RELATIVE DATING OF ROCKS

Relative dating of rocks means putting rock layers in chronological order. The method of reading the order is called stratigraphy.

Law of Superposition - Sedimentary layers are deposited depending on the time sequence, with the oldest on the bottom and youngest on top.
Principle of  Original Horizontality - Rock layers form in a horizontal position
Principle of cross-cutting relationships - Faults are younger than the rocks they cut.

A - Granite: older

B - Basalt: younger

E - Schist: oldest

B - Basalt

C - Limestone

D - Sandstone

A - Siltstone: youngest

G - Conglomerate: oldest

C - Siltstone

A - Limestone

B - Fault

F - Limestone

H - Sandstone

D - Shale

I - Shale

E - Fault - youngest

Geological history of the area where Cross Section C is found:


The rocks were cut by fault (E) - last event to happen
Shale (I) was formed a little on top of Shale (D)
Shale (D) was formed on top of Sandstone (H)
Sandstone (H) formed on top of Limestone (A) and Limestone (F)
Limestone (F) was formed a little on top of Limestone (A)
The rocks were cut by fault (B)
Limestone (A) was formed
Siltstone (C) was formed
Conglomerates (G) were laid down flat - first event to happen




References:
http://www.earthlearningidea.com/PDF/40_What_is_the_geological_history.pdf
https://www.iris.edu/hq/inclass/animation/stratigraphy_geologic_history_of_a_region_in_cross_section
https://www.sciencelearn.org.nz/resources/1485-relative-dating