Lithostratigraphy

This section is taken from Bethan Davies’ PhD thesis.

What is Lithostratigraphy? | Vertical Profiles | Lithofacies Associations | Landsystems | References | Comments |

What is Lithostratigraphy?

Bethan Davies cleaning a face for sedimentological logging in County Durham.

Lithostratigraphy is the ‘classification of bodies of rock based on the observable lithological properties of the strata and their relative stratigraphic positions’1. Stratigraphy includes information about processes, geographical distributions, and the palaeo-environment of past glaciers and glaciation. It involves an attempt to determine the chronological sequence of geological events over a wide area.

Lithofacies associations, landform-sediment assemblages, depositional processes, syndepositional tectonics, landsystems, and geochronology are combined in a hierarchical structure to form a ‘stratigraphy’, through which the history and patterns of past glaciations and their associated environments can be reconstructed and interpreted1,2.

Sedimentological approaches should be based upon the ‘lithostratigraphic unit’, which has distinctive lithological properties, should be capable of being mapped and is typically tabular3,4. The lithostratigraphic unit has a hierarchical system with the Group, Formation, Member and Bed sub-categories5, and each new mappable lithostratigraphic unit must be formally proposed with a stratotype, and described emphasising lithological properties1,3. A lithostratigraphic scheme therefore:

  1. Has a hierarchical structure with the formation as the central (top) unit;
  2. Has a clear nomenclature;
  3. Describes each facies properly;
  4. Contains mappable units only.

Therefore, for a sedimentological investigation, the overall facies architecture and different lithofacies associations are mapped, logged and described in detail. The lithofacies associations are ultimately interpreted within a sediment-landform association, primarily in order to assess the processes by which glacigenic sediments were deposited and deformed. Through detailed lithological and petrological analyses, correlations between lithofacies associations and to regional stratotypes, based on processes of deposition, lithological and petrological similarity, and chronostratigraphy, are possible. Ultimately, it is possible to make statements about provenance, age, and regional glacial lithostratigraphy.

Vertical Profiles

Vertical profile from a coastal cliff section on the Durham coastline. Published in Davies et al., 2012.

Lithostratigraphy must take a hierarchical approach. The first stage is individual sediment logging. Vertical profiles are a method of recording detailed sedimentological information from a section, and they can be used for the comparison and correlation of different localities. They highlight gradual, particularly vertical, trends, and provide a representative summary of exposures6. Detailed sketches of macro-scale features such as deformation structures can provide information regarding the genesis and depositional history of glacigenic sediments. The colour of a sediment is the most immediately visible property, and can indicate more fundamental differences in composition, such as mineralogy7. Identifying the colour of a sediment is essential if the lithology is to be fully characterised. Facies characteristics are noted using standard facies codes (Table 1).

Therefore, to log an onshore field section, one requires that a GPS, photography and sketches are utilised to accurately map the overall facies architecture and to record spatial relationships between lithofacies. Specific exposures should be sketched and logged according to standard procedures8, noting the sedimentary structures, contacts, deformation structures, Munsell colour, texture, particle size, clast lithology and shape, grading, and sorting of each facies. All sections should be levelled to metres O.D. using standard levelling techniques.

An example of a vertical profile is shown in the figure opposite9. This log was taken from the Durham coastline at Warren House Gill and is published in the journal Boreas. The orange diamicton is the Blackhall Till formation. Yellow sands are the Peterlee Sand and Gravel Formation. Brown diamicton is the Horden Till Formation.

Table 1: Glossary of abbreviations used in section logs8,10.

