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Why are ammonoids useful for dating Carboniferous rock layers?
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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.
Ammonoids are highly effective for dating Carboniferous rock layers because they exhibit rapid evolutionary development throughout the period. This rapid evolution, combined with their wide geographic distribution, allows them to serve as reliable index fossils for biostratigraphic correlation.123
Along with calcareous foraminifers, ammonoids provide the essential data required to define and correlate the boundaries and various subdivisions of the Carboniferous Period. As free-swimming cephalopods, their presence in marine strata makes them particularly useful for establishing the age of these deposits.1