Rhythms in Deep Sea, Fine-Grained Turbidite and Debris-Flow Sequences, Middle Ordovician, Eastern Tennessee

  1. Dorrik A. V. Stow
  1. Ganapathy Shanmugam

Published Online: 29 APR 2009

DOI: 10.1002/9781444304473.ch13

Deep-Water Turbidite Systems

Deep-Water Turbidite Systems

How to Cite

Shanmugam, G. (1991) Rhythms in Deep Sea, Fine-Grained Turbidite and Debris-Flow Sequences, Middle Ordovician, Eastern Tennessee, in Deep-Water Turbidite Systems (ed D. A. V. Stow), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304473.ch13

Editor Information

  1. Department of Geology, University of Southampton, UK

Author Information

  1. Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee, 37916, USA

  1. Mobil Field Research Laboratory, Box 900, Dallas, Texas 75221, USA

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 11 NOV 1991

ISBN Information

Print ISBN: 9780632032624

Online ISBN: 9781444304473

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Keywords:

  • Whitesburg formation in outcrops, interbedding of pebblylime mudstones and clayey shale Blockhouse Formation is clayey shale and rare volcanic tuff, forming Blockhouse Formation;
  • rhythm – single layer or multiple bundles;
  • tectonic history of the basin;
  • depositional processes and environments;
  • bioturbation, important in fourth order level

Summary

Rhythms in fine-grained sediments have not previously been studied because of their complex depositional cycles and diagenetic changes. Examination of nearly 9000 layers in outcrops, polished slab samples, and thin sections has led to recognition of rhythms in the Middle Ordovician Whitesburg, Blockhouse, and Sevier formations of east Tennessee. Rhythms have been described in four orders based on relative magnitude. First order cycles (basin-fill sequences, hundreds of metres thick) are composed of thinning upward debris-flow sequences and thickening upward turbiditic shale sequences. Second order cycles (multiple sedimentation units, tens of centimetres thick) consist of: (1) thinning upward cycles; (2) symmetrical cycles; (3) thickening upward cycles; (4) minor multiple cycles; (5) uniform cycles; and (6) dubious cycles. Third order cycles (single sedimentation unit, tens of millimetres thick) have thinning upward and asymmetrical cycles. Fourth order portrays the grain-size variations within a single layer of the third order. First order rhythms were controlled by tectonism and progradation of a deep-sea fan system. Second and third order rhythms were controlled by depositional processes, bottom topography, and sediment source. Depositional processes, sediment source, and bioturbation were the dominant controlling factors in the fourth order. A deep-sea fan model is proposed for the fine-grained turbidites in which channels and lobes coexist in the lower fan. The lower fan/mid fan boundary is marked by the presence of a channel cycle near the top of a lobe sequence. The basin plain/lower fan boundary is suggested by the appearance of minor lobe cycles over the non-cyclic basin plain sequence.