Original paper

Alter, Genese und Paläogeographie der Kammquarzit-Formation (Visé) im Rhenoherzynikum - neue Daten und neue Deutungen

[Age, origin, and palaeogeography of the Kammquartzite Formation (Viséan) in the Rhenohercynian Zone - new data and new interpretations]

Jäger, Hartmut; Gursky, Hans-Jürgen

Zeitschrift der Deutschen Geologischen Gesellschaft Band 151 Heft 4 (2001), p. 415 - 439

61 references

published: May 10, 2001
published online: Sep 1, 2017

DOI: 10.1127/zdgg/151/2001/415

BibTeX file

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Kurzfassung

Die unterkarbonische Kammquarzit-Formation ist die charakteristischste Einheit der Hörre-Gommern-Zone, einem über 350 km langen, rinnenförmigen Sonderfazies-Bereich im Rhenoherzynikum Deutschlands. Infolge des Mangels an Fossilien und Sedimentgefügen in den bisher untersuchten Geländeaufschlüssen war die genaue Alterstellung dieser Formation bislang nicht hinreichend bekannt, und auch die paläogeographische Position wird sehr kontrovers gedeutet (Decke, Schwelle, tiefmarine Rinne). Neue Untersuchungen zur Sedimentologie und Stratigraphie an Bohrkernen und den Geländeprofilen innerhalb der gesamten Zone erlauben die Präzisierung des Bildungsalters und eine realistischere paläogeographische Interpretation. Drei Lithofazies-Typen werden in der Kammquarzit- Formation unterschieden: Quarzit-Fazies, Quarzit-Pelit-Fazies, Pelit-Fazies; diese sind als unterschiedlich konzentrierte Turbidite sowie als pelagische Hintergrund-Sedimente zu deuten. Anhand von Sporen wird die Kammquarzit-Formation erstmals exakt stratigraphisch eingestuft: Sie beginnt an der Vise-Basis, PU-Sporenzone bzw. cu II ß/γ, und reicht bis an die Grenze cu IIIα/ß, NM-Sporenzone. Die sedimentologischen und biostratigraphischen Ergebnisse führen zu dem folgenden paläogeographisehen Modell für die Kammquarzit-Formation: Fluviatil und flachmarin aufbereitetes Sediment des klastischen Küstensaums Laurussias wurde in Regressionsphasen durch unterschiedliche Trübeströme in schmalen Förderkanälen nach Süden, quer zum Kulm-Becken in das tektonisch vorgegebene, rinnenförmige Hörre-Gommern-Teilbecken transportiert und dort rinnenparallel sedimentiert. Diese quarzklastischen Schüttungen vom nördlichen Schelf waren bereits beendet, als die nach Norden vorrückenden Flysch-Schüttungen (Kulm-Grauwacken) die Hörre-Gommern-Zone erreichten (Grenze cu III α/ß). Infolge der fortschreitenden Einengung während der variszischen Orogenese wurde die Kammquarzit-Formation in den akkretionären Keil vor der orogenen Front der Varisziden integriert.

Abstract

In the middle of the classical Lower Carboniferous Culm Basin, a zone more than 350 km long, but only few km wide of diverging lithostratigraphy is known as the HÖrre-Gommern-Zone. From the Upper Devonian onwards, this zone is characterized by quartz-rich, clastic intercalations in the pelitic basin deposits. The thick bedded, massive quartzites of the Kammquartzite Formation, the uppermost unit of the Hörre-Gommern-Zone, differ considerably from the pelagic sediments in the surrounding basin. Due to the lack of fossils and sedimentary structures, the exact stratigraphic position, facies and palaeogeographical significance of the quartzites are under discussion. The quartzites have been variously interpreted as shallow marine deposits on an intrabasinal rise, as deep marine sediments in a narrow basin - as a special flysch facies in the Kulm-Basin - or as a part of a tectonic nappe structure along the southern margin of the basin. Based on core sections and outcrops, the Kammquartzite Formation was sedimentologically and biostratigraphically reinvestigated. Due to the scarcity of macro and micro-fauna the Kammquartzite Formation has been dated by miospores. Deposition of the quartzites started at the base of the Viséan, PU spore zone (cu II ß/γ). The age of the top of the formation is in the Upper Visean, near to the top of the Asbian in the upper NM spore zone (cu III α/ß). The formation spans most of the Viséan (V1a to V3b). Three types of lithofacies can be distinguished: 1) Thick-bedded, mostly homogeneous quartzites of the Quartzite Facies, typical for highly concentrated turbidity currents, are clearly dominant. 2) The Quarzite-Shale Facies, an alternation of cross or horizontally stratified thin bedded quartzites and thin to thick-bedded shales, representing low concentrated turbidites. 3) The dark shales of the Shale Facies that are typical basinal muds. The distribution of lithofacies, bed thickness and mean grain size in the sections show constantly proximal conditions along the axis of the entire quartzite zone, grading to both sides into clearly distal conditions. Palaeocurrents were parallel to the basin axis. A narrow trench-like basin with geometry similar to the present-day quartzite zone is inferred. Within this trench, the sediment was distributed in sinuous f1ow-systems parallel to the axis but in opposite directions. There is no evidence for shallow marine deposition. The composition of the extremely quartz-rich sediment (up to 98 % quartz) and reddish clasts (ferricretes) are typical of siallitic weathering under tropical conditions, which existed in wide areas of southern Laurussia during the Viséan. The commonly high kaolinite contents of the shales suggest mainly terrestrial weathering of the sediment. U/Pb-ratios of zircons in the quartzites reported in literature are typical for Laurussian-derived sandstones. In contrast the Kulm-Greywackes were derived from 'Gondwana' sources. The sands of the Kammquartzite Formation were derived from a siliciclastic zone along the southern coast of Laurussia, supplied by f1uvial systems. Intense continental weathering and shallow marine coastal reworking of the sediment produced quartz-rich sands. During the Viséan, as a consequence of regression, the quartzitic sediments were transported to the outer shelf and then shed into the basin by variable turbidity currents. We infer that the sediment passed through the pelagic Kulm Basin within narrow feeder channels into the Kammquartzite Trench. In the lowermost Brigantian (V3c, cu III ß) the flysch greywackes stepped over the Quartzite Zone to the north. By this time the deposition of quartzitic sediments from the northern shelf had stopped. During the Variscan orogeny the Quartzite Trench was imbricated by and accreted into the Variscan fold belt.

Keywords

Rhenohercynian Orogenysedimentary basinsCulmstratigraphic unitsKammquartzite-FormationViséansedimentary structuressize distributionskewnesslithofaciesgeographic distributionbiostratigraphypalynologysporespaleocurrentspaleogeography Hesse GermanySaxony-Anhalt GermanyRhenish SchiefergebirgeHarz Mountains