Diagenisis

Question 1

What is diagenesis?

Answer 1

Processes occuring after burial – not including metamorphism and weathering

Question 2

What is compaction?

Answer 2

A type of diagenesis. Reduction in volume of loose sediments in response to pressure due to burial.

Question 3

What is cementation?

Answer 3

Crystalline material of varying composition (silica, calcium carbonate, hematite) that is precipitated within the in pore spaces of clastic sediment, binding the individual. Grains together to form a sedimentary rock.

Question 4

In addition to compaction and cementation, a third common diagenetic process is __________, in which new materials grow from old recycled chemicals after burial (in situ).

Answer 4

Authigenesis

Question 5

In _____________, an existing mineral retains its original chemistry, but the crystal sizes grow larger.

Answer 5

recrystallization

Question 6

What is the type of authigenesis where a completely different mineral takes over the space once occupied by another?

Answer 6

Replacement

Question 7

Bands of color caused by precipitation of minerals (such as iron oxides), which resemble bedding but may or may not actually parallel any primary sedimentary structures.

Answer 7

Liesengangen bands

Question 8

A diagenetic structure that are common rounded objects that form around a nucleus. And the version that are irregular and don’t have an obvious nucleus are what?

Answer 8

concretions and nodules

Question 9

What is soft sediment deformation?

Answer 9

A structure where unconsolidated sediments deform during or shortly after deposition. You can typically see it in deltas or shallow marine.

Question 10

What are sand volcanoes? In which gravity flow are they common?

Answer 10

The pressure on water in a very liquefied sand forces some of that sand and water to shoot up. Commonly in fluidized flows.

Question 11

_______-sized particles compact much less than mud.

Answer 11

Sand

Question 12

What is differential compaction?

Answer 12

Different sediment types compact more or less. For example, if you have a sand/mud bedding, the mud will compact way more than the sand, so it looks like the mud layer is thinner.

Question 13

Shales in compaction can lose up to ____% in volume.

Answer 13

50

Question 14

How might looking at the effects of pressure on grains help you?

Answer 14

It can lead to clues about depth of burial

Question 15

What are styolites?

Answer 15

Only found in limestone. Calcite under pressure will dissolve, and anything not calcite will form in a line showing the area of dissolution.

Question 16

Cementation is more likely in poorly sorted or well sorted sands?

Answer 16

Well sorted

Question 17

T/F: You get a lot of traces of mud in a rock that has been cemented.

Answer 17

F, no mud really.

Question 18

Calcite cement is more/less common because it is more soluble than silica.

Answer 18

more

Question 19

What is Eh?

Answer 19

The oxidation potential of an environment. If an area has a high Eh, it is more oxidizing (O2 will grab electrons off of the materials). Eh is a measure of the activity of the electrons.

Question 20

What are some recrystallization examples?

Answer 20

Micrite to sparry calcite or amorphus silica into quartz

Question 21

How do pipey concretions form?

Answer 21

There is a nucleation site that precipitated out, related to ground water flow.

Question 22

What are the different shapes of concretions?

Answer 22

-subspherical, elongate (pipe), tabulat, linear/layered

Question 23

Why would you search for fossils inside of concretions?

Answer 23

The organism can provide local conditions for concretions to appear like the CaCO3, and the reducing conditions. So the CaCO3 forms between the cement. They are common in shales.

Question 24

In a nodule, and you don’t see the fossil crushed at all, would that tell you that the concretion formed early on, or far after burial

Answer 24

Early on

Question 25

What are Leisengang bands?

Answer 25

In sediment, if there is a zone that has the right conditions for concretions, you would see off-colored bands radiating from one section. So the nucleus isn't one spot like a fossil, but rather a zone. The bands are always Iron Oxide.

Question 26

A load cast is an example of ____________ deformation

Answer 26

soft sediment

Question 27

What are some conditions that would tell you soft sediment deformation has happened?

Answer 27

You have a lot of parallel beds, and then there is one section with a lot of wavy/swirly and funky bedding.

Question 28

Why is soft sediment deformation happening?

Answer 28

The sediment is not being buried deep enough to be truly lithified. It is close to the surface. Could happen because of a rock slide, or earthquake, or meteor strike

Question 29

What would cause a clastic dike?

Answer 29

Liquefaction of over-pressured sands. Sand is under pressure and totally saturated with liquid. When that sand/water mix shakes, it forces the water to go up

Question 30

What would happen if a clastic dike was able to rupture the water through the surface?

Answer 30

You would get a sand volcano

Question 31

How would you get flame structures in bedding?

Answer 31

Flame structures, also known as soft-sediment deformation structures, form when a denser, overlying layer of sediment (like sand) is deposited on a less dense, water-saturated mud layer. The weight of the overlying sediment causes the mud to deform and push upwards, creating flame-like protrusions into the denser layer.