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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
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