Historical Geology - Sedimentary environments - marginal marine

Question 1

What is a marginal marine depositional environment?

Answer 1

Refers to deltas and shoreline features. Can be many km in size.

Question 2

Name the three Delta depositional environments and descrbe each.

Answer 2

• Delta plain - coarsest sediments, right at mouth of river, very little slope
• Delta front - intermediate sediments, moderate slope
• prodelta - finest sediments, furthest from river mouth

Question 3

How are Barrier Islands formed?

Answer 3

• from wave action known as longshore currents.

Question 4

What is a longshore current?

Answer 4

An ocean current that moves parallel to shore.

Question 5

What kind of energy will you find in Lagoons, tidal flats and tidal inlets?

Answer 5

low to moderate energy depositional enviroments.

Question 6

Is there much biological activity in lagoons, tidal flats and tidal inlets?

Answer 6

yes

Question 7

What sedimentary structures are included in lagoons, tidal flats, and tidal inlets?

Answer 7

• Bioturbation - reworking of soil and sediment by animals and plants
• Planar lamination - small scale sequence of fine layers

Question 8

How do Marine Depositional environments vary?

Answer 8

They vary with water depth and distance from shore

Question 9

What are Tempestites?

Answer 9

Sedimentary structures caused by storms. Their presence indicates sediments are above storm wave
base

Question 10

What is the importance of fossils in the marine environment?

Answer 10

Many marine enviroments are very similar to each other When ONLY comparing sediments. Fossils give more information.

Question 11

How is a Barrier reef structure built?

Answer 11

• Built up through biogenic processes (a process resulting from the activity of living organisms)
  Calcium carbonate skeletons of reefbuilders form a porous platform
  • Tends not to show bedding
  • Preserved in rock record as limestone
  • Excellent reservoir rock

Question 12

What is an atoll and where can they be found?

Answer 12

A ring-shaped coral reef that creates a lagoon in the middle. They form on volcanic seamounts

Question 13

What is a carbonate platform and where does it form?

Answer 13

It is asedimentary body which possesses topographic relief, and is composed of calcareous deposits.

• reefs often form as part of carbonate platforms
• form in warm, shallow waters

Question 14

What is the chemistry of carbonate precipitation?

Answer 14

CO2 + H2O — H2CO3 (driven right in cold water to left in warm water)

Question 15

The higher the concentration of CaCO3 in water the ______________ it is for reefs to form or precipitate CaCO3.

Answer 15

harder

Question 16

What are Ooids?

Answer 16

• small carbonaceous grains formed by oscillation in currents
• look like small beads

Question 17

Describe a deep-sea depositional environment.

Answer 17

• almost universally fine-grained sediment
• extreme distance from sediment source
• exceptionally low sedimentation rates

Question 18

What are turbidites?

Answer 18

Underwater mass-wasting events. (turbidity flows: dense, sediment-charged water moving downslope)
- the exception to the low energy rule

Question 19

What is mass-wasting?

Answer 19

Mass wasting, also known as slope movement or mass movement, is the geomorphic process by which soil, sand, regolith, and rock move downslope typically as a mass, largely under the force of gravity, but frequently affected by water and water content as in submarine environments and mudslides

Question 20

what makes up pelagic sediments?

Answer 20

Two non-biogenic sources
- Airborne dust
 -Eroded rock (usually marine volcanics)
The rest of the sediment is biogenic
- Skeletons of foraminifera (CaCO3), and diatoms
and radiolarians (Silicious skeletons)

Question 21

What is Carbonate compensation depth (CCD)?

Answer 21

The depth below which the rate of supply of calcite (calcium carbonate) lags behind the rate of solvation, such that no calcite is preserved.

Question 22

What is Siliceous ooze?

Answer 22

Siliceous oozes consist predominantly of the remains of microscopic sea creatures, mostly those of diatoms and radiolarians.