Presentation on theme: "GE0-3112 Sedimentary processes and products Lecture 13. Sequence stratigraphy Geoff Corner Department of Geology University of Tromsø 2006 Literature:"— Presentation transcript:
GE Sedimentary processes and products Lecture 13. Sequence stratigraphy Geoff Corner Department of Geology University of Tromsø 2006 Literature: - Leeder Ch. 14. Changing sea level and sedimentary sequences. - Reading & Levell Ch. 2. Controls on the sedimentary rock record.
Stratigraphy – the subdivision of rocks in time and space ► Lithostratigraphy ► Biostratigraphy ► Chronostratigraphy ► Magnetostratigraphy ► Chemostratigraphy ► Morphostratigraphy ► Climatostratigraphy ► Kinetostratigraphy ► Tectonostratigraphy ► Allostratigraphy ► Sequence stratigraphy
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.
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).
What criteria do we use? ► Stacking patterns - indicate relative sea- level change and or sediment supply. ► Bounding surfaces
Components of a sequence ► Bounding surfaces Sequence boundary Transgressive surface Maximum flooding surface ► Systems tracts LST TST HST/RST ► Parasequences Prothero & Schwab 1996
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. Flooding surfaces Prothero & Schwab 1996
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
Lowstand ST ► Formed immediately following s.l. lowstand. ► Fluvial incision ceases; progradational to aggradational marine parasequences deposited. ► Active submarine fans below the shelf break.
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.
Highstand ST ► Formed during rising and high s.l. ► Accomodation = sediment supply aggradational to progradational parasequences.
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
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
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
An example of sequence stratigraphic subdivision applied to fjord-valley fills Corner, in press
► Deglacial-postglacial transgressive- regressive fill Corner, in press
Transgressive systems tract Highstand systems tract Forced-regressive systems tract Corner, in press ► TST ► HST ► RST
Corner, in press
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.