Struggling with Geology Questions? Get Help Here!

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Homework Statement

My geology profesor gave us 50 questions to practice and check our progress. I have manged to answer all of them but two:

Why would you study a volcanic rock in a sedimentary succession where oil is found?

You work in an area where your sedimentary rock is host to petroleum but the age of deposition of the sediment is unknown. A granite intrudes this rock. Why study the granite?

I really don't know how to answer these two.

Homework Equations

The Attempt at a Solution

I have no clue -- can't find anything related to this in my textbook.

 

[update]

Hi, I know the approximate answer on your second question: the sedimentary rock had been deposited before granite has intruded the rock. So by studying the radioactive minerals of granite we can determine the approximate age of granite. And our sedimentary rock is a bit older, we could even say the same age.
Do you have an answer for following question? : to which geological event relate the rocks in our city?