Ichnology

Question 1

What are ichnofossils and how are they formed?

Answer 1

Trace fossils formed by the movement of organisms

Question 2

What do ichnofossils show and what can they be used to determine?

Answer 2

They represent activity of soft-bodied organisms and can be used to determine current velocity, sedimentation rate, and strength of substrate.

Question 3

Where are boring ichnofossils usually found?

Answer 3

High energy, rocky coastlines

Question 4

Where are simple burrow ichnofossils usually found?

Answer 4

Sandy shores

Question 5

Where are organisms that live and graze on the surface usually found?

Answer 5

Low energy offshore and deepwater environments

Question 6

How are ichnofossils classified?

Answer 6

Ichnogenus, ichnospecies (Linnean binomials)

Question 7

How can one organism produce different types of ichnofossils in its life?

Answer 7

Different activities and different substrates

Question 8

What is the name for locomotion traces?

Answer 8

Repichnia

Question 9

What is the name for resting traces?

Answer 9

Cubichnia

Question 10

What is the name for dwelling traces?

Answer 10

Domichnia

Question 11

What is the name for feeding burrows?

Answer 11

Fodinichnia

Question 12

What is the name for grazing traces?

Answer 12

Pascichnia

Question 13

Describe dwelling traces

Answer 13

Cylindrical tubes with minor branching

Question 14

Name and describe the two different types of dwelling traces

Answer 14

Borings made into hard or semiarid substrate (rock). Burrows made into soft substrate (unconsolidated sand).

Question 15

What can feeding burrows do and what can they show?

Answer 15

They can cross bedding surfaces and the complex patterns represent mining behaviour

Question 16

What do repeating patterns in grazing traces show?

Answer 16

A systematic feeding strategy

Question 17

FOSSIL ROOTS ARE NOT TRACE FOSSILS

Answer 17

Got that?

Question 18

What are fossil roots diagnostic of?

Answer 18

The terrestrial depositional environment

Question 19

Describe the morphology of fossil roots

Answer 19

Highly irregular and downward branching

Question 20

What can bright colours in sedimentary rocks indicate?

Answer 20

Clays (broken down micas and feldspars) and organic material

Question 21

Define diagenesis

Answer 21

The process of loose sediment becoming rock.

Question 22

What does diagenesis destroy?

Answer 22

Rock

Question 23

Describe the conditions of diagenesis

Answer 23

Begins at surface temperature and pressure and continues as T and P increases.

Question 24

Give the names for early and late diagenesis

Answer 24

Eodiagenetic and mesodiagenetic

Question 25

What is bioturbation?

Answer 25

The disturbance of sedimentary structures by organisms

Question 26

Give an example of bioturbation and what it results in

Answer 26

The consumption and excretion of sediment that can change the composition of some clays

Question 27

Describe a eodiagenetic bioturbation

Answer 27

The mechanical and chemical activities of organisms buried near the surface sediment

Question 28

What does the churning and homogenising of sediment result in?

Answer 28

The reduction of deposition barriers to flow in reservoirs

Question 29

What causes mechanical compaction?

Answer 29

Overburden

Question 30

What are two eodiagenetic processes that occur in mechanical compaction?

Answer 30

Grains are rotated to reduce volume and water is expelled upwards

Question 31

Describe the formation of sandstone dykes

Answer 31

Water is explosively expelled upwards after a sudden, large compaction

Question 32

Why types of grains can be highly compacted and why?

Answer 32

Silts and clays have platy morphology and can be compacted up to 90%.

Question 33

What type of grain cannot be highly compacted and why?

Answer 33

Sand because it is mostly quartz, which is often round.

Question 34

What mesodiagenetic process allows further compaction after the rotation of grains?

Answer 34

Mechanical fractioning of the grains

Question 35

What type of process is pressure solution?

Answer 35

Mesodiagenetic

Question 36

Describe the process of pressure solution

Answer 36

The material at the grain contacts (perpendicular to compaction) dissolves. This reprecipitates as cement at contacts that are perpendicular to compaction. Porosity is lost.

Question 37

What causes dissolution?

Answer 37

Changes in temperature and pressure and/or composition of porewater

Question 38

When is a mineral more stable?

Answer 38

In a solution

Question 39

Where does dissolution without reprecipitation occur?

Answer 39

In systems that are subject prolonged pumping of exotic porewater with an abundant fresh supply

Question 40

Describe the process of cementation

Answer 40

Chemical precipitates, forming new crystals in the mores of a sediment/rock, binding the grains together

Question 41

What types of sources can the precipitate have during cementation?

Answer 41

Local or external

Question 42

What are concretions?

Answer 42

Spherical masses of sediment that are more strongly cemented than the surrounding volume

Question 43

What grain size do concretions have compared to the surrounding?

Answer 43

The same

Question 44

What are concretions associated with?

Answer 44

Organic material that reacts with the surrounding chemistry

Question 45

Give an example of a concretion produced by organic material

Answer 45

Iron found in organic matter that forms iron carbonate concretions

Question 46

What is recrystallisation?

Answer 46

The reorientation of the same crystal lattices in mineral grains

Question 47

What processes are involved in recrystallisation?

Answer 47

Solution and reprecipitation of the mineral phase already present

Question 48

Where is the process of recrystallisation commonly seen?

Answer 48

Carbonate shells

Question 49

What is mineral replacement?

Answer 49

Where a newly formed minerals replace preexisting ones in situ

Question 50

How can the new minerals be different to the original mineral?

Answer 50

It can be a polymorph

Question 51

How does mineral replacement affect pore space?

Answer 51

The new structure can have a different volume