South German 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 term South German Jura is used in geological history for a lithostratigraphic rock unit in the hierarchical rank of a supergroup . The rocks of the southern German Jura were essentially deposited during the Jura around 199 to 146 million years ago. However, the boundaries of the southern German Jura and chronostratigraphic or international Jura do not exactly match. The deposits begin a little later than the international Triassic / Jura boundary and end, due to the erosion of the uppermost layers, at different times in the Upper Jurassic , i.e. H. well before the international Jura / Chalk border. The rock unit of the southern German Jura is underlain by the Keuper ; in between, however, there is a small layer gap. About the South German law follows with discordant a large hiatus and also very locally the " Regensburger green sandstone " in the Cenomanian of chalk is dated. In the southern peripheral areas, the South German Jura dips below the paleogenic molasse deposits at the base.

    Geographical distribution

    The southern German Jura stretches geographically from the Upper Palatinate Forest to the south into the Franconian Alb , which then merges to the southwest into the Swabian Alb . The boundary between the Franconian and Swabian Alb forms the impact structure of the Nördlinger Ries . In the southern part of the Franconian Alb and in the Swabian Alb that adjoins it to the west, the layers dip slightly to the south and are covered there by the molasses sediments of the Alps . There are also deposits of chalk locally. The southern German Jura extends over the southern Black Forest to Switzerland. There are also smaller occurrences of Jura in the Upper Rhine Valley, which are assigned to the distribution area of ​​the southern German Jura.

    history

    Alexander von Humboldt proposed the Jura system in 1795 , which quickly established itself in the professional world. However, Humboldt understood the term Jura primarily as Jura limestone ( White Jura ), i.e. essentially only the Upper Jura . As early as 1837, at a meeting of the Academy of Sciences in Berlin, Leopold von Buch suggested expanding the law and dividing it into three departments. When describing the individual parts, however, he did not use the subdivision into Black, Brown and White Jura, as he already recognized the lateral change in lithology. In the headings of the respective chapters, he already referred to the three parts of the Jura, which are known today as series , as "Lower Jura or Lias", "Middle Jura" and "Upper Jura". This new subdivision of the Jura was not published until 1839. The three terms Black, Brown and White Jura were therefore proposed mainly due to lithological peculiarities, not in terms of time units and then recognized as too facies-dependent and immediately discarded. Friedrich August Quenstedt , however, took up these terms in his work Das Flözgebirge Würtembergs , published in 1843, and defined them lithostratigraphically. In contrast, Albert Oppel used the terms Lias, Dogger and Malm for the Jura series , which he understood more in terms of chronostratigraphic units. It was only after the Second World War that these terms were increasingly converted into lithostratigraphic terms, especially in northern Germany. Quenstedt (1856–57) subdivided the three units of the southern German Jura into six “levels”, which he designated with the Greek letters alpha to zeta. Even today, this system is still widely used in popular science literature. However, Quenstedt's graded structure was and is mostly combined with the terms Lias, Dogger and Malm taken from the English quarry industry . The term stage is also used today in chronostratigraphy in a clearly different sense.

    definition

    The lower limit of the South German Jura in the sense of a lithostratigraphic unit is due to the lower edge of the Psilonotenbank of the Psilonotenton formation , the upper limit is erosive. The rock formation is varied and ranges from dark, partly bituminous claystones, marls and limes to iron-rich sandstones, clays and limes, sometimes with iron oids, to light marls and limes. The thickness is up to about 900 m.

    The basis of the lithostratigraphic unit of the South German Jura begins biostratigraphically mostly in the ammonite zone of Psiloceras planorbis . In a few profiles, ammonites were found that belong to the Neophyllites horizon below the Psiloceras planorbis subzone . So far, however, the horizons of Psiloceras erugatum and Psiloceras tillmanni (so-called Praeplanorbis layers) of the Lowest Hettangium have not been detected. The basal hettangium is missing in the southern German Jura. The lower limit of the southern German Jura does not exactly coincide with the beginning of the international Jura system, but is slightly higher. In the most complete profiles of the southern German Jura, the strata extend to the border between the Lower and Upper Tithonium of the Upper Jura series. In the North German Jura, sedimentation continued more or less continuously into the Lower Cretaceous .

    structure

    The South German Jura as a lithostratigraphic supergroup is today divided into three lithostratigraphic groups (with around 50 formations) (from top to bottom):

    Paleogeography

    The deposit area of ​​the South German Jura was a marginal sea of ​​the Tethys Ocean.

    Individual evidence

    1. ↑ "... 1) in a black one at the foot of the mountains and up to a small height, mostly limestone and slate; 2) in a brown or yellow one on the steep slopes, in which there are almost nothing but sandstones; finally 3) in a white part, the upper coral-filled layers of limestone, which border the steep slopes like an often vertical wall. " v. Book, p. 61
    2. ↑ "The lower, middle, and upper Jura are names that have no relation to the changeable mineralogical nature of the strata ..." v. Book p. 63
    3. ↑ Mönnig, 2005, pp. 255ff.

    literature

    • Leopold von Buch: About the Jura in Germany. Treatises of the Royal Academy of Sciences in Berlin, 1837: 49-135, Berlin 1839 online
    • Eckhard Mönnig: The Jura in Northern Germany in the STD 2002. Newsletters on Stratigraphy, 41 (1-3): 253-261, Stuttgart 2005 ISSN  0078-0421
    • Albert Oppel: The Jura formation of England, France and the southwest of Germany. Württemberg scientific annual books , 12-14: 857 S., Stuttgart 1856-58 ZDB -ID 219058-8
    • 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.

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