GE0-3112 Sedimentary processes and products

1. Lecture 13. Sequence stratigraphy GE0-3112 Sedimentary processes and products Literature: - Leeder 1999. Ch. 14. Changing sea level and sedimentary sequences. - Reading & Levell 1996. Ch. 2. Controls on the sedimentary rock record. Geoff Corner Department of Geology University of Tromsø 2006

2. Contents • Stratigraphy • Why sequence stratigraphy? • Parasequences • Systems tracts • Bounding surfaces

3. Stratigraphy – the subdivision of rocks in time and space • Lithostratigraphy • Biostratigraphy • Chronostratigraphy • Magnetostratigraphy • Chemostratigraphy • Morphostratigraphy • Climatostratigraphy • Kinetostratigraphy • Tectonostratigraphy • Allostratigraphy • Sequence stratigraphy

4. What is sequence stratigraphy? • Packages of strata deposited during a cycle of relative sea-level change and/or changing sediment supply. • Genetic/interpretative approach: • packages related to relative sea-level and/or sediment supply. • packages bounded by chronostratigraphic surfaces.

5. Walker 1992

6. Why use sequence stratigraphy? • To correlate and predict facies and unconformities: division of the sedimentary record into time-related genetic units. • To understand the distribution of sedimentary facies and unconformities in time and space. • To determine the amplitudes and rates of change of past relative sea-level and, in turn, understand the cyclic and non-cyclic nature of tectonics and climate change (durations of 10 ka - >50 Ma).

7. What criteria do we use? • Stacking patterns - indicate relative sea-level change and or sediment supply. • Bounding surfaces

8. Components of a sequence • Bounding surfaces • Sequence boundary • Transgressive surface • Maximum flooding surface • Systems tracts • LST • TST • HST/RST • Parasequences Prothero & Schwab 1996

9. Parasequences • Parasequences: the small-scale building blocks of systems tracts and sequences. • A parasequence represents a proximal to distal change in facies accumulated during a minor cycle in the balance between sediment supply and accomodation. • Each parasequence is bounded above by a flooding surface. Prothero & Schwab 1996 Flooding surfaces

10. Stacking pattern of parasequences • Progradational • Retrogradational • Aggradational Prothero & Schwab 1996

11. Sequences • A sequence is composed of a succession of parasequence sets. • Each sequence represents one major cycle of change in the balance between accomodation space and sediment. • A sequence is subdivided into 3 or 4 systems tracts, each representing a specific part of the cycle. Prothero & Schwab 1996

12. Systems tracts • Exxon • LST, TST, HST (incl. RST) • Alternative • LST, TST, HST, RST (forced RST) Walker 1992

13. Lowstand ST • Formed immediately following s.l. lowstand. • Fluvial incision ceases; progradational to aggradational marine parasequences deposited. • Active submarine fans below the shelf break.

14. Transgressive ST • Formed during s.l. rise. • Accomodation space > sediment supply  retrogradational parasequences. • Base of TST is the transgressive surface (=ravinement erosional surface of shoreface). • Top of TST is the maximum flooding surface.

15. Highstand ST • Formed during rising and high s.l. • Accomodation = sediment supply  aggradational to progradational parasequences.

16. Falling stage ST • Formed during a s.l. fall (forced regression). • (Included in late HST in Exxon system). • May be associated with erosion. Walker 1992

17. Bounding discontinuites • Sequence boundary (SB) - surface of subaerial erosion and its correlative marine surface formed during sea-level fall. Corresponds to base of incised valley in proximal areas. • Transgressive (ravinement) surface (TS) - transgressive surface of marine (shoreface) erosion. • Marine flooding surface - surface across which there is evidence of an abrupt increase in water depth (may be used to separate parasequewnces). • Maximum flooding surface (MFS) - surface marking regional transition from trangression to regression and most landward extent of the shoreline - commonly marked by a condensed section (horizon). • Regressive surface of erosion. (NB. may be removed by subaerial erosion or transgressive surface). Prothero & Schwab 1996

18. Wheeler (time-distance) diagrams Prothero & Schwab 1996

19. Sequence stratigraphy and global sea-level cycles • Various orders of global sea-level change distinguisged: • 1st order (200-400 m.y.), e.g. lowstand during Permian Pangea. Controlled by major tectonic cycles. • 2nd order (10-100 m.y.), e.g. Mid-Cretaceous highstand. Controlled by changes in ocean-ridge spreading rate. • Global correlation of sequences related to eustatic sea-level curves is difficult or impossible due to local variations in tectonics and sediment supply. Sequence development is dependent on: 1) sea level, 2) tectonics, 3) sediment supply. Walker 1992

20. An example of sequence stratigraphic subdivision applied to fjord-valley fills Corner, in press

21. Deglacial-postglacial transgressive-regressive fill Corner, in press

22. TST • HST • RST Highstand systems tract Transgressive systems tract Forced-regressive systems tract Corner, in press

23. Corner, in press

24. Further reading • Coe (ed.) 2003. The Sedimentary Record of Sea-Level Change. • Well illustrated, modern treatment of sequence stratigraphy and depositional successions. • Emery & Myers 1996. Sequence stratigraphy. • Similar to above but more dated. Gives background to nomenclature. • E-learning journal. Sequence stratigraphy. • Walker 1992, in Walker & James (Ch. 1, 'Facies, Facies Models and Modern Stratigraphic Concepts'). • Corner, G.D. (in press, 2006). A transgressive-regressive model of fjord-valley fill: stratigraphy, facies and depositional controls. In Dalrymple, R.W., Leckie, D. and Tillman, R.W. (eds.) ‘Incised-Valley Systems in Time and Space', SEPM Special Publication.