Black Jura

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Lithostratigraphy of the South German Jura .
Abbreviations:
  • Humph.-Fm. = Humphriesioolite Formation
  • L.Bk-Fm = Lying bench lime formation
  • H.Bk-Fm = hanging bank lime formation
  • Zm-Fm = cement marl formation
  • S.-Fm = Solnhofen formation
  • Rö.-Fm = Rögling formation
  • U.-Fm = Usseltal formation
  • Mö.-Fm = Mörnshein formation
  • N.-Fm = Neuburg formation
  • R.-Fm = Rennertshofen formation

    • The lowest of the three lithostratigraphic groups of the South German Jura is referred to as the Black Jura , whereby the South German Jura is not understood as a geographical term, but rather as a lithostratigraphic term in the sense of a lithostratigraphic supergroup .

    In the past and in part still today in popular scientific literature, this term was equated with the chronostratigraphic series of the Lower Jurassic . This is not entirely correct, however, as the Black Jura does not exactly coincide with the chronostratigraphic boundaries of the Lower Jurassic. In the past (and in some cases still today) the term lias, which was often used synonymously, should no longer be used in the southern German Jura or the Alpine region (as with the Lias marl ). Lias or North German Lias is expected to be reserved for the approximately time-equivalent lithostratigraphic unit in the North German Jura.

    The Black Jurassic was deposited between about 199 and 175 million years ago ( Sinemurian to Toarcian ). The Black Jura follows the lithostratigraphic group of Keuper and is overlaid by the lithostratigraphic group of the Brown Jura (Dogger).

    history

    The term Schwarzer Jura goes back to Leopold von Buch , who proposed it in 1837 in a lecture at the Royal Academy of Sciences in Berlin; the lecture version was not published until 1839. Friedrich August Quenstedt defined the term in his work Das Flözgebirge Würtembergs, published in 1843, for the first time in today's sense. The name was given because of the dark weathering colors of the rocks of the Black Jura. Previously and z. Sometimes the terms Lias and Lower Jurassic are still used in popular scientific literature. Today the term Unterjura describes a chronostratigraphic series of the Jura . The term Lias will probably be defined in the combination of North German Lias for a lithostratigraphic rock unit in the North German Jura. In the Quenstedt division of the South German Jura, the Black Jura is subdivided into six sections, which are designated with α, β, γ, δ, ε and ζ, for example Schwarzer Jura ε or Black Jura ε. Quenstedt's name with the Greek letters is often combined with the term Lias in popular scientific literature (for example Lias ε).

    definition

    The lower limit of the Black Jura (and thus also the lower limit of the lithostratigraphic supergroup of the South German Jura and also the Psilonote clay formation ) is the basis of the Psilonote bank. The upper limit of the Black Jurassic is the base of the Opalinus Clay Formation . The Black Jura consists mainly of dark sandstones, clays, marls and limestone, which z. Some of them can also be bituminous ( e.g. Posidonia schist formation ). The maximum thickness is about 80 m.

    The lithostratigraphic unit of the Black Jura begins biostratigraphically mostly in the ammonite zone of the Psiloceras planorbis . Ammonites of the Neophyllites horizon below the Psiloceras planorbis subzone have only been found in a few profiles . So far, however, the horizons of Psiloceras erugatum and Psiloceras tillmanni (so-called Praeplanorbis layers) of the Lower Hettangium have not been detected. The basal hettangium is missing in the southern German Jura or is not documented by deposits. The base of the Black Jura does not exactly coincide with the beginning of the international Jura system, but is somewhat higher. The lower limit of the Opalinus Clay Formation (and thus the upper limit of the Black Jura), on the other hand, coincides fairly well with the chronostratigraphic Lower Jurassic / Middle Jurassic boundary in most areas of the South German Jura . Local starts the lower limit of Opalinuston formation, for example in the Upper Rhine area and Upper Franconia, but already in the Pleydellia-aalensis zone, the top zone of the Ammonites Toarciums the Lower Jurassic series. The Black Jura ends here before the start of the international Middle Jura series.

    Breakdown

    The lithostratigraphic unit of the Black Jurassic is currently divided into 12 formations, which are not all on top of each other. Also represented regionally. The formations in their sequence from top to bottom, regional interlocking are side by side.

    Fossil sites

    The fossil deposit Holzmaden in the Posidonia schist formation is due to its excellently preserved fossils, the z. Some of them still show body outlines (partial soft tissue preservation!) Became known worldwide.

    literature

    • Gert Bloos, Gerd Dietl & Günter Schweigert: The Jura of Southern Germany in the Stratigraphic Table of Germany 2002. Newsletters on Stratigraphy, 41 (1-3): 263-277, Stuttgart 2005, ISSN  0078-0421
    • Eckhard Mönnig: The Jura of Northern Germany in the Stratigraphic Table of Germany 2002. Newsletters on Stratigraphy, 41 (1-3): 253-261, Stuttgart 2005
    • Friedrich August Quenstedt: The Flözgebirge Würtembergs. With special consideration for the Jura . Laupp'sche Buchhandlung publishing house, Tübingen 1843.

    Web links

    Commons : Black Jura  - Collection of images, videos and audio files