Final answer:
The statement that biostratigraphic units are correlated over great distances based on their fossil assemblages is true. Biostratigraphy uses fossils to determine the relative age of sedimentary rocks and to correlate these rocks even if they are located far apart.
Step-by-step explanation:
The statement is true: biostratigraphic units are indeed correlated over great distances based on their fossil assemblages. Biostratigraphy is a branch of stratigraphy that utilizes fossils to determine the relative ages of sedimentary rocks and to correlate these rocks over vast areas. William Smith's work in the early 19th century laid the foundation for biostratigraphy when he noticed that fossil assemblages could be used to correlate sedimentary layers across different regions. By identifying and matching similar fossils, geologists can confirm that different rock units were deposited at the same time despite being located far apart, a process known as biostratigraphic correlation.
Geologists perform lithostratigraphic correlation by matching the physical characteristics of rock layers, but when these characteristics are not sufficiently distinctive, fossils within the rock can provide vital information for correlation. For example, if two different rock layers, like sandstone and shale, are composed of different sediment types but contain the same fossil species, it indicates that they were likely deposited during the same geological period. Exercises in biostratigraphy often involve identifying and correlating layers based on fossil content, labeling any identified unconformities, and using this information to interpret geological histories and past environments.