Question

Which one of the following refers to overturned fold?

• A. A fold with an axial plane so inclined that one limb is upside down
• B. A trough-like shape with the youngest rocks in the center
• C. A bend with only one dipping limb
• D. An arch-like shape with the oldest rocks in the centre

Hint:

A fold is a bend in rock layers. Folds are classified by the orientation of their axial plane (the imaginary surface that splits the fold symmetrically) and their limbs (the two sides of the fold).

Answer 1

The Correct Option is A

Step 1: Recall how folds are described.
A fold is a bend in rock layers, described by its axial plane and its two limbs.

Step 2: Rule out the trough option.
A trough-like shape with the youngest rocks in the centre is a syncline, not an overturned fold.

Step 3: Rule out the single-limb option.
A bend with only one dipping limb describes a monocline, not an overturned fold.

Step 4: Rule out the arch option.
An arch with the oldest rocks in the centre is an anticline.

Step 5: Identify the overturned fold.
When the axial plane is tilted so far that one limb is rotated past vertical, that limb ends up upside down. That is exactly an overturned fold.

Step 6: Choose the answer.
The fold with an axial plane so inclined that one limb is upside down, option 1.
\[ \boxed{\text{A fold with an axial plane so inclined that one limb is upside down}} \]