Posidonia Shale

The Posidonia Shale is an Early Jurassic, Toarcian age geological formation found across Germany, northern Switzerland, northwestern Austria, southern Luxembourg and the Netherlands, with its major outcrops near Holzmaden and Dotternhausen in southwestern Germany. It consists of black shales made of fine grained sediments and bituminous limestones deposited in fine alternating layers, along with oil shales, nodular claystone and lime mudstone, laid down 184 to 178 million years ago in a shallow epicontinental sea under strongly reducing, oxygen poor conditions during the Toarcian oceanic anoxic event. These anoxic conditions trapped and exceptionally preserved complete fossils of marine fish and reptiles, making the formation an important source of Jurassic marine fossils. It takes its name from the fossil bivalve historically called Posidonia bronni, though that generic name is now considered invalid.