Sedimentary structures

Question 1

The a layer of the bouma sequence

Answer 1

Poorly sorted, structureless sand, gravel and pebbles with grading upwards

Se docs dokument

Question 2

The b layer of the bouma sequence

Answer 2

Laminated plane bed of sand. Upper flow regime

Question 3

The c layer of the bouma sequence

Answer 3

Ripples, cross laminated sand, HCS + SCS

Question 4

The d layer of the bouma sequence

Answer 4

Laminated plane bed of silt. Lower flow regime

Question 5

The e layer of the bouma sequence

Answer 5

Hemipelagic mud (+clay)

Question 6

Which deposits are found after storm events?

Answer 6

Tempestites, Bouma Sequence, HCS, SCS

Question 7

What is the two main types of ripples?

Answer 7

Symmetrical and asymmetrical

Question 8

What happens to ripples wavelength, when the sea level rises

Answer 8

There is less energy in the ocean, which means less energy to create ripples, which makes the wavelength shorter

Question 9

Define Ladder ripples

Answer 9

where current or wave ripples are modified by a second set of ripples with different orientation, common in tidal flats.

Question 10

Define Antidunes

Answer 10

Stream bed-form in which the dune migrates in the opposite direction of stream flow

Question 11

Define wave ripples

Answer 11

Wave ripples are formed in shallow water by oscillatory motion caused by passage of waves. They are symmetrical ripples

Question 12

What is herringbone cross stratification

Answer 12

bipolar cross-stratification produced by alternating directions of ripple migration

Question 13

Define low angle cross bedding

Answer 13

sedimentary layers whose contacts with each other intersect at a gentle angle (typically less than 10)

Question 14

Define Flute cast

Answer 14

sand-filled, spoon-shaped hollow in a mud layer scooped out by a turbidity current; a sedimentary bottom structure visible at the base of the overlying bed

Question 15

Load casts and flame structures

Answer 15

Sedimentary features that form as the result of an upper sedimentary layer pushing downward and deforming a lower sedimentary layer. Typically the features are softball to basketball in size.

Question 16

Define slump

Answer 16

Sedimentary folding affecting several beds

Question 17

What is the difference between stromatolites and thrombolites

Answer 17

Stromatolites has lamination. Thrombolites doesn’t

Question 18

Laminar flow

Answer 18

Laminar flow: At all points in the flow all molecules are moving downstream. Molecules move parallel to each other.

Question 19

Turbulent flow

Answer 19

Turbulent flow: At any point in the flow, a molecule may be moving in any direction, but the net flow is downstream.

Question 20

Convolute lamination

Answer 20

Disrupted layering by liquefication during or after deposition

Question 21

Mention the symmetrical ripple forms

Answer 21

Wave ripple, Rolling grain ripple, Vortex

Question 22

Mention the asymmetrical ripple forms

Answer 22

Current ripple

Question 23

Define planar cross-lamination

Answer 23

A perfectly straight ripple will generate cross-laminae that all dip in the same direction and lay in the same plane.

Question 24

Define planar cross bedding

Answer 24

Are created at low flow velocities. Sand on the lee slope is not reworked

Question 25

trough cross-lamination

Answer 25

Sinuous and linguoid ripples have lee slope surfaces that are curved, which makes laminae that dip at an angle to the flow as well as downstream

Question 26

Trough cross bedding

Answer 26

Formed by the migration of sinuous subaqueous dunes. Typically has asymptotic bottom contacts and an undulating lower boundary.

Question 27

What does mud drapes indicate?

Answer 27

Indicates tidal influence of transport and deposition

Question 28

What is Flaser, wavy and lenticular lamination associated with?

Answer 28

Tidlly influenced environment

Question 29

What are the two types of diapirism?

Answer 29

Salt and mud diapirism

Question 30

Ways for a particles to move

Answer 30

Rolling, Saltation and suspension

Question 31

What is the difference between 2D and 3D dunes?

Answer 31

2D dunes
- Straight
- Planar cross-bedding

3D dunes - requieres higher velocity!
- Sinuous
- Through cross-bedding

Question 32

The Froude number

Answer 32

The Froude number is a relationship between the flow velocity (v) and the flow depth (h), and the acceleration due to gravity (g).

Question 33

Characteristics of a fluid

Answer 33

Density, effective density and viscosity

Question 34

Reynolds number

Answer 34

Dimensionless quantity that indicates the extent to which a flow is laminar or turbulent.

Question 35

Re < 500 (low value)

Answer 35

Laminar flow indication

Question 36

Re > 2000 (high value)

Answer 36

Turbulent flow indication

Question 37

Define interference ripples

Answer 37

Formed by two waves going against each other at the same time.

Question 38

What are the 3 different types of sedimentary structures?

Answer 38

1. physical processes (erosional, depositional, deformational)
2. biologically (bioturbation, binding)
3. chemically

Question 39

What are marks?

Erosional structures

Answer 39

Marks happen when a little bigger blocks hit ground i river and leave marks behind

Question 40

What are sole marks?

Erosional structures

Answer 40

Sedimentary structures found on the base of certain strata, that indicate small-scalegrooves or irregularities.

Preserved > Sand on top making a cast of the erosional structure

Question 41

Diffenrence between ripples and dunes?

Answer 41

Ripples are smaller than dunes.
Ripples up to 10 cm