Debris Flow (Olistostromes) and Slumping on a Distal Passive Continental Margin: The Palombini Limestone-Shale Sequence of the Northern Apennines

  1. Dorrik A. V. Stow
  1. Michael A. Naylor

Published Online: 29 APR 2009

DOI: 10.1002/9781444304473.ch9

Deep-Water Turbidite Systems

Deep-Water Turbidite Systems

How to Cite

Naylor, M. A. (2009) Debris Flow (Olistostromes) and Slumping on a Distal Passive Continental Margin: The Palombini Limestone-Shale Sequence of the Northern Apennines, in Deep-Water Turbidite Systems (ed D. A. V. Stow), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304473.ch9

Editor Information

  1. Department of Geology, University of Southampton, UK

Author Information

  1. Department of Geology, Sedgwick Museum, Downing Street, Cambridge CB2 3EQ, UK

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:

  • olistostrome accumulation;
  • allochthonous Vara complex;
  • soft-sediment deformation;
  • fold asymmetry;
  • olistostrome beds

Summary

An olistostrome accumulation up to 530 m thick occurs in the Casanova area of the northern Apennines. It lies within or above the calciturbiditic Palombini limestone-shale sequence, and is part of the allochthonous Vara Complex–sediments originally deposited on oceanic crust. The olistostromes are poorly sorted, monomict, matrix-supported, submarine debris flow deposits with rigid plugs. They have a compactional foliation and a compaction-modified, planar clast fabric created during flow. Although diachronous in the main part of the area, the olistostromes have a vertical gradational contact with the overlying slumped Palombini, in which recumbent asymmetric fold hinges and trains and slump boudins are present. Many criteria indicate soft-sediment deformation. Fold asymmetry indicates a uniformly SW-dipping palaeoslope. The textural gradation from slumps to olistostrome beds, plus slump folds and boudins as olistostrome clasts show that the olistostromes are dismembered slumps. In vertical sections, variations in limestone petrography, volume percentage and size of clasts confirm that the olistostromes were derived from the Palombini as a series of bed-by-bed slumps keeping pace with sedimentation of the Palombini. From olistostrome clast sizes and bed thicknesses, a depositional slope of ∼ 4° is estimated. The olistostromes are not precursor sediments shed from advancing nappes, as in the Bracco ridge model of some authors; rather, they were formed at the foot of a distal, block-faulted passive continental margin, long before nappe emplacement.