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

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

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)

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)

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)

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)

References Dickinson, W.; Suczek, C.; 1979. Plate tectonics and sandstone compositions. The American Association of Petroleum Geologists Bulletin 63: 2164-2184. Sames, C.; 1966. Morphometric data of some recent pebble associations and their application to ancient deposits. Journal of Sedimentary Petrology 36: 126-142.