According to the principle of original horizontality, what happens when we see folded or tilted sedimentary layers?

The principle of original horizontality states that layers of sediment are originally deposited in horizontal or nearly horizontal layers due to the influence of gravity. When sedimentary layers are observed to be folded or tilted, it indicates that they have undergone some form of tectonic activity or deformation after their original deposition. This means that while they were initially laid down horizontally, subsequent geological processes, such as folding during mountain-building events or tectonic shifts, caused the layers to become tilted or folded.

Therefore, recognizing that these sedimentary layers must have originally been horizontal helps geologists understand the geological history and processes that have affected the area since those layers were deposited. The current folded or tilted state serves as evidence of not only the past depositional environment but also the dynamic forces that have reshaped the Earth’s crust over time.