Of the following options which is the oldest rock? A) granite G b) Intrusion K C

Question

Of the following options which is the oldest rock? A) granite G b) Intrusion K C) rock unit I D) rock unit L E) rock unit O
What principle or principles can be used ? A. Crosscutting realtionship B. Superposition C. Orginal horizontality Read carefully, study the cross-section: answer all questions 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. U2s8/Pb2o8 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

Explanation / Answer

Cross cutting relationship principle can be used here where one rock literally cuts across another, like when igneous bodies are emplaced in fractures within a stack os sedimentary beds. Here the rock unit I is the oldest among all other rock units.

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