Sedimentary Rocks And Fossils

Front 1

Sedimentary structures

Back 1

1. Macroscopic
A. Outcrop scale
2. 3D

Front 2

Classification

Back 2

1. Primary:
A. formed at time of deposition
B. Produced by currents of deposition
C. Reflect PHYSICAL conditions of transport and depostion
2. Secondary
A. Formed after deposition
B. Reflects post-depositional organic, physical and/or chemical processes

Front 3

Primary structures

Back 3

1. Bedding (seen in 2D)
A. Plane bedding
1. Laminations
i) More than 1 cm thick
2. Cross bedding
A. Associated with bedforms

Front 4

Processes that form Plane bedding

Back 4

1. Sedimentary from suspension
2. Horizontal accretion
3. Encroachment into lee of an obstacle
4. Rapid
A. Single event

Front 5

Causes of bedding

Back 5

1. Variations in mineralogy
2. Variations in color
3. Variations in grain size
4. Can be enhanced by weathering and diagenesis

Front 6

Absence of bedding

Back 6

1. Bioturbidation
2. Grain flow
- Fluids in air
3. Rapid deposition of suspended sediment
- Fluid is water

Front 7

Unidirectional Water Current (Fluvial)

Back 7

1. Bedforms
A. Structures on surface of bed
- Velocity
- Grain size
- Depth of flow
* Form cannot be higher than water is deep

Front 8

Bedform and Velocity

Back 8

1. Founde number less than 0.8
A. Cross bedding surface dips downstream
B. Surface wave velocity more than flow velocity
2. Founde number equal to 0.8
A. Cross bedding dips downstream
3. Founde number more than 1
A. Waves do no move upstream

Front 9

Lower flat bed

Back 9

1. Flat configuration of bedding plane
2. Flat laminae
3. Very little grain support

Front 10

Ripples

Back 10

1. Grain size: Coarse sand or finer
2. Spacing: 1-2 cm
3. Height: few cms
4. Cross beds: dip down current
5. Water surface: flat
6. Flow regime: lower (Froude # <1)

Front 11

Sand waves

Back 11

1. Grain size: Very coarse sand or finer
2. Spacing: >20 cm
3. Height: few cms
4. Cross beds: dip down current
5. Water Surface: flat
6. Flow regime: lower (Froude # <1)

Front 12

Dunes

Back 12

1. Grain size: Very coarse sand to fine sand
2. Spacing: 0.5 m - 10 m
3. Height: 30 cm - 1 m+ (less than flow depth)
4. Cross beds: dip down current
5. Water Surface: surface waves out of phase with dunes
6. Flow Regime: lower (Froude # <1)

Front 13

Plane Bed (Upper Flat Bed)

Back 13

1. Grain size: Very coarse sand or finer
2. Spacing: NA
3. Height: NA
4. Cross beds: NA but may have current or parting lineations (streaks in bedding surface) sediment transported as bed and suspended load
5. Water Surface – flat
6. Flow Regime – upper (Froude # <1)

Front 14

Antidunes

Back 14

1. Grain size: Very coarse sand to very fine sand
2. Spacing: > 5 m
3. Height: 30 cm - 1 m
4. Cross beds: dip up current at <10°
5. Water Surface: standing waves in phase with antidunes
6. Flow Regime: upper (Froude # <1)
7. Rarely preserved

Front 15

Pools and Chutes

Back 15

1. Grain size: Very coarse sand to very fine sand
2. Spacing: NA
3. Height: NA
4. Cross beds: NA
5. Water Surface: standing waves breaking up current
6. Flow Regime: upper (Froude # >1)
7. No Bedform: mostly erosional

Front 16

Bedform

Back 16

Velocity and Size

Front 17

Migrating dunes and ripples

Back 17

Front 18

Unidirectional Currents: Current Ripples

Back 18

1. Differences:
A. River Current
- Assymetrical
- Low angle Stoss Slope
- Steep Angle Lee Slope
- Cross bed dip in the direction of current flow

Front 19

Ripple variation

Back 19

Depth

Front 20

Ripple variation

Back 20

Grain size

Front 21

Ripple variation

Back 21

High Sediment Supply

Front 22

Ripples with Low Suspended Load and High Bed Load

Back 22

1. Stoss cross bedding
2. Angular contacts

Front 23

Top and Bottom

Back 23

1. Upside down
2. Top: angular
3. Bottom: tangential

Front 24

Ripple Variation: High Suspended Load and Low Bed Load

Back 24

1. Large Suspended Load
2. Scour on lee slope
3. Trough cross stratification

Front 25

Cross bedding

Back 25

Front 26

Top and Bottom

Back 26

1. Scoured at base
2. Upside down

Front 27

Formation of Ripple Marks

Back 27

Front 28

Bidirectional Current : Oscillation Ripples on Beaches

Back 28

1. Differences
A. Beach ripples
- Symmetrical Stoss and Lee slopes
- Peaked crests
- Rounded troughs
- Cross laminae dip in direction of dominant current flow (onshore)

