Cyclic Sedimentation in Carbonate and Mixed Carbonate—Clastic Environments: Four Simulation Programs for a Desktop Computer

  1. Maurice E. Tucker3,
  2. James Lee Wilson4,
  3. Paul D. Crevello5,
  4. J. Rick Sarg6 and
  5. J. Fred Read7
  1. G. M. Walkden1 and
  2. G. D. Walkden2

Published Online: 15 APR 2009

DOI: 10.1002/9781444303834.ch3

Carbonate Platforms: Facies, Sequences and Evolution

Carbonate Platforms: Facies, Sequences and Evolution

How to Cite

Walkden, G. M. and Walkden, G. D. (1986) Cyclic Sedimentation in Carbonate and Mixed Carbonate—Clastic Environments: Four Simulation Programs for a Desktop Computer, in Carbonate Platforms: Facies, Sequences and Evolution (eds M. E. Tucker, J. L. Wilson, P. D. Crevello, J. Rick Sarg and J. F. Read), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303834.ch3

Editor Information

  1. 3

    Durham, UK

  2. 4

    New Braunfels, Texas, USA

  3. 5

    Littleton, Colorado, USA

  4. 6

    Midland, Texas, USA

  5. 7

    Blacksburg, Virginia, USA

Author Information

  1. 1

    Department Geology and Petroleum Geology, University of Aberdeen, Aberdeen AB9 1AS, UK

  2. 2

    Department of Geological Sciences, University of Durham, Durham DH1 3LE, UK

Publication History

  1. Published Online: 15 APR 2009
  2. Published Print: 22 DEC 1986

ISBN Information

Print ISBN: 9780632027583

Online ISBN: 9781444303834

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Keywords:

  • cyclic sedimentation in carbonate and mixed carbonate-clastic environments – four simulation programs;
  • cyclothem;
  • Walther;
  • Milankovich;
  • croll

Summary

Four programs are introduced for the BBC range of microcomputers that can produce simple simulations of tectonic, eustatic or other types of cyclothem in a variety of shallow- or deep-water carbonate and mixed carbonate–clastic environments. Cycle periods and magnitudes can be preset, randomized or expressed as the sum of up to three independent wave periods, and symmetric and asymmetric options are available. Where appropriate, subsidence is separated into a user-definable tectonic component and a facies-dependent compactional component. Compaction of the appropriate sediments takes place as the program is running. The programs generate synthetic sediment columns comprising a succession of depth- or lithology-defined facies, the accumulation rates of which are separately controllable.

‘Cyclothem’ simulates sedimentation on a shallow-water carbonate platform modelled from the late Dinantian of northern Britain. The program will reproduce tectonic or eustatic cycles and whilst shoaling will interrupt sedimentation, emergence will produce a subaerially-modified surface as commonly seen in the field. Marine facies are depth-defined, and where these are given uniform sedimentation rates the simulations assume a broadly chronostratigraphic character. The causes and significance of cyclothem asymmetry are examined. Cycle magnitude, sedimentation rates and subsidence rates can be separately defined and the effects of these on facies diversity and cyclothem thickness are discussed.

‘Walther’ uses an additional machine code routine to create an inset window that maps a delta. This grows, strands or drowns according to independent water depth controls and is used to introduce up to four non-carbonate facies. The program simulates British ‘Yoredale’-type cyclothems and has parallels with Pennsylvanian mid-continent cycles of the USA. Both of these are considered to be eustatically controlled. The significance of an asymmetric wave and of compactional subsidence in maintaining conditions favourable for coal formation are also examined.

‘Milankovich’ returns to the shallow-water carbonate setting and simulates cyclothem distribution patterns arising from the simultaneous interaction of two or three secular controls on sea-level. The screen can be time- and thickness-scaled automatically to enable the investigation of fifth order (Milankovich-type) to third order (Vail-type) cycles. Modelling using this program demonstrates some of the dangers inherent in counting cycle numbers as a means of determining the lengths of Milankovich periods.

‘Croll’ models off-platform environments where sedimentation is not interrupted by emergence. Limestone–shale successions are an appropriate application, where controls on facies repetitions may be through factors other than sea-level fluctuations. Three facies can be simulated and independent accumulation rates set for each. Using the sum wave of up to three Milankovich periods to trigger facies changes it can be demonstrated once again that data derived from the geological record may provide misleading information as to the actual periods involved.