Early Jurassic
The Lower Jurassic (also Lower Jurassic ) is the international chronostratigraphic designation for the lower series of the Jura in the Earth's history. In the older literature, sometimes even in the popular scientific literature of the stratigraphic section is often referred to as Lias or black Jura ( Jura Black ). These terms are now considered only as lithostratigraphic units. The Lower Jurassic following the series of the Upper Triassic (or Upper Triassic ) or the top step of the Triassic, the Rhaetian. About the Lower Jurassic the series follows the Middle Jurassic ( Middle Jurassic ). The Lower Jurassic is roughly the period from 201.3 to 174.1 million years ago.
Older terms
For this stratigraphic series of the Jura, the terms Black Jura ( Jura Black ) Lias and may not be used. They are reserved for rock units. Under the new lithostratigraphic division of the South German law, the term Black Jura is used in the sense of a group of formations. In the Jura, Northern and Central Germany, the lowermost lithostratigraphic group is seen provisionally called Lias ( in the form of North German Lias ). Lias and Black Jura are defined purely lithological or with the methods of lithostratigraphy, the boundaries are purely determined by changes in the rock characteristics. Black Jura and North German Lias correspond in time essentially the Jurassic series, but only approximately. The deposits of the Black Jura and North German Lias put an end only after the Trias-/Jura-Grenze and regionally before the Unter-/Mitteljura-Grenze. Also between the individual formations of the North German Lias and the Black Jura hiatuses are present again and again. North German Lias and Black Jura are essentially characterized by dark shales and marls, which are now divided into numerous formations. The terms in the North German law have so far defined only preliminary and not yet final.
Chronostratigraphic subdivision of the Lower Jurassic
The Lower Jurassic is divided by the following international levels:
- System: Jurassic ( 201.3 to 145 mya ) Series: Upper Jurassic ( 163.5 to 145 mya )
- Series: Middle Jurassic ( 174.1 to 163.5 mya )
- Series: Lower Jurassic ( 201.3 to 174.1 mya ) Level: Toarcian ( 182.7 to 174.1 mya )
- Stage: Pliensbachian ( 190.8 to 182.7 mya )
- Level: Sinemurian ( 199.3 to 190.8 mya )
- Level: Hettangian ( 201.3 to 199.3 mya )
Faunas
A common fossil of the Lower Jurassic is the oyster -like shell Gryphaea. The black Posidonienschiefer with its famous fossil deposit in wood grubs in Baden- Württemberg is dated in the Toarcian stage of the Early Jurassic series.