GE0-3112 Sedimentary processes and products Lecture 13. Sequence stratigraphy 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

Contents Stratigraphy Why sequence stratigraphy? Parasequences Systems tracts Bounding surfaces

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.

Walker 1992

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. Prothero & Schwab 1996 Flooding surfaces

Stacking pattern of parasequences Progradational Retrogradational Aggradational 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

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

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

Wheeler (time-distance) diagrams Prothero & Schwab 1996

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

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

Deglacial-postglacial transgressive-regressive fill Corner, in press

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

Corner, in press

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.