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Which fossils help geologists date and correlate Carboniferous rocks?
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Carboniferous Period
Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Carboniferous Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.
To date and correlate Carboniferous rocks, geologists rely on biostratigraphic data provided by specific groups of fossils that evolved rapidly and were widely distributed.1
The primary fossils used for these purposes include:
- Ammonoids: These extinct cephalopods are highly valued as index fossils due to their rapid evolutionary development throughout the Carboniferous, their easily recognizable features, and their wide geographic distribution in shallow marine waters.12
- Calcareous foraminifers: These unicellular organisms, particularly the fusulinids that appeared in the Pennsylvanian subperiod, are essential for correlating and dating various subdivisions of the Carboniferous.1
- Conodonts: These minute, toothlike microfossils are extremely useful for the identification and correlation of Paleozoic strata. They evolved rapidly, and their distinct assemblages allow geologists to define specific zones within the Carboniferous system.3
By integrating these fossil sequences with other methods, such as radiometric dating, geologists can establish a precise and consistent geologic time scale.45