Santonian

The Santonian is a stage of the Late Cretaceous epoch in the International Chronostratigraphic Chart. It follows the Coniacian and precedes the Campanian, spanning roughly 86.3 to 83.6 million years ago.

In stratigraphy, the Santonian is defined by global fossil markers and is used to coordinate rock correlations. The lower boundary is commonly tied to changes in ammonite faunas and microfossils, while the upper boundary aligns with the onset of Campanian characteristic assemblages.

Paleogeography during the Santonian featured relatively high sea levels, which produced extensive shallow seas in some regions and led to widespread marine sedimentation such as limestone and chalk; other areas preserved continental or deltaic deposits.

The fossil record from Santonian rocks includes abundant marine invertebrates, notably ammonites and inoceramids, and provides important data on climate and biotic evolution in the Late Cretaceous. The stage is used by geologists and paleontologists to correlate rock sequences and study evolutionary and environmental changes during this interval.