Brown 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 middle of the three lithostratigraphic groups of the South German Jura is referred to as the Brauner Jura (also Braunjura ) , whereby the South German Jura is not understood as a geographical term, but 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 is equated with the chronostratigraphic series of the Middle Jurassic . This is not entirely correct, as the Brown Jura does not exactly coincide with the chronostratigraphic boundaries of the Central Jurassic. The term dogger, which was often used synonymously in the past (and in some cases still today), should no longer be used in the southern German Jura. The term Dogger is expected to be reserved for the roughly equivalent lithostratigraphic unit in the North German Jura. The sediments of the Brown Jurassic were deposited between 175 and 161 million years ago. The Brown Jura follows the lithostratigraphic group of the Black Jura and is overlaid by the lithostratigraphic group of the White Jura .

    history

    The term Brauner 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 for the first time in its current sense in his work “Das Flözgebirge Würtembergs”, published in 1843. The name was given because of the predominantly brown weathering colors of the rocks of the Brown Jura. In the past, the terms Dogger and Middle Jura (or Middle Jura) were often used as synonyms . The term Middle Jurassic refers to a chronostratigraphic series of the Jurassic . The term Dogger or North German Dogger will likely be reserved for a lithostratigraphic rock unit in the North German Jura. The defined boundaries of the Middle Jura, Brown Jura and North German Dogger therefore differ. In the Quenstedt structure of the South German Jura, the Brown Jura is subdivided into six sections, which are designated as α, β, γ, δ, ε and ζ, e.g. B. Brown Jura β or Brown Jura β. In popular scientific literature, these terms are often combined with the term Dogger (e.g. Dogger β).

    definition

    The lower limit of the Brown Jura is the base of the Opalinus Clay Formation , a package of claystones up to 120 m thick. The upper limit of the Brown Jura is the base of the first light limestone bank of the Impressamergel Formation of the White Jura. The Brown Jura consists predominantly of iron-rich sandstones (the iron sandstone ), clays, marls and limes, partly with iron oxides that weather brownish. The maximum thickness is about 260 m.

    The lithostratigraphic unit of the Brown Jurassic begins biostratigraphically mostly in the ammonite zone of the Leioceras opalinum , the first ammonite zone of the chronostratigraphic Middle Jurassic series. In some sections, the lower limit of the Opalinus Clay formation and thus the Brown Jurassic is but already in the Pleydellia aalensis zone, the top zone of the Ammonites Toarciums and thus still in the Jurassic series. The chronostratigraphic boundary between the Brown and White Jura is already in the lower parts of the Upper Jura series. The Kandern formation even extends into the Middle Oxfordium .

    Breakdown

    The lithostratigraphic unit of the Brown Jura is subdivided into 15 formations, which, however, do not all lie on top of each other, but rather interlock laterally. The formations in their sequence from bottom to top, regional interlocking are side by side.

    Fossil sites

    Some of the layers of the Brown Jura are extraordinarily rich in fossils. However, the exposure conditions are often very poor.

    literature

    • Gert Bloos, Gerd Dietl & Günter Schweigert: The Jura of Southern Germany in the Stratigraphic Table of Germany 2002. Newsletter on Stratigraphy, 41 (1-3): 263-277, Stuttgart 2005, ISSN  0078-0421
    • Volker Dietze1, Günter Schweigert, John H. Callomon, Gerd Dietl and Martin Kapitzke: The Middle Jura of the Ipf area (eastern Swabian Alb, southern Germany). Correlation of the southern German ammonite fauna horizons from the Upper Bajocian to the Lower Callovian with southern England and France. Zitteliana, A47: 105-125, Munich 2007, ISSN  1612-412X
    • 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.
    • Friedrich August Quenstedt: The Jura. Verlag der Laupp'schen Buchhandlung, Tübingen 1856–57.

    Web links

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