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Which other fossils can geologists use to correlate Cretaceous rock layers?
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Cretaceous Period
Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Cretaceous Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.
Geologists use a wide variety of fossils to correlate Cretaceous rock layers, as no single group is effective for all environments or latitudes. While ammonites are the most widely employed, other significant fossils include:
- Microfossils: Planktonic foraminiferans, calcareous nannofossils, radiolarians, and calpionellids are valuable due to their drifting life habits, which allow for regional and sometimes global correlation. Ostracods are also used in specific regional contexts.1
- Bivalves: Inoceramid, rudist, and exogyrid bivalves are frequently used to zone Cretaceous sediments.1
- Echinoderms: Echinoids and crinoids serve as important markers for defining stage boundaries and local zoning.1
- Cephalopods: Belemnites are commonly used, particularly in boreal regions.1
- Plant Remains: Angiosperm pollen is essential for recognizing zones in nonmarine or coastal plain environments.12
- Vertebrates: In specific nonmarine settings, such as the North American western interior, the dinosaur genus Triceratops is used to identify the youngest Cretaceous biozone.1