If you are examining unconformities in the Grand Canyon, the oldest gap in the rock record is no more than 200 million years between the igneous and metamorphic rocks in the gorge to the younger sedimentary rocks directly above them.

Question

Quizplus · Accepted Answer

The statement is incorrect. The oldest unconformity in the Grand Canyon is between the igneous and metamorphic rocks (Vishnu Basement Rocks) and the overlying sedimentary rocks, which separates rocks that are about 1.8 billion years old from younger rocks that are about 500 million years old.

If You Are Examining Unconformities in the Grand Canyon, the Oldest