Presentation on theme: "GE Sedimentary processes and products"— Presentation transcript:
1 GE0-3112 Sedimentary processes and products Lecture 13. Sequence stratigraphyLiterature:- Leeder Ch. 14. Changing sea level and sedimentary sequences.- Reading & Levell Ch. 2. Controls on the sedimentary rock record.Geoff CornerDepartment of GeologyUniversity of Tromsø2006
2 Contents Stratigraphy Why sequence stratigraphy? Parasequences Systems tractsBounding surfaces
3 Stratigraphy – the subdivision of rocks in time and space LithostratigraphyBiostratigraphyChronostratigraphyMagnetostratigraphyChemostratigraphyMorphostratigraphyClimatostratigraphyKinetostratigraphyTectonostratigraphyAllostratigraphySequence 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.
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 surfacesSequence boundaryTransgressive surfaceMaximum flooding surfaceSystems tractsLSTTSTHST/RSTParasequencesProthero & Schwab 1996
9 ParasequencesParasequences: 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 1996Flooding surfaces
10 Stacking pattern of parasequences ProgradationalRetrogradationalAggradationalProthero & 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
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 tractCorner, in press
24 Further readingCoe (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.