What type of fold is characterized as resembling a "sink" with the youngest rock layers at the center?

A fold characterized as resembling a "sink" with the youngest rock layers at the center is known as a syncline. In geological terms, a syncline is formed when rock layers bend downward in a U-shape. This structural feature occurs due to compressional forces that cause the crust to deform. In a syncline, the youngest rock layers are located at the center of the fold, with progressively older layers on the outer edges.

Understanding the formation of synclines is essential as they often indicate past tectonic activity and can influence the distribution of resources and groundwater in the area. In contrast, an anticline, which is the opposite of a syncline, has the oldest rock layers at its core and appears as an upward arching structure. Xenoliths refer to fragments of rock that are embedded in a larger rock body but are not relevant to folding. An angular unconformity is a geological feature that represents a gap in the geological record where layers of sedimentary rock have been tilted and then eroded before subsequent layers were deposited, which doesn’t describe a fold. Thus, the characteristics of a syncline clearly delineate it as the correct answer.