1. Minerals, rock types

& sedimentary rocks Graduate program - Introduction to Sedimentology

20-21.01.2014 Classification: Internal

Classification of rocks

• Igneous (cooling of magma, crystallisation)

• Sedimentary (burial & lithification of sediments (sand, clay, biogenic material, salt etc.))

• Metamorphic (recrystalization of rocks due to heating, pressure and fluids)

Dolomite

Evaporaites Siltstone

Mudstones

Conglomerate

Breccia

+ Biogenic

(coal/chert)

Gneiss

3 Classification: Internal

Rock cycle

Description/classification factors of sedimentary rocks

• Mineralogy (quartz, felspars, pyrite, anhydrite, etc.)

• Texture (grain size, sorting, shape, roundness, sphericity, fabric)

• Lithology (sand, clay, salt, carbonate, etc.)

• Primary and secondary structures (stratification, grading, biogenic

(traces), and deformational)

5 Classification: Internal

Minerals in rocks

Clastic:

• Quartz

• Feldspar (K and Pl)

• Mica (biotite, muscovite)

• Heavy minerals

• Pyroxene, Amphybol

• Olivine

Chemical precipitation:

• Calcite

• Gypsum, anhydrite

• Salts

• Pyrite

• Igneous, metamorphic and existing sedimentary

rocks are reworked into sediments

• Sediments are buried and lithified into

sedimentary rocks.

Clastic rocks = Mineral (Q, F) + Rock (R) fragments

F R

Q

R%

Q%

F%

• arenite

• arkose

• lithic

2013-11-15 7 Classification: Internal

Udden-Wentworth’s grain size scale, Φ = - log2D

Φ

Texture: Grain size classification

Study methods: Counting, Sieving, Settling tubes, Coulter counter, Laser granulometer

2013-11-15 8 Classification: Internal

Texture: Sorting – grain size distribution – «standard deviation»

Very well sorted

Well sorted

Moderately well sorted

Moderately sorted

Poorly sorted

Very poorly sorted

< 0.35

0.35-0.5

0.5-0.71

0.71-1

1-2

>2

2013-11-15 9 Classification: Internal

Texture:

Roundness – how smooth are grains

Sphericity - how close is grain to a sphere

(Pettijohn et al., 1987)

Lithology of terrigenous sedimentary rocks

• Based on grain size:

− Claystone

− Siltstone

− Sandstone

− Conglomerate

• Mixed grain size:

− Mudstone

− Heteroliths

11 Classification: Internal

12

Heteroliths

• Rocks composed of more than one lithology.

• Deposited on tidal flats, deltaplains, delta fronts,

estuaries or other environments with variable

energy conditions.

100 Km

13

Primary and secondary structures

• Primary physical structures (generated during sedimentation)

− Surface structures (lineations, tool marks, flute casts)

− Bedding structures (planar bedding, cross bedding, graded)

• Secondary structures (generated after deposition of sediment)

− Biogenic structures (animal traces, roots)

− Soft sediment deformation (convolute, slumping, water escape)

− Cracks (desiccation cracks, syneresis cracks)

Carbonate sedimentary rocks Graduate programm – Introduction to Sedimentology

2013-11-15 Classification: Internal

Carbonate reservoirs

2013-11-15 15 Classification: Internal

• Statoil is not producing

from carbonate reservoirs

Components of carbonate rocks

2013-11-15 16 Classification: Internal

Mineral components:

Calcite, Aragonite, Dolomite, Siderite

Components:

• skeletal fragments,

• algae and nanoplankton,

• cyanobacteria (mats),

• ooids/pesoids,

• intraclasts

Carbonate mud, lime, micrite

Crystalline cement - sparite

Classification of carbonate sedimentary rocks Dunham’s classification

2013-11-15 17 Classification: Internal

Sedimentology and stratigraphy (Gary Nichols, 1999)

2013-11-15 18 Classification: Internal

Depositional environments

Shallow marine:

• Tidal flats sabhkas

• Shoals/Beach/Barriers/Lagoons

• Reefs

• Mud Mounds

Outer shelf /ramp:

• Chalk

Continental:

• Lacustrine

• Diagenetic cementation

• Detritic limestone

• Biogenic (skeletal fragments)

• Inorganically precipitated (most is biogenically

induced)

• Evaporites

Carbonate compensation depth (CCD)

• CaCO3 desolves below 4.5-5 km water depth as water is undersaturated with CO2

• Clay is accumulated deeper than CCD

2013-11-15 19 Classification: Internal

rate of dissolution

of calcite increases

dramatically below

lisocline

Porosity in carbonates

2013-11-15 21 Classification: Internal

Presentation title

Presenters name

Presenters title

E-mail address ……@statoil.com

Tel: +4700000000 www.statoil.com

23 Classification: Internal