Sinemurian

The Sinemurian is the earliest age of the Early Jurassic epoch in the international timescale. It spans roughly from 199.3 to 190.8 million years ago, lying after the Hettangian and before the Pliensbachian. The stage is commonly divided into Lower Sinemurian and Upper Sinemurian in many stratigraphic schemes, with regional subdivisions varying by source.

Stratigraphy and boundaries are defined in relation to the adjacent stages: the lower boundary marks the boundary with the Hettangian, and the upper boundary marks the boundary with the Pliensbachian. Global correlation relies heavily on ammonite and other fossil zonations, along with available radiometric data from suitable sequences.

Paleogeography and climate during the Sinemurian were influenced by the continued breakup of the supercontinent Pangaea. Global climate was generally warm, with relatively high sea levels that produced extensive shallow epicontinental seas. Sedimentary rocks from this time are widespread in Europe, Asia, and North America, reflecting alternating marine and nearshore environments.

Biota and ecology were characterized by broad marine invertebrate diversity, especially ammonites and belemnites, as well as marine reptiles in suitable deposits. On land, gymnosperms and primitive dinosaurs coexisted with various plant and invertebrate communities, contributing to a developing Jurassic ecosystem mosaic.

In modern stratigraphy, the Sinemurian is used as a standard interval for correlating Early Jurassic rocks across continents. Its ammonite- and fossil-based zoonomies remain central to regional lithostratigraphic and biostratigraphic frameworks.