Shales sandstones and associated rocks

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Shales sandstones and associated rocks

• Chapter 4

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Pyroclastic versus Epiclastic

• Clast a particle, or grain
• Epiclastic rocks are those composed of
  (nonvolcanic) particles of all sizes, clay to
  boulders
• Pyro fire, volcanic
• Pyroclastic rocks are those composed of eruptive
  volcanic rock particles

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Ch 4.1 mineral and rock grains

• textural and compositional terms
• Table 4.1

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Grade or fraction

• Friktion
• gt 0,06 mm
• Cohesion
• lt 0,06 mm

• Grade size in mm
• Boulder over 200
• Cobbles 60-200
• Gravel 2-60
• pebbles 4-60
• granules 2-4
• Sand 0,06-2
• Silt 0,002-0,06
• Clay lt 0,002

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Cohesion

• Surface charges and water that hold the sediment
  together

• clay and silt - charges are great compared to
  grain weight
• sand charges weak compared to grain weight but
  capillary water important

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? what two meanings has the word clay?

1. clay mineral
2. grade size

• To avoid genetic inferences other terms are used
  
• clay size - lutite, lutiteous, argillite,
  argillaceous
• sand size arenite, arenaceous
• courser than sand size rudite, rudaceous

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Clay minerals

• Brucite - expansive
• Gibbsite
• Kaolinite NOT expansive
• Montmorillonite (also called Smectite) expansive
  (deposition env. near shore)
• Illite expansive (deposition env. deep sea)
• Bentonite expansive (formed by weathering of
  volcanic ash)
• similar clay minerals
• chlorite
• halloysite
• vermiculite

• important but a lot of names based on composition
  
• some are expansive others not

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expansive clay
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Slide risk with clay

• Clay fresh deposited slides on slopes as
  little as 1 degree!!!
• Clay fills in the bottoms of basins first

• Glacial and post glacial clay in Sweden

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Source of clay

• Glacial clay rock flour produced by abrasion of
  rocks in the glacier

• Post glacial clay normal clay consists of
  clay minerals
• the product of weathering
• thus the clay rich rocks are not very effected by
  weathering

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?? How is the age of a clay rich rock related to
the or expected occurrence of swelling clays??

• Answer p. 85 Table 4.2

• the older they are the less expansive the clay is

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?? What could you say about the glacial clay
deposits from the Weichselian Glaciation?

• ?? Post glacial clay??

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4.2 Lithification

• To make into a rock
• lithic, litho rock

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4.2 Lithification

• consolidation water squeezed out
• compaction air squeezed out
• densification both consolidation and compaction
• diagenesis both densification and cementation

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Lithification
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Types of cement Fig 4.5,

• Different strengths
• Weathering can remove cement

• quartz
• iron oxide
• calcite
• dolomite
• gypsum
• halite
• clay

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Characteristics of cement

• quartz strongest
• iron oxide - strong
• calcite - soluble, crystalline intergrowths
• dolomite soluble but less than calcite
• gypsum extremely soluble
• halite extremely soluble
• clay - (not true cement) can be leached by ground
  water

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Classification Rock or Soil

• an engineer would classify a sediment that was
  either loose and unconsolidated or hard and
  rocklike as a soil if it lacked cement
• a geologist would classify it as a rock if it was
  pre-quaternary in age

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Cementation of clay

• movement of ground water is low
• difficult to consolidate squeeze out water
• difficult for cement to migrate into voids

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Cementation of clay

• How can thin layers of sand in clays and silts
  enhance lithification?
• Glacial clays are varved winter layer and
  summer layer / some sand in summer layers

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Consolidation of glacial clay

• If the water is caught in the basin then it
  will support the clay
• If it is allowed to drain out the clay will
  consolidate resulting in subsidence of the
  ground surface

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Consolidation of glacial clay

• Problems when a basin of clay is punctured and
  water is allowed to escape
• example Stockholm area Huddinge, slussen
  subway, and more!

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Strength versus porosity

• ?? How is rock strength and porosity related in
  clay rocks??
• Can you draw a simplified curve showing this
  relationship??
• p. 87, 88 Figure 4.6.

