Integrating the concepts of lithostratigraphy and lithofacies in applied geological mapping

1
Integrating the concepts of lithostratigraphy and
lithofacies in applied geological mapping

• Jeroen Schokker, Wim Westerhoff Henk Weerts
• Deltares / TNO Geological Survey of the
  Netherlands

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Aim

• Context
• Based on the interpretation of core material, not
  outcrops
• Regional to nation-wide modelling scale
• Presence of a well-structured core description
  database
• Presence of elaborate computer modelling skills
• Addressing geohydrological, geotechnical and
  geochemical problems requests spatial information
  on layer properties that are intimately linked to
  sedimentary architecture and lithology

• To show that a combination of lithostratigraphic
  classification and lithofacies modelling allows
  for the construction of subsurface models that
  are best capable to address applied geological
  questions

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Lithostratigrapic concept

• Criteria for stratigraphic subdivision
• Based on lithological characteristics that are
  macroscopically visible in core material
• Units have an unequivocal stratigraphic position
  and distinct boundaries
• Units are mappable on a 1/50,000 scale
• System characteristics
• Hierarchical structure with the formation as
  central unit (cf. Salvador
  (ed.), 1994)
• Applicable on large sets of standardised core
  decriptions
• Basis for parameterisation of layer properties

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Lithostratigraphy and scale
(after Heinz Aigner, 2003)
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Lithostratigraphic modelling
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But what about the application?

• The concept and scale of a lithostratigraphic
  unit do not allow for a sensible schematisation
  in applied geological modelling
• Sediment properties are highly variable on small
  spatial scales
• Fluvial sand ? fluvial sand (channel, levee,
  crevasse, etc.)
• Interpolation does not resolve this problem
• The lithofacies concept and sensible spatial
  modelling might help

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Model complexity
Nation-wide to regional model geological units
at the formation / member / bed level
Top-layer model based on facies distribution
within stratigraphic units used in numerical
parameterisation
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Lithofacies concept

• Sediment properties are directly derived from the
  sedimentary environment the deposits originated
  in. This includes lithology and sedimentary
  architecture
• Unit scale depends on the model application, but
  is typically m-scale
• Units are lithofacies associations rather than
  individual lithofacies (cf. Miall. 1999)
• Sedimentary environments repeat itself in
  geological time. Therefore, only 27 lithofacies
  units are needed to characterise all Quaternary
  deposits in the subsurface of the Netherlands

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Example estuarine environment

• Lithofacies units
• Marine lithofacies units
• Coastal lithofacies units
• Tidal channel
• Tidal flat
• Salt marsh
• Coastal lagoon
• Fluvial lithofacies units

(after Allen, 1991)
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Lithostratigraphy, lithofacies and scale
(after Heinz Aigner, 2003)
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Lithofacies modelling
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Example Province of Zeeland
N
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Conclusions

• Lithostratigraphic classification is a first step
  in organising the apparent chaos in the
  subsurface up to the level of architectural
  elements. Beyond that level, further
  lithostratigraphic subdivision is not very useful
• A combination of lithostratigraphic
  classification and lithofacies modelling enables
  the construction of subsurface models that are
  best capable to address applied geological
  questions

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More information

• Lithostratigraphy and 2D lithostratigraphic
  modelling
• www.dinoloket.nl
• 3D lithofacies modelling
• Session IEI-2225. August 9, 1500 (room A1-1)
• 3D subsurface characterization of the
  Netherlands Results from stochastic modelling
  by Jan Stafleu
• Thank you for your attention
• jeroen.schokker_at_tno.nl

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Integrating the concepts of lithostratigraphy and
lithofacies in applied geological mapping

• Jeroen Schokker, Wim Westerhoff Henk Weerts
• Deltares / TNO Geological Survey of the
  Netherlands