Question

A deposit contains very little sand and mud, but instead a lot of broken-up carbonate shells of marine organisms. What was the likely depositional environment?

a) river
b) glacier
c) delta
d) reef

Answer 1

A deposit with little sand and mud but many broken-up carbonate shells of marine organisms most likely represents a reef environment, where calcareous organisms can grow and contribute to extensive carbonate deposits.

Step-by-step explanation:

If a deposit contains very little sand and mud, but a significant amount of broken-up carbonate shells of marine organisms, the likely depositional environment for such a deposit is a reef. Reefs are marine environments where conditions are conducive to the growth of coral and other calcareous organisms whose skeletal remains can form extensive carbonate deposits. Evidence from Figure 5.29, which shows sandstones and fossiliferous shales with oyster shells, supports the presence of a marine environment where oysters thrive, similar to the conditions required for reef development. The lack of sand and mud sediments indicates minimal influence from river or glacier deposits and the absence of delta characteristics. Additionally, the CHAPTER 3: BOUNDARIES section describes massive deposits of carbonate-producing marine algae, such as coccolithophores, which are also indicative of a marine reef environment. The close association of an abundance of shell material, including bivalves, corals, and trilobite imprints further points to this depositional environment reflecting a reef or a similar shallow, marine ecosystem.