Sedimentary rock classification

Question 1

What is a sedimentary rock made of?

Answer 1

+/- Components +/- Matrix + Cement

There is always cement but it’s not always possible to see with the eye

Question 2

Name 8 types of sedimentary rocks

Answer 2

• Siliciclastics
• Pyroclastics
• Carbonates
• Siliceous
• Coal
• Evaporites
• Ore stones
• Phosphates

Question 3

First the rock is classified on the grain size.
Name the 3 sizes

Siliciclastic rocks

Answer 3

Pelites (silt/mud)
Arenites (sand, 1/16 mm -2 mm )
Rudites (gravel, > 2mm)

Question 4

How are Arenites named?

Siliciclastic, sand sized grains

Answer 4

3D-trekanten:
- Arenite (0-15% matrix)
- Wacke (15-75% matrix)
- Mudstone (>75% matrix)

Amount of matrix vs. grains

Question 5

How are Rudites named?

Siliciclastic, grain size > 2mm = gravel

Answer 5

Grains:
- rounded = Conglomerate
- sharp edges = Breccia

Types of grains:
- 1 type = monomict
- 2-3 types = oligomict
- Many types = polymict

The type af matrix

Matrix supported vs. grain supported

Question 6

Why is it important to analyse the amount of sorting of the grains?

Answer 6

Tells you about the energy when it was deposited

Question 7

What is the Carbonate ion?

Carbonates

Answer 7

CO3 (2-)

Question 8

Name 2 types of carbonate rocks

Answer 8

Limestone CaCO3
Dolomite CaMg(CO3)2

Only limestone reacts with HCL

Question 9

What is a carbonate rock made of?

Answer 9

+/- Components +/- matrix +cement

There is always cement

Question 10

Name 4 types of possible components (allochems) in carbonate rock

Answer 10

Bioclasts
Ooids (nucleus)
Peloids (no nucleus, smaller)
Intraclasts (Fragments of carbonate rock)

Question 11

Name types of bioclasts

Answer 11

• Crinoids (sølilje)
• Bivalves
• Brachiopods
• Gasteropods (snegle)
• Foraminifers ( fx. orbitolina, nummulites)
• Green algea
• Corals

Question 12

What is carbonate cement?

Answer 12

Formed by percipitation of calcite by carbonate rich liquids

Visible with the handlens is called Sparite

Sparite shines,

Question 13

What is carbonate mud?

Answer 13

Micrite
Looks like yogurt

Matrix can be made of micrite

Question 14

What is the Dunham classification based on?

Carbonate rocks

Answer 14

Amount of matrix vs. grains

Question 15

Name the 4 types of rocks in Dunham classification

Answer 15

Mudstone (Mud s. < 10% grain)
Wackestone (Mud s. > 10% grain)
Packstone (Grain s., +Micrite)
Grainstone (Grain s. - Micrite)

Question 16

Name 3 organisms that make biogenic silica

SiO2

Answer 16

Radiolara (Radiolarite)
Diatoms (Diatomite)
Sponges (rare Spiculite)

Silica (SiO2) from these form chert (flint)

Question 17

Name 5 stages of coal

Named after % of carbon

Answer 17

Peat (< 50 % C)
Lignite
Bituminous coal
Antrachite
Graphite (100% C)

Formed from organic matter on land

Question 18

Name 4 evaporites

Evaporites named after the mineral

Answer 18

Calcite (CaCO3)
Gypsum (CaSO4 * 2H2O)
Halite (NaCl)
K and Mg salts

Question 19

Pyroclastic rocks:
Name 4 types of tephra

Named after grain size

Answer 19

Fine ash –>Fine grained tuff
Coarse ash –> coarse grained tuff
Lapillus –> Lappilituff
Blocks/Bombs –> Pyroclastic breccia

Tephra is unconsolidated fragments

Question 20

How are terriginous rocks classified

Siliciclastic

Answer 20

Grainsize (Pelites, Arenites, Rudites)
Amount of matrix (Arenites =Trekant)
Mineralogi

Roundnes of grains (Rudites)

Sorting of grains

Question 21

What is an allochem?

Answer 21

Grains in a corbonate rocks
- Bioclasts
- intraclasts
- Ooids
- Peloids

Question 22

What is the difference between a peloid and an Ooid?

Answer 22

Peloid = No nucleus
Ooid = Spherical, with nucleus