Diamicton Fine Gravel (2-8 mm)
Dm Diamicton, matrix-supported GRcl Massive with clay laminae
Dmm Diamicton, massive, matrix-supported GRch Massive and infilling channels
Dms Stratified matrix-supported diamicton GRh Horizontally bedded
Dcm Clast-supported diamicton GRm Massive and homogenous
Dmg Matrix-supported, graded GRmb Massive and pseudo-bedded
Dml Matrix supported, laminated GRmc Massive with isolated outsize clasts
— (p) Includes clast pavement GRmi Massive with isolated, imbricated clasts
— (g) Graded diamicton GRmp Massive with clast stringers
— (b/s) Banded / sheared GRo Openwork structure
  GRruc Repeated upward-coarsening cycles
Silts and Clays (<0.063 mm) GRruf repeated upward-fining cycles
Fm Fines, massive GRt Trough cross-bedded gravel
Fl Fines, laminated. GRcu Upward coarsening (inverse grading)
Flv Fine lamination with rhythmites or varves. GRfu Upward fining (normal)
Frg Graded or climbing-ripple cross-lamination GRp Cross-bedded
Fcpl Cycopels GRfo Deltaic foresets
Fp Intraclast or lens
—(d) with dropstones Coarse Gravel (8-256 mm)
— (w) with dewatering Gms Matrix supported, massive gravel
  Gm Clast supported, massive
Sands (0.063 to 2 mm) Gsi Matrix supported, imbricated
Sm Massive sand Gmi Clast supported, massive, imbricated
St (A) Ripple cross laminated (Type A) Gfo Deltaic foresets
St (B) Ripple cross laminated (Type B) Gh Horizontally-stratified gravel
St (S) Ripple cross laminated (Type S) Gt Trough cross-bedded gravel
Scr Climbing ripples Gp Gravel, planar-cross bedded
Ssr Starved ripples Gfu Upward fining (normal grading)
Sr Sand, ripple-cross laminated Gcu Upward coarsening (inverse grading)
Sh Very fine to very coarse and horizontally / planar bedded or low angle cross lamination Go Open framework gravels
Sd Deformed bedding Gd Deformed bedding
St Medium to very coarse trough cross-bedded Glg Palimpsest (marine) or bedload lag
Sp Medium to very coarse planar cross-bedded  
Sl horizontal or draped lamination Boulders (>256 mm)
Sh Sheared sand B Boulders
Sfo Deltaic foresets Bh Horizontally-bedded boulders
Sfl Flasar bedded Bms Matrix supported, massive
Se Erosional scours with intraclasts and crudely cross-bedded Bcg Clast supported, graded
Su Fine to coarse with broad shallow scours and cross-stratification BL Boulder lag or pavement
Sc Steeply dipping planar cross bedding Bfo Deltaic foresets
Suc Upward coarsening Bmg Matrix supported, graded
Suf Upward fining  
Srg Graded cross-lamination Structure
SB Bouma sequence Bo Boudinage
Scps Cycoplasms Be Bedding
— (d) with dropstones Ba Banding
— (w) with dewatering  

Lithofacies Associations

Each facies is characterised by its individual properties in the vertical profile. On the basis of physical similarities, these sedimentary facies are correlated to form ‘lithofacies’8. Lithofacies are sediments with a distinctive combination of properties, classified on the basis of their colour, texture, the lithology of clastic particles, thickness and geometry, presence / absence of fossils, and other sedimentary structures11. Their spatial organisation is logged using an overall facies architecture sketch. It is important to separate detailed field description and labelling from genetic perspectives and terminology. Inadequate field descriptions thwart later sophisticated environmental re-interpretation12, as the interpretation of a genetic facies is subject to revision as ideas and knowledge change and the science develops. Lithofacies therefore are identified only on their physical, biological and chemical characteristics, with no inferred genesis8. This separation of description and interpretation ensures a more objective approach, less prone to bias, error and subjectivity. In this thesis, each chapter is analysed separately and the sediments are assigned to lithofacies associations particular to that specific site.

A hierarchical approach to sedimentology is a powerful tool for describing how sediments, landforms and landscapes fit together, and in determining how the landscape reflects depositional processes and external controls on the environment13. However, sediments are laid down in associations; these assemblages reflect a range of processes active in any one given environment, which can be deposited at a range of scales. ‘Lithofacies Associations’ (LFAs) are distinct vertical successions of genetically related lithofacies11. Through recognising these packages, ancient glacial settings can be recognised and reconstructed.

Landsystems

Lithofacies associations can be analysed in conjunction with landforms to create sediment-land for associations14. Sediment-landform suites are indicative and characteristic of specific styles of glaciation (‘glacial landsystems’), such as surging glaciers, ice streams, plateau ice fields, sub-aquatic landsystems, and active-temperate terrestrial ice margins15. Glacial landsystems are composed of ‘land units’ (geomorphological features such as drumlin fields, moraine belts, etc.) and ‘land elements’ (a tunnel valley, a moraine, an esker, and the associated sediments), which together form a landsystem, a ‘recurrent pattern of genetically linked land units’16. Recent analyses of glacial landsystems stress their complexity and the fact that sediment-landform associations are dictated by the location and style of deposition17-21.

Citation

Davies, B.J., 2009. British and Fennoscandian Ice-Sheet Interactions during the Quaternary, Unpubl. PhD Thesis. Department of Geography, Durham University, Durham, 502 pp.

Bethan Davies Thesis (Zipped PDFs – 70MB)

References


1.         Weerts, H.J.T. & Westerhoff, W.E. Quaternary Stratigraphy. Lithostratigraphy. in Encyclopedia of Quaternary Science (ed. Elias, S.A.) 2826-2840 (Elsevier, Amsterdam, 2007).

