The effects of solution during diagenesis are observable in which of the following?

The effects of solution during diagenesis are particularly observable in stylolites. Stylolites are irregular, serrated surfaces within sedimentary rocks that form through a process known as pressure dissolution. This occurs when mineral grains dissolve along certain planes under pressure, typically due to compaction and overburden in sedimentary environments. The solution of minerals can lead to the formation of these distinct features, which often have a characteristic appearance marked by the interlocking of mineral grains and the accumulation of non-dissolved residues along the stylolite surfaces.

While sedimentary layers, fossil assemblages, and mineral coatings can also be influenced by diagenetic processes, these phenomena do not specifically highlight the effects of solution in the same manner as stylolites. Sedimentary layers might show evidence of compaction and alteration but do not necessarily display the unique features of pressure dissolution that stylolites do. Similarly, fossil assemblages can be affected by various geological processes, but they do not illustrate the direct effects of solution. Mineral coatings might occur from precipitation of minerals but are not as directly linked to the solution processes as stylolites are. Hence, stylolites stand out as the best example of the observable effects of solution during diagenesis.