Sea-level changes: group of answer choices a) are reflected by blankets of marine sediment called clathrates. b) are cyclic, consisting of episodes of transgression and regression. c) have been as great as 3,000 m during the phanerozoic eon. d) are termed eustatic if they affect only a local area.

Option (D)

Explanation:

Sea level refers to the average elevation of the ocean surface measured between the level of high and low tides. This sea level has been constantly changing in the geological past and these changes are caused due to several factors.

A sea level is considered to be eustatic if there occurs a global change in the total concentration of water that is being accumulated in the oceans. It also takes place if there occur changes in the shape and size of the ocean basin, which again directly causes changes in the volume of water it can hold.

Thus, the correct answer is option (D).