Callovian
The Callovian is a stage of the Middle Jurassic, part of the International Chronostratigraphic Chart. It spans roughly from 166.1 to 163.5 million years ago, making it the middle subdivision of the Jurassic. The Callovian follows the Bathonian and precedes the Oxfordian. The lower and upper boundaries are defined by Global Boundary Stratotype Section and Point (GSSP) markers, tied to distinctive biostratigraphic signals such as ammonite faunas, and mark the transition to and from adjacent stages.
During the Callovian, global climate was generally warm with relatively high sea levels, producing widespread epicontinental
Biostratigraphy for the Callovian relies heavily on ammonites and other marine microfossils to define regional zones
Subdivisions within the Callovian are based on fauna and lithology observed in different regions, with biostratigraphic