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_238/Pb_206 age dating thee 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. 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 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. Superposition c. Original horizontality d. Both a and b e. Both b and c f. Both a, b and To which Geological period/periods do rocks units 'G' and 'k' belong? Why? ________ Can rock unit 'L' be correlated across the French Girl Valley ______? Why? ______ What does the 'wiggly line' at the base of Rock Unit 'L' represent? Which Geological Periods are missing? ___________
Explanation / Answer
1 answer - rock unit G
the sequence of events from oldest to youngest is as follows,
(oldest )A, B, C, D, E, F, H, I, J, G, K, L, M, N, O.(youngest)
answer 2 - both a and b
based on the order of superposition we can say that the ABCDEHIJ layers were deposited early and then G intruded the layers.
answer 3 -M is the youngest
answer 4 - superposition.
answer 5 - rock G is cambrian while K is devonian
why because the dating of these rock untis gave ages of 430 and 490 million years, which fall in devonian and cambrian in the geological time scale respectively.
answer - 8 yes
because the frenchgirl valley cuts through the rock unit L
8 answer - the line represents an unconformity
K is devonian in age while L is jurrasic in age according to the data given above, so we can say that odrovician, carboniferous, permian, triassic are the periods which are missed.