Final answer:
Sedimentary rocks are typically deposited in a horizontal orientation due to the gravitational effects that cause sediments to slide down steep surfaces, making flat surfaces the most stable areas for accumulation and layer formation.
Step-by-step explanation:
Sedimentary rocks are typically deposited in a horizontal orientation because sediments tend to slide down steeply dipping surfaces but can more easily accumulate on horizontal surfaces. This accumulation occurs due to the force of gravity, which causes loose materials to move downwards. Steeply dipping surfaces, on the other hand, present an angle of repose that tends to be unstable for sediment accumulation. The angle of repose is the steepest angle at which material remains stable without sliding down due to gravity. Horizontal or near-horizontal surfaces provide conditions where sediments can settle out of water or air and form layers without being disturbed by the constant downward movement that affects sloped surfaces.
Diagenesis, which refers to the physical and chemical changes occurring during the conversion of sediment to sedimentary rock, can operate on sediments regardless of orientation — not only on horizontally oriented sediments. Also, the presence of steeply inclined surfaces on Earth is undeniable, as observed in various geographical features such as mountain ranges and continental margins. Therefore, the correct explanation for why sedimentary rocks are typically deposited in a horizontal orientation is due to the gravitational effects and stability of sediments on flat surfaces compared to angled ones.