Environmental and Tectonic Controls on Preservation Potential of Distal Fallout Ashes in Fluvio-Lacustrine Settings: The Carboniferous–Permian Saar–Nahe Basin, South–West Germany

  1. James D. L. White2 and
  2. Nancy R. Riggs3
  1. S. Königer and
  2. H. Stollhofen

Published Online: 24 MAR 2009

DOI: 10.1002/9781444304251.ch13

Volcaniclastic Sedimentation in Lacustrine Settings

Volcaniclastic Sedimentation in Lacustrine Settings

How to Cite

Königer, S. and Stollhofen, H. (2009) Environmental and Tectonic Controls on Preservation Potential of Distal Fallout Ashes in Fluvio-Lacustrine Settings: The Carboniferous–Permian Saar–Nahe Basin, South–West Germany, in Volcaniclastic Sedimentation in Lacustrine Settings (eds J. D. L. White and N. R. Riggs), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304251.ch13

Editor Information

  1. 2

    Department of Geology, University of Otago, PO Box 56, Dunedin, 9015, New Zealand

  2. 3

    Geology Department, Northern Arizona University, Box 4099, Flagstaff, AZ 86011, USA

Author Information

  1. Institut für Geologie, Universität Würzburg, Pleicherwall 1, D-97070 Würzburg, Germany

Publication History

  1. Published Online: 24 MAR 2009
  2. Published Print: 18 APR 2001

ISBN Information

Print ISBN: 9780632058471

Online ISBN: 9781444304251

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Keywords:

  • environmental and tectonic controls of distal fallout ashes - the Carboniferous–Permian Saar–Nahe Basin, south-west Germany;
  • Saar–Nahe Basin - geological setting and structural framework;
  • syn-rift evolution of the Saar–Nahe basin;
  • upper stephanian depositional environments and volcanism - tephrostratigraphy, petrography, lithofacies;
  • transgressive–regressive cycles;
  • preservation of the volcanic ash;
  • tectonic control on ash preservation;
  • preservation potential of fallout ash in various fluvio-lacustrine subenvironments;
  • complex architecture of the Odernheim and Jeckenbach units;
  • tectonic model for fluviolacustrine settings

Summary

Thin but widespread fallout tuff layers form important stratigraphic markers in purely continental settings such as the Carboniferous–Permian Saar–Nahe Basin. They provide tools for the correlation of laterally variable lacustrine–deltaic sections and for the recognition of tectonically induced facies and thickness changes across faults. Not all the ash layers, however, were preserved as primary deposits; many were affected by reworking to varying degrees to form mixed pyroclastic–siliciclastic beds. The preservation of volcanic ash in the Saar–Nahe Basin was strongly influenced by the depositional environment. Specifically, volcanic ash falls deposited during the transgressive phases of sedimentary cycles had a high preservation potential. In addition, the preservation potential was strongly controlled by contemporaneous fault displacements. Ash beds deposited in footwall positions were highly affected by reworking and erosion and usually preserve only reduced thicknesses. In contrast, hanging-wall blocks provide an enhanced preservation potential for both primary and reworked ashes. Such sections record enhanced thicknesses, and the intercalation of siliciclastic interbeds cause complex lithological build-ups.

The Late Variscan, intermontane Saar–Nahe Basin in south-west Germany developed as a north-east–south-west-trending 120 km × 40 km half-graben, which is subdivided by sets of orthogonal transfer faults. Its basin fill is characterized by purely continental, fluvio-lacustrine sediments revealing complex thickness and facies patterns as a result of contemporaneous tectonic faulting. During Stephanian (Kasimovian–Gzelian) and earliest Permian (Asselian) time, extrabasinally derived acidic volcanic ashes were deposited as distal pyroclastic fallout in lacustrine–deltaic dominated settings and subsequently altered to various clay mineral assemblages. Essentially three depositional settings with contrasting preservation potential can be distinguished: tuffs interbedded with offshore-lacustrine (black) shales have the highest preservation potential, and are usually preserved as primary deposits showing sharp and planar contacts, planar lamination (multiple) graded bedding, and laterally constant thickness; ashes reworked by turbidity currents form erosionally based, climbing-ripple and planar-bedded graded tuff horizons with load and flute casts at their bases; and tuffs interbedded with flood plain and crevasse splay sediments are often cross-bedded and display both current and tool marks. Reworking is common and associated with abundant admixture of siliciclastic detritus or erosion of the entire tuff bed.