The porosity decreases with time and depth of
burial Thus the lower the porosity the stronger
the rock
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4.3 Description of some epiclatic rocks

• Rocks with grains coarser than 2mm
• Conglomerate or Rudite
• Breccia (fault breccia)
• Tillite

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Conglomerate or Rudite

• Conglomerate or Rudite more than 30 rounded
  particles larger than 2mm
• deposition environments rivers, mouth of
  streams, beaches, and colluvium

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Conglomerate or Rudite

• physical character bimodal, open work,
  imbricate structure Fig. 4.8, clast or matrix
  supported structure

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Packning av partiklar
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Conglomerate or Rudite

• Imbricate structure

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Conglomerate or Rudite

• not common but due to resistance to weathering
  they often stand out in the landscape as ridges

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Breccia

• more than 30 angular particles larger than 2mm
• deposition environments - tallus and scree rock
  fall, movement, glaciers, volcanic activity,
  landslides, meteorite impacts

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talus
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landslide
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Glacial breccia
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meteorite impact
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Fault breccia

• Fault breccia, fault gouge, mylonite
• sheets of crushed material in a fault or fault
  zone
• course angular rock fragments breccia
• fine clay, pulverized rock from intense grinding
  mylonite
• Very important with respect to permeability of
  hard rocks

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Fault breccia / gouge
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Permeability

• along grain boundaries
• along faults, fractures and joints

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Tillite

• unstratified, unsorted soil deposited from
  glacial ice
• depositional environment glaciated areas
• physical character highly variable thickness
  both laterally and vertically and extremely
  variable grain-size distribution (boulder clay,
  gravel rich till)

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tillite
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tillite
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Rocks with sand-size grains (0.06 to 2 mm)

• Sandstone and Arenaceous rocks
• sandstone often suggests that the grains are
  composed of quartz and feldspar
• arenites often are sandstones with grains other
  than quartz and feldspar (kalkarenite)

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Texture

• Texture refers to
• Kornstorleksfördelning
• Sortering
• Kornform
• Packning
• Geometry of beds

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Grain size

• Includes several qualities
• mean grain size
• predominant grain size
• range of grain size
• Grain-size distribution
• Sorting

grain form plays a role!
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grain size

• range of paticles
• sorting
• of different fractions

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Texture packing of grains

• grain grain
• matrix supported

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grain form - maturity

• the longer time a particle is transported
• the better rounded it will become

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question in notes on homepage

• Explain the concept of maturity or immaturity of
  sandstones.
• Give an example (name) of both a mature and
  immature sandstone.
• What is the main physical difference between
  these two.

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Layering or bedding

• Thickness defined
• very thick gt 100 cm
• thick 30-100
• medium 10-30
• thin 1-10
• very thin lt 1 cm

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Nature of bedding

• describes the partings within a bed
• massive gt100 cm
• blocky 30-100
• slabby 10-30
• flaggy 1-10
• laminated lt 1 cm

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geometry of bedding

• planar
• crossbedded
• trough
• wedge

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geometry of bedding

• planar
• cross bedded
• trough
• wedge

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geometry of bedding

• planar
• cross bedded
• trough
• wedge

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Example

• Thick massive bed the bed is between 30 and 100
  cm thick and there is NO internal layering
• Thin laminated bed the bed is between 1 and 10
  cm and there are thin lt1 cm internal layering

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Describe these
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Classification after Pettijohn p96

• 3 criterion
• detrital matrix (arenite lt 15 gt graywacke)
• quartz versus feldspar and rock fragments
• rock fraagments versus feldspar

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classification summarized
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Main rock types

• Arkose friable, pinkish or grey, porous formed
  from weathering of granite
• Orthoquatzite strong grains of quartz, rock
  strength dependent upon cement type SiO2 or CaCO3
• Graywacke not friable due to large quantity of
  matrix, often graded, sorting poor, thus low
  porosity

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Organic matter in sandstone

• coal formed from plant debris
• oil and gas formed from decomposition of sea
  organisms, foraminifera and diatoms

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Organic matter

• Positive if we want to explore for gas and oil
  reserves
• sandstone is permeable and allows the formation
  of concentrations of gas and oil
• requires a trap

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Organic matter

• Negative
• gas is highly explosive
• tunneling and underground works risk explosions!!!

