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Devonian of Germany
The classical Devonian of Germany, containing the stratotypes of several stages and substages, is exposed in uplifted Palaeozoic massifs as well as in additional isolated outcrops. It has been identified in the subsurface of northern Germany but it seems to be absent in the south. Its sediments were deposited in the central parts of the Variscan geosyncline, folded by the Sudetic and in the north by the Asturian orogeny of the Variscan (“Hercynian”) orogenetic cycle.
According to their lithologic characters and faunal assemblages the German Devonian formations belong either to the Rhenish or to the Hercynian magnafacies or to a mixed facies transitional between both. At the beginning of the geosynclinal development, in earliest Devonian time, the Rhenish magnafacies covered large northwestern and northern parts of the Devonian trough while the Hercynian magnafacies was restricted to its central and southeastern parts. During the general subsidence of the geosyncline in Middle to Late Devonian time, the Hercynian magnafacies advanced towards the northwest until it occupied, in Late Devonian time, almost all those parts of the geosyncline which are observable today.
The Devonian sea in Germany extended in an east-west direction and possibly included several small islands. It was bordered in the north by the shore of the Old Red Continent and in the south by a large Franco-Alemannian island. In the west it continued into the Ardennian (Belgium) and the Armorican (NW France, SE England) parts of the Devonian sea, in the east into a marine embayment in Poland. Towards the south it was connected with the central Bohemian sedimentary basin (Barrandian). Rather intense subsidence was in part counter-balanced by accumulation of large amounts of sediments both resulting in dominantly shallow water conditions. In early Middle Devonian time the first biostromes developed. In late Middle Devonian time strong submarine volcanism caused thick accumulations of lavas and tuffs on top of which extensive bioherms developed. These disappeared in late Devonian time when subsidence increased in the whole geosyncline.
Stratigraphical subdivision of the German Devonian is based on an orthochronological (standard) succession of biozones characterized by ammonoids. In the earliest Devonian, when ammonoids had not yet appeared, a continuation of the Ordovician-Silurian orthochronology based on graptolites can be applied. For correlation purposes and in addition to the above-mentioned orthochronological zonation, various parachronological successions of conodonts or (in the Upper Devonian) ostracods are used. Other useful tools for stratigraphical purposes are trilobites, brachiopods and corals.
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