Bartonian

The Bartonian is a stage of the Paleogene period, representing the middle division of the Eocene epoch. It covers roughly 41.2 to 37.8 million years ago, a span used by geologists to subdivide sedimentary sequences of the mid-Eocene. The name Bartonian comes from Barton-on-Sea in Hampshire, England, where rocks of this age were studied and described in the 19th century.

Stratigraphically, the Bartonian sits between the Lutetian Stage to the west and the Priabonian Stage to the east, reflecting a global framework for correlating rocks and fossils across regions. In practice, its boundaries are defined by regional biostratigraphic markers, including the appearance and extinction patterns of certain microfossils, such as foraminifera and calcareous nannoplankton, which are used to correlate marine sequences worldwide.

During the Bartonian, global climates remained warm compared with modern conditions and sea levels were relatively high. This combination supported extensive shallow marine habitats as well as subtropical to temperate terrestrial vegetation in many regions. The fossil record from this interval yields rich marine assemblages and provides important evidence for the evolution and diversification of modern marine and some terrestrial groups that continued into the later Eocene.

The Bartonian is recognized in the International Chronostratigraphic Chart and is employed by scientists to synchronize data across continents, aiding studies of paleoceanography, paleoclimate, and biotic change during the middle part of the Eocene.