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Sedimentary Rx lt 0,02 mm

• Shale
• Mudstone
• Mud rocks

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gt50 of sedimentary rocks are fine grained gt0,02

• Formation in
• still water
• lakes
• deep seas
• swamps
• flood plains

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Grain size and composition

• Normally a mixture of silt and clay
• of these can be determined by a chemical
  analysis
• silt usually composed of silica and lacks
  alumina
• clay usually composed of alumina

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Names numerous, p99

• Distinctly different compositions and names
• marl calcarious rich clay
• diotomite silica fossils of diatoms
• chert or flint recrystalized diatomite
• alum shale contains FeS2 and mineral alum
  (hydrous potassium alumina sulfate)

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Names

• less distinct difference between rock types
• Shale and Argillite vs Mudstone and Claystone

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Names

• shale and argillite fissil, fissility
• mudstone and claystone lack fissility
• Fissility is a textural term a tendency to
  break apart along closely spaced sets of joints
  in dice like cubes

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Fissility
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Fissility
Fissility is limited in size lt 10 cm Flaggy or
blocky is the same quality but gt 10 cm
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Fissil and Flaggy
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More Names of Rocks

• Slate slightly metamorphic
• Phyllite more metamorphic and with visible mica

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More Names of Rocks

• Volcanic origin
• tuffaceous mudstone ash rich mudstone
• tuff volcanic ash

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Age relationship

• Shale Palaeozoic
• Mudstone - Tertiary

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Engineering classification
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Slaking

• deterioration and breakdown of a rock after
  exposure by excavation
• cracking and heaving
• most common in expansive clays
• size of chunks varies
• dissolves in water
• proportional to permeability

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Slaking test

• Clay wet
• Clay dry
• Clay low fired
• Clay high fired

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Deformation structures

• slickensides polished surfaces in mudstones
  which is believed to be due to shearing due to
  volume changes associated with wetting and drying

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Deformation structures

• shale mylonite sheared and crushed mudstone

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Deformation structures

• bedding plane mylonite shear along bedding
  planes due to folding

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Sedimentary Facies

• Facies environment of deposition
• Rocks that are common and are associated with
  unique environments are given facies names

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Flysch or turbidite facies

• rock description
• rhythmically bedded thin beds of shale
  alternating with graywacke
• environment of deposition
• deposited in sub marine by submarine landslides
  from the continental shelf down to the deep ocean
  basin

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Flysch or turbidite facies
rhythmically bedded thin beds of shale
alternating with graywacke
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Flysch or turbidite facies
rhythmically bedded thin beds of shale
alternating with graywacke
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Cyclothemic deposits Molasse Facies

• Repeated sequence of, from the bottom up,
  sandstone, clay, coal, limestone (sometimes), and
  shale.
• Deltaic environment with a oscillating relative
  sea level change.

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environment for molasse
Deltaic environment with a oscillating relative
sea level change
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Molasse

• shale
• limestone (sometimes)
• coal,
• clay,
• sandstone

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Molasse

• shale
• limestone (sometimes)
• coal,
• clay,
• sandstone

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Molasse

• Aerial view of the Eocene-Oligocene Indus Molasse
  Group, India.
• This sequence is interpreted as the deposits of a
  paleo-Indus River and shows that the river
  started to flow soon after initial collision and
  uplift of southern Tibet (Clift et al., 2001).

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Accretionary wedge deposit melange Facies

• Disturbed beds of shale, graywacke, sandstone,
  which are sheared and folded.
• Melange is French for mixture and that is what
  this is a big mix of rocks in different
  structures.
• (Fig. 4.22) forms along an accretionary wedge
  where a continental plate and oceanic plate
  collide.

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accretionary wedge
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wedge thrust faults
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Melange
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Melange