Sedimentation, Diagenesis and Syntectonic Erosion of Upper Cretaceous Rudist Mounds in Central Tunisia

  1. C. L. V. Monty,
  2. D. W. J. Bosence,
  3. P. H. Bridges and
  4. B. R. Pratt
  1. M. H. Negra1,
  2. B. H. Purser2 and
  3. A. M'Rabet3

Published Online: 14 APR 2009

DOI: 10.1002/9781444304114.ch14

Carbonate Mud-Mounds: Their Origin and Evolution

Carbonate Mud-Mounds: Their Origin and Evolution

How to Cite

Negra, M. H., Purser, B. H. and M'Rabet, A. (1995) Sedimentation, Diagenesis and Syntectonic Erosion of Upper Cretaceous Rudist Mounds in Central Tunisia, in Carbonate Mud-Mounds: Their Origin and Evolution (eds C. L. V. Monty, D. W. J. Bosence, P. H. Bridges and B. R. Pratt), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304114.ch14

Author Information

  1. 1

    Faculté des Sciences de Tunis, Département de Géologie, Laboratoire de Sédimentologie et Bassins Sédimentaires, Campus Universitaire, 1020 Tunis-Belvédaire, Tunisia

  2. 2

    Université de Paris-Sud, Centre d'Orsay, Laboratoire de Pétrologie Sédimentaire, Batiment 504, 91405 Orsay Cedex, France

  3. 3

    ETAP, 27 bis, avenue Khéreddine Pacha, 1002-Tunis, Tunisia

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 17 JUL 1995

ISBN Information

Print ISBN: 9780865429338

Online ISBN: 9781444304114

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Keywords:

  • Conglomerates containing blocks reworked from the rudist carbonates;
  • Erosion of the lithified mounds;
  • massive micritic carbonates;
  • laminated argillaceous planktonic foraminiferal micrites;
  • carbonate conglomerates;
  • Laminated argillaceous planktonic foraminiferal micrites

Summary

The Upper Cretaceous carbonates of central Tunisia include lensoid mounds composed essentially of micrite locally rich in rudist and corals. Although these organisms can be closely packed and contribute actively to the creation of bioherms, the majority (70–80%) are scattered in micritic mounds. Their debris forms graded sequences indicating a hydrodynamic accretion. Three types of mud-mound are recognized: type 1, essentially a wackestone, contains debris of rudists, corals, echinoderms, associated peloids and scarce calcispheres. Type 2 is a composite mud-mound comprising a type 1 mud-mound directly overlain by a type 3 bioherm. Type 3 is a muddy, bioconstructed rudist-coral bioherm in which interrudist spaces are filled with fine (wackestone) sediment rich in rudist–coral and echinoderm debris.

Conglomerates containing blocks reworked from the rudist carbonates are volumetrically important. They clearly indicate significant Late Cretaceous lithification and erosion. Within the mounds, early diagenesis is expressed by neogenic microspar and by interlocking or coalescing nanofabrics which characterize the upper part of type 1 micritic mounds or certain reworked pebbles. It is clear that early lithification is responsible, at least in part, for the rigidity of the mounds expressed by steep margins. Erosion of the lithified mounds is related to tectonic instability, notably during the Campanian. Micrites rich in planktonic microfaunas intercalated between rudist mounds suggest that mounds formed below wave base, possibly on an open marine slope. The fact that organic activity is not the major factor responsible for their construction will be demonstrated in this paper.