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Deutsche Hydrografische Zeitschrift

, Volume 46, Issue 3, pp 229–244 | Cite as

Sedimentary facies associations of the shoreface-connected ridge systems in the German Bight, southern North Sea

  • Effiom E. Antia
  • Burghard W. Flemming
  • Gerold Wefer
Article

Summary

The sedimentary facies of the shoreface-connected ridges off Spiekeroog Island, German Bight, are presented and compared with their counterparts in other shelf settings in order to better understand the processes that form and maintain the ridges. Core samples from successive morphozones of two adjacent (inner and outer) 3–5m high ridges show that: (1) the ridges consist of a ca. 60 cm thick surficial unit characterized by orange-brown, medium-to coarse-grained, shell-rich sands that overlie a subsurface unit of finegrained, horizontally laminated greyish sands; (2) one or more 10–18 cm thick, upward-fining storm beds are commonly present; (3) the trough facies of the inner ridge differs from its outer ridge counterpart by a broader range of grain sizes, a more frequent occurrence of storm beds, and a paucity of internal sedimentary structures relating to tidal current activity; (4) the landward flank facies comprise massive to poorly bedded, coarse-grained shelly sands, whereas the sands of the seaward flanks are fine-grained and mostly bioturbated; (5) on ridge crests a variety of stratification types, reflecting tidal, wave and storm currents, are observed.

Given their close spatial association, the marked lithological contrasts between adjacent facies and comparable ridge morphozones are surprising. The fact that the sediment transport capacity of normal fairweather tidal currents is high, suggests that these tides play an important role in the maintenance of the shoreface-connected ridges in the German Bight.

Keywords

Stratification Crest Sediment Transport Core Sample Tidal Current 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Fazielle Differenzierung in den Zungenriff-Systemen der Deutschen Bucht, südliche Nordsee

Zusammenfassung

Die Sedimentfazies der Zungenriff-Systeme nördlich der Insel Spiekeroog werden beschrieben und mit analogen Gebilden anderer Schelfmeere verglichen, um ihre Genese und Erhaltung besser zu verstehen. Sedimentkerne von den verschiedenen morphologischen Zonen zweier benachbarter, 3–5 m hoher Zungenriffe zeigen, daß: (1) die Riffe sich in eine obere, etwa 60 cm mächtige, aus orange-braunen, mittel- bis grobkörnigen, schillreichen Sanden bestehende und eine darunterliegende, aus feinkörnigen und horizontalgeschichteten grauen Sanden bestehende Schicht unterteilen lassen; (2) mindestens eine, zum Hangenden hin feinerwerdende Sturmlage vorkommt; (3) sich die Trogfazies des inneren Riffes von der des äußeren Riffes durch ein breiteres Korngrößenspektrum, häufiger auftretende Sturmlagen und dem Fehlen von tidestromerzeugten Gefügemerkmalen auszeichnet; (4) die Sedimente der landseitigen Flanken aus massiven oder schlecht geschichteten, grobkörnigen und schilldurchsetzten Abfolgen aufgebaut sind, während die Sedimente der seewärtigen Flanken feinkörniger und durch Bioturbation geprägt sind; (5) die Riffkämme verschiedenartige, durch tiden-, wellen-und sturmerzeugte Strömungen geprägte Stratifikationstypen aufweisen.

Dieser engräumige lithologische Kontrast der Sedimente sowohl in benachbarten als auch in morphologisch analogen Zonen ist überraschend. Die Tatsache, daß die normalen Tidenströme mit ihrem hohen Sedimenttransportpotential die Zungenriffe nicht zerstören, deutet darauf hin, daß diese einen wichtigen Beitrag zum Erhalt der Zungenriffe in der Deutschen Bucht spielen.

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Copyright information

© Bundesamt für Seeschiffahrt und Hydrographie 1994

Authors and Affiliations

  • Effiom E. Antia
    • 1
  • Burghard W. Flemming
    • 2
  • Gerold Wefer
    • 3
  1. 1.Department of Physical OceanographyUniversity of CalabarCalabar/CRSNigeria
  2. 2.Abteilung für MeeresforschungForschungsinstitu SenckenbergWilhelmshavenGermany
  3. 3.FB GeowissenschaftenUniversität BremenBremenGermany

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