Shales sandstones and associated rocks

1
Shales sandstones and associated rocks

• Chapter 4

2
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

3
Ch 4.1 mineral and rock grains

• textural and compositional terms
• Table 4.1

4
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

5
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

6
? what two meanings has the word clay?

• clay mineral
• 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

7
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

8
(No Transcript)
9
expansive clay
10
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

11
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

12
?? 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

13
?? What could you say about the glacial clay
deposits from the Weichselian Glaciation?

• ?? Post glacial clay??

14
4.2 Lithification

• To make into a rock
• lithic, litho rock

15
4.2 Lithification

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

16
Lithification
17
(No Transcript)
18
(No Transcript)
19
Types of cement Fig 4.5,

• Different strengths
• Weathering can remove cement

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

20
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

21
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

22
Cementation of clay

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

23
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

24
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

25
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!

26
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
27
4.3 Description of some epiclatic rocks

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

28
Conglomerate or Rudite

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

29
Conglomerate or Rudite

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

30
Packning av partiklar
31
Conglomerate or Rudite

• Imbricate structure

32
Conglomerate or Rudite

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

33
Breccia

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

34
talus
35
landslide
36
Glacial breccia
37
meteorite impact
38
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

39
Fault breccia / gouge
40
Permeability

• along grain boundaries
• along faults, fractures and joints

41
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)

42
tillite
43
tillite
44
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)

45
Texture

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

46
Grain size

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

grain form plays a role!
47
grain size

• range of paticles
• sorting
• of different fractions

48
Texture packing of grains

• grain grain
• matrix supported

49
grain form - maturity

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

50
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.

51
Layering or bedding

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

52
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

53
geometry of bedding

• planar
• crossbedded
• trough
• wedge

54
geometry of bedding

• planar
• cross bedded
• trough
• wedge

55
geometry of bedding

• planar
• cross bedded
• trough
• wedge

56
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

57
Describe these
58
Classification after Pettijohn p96

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

59
classification summarized
60
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

61
Organic matter in sandstone

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

62
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

63
Organic matter

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

64
Sedimentary Rx lt 0,02 mm

• Shale
• Mudstone
• Mud rocks

65
gt50 of sedimentary rocks are fine grained gt0,02

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

66
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

67
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)

68
Names

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

69
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

70
Fissility
71
Fissility
Fissility is limited in size lt 10 cm Flaggy or
blocky is the same quality but gt 10 cm
72
Fissil and Flaggy
73
More Names of Rocks

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

74
More Names of Rocks

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

75
Age relationship

• Shale Palaeozoic
• Mudstone - Tertiary

76
Engineering classification
77
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

78
Slaking test

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

79
Deformation structures

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

80
Deformation structures

• shale mylonite sheared and crushed mudstone

81
Deformation structures

• bedding plane mylonite shear along bedding
  planes due to folding

82
Sedimentary Facies

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

83
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

84
Flysch or turbidite facies
rhythmically bedded thin beds of shale
alternating with graywacke
85
Flysch or turbidite facies
rhythmically bedded thin beds of shale
alternating with graywacke
86
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.

87
environment for molasse
Deltaic environment with a oscillating relative
sea level change
88
Molasse

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

89
Molasse

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

90
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).

91
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.

92
accretionary wedge
93
wedge thrust faults
94
Melange
95
Melange