Sedimentary Rocks and Diagenesis

Question 1

Laminated siltstone vs bedded siltstone

mudstone vs shale

Answer 1

Laminated siltstone
laminae <10mm thick

Bedded siltstone:
beds are >10mm thick

Mudstone:
clay content is between 33-65%

Shale: Laminated and clay content is >65%

Question 2

Type, composition, origin of conglomerates and diamictites

Answer 2

Quartzose (Oligomict) conglomerates
* Derived from rocks containing quartzite beds, or quartz veins, or chert beds
* Common
* thin layers in sandstone units
* Most fluvial in origin (braided streams)
* some littoral (beach) environment

Polymict, petromict conglomerates, and diamictites
* Various lithologies; petromict contain metastable clasts
* May reach great thicknesses (thousands of meters)
* Rapid erosion of highlands
* Sediment gravity-flow processes
* Glacial deposits

Intraformational conglomerates
* Clasts from within the depositional basin
* Deformation structures, fragments of deformed sediments (e.g. mud and lime clasts)
* Sediment rip-ups by tidal currents, storms, etc.

Question 3

Siliciclastic rocks

Answer 3

Siliciclastic sediments are classified according to grain size and composition

• Terrigenous particles; minerals, rock fragments (may incl. minor bioclast particles)
  Conglomerates and diamictites:
• Epiclastic conglomerates/diamictites -> Extraformational & Intraformational
• Clast-supported -> Conglomerates, orthoconglomerates
• Matrix-supported -> paraconglomerates and diamictites
• Further subdivision: Clast stability, Clast lithology:
  >90 supported clasts:
  clast supported = quartzose conglomerate
  matrix supported = quartzose diamictite
  <90 supported clasts:
  clast supported = petromict conglomerate
  matrix supported = petromict diamictite
  breccias
• Cataclastic breccia (landslide or slump, tectonic, collapse)
• Solution breccia (remaining insoluble fragments)

, sandstones, wackes, mudrocks: laminated siltstone, bedded mudstone

*Carbonate rocks
- Limestones, dolostones, reef rocks
- Carbonate particles; framework grains, matrix

Question 4

Carbonate rocks

Answer 4

• Limestones
  Main types of sediment particles:
• Gravel size
  -(Large skeletal particles, Extraclasts, Intraclasts)
• Sand-sized particles
  -(Skeletal particles, Fragments of calcareous algae, Ooids, Pellets)
• Mud-sized particles (carbonate oozes)
  -Coccolithophores, Foraminifers, Other mud-sized skeletal fragments, Mud-sized “extraclasts’,Micrite
• Other types (framework carbonates)
• Stromatolites, Reef rocks, Dolostones
• Form largely by replacement of limestone precursor
  ‘
• Dolostones
  -Form largely by replacement of limestone precursor

Question 5

Diagenesis

Answer 5

Three main stages
* Shallow, deep burial, uplift/erosion (back to surface)
* Different types of cement and textures
* May record complex diagenetic history (precipitation/dissolution and temporal changes)