Which of the following is a correct association of depositional environment and fossil assemblages?

• A. Coral reef with trilobites
• B. Deltaic sandstones with fossil wood
• C. Deep-sea mud with dinosaurs
• D. Glacial till with reef fossils

Answer: (B)

Fossil assemblages reflect the conditions of the environment where they were deposited. In a deltaic setting, rivers bring in plant material from the land and deposit sands as the delta builds outward. Those sands can rapidly bury and preserve pieces of wood, so finding fossil wood within deltaic sandstones is a natural and common combination.

In contrast, a coral reef is a shallow, warm marine system dominated by corals and related invertebrates, so trilobites aren’t a typical or expected major component of a reef assemblage. Deep-sea mud represents a very different, deeper and often food-poor setting, where terrestrial dinosaurs could not be preserved. Glacial till is icy, poorly sorted material from glaciers and generally lacks reef-building organisms, making reef fossils unlikely there. Thus, deltaic sandstones with fossil wood best matches the depositional environment–fossil assemblage pairing.