(TB) Paleocurrents Flashcards
Name five possible unidirectional paleocurrent indicators
- Cross-lamination
- Cross-bedding
- Large scale cross-bedding
- Clast imbrication
- Flue casts
Where would one expect to see cross-lamination?
Ripples
Where would one expect to see cross-bedding?
Aeolian and sub-aqueous dunes
Where would one expect to see large scale cross-bedding?
Bars - shallow marine and deltas
What are flute casts?
Local scours created by lifted vortices in a flow - asymmetric mark where the steep side is upstream
What are flow axis indicators?
Paleocurrent indicators which have two possible directions
When are flow axis indicators most useful?
When found in proximity to unidirectional paleocurrent indicators
Name four possible flow axis indicators
- Primary current lineations
- Groove casts
- Elongate clast orientation
- Channel/scar margins
What are groove casts?
grooves created by movement of a particle within the flow to create a groove
Explain “elongate clast orientation”
Wood or elongate minerals which line up with the flow
What is the most commonly observed indicator of paleocurrents?
Cross-strata
What is needed to measure cross-stratification?
Two 90 degrees vertical faces - faces at a right angle OR a horizontal surface which cuts through the cross-bedding
Why is a single vertical cut through cross-stratification not enough to determine paleo-flow direction?
Gives only the apparent dip
What grain size is needed to observe imbrication?
Gravel/conglomerate
What are the two main potential complicators for observing paleo-flow in the geological record
Deformation of flow or tectonic changes in orientation
Why is it important to record the nature of the data in the field? (i.e. facies)
Some forms may act differently in different facies
What is the best way to represent statistical paleo-flow data?
Rose diagram - incrementally, i.e. 11-20 degrees, 21-30 degrees
Aside from the data correctly displayed on a rose diagram, what other piece of information needs to be supplied a long side the diagram?
The number of data points, i.e. N=50
How does one calculate the mean of paleo-current data?
Need to translate all of the bearings into rectangular co-ordinates
What is the equations for translating paleo-current data into rectangular co-ordinates?
x=sinθ & y=cosθ
Add all x’s and add all y’s to determine the mean and thus the quadrant
Why are bedding structures useful to hydrocarbon exploration?
Indication of the lateral forms and thus reservoir potential
