A cross-section is a slice through the Earth\'s crust and in this image you are

Question

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_23d/Pb_206 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. Which is the oldest rock? Rock unit B Rock unit D Rock unit J Rock unit L Rock unit O What geological principle(s) did you use? Crosscutting relationships Superposition Original horizontality Both (1) and b Both b and c Both a, b and c Which is the oldest rock? Granite G Intrusion Rock unit F Rock unit I Rock unit L What geological principle(s) did you use? Crosscutting relationships Superposition Original horizontality Both a and b Both b and c Both a, b and c Which is the youngest: Granite G or Rock unit L? Why? To which Geological Period/Periods do rocks units 'G' & 'K' belong? Why? To which Geological ERA do to rocks units 'A'to 'J' belong? Which Geological PERIODS are missing between intrusion 'K' and rock unit 'L'? Give the equivalent amount of geological time between intrusion 'K' and rock unit 'L' in YEARS? Can rock unit 'L' be correlated across the French Girl Valley ? Why?

Explanation / Answer

1) rock unit B is the oldest

2) both b and c

3) rock I

4) both a b c

5) L because it is above unconformity

6) Cambrian and silurian

7) Proterozoic

8) odrovician , Silurian, Devonian, carboniferous, Permian and Triassic

9) 230 my approximately

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