2.         Rose, J. & Menzies, J. Glacial Stratigraphy. in Past Glacial Environments: Sediments, Forms and Techniques. (ed. Menzies, J.) 253-284 (Butterworth-Heinemann Ltd, Oxford, 1996).

3.         Salvador, A. The International Stratigraphic Guide: a guide to stratigraphic classification, terminology, and procedure., 214 (International Subcommission on Stratigraphic Classification. International Union of Geological Sciences, Boulder, 1994).

4.         McMillan, A. A provisional Quaternary and Neogene lithostratigraphical framework for Great Britain. Netherlands Journal of Geosciences – Geologie en Mijnbouw 84, 87-107 (2005).

5.         Rawson, P., Allen, P., Brenchley, P., Cope, J., Gale, A., Evans, J., Gibbard, P., Gregory, F., Hailwood, E., Hesselbo, S., Knox, R., Marshall, J., Oates, M., Riley, N., Smith, A., Trewin, N. & Zalasiewicz, J. Stratigraphical Procedure, 57 (The Geological Society, London, 2002).

6.         Jones, A.P., Tucker, M.E. & Hart, J.K. The description and analysis of Quaternary stratigraphic field sections. Technical Guide No. 7., 293 (Quaternary Research Association, Cambridge, 1999).

7.         Gale, S.J. & Hoare, P.G. Quaternary Sediments: Petrographic methods for the study of unlithified rocks., 323 (John Wiley & Sons, New York, 1991).

8.         Evans, D.J.A. & Benn, D.I. (eds.). A practical guide to the study of glacial sediments, 266 (Arnold, London, 2004).

9.         Davies, B.J., Roberts, D.H., Bridgland, D.R. & Ó Cofaigh, C. Dynamic Devensian ice flow in NE England: a sedimentological reconstruction. Boreas 41, 337-366 (2012).

10.       Krüger, J. & Kjær, K.H. A data chart for field description and genetic interpretation of glacial diamicts and associated sediments – with examples from Greenland, Iceland, and Denmark. Boreas 28, 386-402 (1999).

11.       Eyles, N. & Lazorek, M. Glacial Landforms, Sediments. Glacigenic Lithofacies. in Encyclopedia of Quaternary Science (ed. Elias, S.A.) 920-932 (Elsevier, Oxford, 2007).

12.       Eyles, C.H. & Eyles, N. Sedimentation in a large lake: a reinterpretation of the late Pleistocene stratigraphy at Scarborough Bluffs, Ontario, Canada. Geology 11, 146-152 (1983).

13.       Benn, D.I. & Evans, D.J.A. Introduction and rationale. in A practical guide to the study of glacial sediments (eds. Evans, D.J.A. & Benn, D.I.) 1-10 (Arnold, London, 2004).

14.       Evans, D.J.A. & Benn, D.I. Glacial Landforms. Introduction. in Encyclopedia of Quaternary Science (ed. Elias, S.A.) 757-772 (Elsevier, Oxford, 2007).

15.       Evans, D.J.A. Introduction to glacial landsystems. in Glacial Landsystems (ed. Evans, D.J.A.) 1-11 (Arnold, New York, 2003).

16.       Evans, D.J.A. Glacial Land Systems. in Encyclopedia of Quaternary Science (ed. Elias, S.A.) 808-818 (Elsevier, Oxford, 2007).

17.       Alexanderson, H., Adrielsson, L., Hjort, C., Möller, P., Antonov, O., Eriksson, S. & Pavlov, M. Depositional history of the North Taymyr ice-marginal zone, Siberia – a landsystem approach. Journal of Quaternary Science 17, 361-382 (2002).

18.       Evans, D.J.A. & Twigg, D.R. The active temperate glacial landsystem: a model based on Breiethamerkurjokull and Fjallsjokull, Iceland. Quaternary Science Reviews 21, 2143-2177 (2002).

19.       Jennings, C.E. Terrestrial ice streams – a view from the lobe. Geomorphology 75, 100-124 (2006).

20.       Lukas, S. Morphostratigraphic principles in glacier reconstruction – a perspective from the British Younger Dryas. Progress in Physical Geography 30, 719-736 (2006).

21.       Ottesen, D., Dowdeswell, J.A., Benn, D.I., Kristensen, L., Christiansen, H.H., Christensen, O., Hansen, L., Lebesbye, E., Forwick, M. & Vorren, T.O. Submarine landforms characteristic of glacier surges in two Spitsbergen fjords. Quaternary Science Reviews 27, 1583-1599 (2008).

Share this

If you enjoyed this post, please consider subscribing to the RSS feed to have future articles delivered to your feed reader.

Leave a Reply

Your email address will not be published.