Question

question 4
the sequence of a - d represents what?
transgression
regression
unconformity
land deposits

Explanation:

Transgression refers to the advance of a sea or lake over land, resulting in the deposition of sediments. In the geological cross - section, if the sequence from A to D shows a progression where each successive layer (from A to D) represents a deeper water environment (for example, if A is a terrestrial or shallow - water deposit and D is a deeper - water deposit), this is characteristic of a transgression. Regression is the opposite (sea or lake retreating, shallower water deposits). Unconformity is a gap in the geological record (a surface of erosion or non - deposition). Land deposits would typically be more terrestrial - looking (e.g., with soil horizons, less fossiliferous in a marine sense).

Answer:

Transgression