Front 29

Bidirectional Current: Oscillation Ripples in Tidal Zones

Back 29

1. Differences
A. Tidal ripples
- Symmetrical Stoss and Lee slopes
- Rounded crests
- Rounded troughs
- Cross laminae dip in two direction
i) Herringbone Structure
5. May have interference ripples if current directions are oblique

Front 30

Ancient ripple marks

Back 30

Symmtrical oscillation ripples

Front 31

Reactivation surfaces

Back 31

1. Dominant tidal
2. Substrate tidal (destructive)

Front 32

Common tidal bedding

Back 32

1. Sand in troughs of muddy bedding
2. Coarse material accumulates on stoss side
3. Equal mistunes of sand and muddy beds
4. Dominant sand bedding with clay drapes (Flaser)

Front 33

Wind transported Bedforms

Back 33

1. Mostly move by saltation
2. Large particles not transported
A. Air viscosity less than water viscosity
B. Accumulates as lag, desert pavement
C. Coarse material on crests
3. Erosion dominates on stoss side
4. No scouring on lee side

Front 34

Differences in Water and Wind Bedforms

Back 34

Front 35

Bottom-of-Bed Sedimentary Structures

Back 35

1. Flute Casts
A. Scour filled by overlying bed
B. Deeper upcurrent
2. Tool mark
A. Scratching underlying bed by object being transported

Front 36

Top-of-Bed Sedimentary StructuresSubaerial Environments

Back 36

1. Mudcracks
A. Wide at top
B. Curls (concave) upward
2. Raindrop imprints
3. Salt Crystal pseudomorphs

Front 37

Mud Crack Formation and Preservation

Back 37

Front 38

Mudcracks Forming

Back 38

Front 39

Ancient Mud Cracks Preserved

Back 39

Front 40

Other Within-Bed Sedimentary Structures

Back 40

1. Graded bedding
2. Inverse graded bedding

Front 41

Secondary (Mechanical) Sedimentary Structures

Back 41

1. Load Casts
A. Ball and Pillow
B. Sand deposited on mud
C. Foundering down into muddy slurry
D. Bedding deformed
2. Liquefaction
A. Flame Structures
B. Sand moving up into overlying bed as a tongue

Front 42

Load cast

Back 42

Front 43

Mud Squeezed Up Around Ball and Detaching Ball

Back 43

Front 44

Load Casts Side View

Back 44

Front 45

Ball of Sand Foundering into Mud Without Deformed Bedding

Back 45

Front 46

Deformed bedding

Back 46

Front 47

Ball and Pillow and Deformed Bedding

Back 47

Front 48

Flame Structure

Back 48

Front 49

Biogenic Sedimentary Structures: Trace Fossils (Ichnofossils)

Back 49

1. Indirect evidence of life
2. Used for environmental interpretations
3. Paleobythemetry
4. Paleo oxygen levels

Front 50

Biogenic Sedimentary Structures: Trace Fossils (Ichnofossils) - Burrows

Back 50

1. Burrows into sediment for shelter and food
A. Vertical burrows
B. Vertical with connecting horizontal burrows
C. U-shaped burrows
D. 3D network of burrows
E. SHALLOW MARINE OR SUBAERIAL

Front 51

Bioturbated: Numerous interconnecting burrows

Back 51

1. Abundant organisms
2. SLOW SEDIMENTATION RATE
3. SOIL

Front 52

Biogenic Sedimentary StructuresTrace Fossils (Ichnofossils) - Tracks

Back 52

1. Borings into hard surfaces
A. INTERVENING SUBEARIAL EXPOSURE
2. Tracks
A. Superficial horizontal burrows
- LOW OXYGEN LEVEL
- ABUNDANT ORGANIC MATTE
- QUIET WATER
3. Foot prints
A. SUBAERIAL

Front 53

Biogenic Sedimentary StructuresTrace Fossils (Ichnofossils) - Stromatolites

Back 53

1. Stromatolites
A. domal structure
B. laminated
C. formed by metabolism of blue-green algae
D. SHALLOW INTERTIDAL
F. Precambrian (Archean – 3.5 bya)

Front 54

Absence of Trace Fossils

Back 54

ANOXIC ENVIRONMENT – no organisms