Final answer:
Horizontally directed, compressive stresses result in the folding of flat-lying sedimentary strata, forming structures like anticlines and synclines.
Step-by-step explanation:
The stress situation resulting in the folding of flat-lying sedimentary strata is b) horizontally directed, compressive stresses. In geology, folding occurs when the earth's crust is subjected to a compressive force, causing it to buckle and fold. This type of stress squeezes the layers together and results in structures such as anticlines and synclines.
For example, if a sequence of sedimentary layers is compressed horizontally, the layers will bend and fold rather than break, given they are relatively soft and pliable. The exact nature of these folds – whether they are anticlines (convex up) or synclines (concave up) – depends on the specific characteristics of the deformation event, such as the direction and intensity of the applied stress, as well as the properties of the rock itself.
Understanding the directional forces that cause such features is critical for geologists as they interpret the geologic history of a region and helps in identifying potential resources or assessing geological hazards.