1. Do you think the types of clasts present in ancient conglomerates can be used to interpret the tectonic setting in which the conglomerate formed?
2.7Ga conglomerate from Witwatersrand

2. Generally speaking,
Particle history can only be traced back to the last effective shaping event caused by
Littoral
Fluviatile or
Detrital conditions
Also, the lithological
makeup of the clasts can
tell about its origin
Ancient conglomerate from Switzerland

3. Method of Measuring σ – Degree of elongation π – Degree of flatness
percentage of breadth l compared with greatest length L
π – Degree of flatness
percentage of thickness E compared with greatest length L
ρ – Roundness
Percentage of convex
parts the exterior
circumference
Most important and most
characteristic
Examples of ρ
(Sames, 1966)

4. Example – Tama River, Japan
Fluviatile contains a percentage of angular components
Littoral tends to contain rounded particles
Difference due to movement
Pebbles in rivers move by shoving and rolling with interrupted times of rest; less sorted
Littoral conditions favor intensified rolling;
more sorted
(Sames, 1966)

5. Determination Graph Graph shows the relationship between ρ and σ
Shows littoral conditions produce more round and slightly less elongate clasts
Also, shows what turbulent rivers and debris flows produce
(Sames, 1966)

6. Clast Composition
The amount of specific minerals can tell a clast’s most likely origin
Q – total quartzose grains, F – total feldspar grains, L – total unstable lithic fragments,
Qm – monocrystalline quartz grains, Lt – polycrystalline litic fragments
(Dickinson et al., 1979)

7. References
Dickinson, W.; Suczek, C.; Plate tectonics and sandstone
compositions. The American Association of Petroleum
Geologists Bulletin 63:
Sames, C.; Morphometric data of some recent pebble
associations and their application to ancient deposits.
Journal of Sedimentary Petrology 36: