Sequence Stratigpygraphy the study of rock relations within a time‐ stratigraphic framework of repetitive, genetically related strata bounded by surfaces of erosion or non‐deposition, or their correlative conformities. Important because it places strata into a predictable, cronostratrigraphic framework and relates them to accommodation space Lithostratigraphy vs. Sequence stratigraphy Historical prospective • Barrell 1917 ::Sedimentation”Sedimentation controlled by base level will result in divisions of the stratigraphic series separated by breaks”. • The term “”“sequence” was iddintroduced by Sloss et al. (1949) to designate a stratigraphic unit bddbounded by subilbaerial unconfiiformities. He identified 6 major unconformities in North AiAmerica. Correlative conformities Seismic stratigraphy • Vail et al. (1977): eustasy is the main driving force behind sequence formation at all levels of stratigraphic cyclicity. Seismic stratigraphic + global sea level chart. • Winter (1984): tectonic stratigraphy… • This is why it is all about relative sea level change vs. sea level change…. Accommodation space (i.e. relative sea level change) EUSTACY SUBSIDENCE / UPLIFT Posamentier, 198 Accommodation space equation Space is created by changgging in tectonic Space is filled with subsidence and Eustasy TESWT+E=S+W water and sediments T: Tectonic subsidence E=rate of Eustatic sea level rise S: sedimentation rate W: water depth Hierarchy 1) Depositional sequence (bounded by sequence boundary) 2) System tracts: a linkage of contemporaneous depositional systems 3) Parasequence set (stacking patterns: progradational, aggradational, retrogradational) 4) Parasequence (bounded by flooding surfaces) 5) Flooding surface Depositional system • A 3D assemblage of lithofacies genetically linked and coexisting today (fluvial, delataic, barrier‐island) Depositional sequence • A relative conformable succession of genetically related strata bouned by unconformities (i. e. sequence boundary) or related conformities. • Important: every depositional sequence is the record on one cycle of relative sea level • Important: every DiilDepositional sequence is bounded above and below by unconformities or correlilative conffiiormities. System tract (subdivision of the depositional system) Genetically associated stratigraphic units that were dddeposited during specific phases of the relative sea‐level cycle (Posamentier, et al, 1988) and represented in the rock record as three‐dimensional facies assemblages. They are defined on the basis of bounding surfaces, position within a sequence, and parasequence stacking pattern (Van Wagoner et al., 1988) The original 3 system track HST TST LST Highstand systems tract (HST): slow rose of relative sea level • During such a slow rise in relative sea level, sediment suppl y is > rise, driving a seaward building of the coast known as progradational stacking. The HST will contain an increasingly progradational set of parasequences. In the late highstand systems tract, eustatic sea level begins to fall, but subsidence > fall, such that relative sea‐level is rising, albeit at ever‐ slower rates. • Eventually, as the rate of eustatic fall increases, it eventually exceeds the rate of subsidence, leading to a relative fall in sea level (Falling stage system track + Sequence boundary). Lowstand systems tract (LST) • As the rate of eustatic fall slows, it eventually equals the rate of subsidence and is then exceeded by the rate of subsidence, leading to a slow relative rise in sea‐level. Just as in the highstand systems tract, this slow rise is outpaced by sedimentation rate, leading to a progradational set of parasequences called the lowstand systems tract (LST). Transgressive systems tract (TST) • As the rate of eustatic rise increases, the rate of relative sea‐level rise also increases and eventually outpaces the supply of sediment, leading to retrogradational parasequence stacking. Such retrogradational stacking is called the transgressive systems tract (TST). Hierarchy of surfaces • Sequence boundary (Depositional sequence) • Transgressive surface (System tract) • Maximum floo ding surface ()(Parasequence) The key vertical succession in all dldepositional sequences: From bottom to top: 1) Sequence boundary 2) Low Stan d system Track (LST) 3) Transgressive surface 4) Transgressive system track (TST) 5) Maximum flooding surface 6) Highs stand system track (HST) How do you recognize a sequence boundary? PARASEQUENCE Definition • Genetically related, relatively conformable successions of beds and bedsets bounded by flooding surfaces and their correlative surfaces Beds and bedsets are part of the same progradational event The deposits of a simple progradation of the shoreline Van Wagoner et al., 1990 Flooding Surface Surface marked by deeper‐water strata resting on shallower‐water strata Van Wagoner et al., 1990 Can be caused by: • A reltilative rise in sea lllevel due to tectonic subsidence or faulting • Eustacy • Simple delta lobe compaction Flooding Surface Van Wagoner, Mitchum, Campion and Rahmanian 1990 Origin and scale of Parasequences Because shallow water facies within a parasequence will pinch out laterally in a downdip direction and deeper water facies within a parasequence will pinch out in an updip direction, the facies composition of a single parasequence changes predictably updip and downdip. Thus, a single parasequence will be composed of deeper water facies downdip and shallower water facies updip, as would be expected. Parasequences Example of siliciclastic wave dominated shoreline: 1) bioturbated offshore mudstones, 2) pass thhhrough the storm bdbeds of the transition zone or lower shoreface, 3) continue through the trough crossbedding of the shoreface, 4) pass upwards into the seaward inclined laminae of the foreshore, 5) and be capped by a backshore or coastal plain coal bed. System tracks and parasequences are arranged into parasequence sets (stacking pattern) • A succession of ggyenetically related parasequences that form a distinctive stacking pattern ((pexample: ppgrogradatioal , retrogradational, aggradational) Stacking patterns Sedimentation>accomodation Stacking patterns Sedimentation=accomodation Stacking patterns Sedimentation<accomodation Loss of accommodation 0 Increasing rate of accommodation S R Incision ed e im g e ional n t Retrogradational s Parasequence Aggradational u Parasequence p p ly = A cc Sequence Boundary o m m o d a ti o Rate of sediment supply < Sediment bypass n Rate of accommodation Rate of sediment supply > Rate of accommoda Pro Parasequence g rada t io n 96_0118_13 t al ion Sediment Su Accommodation Increasing rate of sediment supply (modified from Shanley andMcCabe, vs pp y 1996) l y Transition from marine tito non marine After Catuneanu, 2006 Mississippi River Birdsfoot delta What are we looking at? (Cretaceous Mancos Shale near Woodside, Utah) Tidal influence HST TST LST What is this? HST Low Stand system Tract Progradational sequence, LST, sed rates>accomodation rates, shallowing upward Lowstand systems tract Transgressive systems tract Highstand systems tract.