Lecture 4 - Sedimentary Structures

Question 1

Define bedding:

Answer 1

Sedimentary layer thicker than 1cm (can be done in hours or 100s of years)

Question 2

Define lamination:

Answer 2

Fine scale bedding, less that 1 cm thick

Question 3

What effects the type of bedforms made?

Answer 3

Verlocity of the flow, grain size, depth of flow.

Question 4

What can happen to these bedrocks to help us learn about the past

Answer 4

these structures can become fossilised

Question 5

What does the absense of lamination show?

Answer 5

Bioturbidation

Question 6

Can you draw a diagram about the formation of ripples?

Answer 6

Yes

Question 7

What are the different bedform types?

Answer 7

Ripples
Sandwaves
Dunes

Question 8

What gorms waves as aposses to ripples

Answer 8

Waves are formed by two currents meaning deposition and eroisin is equal on either side

Question 9

Ripples. Slowest to fastest

Answer 9

straight crested
sinuous
catenary

Question 10

Dunes slowest to fastst

Answer 10

lunate

lingouid

Question 11

what are the differencens between two dimesnial and three dimesnal crests

Answer 11

straight crested ripples are the only 2D ones as they are just parrel lines

Question 12

What is the Herring bone cross bedding associated with?

Answer 12

Tidal regieme, two undirectional currents at 180 degrees to each other. although it can be difficult to distingues between these waves and ripples.

Question 13

In general what sets waves apart

Answer 13

Sharper crests, more symetrical cross section.

Question 14

The above are straight unidrection currents what are the others more complex currents known as

Answer 14

Turbidity currents

Question 15

What are turbidity currents

Answer 15

Sediment laden (turbid), fast flowing, common on seafloor. sediment often disturbed by storms or earth quakes.

Question 16

Can you draw a flute mark? also explain a flute mark

Answer 16

Sand laded current erodes and marks cohesivce mud prior to deposition creating a half conical shape in the mud. These are then in filled with depoistion creating smooth conical flute marks.

Question 17

What are groove marks?

Answer 17

Objects carried in flow groove into the mud, the space is filled in by the turbidite sediment

Question 18

Wjat is graded bedding?

Answer 18

Graded bedding is where the larger rocks settle out first and then as it goes up the smaller sediments settle.

Question 19

What is the sequence of these graded beds called

Answer 19

Bouma Sequence

Question 20

What do mudcracks show?

Answer 20

Subarial exposure, in a dry climate causing the rocks to dry out.

Question 21

What are trace fossils?

Answer 21

These are “traces” or marks in the sediment that are made by an activity, they are not classfied by organisms

Question 22

What are the two mains groups of trace fossils?

Answer 22

1) formed on sediment surface such as tracks and trails EPIBENTHIC
2) formed within a sediment such as burrows ENDOBENTHIC

Question 23

Sedimentation rates, what do borings or burrows show

Answer 23

There is zero sedimenation

Question 24

Intenstly bioturbated sediment indicates

Answer 24

slow sedimentation

Question 25

U shaped burrows inidcate…

Answer 25

rapid sedimenation

Question 26

What can these be used to do (with regards to superposition)

Answer 26

They can be used to work out if there bed has been turned upside down (anticline)