Sedimentary structures

Question 1

what are sedimentary structures?

Answer 1

-Features formed during or shortly after sediment deposition that record how sediments were deposited and the environment of deposition.

Question 2

what are 3 examples of sedimentary structures?

Answer 2

• features of fossil tracks, ripple marks, bedding

Question 3

what does beddings show?

Answer 3

Layers of sediment deposited over time, often indicating changes in conditions.

Question 4

What do ripple marks indicate?

Answer 4

Movement of water or wind and current direction.

Question 5

What are the size and wavelength features of subaqueous dunes?

Under what flow conditions do they form?

How do they develop?

Answer 5

Much larger bedforms than ripples.

Wavelengths range from metres to hundreds of metres.

Form in strong flow conditions.

Build up from migration of the whole bedform.

Question 6

Ripples vs Dunes

Answer 6

Ripples: small, short, water/wind

Dunes: big, tall, wind, long-lasting

Question 7

What is the angle of repose?

Answer 7

Steepest angle at which loose sediment can pile without collapsing.

Question 8

Why is the angle of repose important?

Answer 8

Shows how steep sediment can naturally build before collapsing

Helps identify sediment type (fine sand vs pebbles)

Reveals how grain size & shape affect stability

Useful in engineering, hazard assessment, predicting landslides/sand movement

Question 9

How does sediment size affect angle of repose?

Answer 9

Angular grains (pebbles): higher angle, more stable

Fine grains (sand): lower angle, slump easily

Question 10

in terms of bedform stability, low flow velocity abd large grain size leads to

Answer 10

• no movement on flat bed

Question 11

what are scour marks?

Answer 11

Marks on the sediment bed formed by water erosion.

Question 12

what are tool marks?

Answer 12

Marks made by objects being dragged, bounced, or rolled along the bed.

Question 13

Importance of erosional sed structures

Answer 13

• help geologists reconstruct past environments
• Flow Reconstruction: Shows the direction, speed, and turbulence of past water flow.

Material Transport: Reveals what kind of sediment or debris was carried by the water.

Question 14

what is the difference between scour and tool marks?

Answer 14

• the water itself causes scour whereas tool marks is caused by objects moved by the water

Question 15

what is convulate beddings?

Answer 15

• A sedimentary structure in which originally flat or gently layered sediment becomes folded into complex patterns - wavy and crumpled
• formed by soft water rich sediment

Question 16

what is the way up criteria?

Answer 16

• Features in sedimentary rocks that show which way was originally up when the layers were deposited - the direction

Question 17

what is bioturbation?

Answer 17

Disturbance of sediment by living organisms i.e worms burrowing

Question 18

difference between trace fossil and body fossil?

Answer 18

• body fossil shows physical evidence of an organism that lived in the past
• trace fossil - evidence of the activity of an organism

Question 19

are traces caused by i.e tracks of walking animals called ichnofauna?

Answer 19

yes

Question 20

What controls the shape and distribution of different sedimentary rocks?

Answer 20

• Type and source of sediment
  
  • Depositional environment i.e lake or beach
    Energy of the transporting medium

Question 21

what is lithification?

Answer 21

compaction + cementation, turning loose grains into solid rock.

Question 22

what is mud

Answer 22

refers to a very fine grained sediment made of silt and clay - sized particle
- deposited in deep marine settings = low energy environment

Question 23

how are evaporites formed?

Answer 23

• body of water is saturated with dissolved salts and minerals - evaporation exceeds precip
• crystals interlock = no porosity

Question 24

what are three continental sedimentary environments?

Answer 24

• glacial
• lakes
• river

Question 25

what are three marine sedimentary environments?

Answer 25

- deltas - deep marine environments - coast / estuaries

Question 26

What is a delta?

Answer 26

A landform that develops where a river meets a standing body of water (sea, lake, or reservoir). It is fan-shaped and forms where the river loses energy and drops its sediment.

Question 27

Why are deltas important for humans?

Answer 27

They are fertile regions for agriculture and often contain sandstone reservoirs that hold oil and gas. A delta creates stacked layers of sand and mud, perfect for trapping hydrocarbons, which is why the Nile Delta is rich in natural gas

Question 28

How do deltas help geologists?

Answer 28

They help interpret past environments, sea level changes, and gas-bearing intervals because deltas create stacked layers of sand and mud that trap hydrocarbons.

Question 29

what is a delta facies?

Answer 29

refers to the distinct layers or types of sediment deposited in different parts of a delt

Question 30

what are the three controls of the delta facies distribution?

Answer 30

- sea level change - climate = temp, rainfall = amount and timing of rainfall - tectonics = controls landform and relief

Question 31

What happens if sea level rises to deltas?

Answer 31

- deltas move inland