Sedimentary Structures

Question 1

What different types are there?

Answer 1

Induced by physical processes
- Erosional (before deposition)
- Depositional (during deposition)
- Deformational (after deposition)

Biologically induced
- Bioturbation
- Binding

Chemically induced

Question 2

What are “sole marks”?

Answer 2

Erosional structure.

When a stone bounces/skips/etc. on a bottom of cohesive, fine-grain sediment (usually mud) and then leaves marks after that.

Two main types: Scour & Tool marks

Question 3

Hvordan ser scour marks ud?

Answer 3

L__—

Dvs. der er en hård kant ned i sedimentet, der flader ud på den anden side, så det igen flugter med sedimentets overflade.

Når sand aflejres ovenpå, vil det derfor give små “buler”. Vandets retning kan aflæses som at den hårde kant bliver ramt først, og så flader det ud bagved = vandet rammer først kanten.

Question 4

What makes laminations/bedding visible?

Answer 4

Differences in grain type, size and/or sorting

Question 5

What are the two types of cross-bedding?

Answer 5

Planar (2D) and trough (3D)

Planar = skrå streger i rækker m. fladt lag mellem rækker, der står på hinanden

Trough = halvcirkler i halvcirkler ved siden af halvcirkler m. flade rækker oven på. Her vil vandretningen altid være, så strømmen rammer den mest buede del.
The curvature will always go ‘out’ towards the sides, and so we know the direction of the water

Question 6

What are vortex ripples?

Answer 6

High energy, creates eddies

Question 7

What does a fork in an area with ripples indicate?

Answer 7

Changes in the wave length of the flow

Question 8

What is a linguoid ripple?

Answer 8

Looks like tongues

Linguoid —> language —> tongue (roman word)

Question 9

Where are ladder ripples formed?

Answer 9

Deposited in very shallow marine environment; wind moves sediments across existing ripples.

The long ripples will be linear

Question 10

What is true about the angle of climbing ripples?

Answer 10

Increase in angle of climb from sub- to supercritical

Question 11

Where is the stoss side on a ripple?

Answer 11

The long stretch on the dune-ish looking ripple

Question 12

What is HCS?

Answer 12

Hummocky cross-stratification

Hummocky is when it goes down (happy smile - think of a hammock)

Question 13

What is SCS?

Answer 13

Swaley cross-stratification

Swaley is when it goes up (sad smile)

Question 14

What is HCS and SCS?

Answer 14

Product of strong and complex wave activity, mainly in areas below fair-weather wave base.

Typically interpreted as produced by !storm activity!

Typically found in silt or fine sandstones

Question 15

What is the lower flow regime?

Answer 15

A tranquil flow

Ripples and dunes

Question 16

What is the upper flow regime?

Answer 16

A rapid flow

Plane bed and antidunes migrating upstreams

Question 17

What is an antidune?

Answer 17

Moves upward against the stream; need high velocity and high amount of sediments.

Look like dunes but aren’t; smooths surfaces.

Accumulates sediments opposite of the stream.

Rarely preserved in the rock record.

Most examples are from volcanoclastic setting (very high velocity and large sediment load during pyroclastic surges).

Question 18

What does herring-bone cross-bedding look like?

Answer 18

Like a herring-bone…

Question 19

What types of laminations are associated with tidally-influenced environments?

Answer 19

Flaser, wavy and lenticular lamination

Question 20

What does flaser lamination look like?

Answer 20

Like someone has dug their nails (of various sizes of course) into the bedding

Question 21

What does imbricated pebbles indicate?

Answer 21

The flow direction.

Imbricated pebbles = the pebbles have aligned each other around each other so that the water can move the fastest above them

Question 22

What is the Bouma sequence?

Answer 22

Describes a classic set of sedimentary structures in turbidite beds deposited by turbidity currents at the bottoms of lakes, oceans and rivers.

Ie. the ideal vertical succession of structures deposited by low-density

Divided into 5 distinct layers labelled A through E, with A being at the bottom and E being at the top - with the layers overall getting finer-grained from bottom to top.

A: Erosive base at the bottom
B + D: horisontal lamination (horisontal lines)
C: current ripples
The higher up in the alphabeth, the finer the grains