Final answer:
Concurrent range biozones are used by geologists to determine the age of geological units by matching fossil assemblages in rock layers. This form of biostratigraphic correlation is a relative dating technique that helps constrain the possible age ranges for rocks, which can be visually represented in a geologic map.
Step-by-step explanation:
In the context of biozones, a concurrent range occurs when two or more species have overlapping ranges in the geologic record. This provides a powerful tool for constraining the age of geological units. By identifying the specific fossils present in a layer of rock, and comparing these with known ranges of these fossils, geologists can determine a more precise age for the rock layer. This process is particularly useful in areas where the type of sediment (such as sandstone or shale) does not provide a clear indication of the rocks' age. Reliable correlations are made by matching rocks that contain the same assemblages of fossils, which indicates they were deposited during the same time period, a process known as biostratigraphic correlation.
For example, if an assemblage of fossils includes Species A, which lived from 100 to 200 million years ago, and Species B, which lived from 150 to 250 million years ago, the layer containing both species must be between 150 to 200 million years old. Therefore, the concurrent range zone helps narrow down the possible age of the rock layer. This kind of fossil-based dating is a form of relative dating, which, unlike absolute dating techniques that provide numerical ages, places rocks and events in chronological order without specifying how long ago they occurred.
Additionally, such correlations can be visualized and plotted on a geologic map, where different colors represent different geological ages and labels indicate specific formations, such as 'Pk' for the Permian Kaibab Formation. Understanding the age progression is crucial when interpreting features in sequence stratigraphy, such as identifying clinoforms in seismic images.