integrating the concepts of lithostratigraphy and lithofacies in applied geological mapping
DESCRIPTION
Integrating the concepts of lithostratigraphy and lithofacies in applied geological mapping . Jeroen Schokker , Wim Westerhoff & Henk Weerts Deltares / TNO – Geological Survey of the Netherlands. Aim. - PowerPoint PPT PresentationTRANSCRIPT
Integrating the concepts of lithostratigraphy and lithofacies in applied geological mapping
Jeroen Schokker, Wim Westerhoff & Henk Weerts
Deltares / TNO – Geological Survey of the Netherlands
August 8, 2008Schokker, Westerhoff & Weerts 2
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
Aim
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
August 8, 2008Schokker, Westerhoff & Weerts 3
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
August 8, 2008Schokker, Westerhoff & Weerts 4
Lithostratigraphy and scale
(after: Heinz & Aigner, 2003)
August 8, 2008Schokker, Westerhoff & Weerts 5
Lithostratigraphic modelling
August 8, 2008Schokker, Westerhoff & Weerts 6
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…
August 8, 2008Schokker, Westerhoff & Weerts 7
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
August 8, 2008Schokker, Westerhoff & Weerts 8
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
August 8, 2008Schokker, Westerhoff & Weerts 9
Example: estuarine environment
(after: Allen, 1991)
Lithofacies units:• Marine lithofacies units• Coastal lithofacies units
• “Tidal channel”• “Tidal flat”• “Salt marsh”• “Coastal lagoon”
• Fluvial lithofacies units
August 8, 2008Schokker, Westerhoff & Weerts 10
Lithostratigraphy, lithofacies and scale
(after: Heinz & Aigner, 2003)
August 8, 2008Schokker, Westerhoff & Weerts 11
Lithofacies modelling
August 8, 2008Schokker, Westerhoff & Weerts 12
Example: Province of Zeeland
Tidal flat depositsTidal channel deposits (sand)Tidal channel deposits (shells)
N
August 8, 2008Schokker, Westerhoff & Weerts 13
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
August 8, 2008Schokker, Westerhoff & Weerts 14
More information
Lithostratigraphy and 2D lithostratigraphic modelling:www.dinoloket.nl
3D lithofacies modelling:Session IEI-22–25. August 9, 15:00 (room A1-1)“3D subsurface characterization of the Netherlands: Results from stochastic modelling” by Jan Stafleu
Thank you for your attention
Integrating the concepts of lithostratigraphy and lithofacies in applied geological mapping
Jeroen Schokker, Wim Westerhoff & Henk Weerts
Deltares / TNO – Geological Survey of the Netherlands