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Facies

, Volume 25, Issue 1, pp 51–89 | Cite as

Age and depositional environment of upper devonian (early Frasnian to early famennian) black shales and limestones (Kellwasser facies) in the eastern Anti-Atlas, Morocco

  • Jobst Wendt
  • Zdzislaw Belka
Article

Summary

The so-called Kellwasser facies consists of black bituminous limestones and shales which were deposited on pelagic platforms and in adjacent shallow basins. In contrast to the well-known European counterparts, Moroccan Kellwasser lithologies are extremely fossiliferous and, in addition to the predominating nektonic and planktonic, also contain different groups of benthic organisms. A first short-time Kellwasser episode during the lowermost Frasnian is succeeded, after an interval of grey nodular and crinoid limestone deposition, by a second longer one during the late Frasnian/early Famennian. On the platforms the upper member consists of slowly deposited cephalopod/tentaculitid/styliolinid coquinas and debris flows. Towards the basins they pass into shales with intercalated fine-grained sandstones and limestone lenses. This facies pattern reflects not only the regional palaeogeography but also local depositional environments on the platforms which were formed by differential subsidence, synsedimentary tensional tectonics and submarine erosion. Uni- or bidirectional bottom currents which reflect the overall palaeogeographic pattern are very pronounced in the platform environments but decrease towards the basins. The discontinuous stratigraphical record of the pelagic platforms images major sea-level oscillations which left only minor traces in the continuous basinal sequences. Widespread transgressions occurred during the Lowerasymmetricus, the Lower and Uppergigas, the Lowermarginifera and the Lowerexpansa Zones. They are separated by sea-level lowstands during the Middleasymmetricus/A. triangularis, therhomboidea and the (Middle?)praesulcata Zones. In contrast to the inferred fluctuations at the Frasnian/ Famennian transition in Euramerica, this interval in Morocco is represented by a more or less continuous highstand of sea-level.

Keywords

Palaeogeography Sedimentology Black Shales Anti-Atlas (Morocco) Upper Devonian 

Alter und Ablagerungsraum oberdevonischer (Unter-Frasne bis Unter-Famenne) Schwarzschiefer und Kalke (Kellwasser-Fazies) im östlichen Anti-Atlas, Marokko

Zusammenfassung

Die sog. Kellwasserfazies besteht aus schwarzen bituminösen Kalken und Tonen, die auf pelagischen Plattformen und in benachbarten flachen Becken abgelagert wurden. Im Gegensatz zu ihren gut bekannten europäischen Äquivalenten ist die marokkanische Kellwasserfazies sehr fossilreich und enthält neben den vorherrschenden nektonischen und planktonischen auch verschiedene Gruppen benthonischer Organismen. Einer ersten kurzzeitigen Kellwasser-Phase im untersten Frasne folgt nach einer Einschaltung grauer Crinoiden- und Knollenkalke eine zweite, länger andauernde im oberen Frasne/unteren Famenne. Sie besteht aus langsam abgelagerten Cephalopoden-Tentakuliten-Styliolinen-Schillkalken und Debrisflows auf den Plattformen, die in Tone mit eingeschalteten feinkörnigen Sandsteinen und Kalklinsen in den Becken übergehen. Dieses Faziesmuster ist nicht nur ein Abbild der größerräumigen Paläogeographie sondern auch von lokalen kleinerräumigen Ablagerungsmustern, die durch unterschiedliche Absenkung, synsedimentäre Dehnungstektonik und submarine Erosion gebildet wurden. Von den paläogeographischen Konturen bestimmte Bodenströmungen mit ein- oder zweigipfligen Maxima sind auf den Plattformen deutlich und nehmen gegen die Becken hin ab. Die diskontinuierliche stratigraphische Abfolge der pelagischen Plattformen spiegelt bedeutende Meeresspiegelschwankungen wider, die sich in den kontinuierlichen Becken-Ablagerungen nur undeutlich abbilden. Großräumige Transgressionen erfolgten in der unterenasymmetricus-, der unteren und oberengigas-, der unterenmarginifera- und der unterenexpansa-Zone. Sie wurden abgelöst durch Regressionen in der mittlerenasymmetricus-bisA. triangularis-Zone, derrhomboidea-Zone und der (mittleren?)praesulcata-Zone. Im Gegensatz zu den vermuteten eustatischen Meeresspiegelschwankungen an der Frasne/Famenne-Grenze in Euramerica ist dieser Zeitraum in Marokko durch einen mehr oder weniger hohen Meeresspiegelstand gekennzeichnet.

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Copyright information

© Institut für Paläontologie, Universität Erlangen 1991

Authors and Affiliations

  • Jobst Wendt
    • 1
  • Zdzislaw Belka
    • 1
  1. 1.Institut und Museum für Geologie und Paläontologie der UniversitätTübingen

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