(TB) Paleocurrents

Question 1

Name five possible unidirectional paleocurrent indicators

Answer 1

1. Cross-lamination
2. Cross-bedding
3. Large scale cross-bedding
4. Clast imbrication
5. Flue casts

Question 2

Where would one expect to see cross-lamination?

Answer 2

Ripples

Question 3

Where would one expect to see cross-bedding?

Answer 3

Aeolian and sub-aqueous dunes

Question 4

Where would one expect to see large scale cross-bedding?

Answer 4

Bars - shallow marine and deltas

Question 5

What are flute casts?

Answer 5

Local scours created by lifted vortices in a flow - asymmetric mark where the steep side is upstream

Question 6

What are flow axis indicators?

Answer 6

Paleocurrent indicators which have two possible directions

Question 7

When are flow axis indicators most useful?

Answer 7

When found in proximity to unidirectional paleocurrent indicators

Question 8

Name four possible flow axis indicators

Answer 8

1. Primary current lineations
2. Groove casts
3. Elongate clast orientation
4. Channel/scar margins

Question 9

What are groove casts?

Answer 9

grooves created by movement of a particle within the flow to create a groove

Question 10

Explain “elongate clast orientation”

Answer 10

Wood or elongate minerals which line up with the flow

Question 11

What is the most commonly observed indicator of paleocurrents?

Answer 11

Cross-strata

Question 12

What is needed to measure cross-stratification?

Answer 12

Two 90 degrees vertical faces - faces at a right angle OR a horizontal surface which cuts through the cross-bedding

Question 13

Why is a single vertical cut through cross-stratification not enough to determine paleo-flow direction?

Answer 13

Gives only the apparent dip

Question 14

What grain size is needed to observe imbrication?

Answer 14

Gravel/conglomerate

Question 15

What are the two main potential complicators for observing paleo-flow in the geological record

Answer 15

Deformation of flow or tectonic changes in orientation

Question 16

Why is it important to record the nature of the data in the field? (i.e. facies)

Answer 16

Some forms may act differently in different facies

Question 17

What is the best way to represent statistical paleo-flow data?

Answer 17

Rose diagram - incrementally, i.e. 11-20 degrees, 21-30 degrees

Question 18

Aside from the data correctly displayed on a rose diagram, what other piece of information needs to be supplied a long side the diagram?

Answer 18

The number of data points, i.e. N=50

Question 19

How does one calculate the mean of paleo-current data?

Answer 19

Need to translate all of the bearings into rectangular co-ordinates

Question 20

What is the equations for translating paleo-current data into rectangular co-ordinates?

Answer 20

x=sinθ & y=cosθ

Add all x’s and add all y’s to determine the mean and thus the quadrant

Question 21

Why are bedding structures useful to hydrocarbon exploration?

Answer 21

Indication of the lateral forms and thus reservoir potential