18 O and enriched in 16 O

In what temp of water is 18 O remobved and enriched

• in warm water it is depleted and in cold water it is enriched

• depleted in fresh water

• enriched in evaporated water (stays behind after evaporation)

Why does ratio in elements not reflect ocean chemistry conditions

• Brachiopods are best indicators for paleocean compotion

• orgnaisms often modify chemistry before they can use it

• factor of kinetics in precipitation

Strongtium isotopes

• no fractionation in carbonates and concentration doesnt change with isotopes

• 86Sr is stable

• 87 Sr comes from crystalline rocks

What is hardground?

• The ground a few cm below the sand/ unlithified bottom

• sediment above can be moved by storms or currents

What is submarine diagenesis ?

• The diagenesis that doesnt require sediment compaction

• occurs underwater

• on sea floor

• pore waters

• low temp early diagenetic environments

• aragonite to calcite transition

• micrtitizartion

What are neptunian dykes

• reef collapse creating fissures that were filled from the unstable broken reef

• characteristic of early cementation

Why do gastropods represent a drop in alkalinity

• mainly make aragonitic shells, if there are many gastropods they take out a lot of the available Caco3 in the water colium

• caco3 is a buffer for pH so this represents a pH drop as the buffer is removed

What is meteteoric diagenesis ?

• The changes in sediment in meteroic (fresh/mixed) water from rainfall

• in the surface or vadose zone

• wherever rainfall falls

What controls meteoric diagenesis

• Intrinsic

• mineralogy

• grain size

• porosity

• extrinsic

• climate

• vegetation

• time

How does alterations in fresh water impact meteoric diagenesis

• Mineral controlled always alters to low mg calcite and is fabric selective

• water controlled is based on carbonate dissolution and is not fabric selective (vugs and karst)

What is mienral controlled meteoric diagenesis

• Based on specific mineralogy dissolution cementation neomorphism

• controlled by original meteorology climate texture

• enhanced by dissolution reduced by cementation (closed off pores)

What are the 3 stages on meteoric diagenesis

• Sea floor sediment

• Meteoric diagenesis (alteration of HMC to LMC)

• Later stages all LMC multiple stages of cement growth

How does climate impact meteoric diagenesis

• Arid Mg- Ca and Aragonite

• Semi-Arid: aragonite calcite and calcite

• Wet: all calcite (aragonite cannot survive in freshwater meteoric environments)

Why cannot aragonite and High mg-Ca survive in meteoric environment

• slightly acidic dissolves the aragonite

• is often unstable and recrystalized to low Mg ca

water controlled meteoric diagenesis

• Only cares about dissolution water flow water mineraology climate time

• porosity and cementation also have impacts

• (reduced by calcite precipitation)

What is surface karst

• Flute sgrooves and heelprints

• - Land forms and features on the surface, made from chemical wathering of limestone from rainwater and dissolution

Subsurface karst

Underground caves from dissolution of limestone and other Caco3 rocks

• can be caused by dissolution and precipitation

Cave formation through dissolution mixing

• closed to atmopshere

• CO2 +rain dissolves Ca co3

Cave formation via degassing

• open to the atmopshere

• high Pco2 dissolves caco3 from vadose to phreatic zone

What is caliche

• Hard calcium carbonate rich layer that forms in the soil profile of arid

• high evaporation

• as water evaporates the Caco3 is let behind and then combines with the soils

What Is a Rhizocretion?

A root shaped concretion or cemented structure formed around roots

happens when there is Caco3 inthe system

cylindrical tubes

minerals precipotated from water moving through the root zone