The diagram below represents a simplified and hypothetical geological cross-sect
ID: 112528 • Letter: T
Question
The diagram below represents a simplified and hypothetical geological cross-section, depicting the relationship of various sedimentary and igneous rocks beneath the surface. A cross-section is a slice through the Earth's crust and in this image you are looking at a side-view of the rock layers that exist beneath that surface. Different sedimentary rock layers are identified 'A' through to 'O', although units 'K' and 'G' are two different types of igneous intrusion. U /Pb age dating the intrusion 'K' gave a date of 430 Million Years, age dating the intrusion 'G' gave a date of 490 Million Years and age dating 'A' gave 560 Million Years. Note, rock unit 'L' contains fossils (Ammonites), which are lower Jurassic age fossils. Note the presence of an Angular Unconformity at the base of rock unit 'L' You will need to refer to the Geological Time scale and apply one (or more) geological principal as you work through this assignment. 1) Of the following choices, which is the oldest rock? a. Granite 'G' b. Intrusion 'K' c. Rock unit 'I' What geological principle(s) did you use? a. Crosscutting relationships b. Superposition c. Original horizontality d. Both a and b e. Both b and c f. Both a, b and c a. Of the following choices, which is the youngest rock? a. Granite 'G' b. Intrusion 'K' c. Rock unit 'F' d. Rock unit 'I' e. Rock unit 'M' What geological principle(s) did you use? a. Crosscutting relationships b. Superpositon c. Original horizontality d. Both a and b e. Both b and c f. Both a, b and c To which Geological Period/Periods do rocks units 'G' & 'K' belong? _____ why? _____ Can rock unit 'L' be correlated across the French Giri Valley _____? Why? _____ What does the 'wiggly line' at the base of Rock Unit 'L' represent? Which Geological Periods are missing? _____Explanation / Answer
1. (c) Rock Unit I is the oldest rock.
2. The geological principles used were (f) both a,b,c
3. The youngest rock is (b) Intrusion k
4. The geological principle used is (a) cross-cutting relationships.
5. The rock unit G belong to the Ordovician Period
Reason: Rock unit G dates 490 million years which falls in Ordovician Period (438-505 million years)
The rock unit K belongs to Silurian Period.
Reason: Rock unit K dates 430 million years which falls in Silurian Period (408-430 million years).
8. Yes, the rock unit 'L' can be correlated across the French Girl Valley.
Reason: Both sides of the French Girl Valley contains the rock unit L and also the same fossils (Ammonites). So, according to the Principles of Faunal succession, Original Horizontality and Cross-cutting relationships, the rock unit L can be correlated across the valley.
8. The wiggy line at base of rock units represent the Line of Unconformity.
Devonian, Carboniferous, Permian and Triassic Periods are missing. This is because the intusion K just below the line of unconformity dates to Silurian and the rock unit L just above the unconformity dates to Jurassic. Therefore, the intermediate periods are missing.