The diagram below represents a simplified and hypothetical geological cross-sect
ID: 112715 • 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. 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 $60 Million Yeats. 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 horizontally d. Both a and b e. Both 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 horizontally d. Both a and b e. Both b and c To which Geological Period/Periods do rocks units G & 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
5. Silurian and Ordovician. Reason behind the age of G and K: in the given data it is specified that G and K age are 490 million and 430 million years respectively. This data corresponds to Silurian and Ordovician ages. The missing geological periods are triassic, Permian, Pennsylvanian, Mississippian, Devonian. The reason is that the fossils belong to lower jurassic era which is 203.1 million years old. The granite unit is 490 million years old. So the geologic period between 203.1 and 490 million years are missing in the unconformity.