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GE Sedimentary processes and products

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1 GE0-3112 Sedimentary processes and products
Lecture 13. Sequence stratigraphy Literature: - Leeder Ch. 14. Changing sea level and sedimentary sequences. - Reading & Levell 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 Alternative LST, TST, HST (incl. RST)
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 ( m.y.), e.g. lowstand during Permian Pangea. Controlled by major tectonic cycles. 2nd order ( 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.) The Sedimentary Record of Sea-Level Change. Well illustrated, modern treatment of sequence stratigraphy and depositional successions. Emery & Myers 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.

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