UNIVERSITY OF SOUTH ALABAMA GY 402: Sedimentary Petrology Lecture 28: Student Choice Lecture 1: Sequence Stratigraphy Instructor: Dr. Douglas W. Haywick Today Sequence Stratigraphy • • • The basic concept (systems tracts) All sorts of STs (systems tracts) Boundaries Sequence Stratigraphy Is derived from seismic profiles whereby you recognize distinct sedimentary packages Sequence Stratigraphy Is derived from seismic profiles whereby you recognize distinct sedimentary packages (systems tracts) From Carter et al., 1991 Sequence Stratigraphy A Short History The “Vail Curve” is synonymous with eustasy Sequence Stratigraphy A Short History "Pete's ideas evolved naturally from his first pioneering work on the importance of stratal surfaces in rocks as geologic time lines," wrote Robert Mitchum, a longtime friend and former Exxon colleague. "He soon recognized the cyclic occurrence of bundles of strata he called sequences in well logs, seismic reflections and outcrops. "Observing that sequence boundaries appear synchronous globally, he postulated that cyclic eustatic sea level changes are major controls on stratigraphy, along with basin tectonics and sediment supply," Mitchum said. "This realization led to the development of eustatic cycle charts”. (2003 AAPG Address) Sequence Stratigraphy A Short History Why? Because sea level controls what sediment is produced and where it is deposited. http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy A Short History Accommodation Space: The thickness of sediment that can be deposited (it’s sea level-controlled) http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy A Short History Accommodation Space: (+) with sea level highstands; (-) with sea level lowstands http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy A Short History Note: Vail’s surfaces actually define packages of sedimentary rock. Those associated with specific states of sea level are called systems tracts. http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) System Tracts come in numerous styles and are named according to sea level position/state during deposition. The 6 most important are 1) LST: Low stand systems tract 2) HST: High stand systems tract 3) TST: Transgressive systems tract 4) FSST: Falling stage systems tract 5) RST: Regressive systems tract 6) FRST: Forced regressive systems tract Chalk Board Sequence Stratigraphy (System Tracts) LST: Low stand systems tract: includes deposits that accumulate after the onset of a relative sea-level rise (during maximum sea level lowstand). http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) LST sediments often fill or partially infill incised valleys that were cut into the Highstand Systems Tract, and other earlier deposits, during the FSST. http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) LST: Low stand systems tract: stacking patterns exhibit •backstepping, •onlapping, •retrogradational, •aggrading clinoforms that thicken updip Sequence Stratigraphy (System Tracts) http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) Remember that you are doing all this via seismic traces Sequence Stratigraphy (System Tracts) Remember that you are doing all this via seismic traces. The nature of the surfaces can tell you the stage(s) of sea level during deposition. Clinoforms are parallel but inclined surfaces http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) LST: Low stand systems tract: includes deposits that accumulate after the onset of relative a sea-level rise. http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) HST: High stand systems tract: the progradational deposits that form when sediment accumulation rates exceed the rate of increase in accommodation space. Stacking patterns exhibit prograding aggrading clinoforms that thin upward. http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) HST: High stand systems tract: the progradational deposits that form when sediment accumulation rates exceed the rate of increase in accommodation space. Stacking patterns exhibit prograding aggrading clinoforms that thin upward. http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) TST: Transgressive systems tract: the deposits accumulated from the onset of coastal transgression until the time of maximum transgression of the coast. Parasequences onlap the sequence boundary in a landward direction and downlap onto the transgressive surface in a basinward direction. http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy (System Tracts) TST: Transgressive systems tract: the deposits accumulated from the onset of coastal transgression until the time of maximum transgression of the coast. Parasequences onlap the sequence boundary in a landward direction and downlap onto the transgressive surface in a basinward direction. http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy Summary http://strata.geol.sc.edu/terminology/system-tract.html Sequence Stratigraphy Summary Bounding Surfaces http://strata.geol.sc.edu/terminology/system-tract.html Boundaries Systems tracts are separated by sequence boundaries (SB) which by definition, occur at the base of LSTs. http://www.uga.edu/~strata/sequence/tracts.html Boundaries Systems tracts are separated by sequence boundaries (SB) which by definition, occur at the base of LSTs. These are unconformable surfaces generally overlain by fluvial sediments. Correlative conformities are lateral equivalents to SB’s. They still separate LSTs from earlier HSTs but are really hard to spot in seismic profiles. http://www.uga.edu/~strata/sequence/tracts.html Boundaries Transgressive surfaces (TS) are commonly marked by lag deposits http://strata.geol.sc.edu/ss-well-log.html Boundaries The maximum flooding surface (MFS) is the point of maximum sea level rise. It is commonly marked by a lag deposit of shells. http://strata.geol.sc.edu/terminology/transgression.html Evolution of an idea Sequence stratigraphy is still evolving… ..unfortunately, that means more jargon. http://strata.geol.sc.edu/terminology/transgression.html Outcrops and Sequence Stratigraphy Since the mid 1980s, researchers have attempted to relate outcrops with sequence stratigraphy. Haywick et al. (2000) Outcrops and Sequence Stratigraphy Haywick et al. (2000) Outcrops and Sequence Stratigraphy S5 SB S4 SB S3 Haywick et al. (2000) Outcrops and Sequence Stratigraphy CC S3 CC S2 Haywick et al. (2000) Upcoming Stuff Homework 1) Moscow Landing due Thursday! 2) Thin Section 8 due Thursday 3) Final Lab Test Thursday 4) Thursday is gonna suck Lab this Week Nothing…… GY 402: Sedimentary Petrography Lectures 27: Student Choice 1 Instructor: Dr. Doug Haywick [email protected] This is a free open access lecture, but not for commercial purposes. For personal use only.
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