Black Jurassic (Early Jurassic) – the Posidonia Shale Sea

During of the Early Jurassic, Central Europe was covered by an epicontinental sea up to 150 metres deep. Extreme stratification of the seawater is the reason for the formation of unique fossils at that time. Warm, less salty water floated on top of cool, dense water of higher salinity. The unequal density of these two layers resulted in little mixing of the water column. Thus, not enough oxygen-rich surface water entered the lower layers to compensate for oxygen consumption by bacteria decomposing organic matter at the sea floor. The consequences were anaerobic decay at the bottom, generating toxic hydrogen sulphide, and the formation of a “death zone” limiting oxygen-dependent life. Sunken carcasses of ichthyosaurs, for instance, were therefore neither eaten by scavengers nor dispersed by currents. After millions of years, they remain almost completely preserved.

Life on the coast

Ichthyosaur: Temnodontosaurus trigonodon

Ichthyosaur: Stenopterygius quadriscissus

Ichthyosaur: Stenopterygius quadriscissus

Sea crocodile: Steneosaurus bollensis

Shark: Hybodus hauffianus

Sea lily: Seirocrinus subangularis

Ammonites: ‘Arieten-Pflaster’ – a little older but still Lower Jurassic Sea