Final answer:
The fold identified is a syncline, which is recognized by its concave shape with youngest rocks at the center of the fold. Synclines and anticlines are typically formed by compressional stress from tectonic forces.
Step-by-step explanation:
The fold pictured is a syncline. Synclines are geological folds, typically concave in shape, where the youngest rocks are found at the center and the oldest at the outer flanks. In an anticline, the oldest rocks are at the core of the fold, and the youngest are on the outside. The defining characteristic of a syncline is this age progression of the rock layers.
The visual cues for identifying a syncline in a photograph or diagram include noting the concave shape of the strata and the sequence of the rock layers' ages. Geologic maps often use symbols to depict synclines, usually shown as a line with a trough shape on top indicating the concave nature of the fold.
If we consider geological stress, synclines and anticlines are usually formed as a result of compressional stress due to tectonic forces that push the earth's crust inward and upward, resulting in the folding of rock layers. This stress causes the rock layers to buckle and fold into the shapes we identify as synclines and anticlines.