7.5 | Diagenesis

Diagenesis

chem, phys, & bio changes taking place after sediments are deposited & buried

Where does diagenesis take place?

upper few km of crust, less than 150-200°C

Why does burial promote diagenesis?

increasing temps & pressures

Recrystallization

diagenetic change, development of more stable minerals from less stable minerals

Provide an example of recrystallization:

aragonite becomes more stable calcite due to burial

Plant material being converted to coal is an example of…

diagenesis

Lithification

unconsolidated sediments transformed into solid sedimentary rocks

What are the 2 lithification processes?

compaction & cementation

What is the most common physical diagenetic change?

compaction

Compaction

weight above buried sediments compresses more deeply buried sediment

What happens to pore space during compaction?

reduction in pore space, water driven out

What rocks are impacted significantly by lithification through compaction?

shale, fine-grained rocks

Cementation

ions in solution crystallize among individual sediment grains

Describe the process of cementation briefly:

material precipitates from water, fills open pores between sediments, reduces porosity, glues grains

What are the most common cements?

calcite, silica, iron oxide

The hardest sedimentary rocks are cemented with…

silica

Sedimentary rocks cemented with calcite will…

effervesce in hcl

Sedimentary rocks cemented with iron oxide display…

red or orange color

Provide an example of a sediment undergoing diagenesis:

caco3 rich skeletal debris recrystallized into limestone

What types of sedimentary rocks are impermeable? Why?

crystalline limestone, evaporites; lack pore spaces due to growing crystals