GY 402: Sedimentary Petrology

Transcription

1 UNIVERSITY OF SOUTH ALABAMA GY 402: Sedimentary Petrology Lecture 28: Student Choice Lecture 1: Sequence Stratigraphy Instructor: Dr. Douglas W. Haywick

2 Today Sequence Stratigraphy The basic concept (systems tracts) All sorts of STs (systems tracts) Boundaries

3 Sequence Stratigraphy Is derived from seismic profiles whereby you recognize distinct sedimentary packages

4 Sequence Stratigraphy Is derived from seismic profiles whereby you recognize distinct sedimentary packages (systems tracts) From Carter et al., 1991

5 Sequence Stratigraphy A Short History The Vail Curve is synonymous with eustasy

6 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)

7 Sequence Stratigraphy A Short History Why? Because sea level controls what sediment is produced and where it is deposited.

8 Sequence Stratigraphy A Short History Accommodation Space: The thickness of sediment that can be deposited (it s sea level-controlled)

9 Sequence Stratigraphy A Short History Accommodation Space: (+) with sea level highstands; (-) with sea level lowstands

10 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.

11 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

12 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).

13 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.

14 Sequence Stratigraphy (System Tracts) LST: Low stand systems tract: stacking patterns exhibit backstepping, onlapping, retrogradational, aggrading clinoforms that thicken updip

15 Sequence Stratigraphy (System Tracts)

16 Sequence Stratigraphy (System Tracts)

17 Sequence Stratigraphy (System Tracts)

18 Sequence Stratigraphy (System Tracts) Remember that you are doing all this via seismic traces

19 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

20 Sequence Stratigraphy (System Tracts) LST: Low stand systems tract: includes deposits that accumulate after the onset of relative a sea-level rise.

21 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.

22 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.

23 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.

24 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.

25 Sequence Stratigraphy Summary

26 Sequence Stratigraphy Summary Bounding Surfaces

27 Boundaries Systems tracts are separated by sequence boundaries (SB) which by definition, occur at the base of LSTs.

28 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.

29 Boundaries Transgressive surfaces (TS) are commonly marked by lag deposits

30 Boundaries The maximum flooding surface (MFS) is the point of maximum sea level rise. It is commonly marked by a lag deposit of shells.

31 Evolution of an idea Sequence stratigraphy is still evolving..unfortunately, that means more jargon.

32 Outcrops and Sequence Stratigraphy Since the mid 1980s, researchers have attempted to relate outcrops with sequence stratigraphy. Haywick et al. (2000)

33 Outcrops and Sequence Stratigraphy Haywick et al. (2000)

34 Outcrops and Sequence Stratigraphy S5 SB S4 SB S3 Haywick et al. (2000)

35 Outcrops and Sequence Stratigraphy CC S3 CC S2 Haywick et al. (2000)

36 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

37 GY 402: Sedimentary Petrography Lectures 27: Student Choice 1 Instructor: Dr. Doug Haywick dhaywick@southalabama.edu This is a free open access lecture, but not for commercial purposes. For personal use only.