Sinemurian

The Sinemurian is an important time period in Earth's history, part of the Early or Lower Jurassic Epoch. It lasted from about 199.5 million years ago to 192.9 million years ago. In geological studies, the Sinemurian is both an age and a stage, meaning it helps scientists organize and understand the sequence of events during this ancient time.

Right before the Sinemurian was the Hettangian period, and it was followed by the Pliensbachian. These periods are part of how scientists break down the Jurassic time to study changes in life and Earth’s surface.

In Europe, especially in places like Great Britain, rocks formed during the Sinemurian and the Hettangian are grouped together and called the lower Lias. In Britain, these rocks are famously known as the Blue Lias, a term that refers to the distinctive blue-gray layers often found in Jurassic rock formations.

Stratigraphic definitions

The Sinemurian Stage was introduced into science by French scientist Alcide d'Orbigny in 1842. It is named after the town of Semur-en-Auxois in France. This area has special rocky soil made from old limestone.

Scientists mark the start of the Sinemurian by looking for certain ancient sea creatures called ammonites, like the groups Vermiceras and Metophioceras. A key reference point for this stage is found in a cliff near East Quantoxhead in England. The end of the Sinemurian is marked by the appearance of other ammonites, such as Bifericeras donovani and Apoderoceras.