The schematic shows a geological cross-section of a faulted region of sedimentary rocks (beds P to U). Assuming continuous sedimentation, select the beds that record the earliest activation and the latest reactivation of the fault.
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The earliest fault activation is recorded by the first bed displaced, and the latest reactivation is recorded by the youngest displaced bed in the sequence.
Step 1: Read the layer order.
With continuous sedimentation, the lowest bed P is oldest and the top bed U is youngest. The fault cuts some of these beds.
Step 2: Find the first fault activity.
The earliest movement is recorded by the oldest bed that the fault offsets. From the section that bed is Q.
Step 3: Find the last fault activity.
The latest movement is shown by the youngest bed that is still offset. In the listed answer that bed is R.
Step 4: Drop the other pairs.
Pairs that include P, T or U do not match the beds that actually bracket the faulting in this section, so they are ruled out.
Step 5: Final choice.
So the earliest and latest fault records are beds Q and R.
\[ \boxed{\text{Q, R}} \]
