1. Sequence Stratigraphy
Template for “Conceptual Models”
Used to Interpret
Depositional Systems
- beauty but not truth? -
Christopher G. St. C. Kendall
University of South Carolina
Sequence Stratigraphy Defined

2. Sequence Stratigraphy Defined
Why codify ‘rules’ for sequence stratigraphic nomenclature?
We use common terms and know their meaning
Have a standard hierarchy of subdivisions
Have a uniform methodology
Guidance for revision
Teaching resource: each new generation of students & practitioners have a common understanding
Sequence Stratigraphy Defined

3. Sequence Stratigraphy Defined
A framework of genetically related stratigraphic facies geometries and their bounding surfaces used to determine depositional setting
Sequence Stratigraphy Defined

4. Sequence Stratigraphy – Terminology
Stratigraphers have a position on terminology similar to the of Humpty Dumpty's from Lewis Carroll’s Through the Looking Glass
"When I use a word, it means just what I choose it to mean - nothing more nor less".
Sequence Stratigraphy Defined

5. Sequence Stratigraphy Defined
Talk Organization
Sedimentary Analysis & Sequence Stratigraphy
History of Sequence Stratigraphy
Sequence Stratigraphy Analysis Defined
Geometries & Stacking Patterns
System Tracts & Relative Sea Level
Bounding Surfaces
Conceptual Models
Terminology That Should be Defined
Conclusions
Sequence Stratigraphy Defined

6. Sequence Stratigraphy Defined
Sequence Stratigraphy – The process
Interpretation of the Sedimentary section involves:
From oldest to youngest, identify the subdividing surfaces that envelope & enclose the discrete geometric bodies of sediment of the sedimentary section & build a template
Backstrip these geometries & then use the template of surfaces to reassemble them in order of their accumulation
The subdividing surfaces, geometry, lithofacies & fauna are input to a conceptual model to determine the evolving character of the depositional setting
‘‘Each stratal unit is defined and identified only by physical relationships of the strata, including lateral continuity and geometry of the surfaces bounding the units, vertical stacking patterns, and lateral geometry of the strata within the units." (Van Wagoner et al., 1990).
Sequence Stratigraphy Defined

7. 'Depositional' sequence Vail et al 1971
Sequence Stratigraphy Defined

8. Establish a framework of genetically SB
mfs TS
Establish a framework of genetically
related stratigraphic facies geometries
and their bounding surfaces to
determine depositional setting
Sequence Stratigraphy Defined

9. Barrier Coastal Elements

10. Sequence Stratigraphy Defined
Sedimentary Analysis
Potential flow of interpretation
Scheme used
to characterize depositional systems so they can be compared
data
data
interpretation
interpretation
interpretation
Sequence Stratigraphy Defined

11. Power of Sequence Stratigraphy
Determines depositional setting by:
Establishing the order in which strata were laid down in
Explains the geometric hierarchy of sedimentary strata & the elements they form
Uses the major surfaces marking breaks in the character of sedimentary section as a template for conceptual depositional models, independent of time (relative ages)
Geologic time derived from:
Radiometric markers
Biostratigraphic markers
Sequence Stratigraphy Defined

12. Building Block Sedimentary Fill Hierarchy
Sediment body characterization in order of decreasing complexity
Complex Set
Complex
Story
Element
Bed
These are the fundamental components of Sequences and System tracts
Sequence Stratigraphy Defined

13. Fluvial - Architectural Elements
Sequence Stratigraphy Defined

14. Deepwater - Architectural Elements
Sequence Stratigraphy Defined

15. Deepwater - Architectural Elements
Sequence Stratigraphy Defined

16. Deepwater - Architectural Elements
Sequence Stratigraphy Defined

17. Hierarchy of Carbonate Shelf Architectural Elements
COMPLEX
PROGRADING MARGIN
ONLAPPING MARGIN
PROGRADING MARGIN
MARGIN
COMPLEX
PROGRADING MARGIN
STACKED BED CYCLES
BED,
LITHOLOGY,
SEDIMENTARY
STRUCTURES
FAUNA
ALLOCHEMS
CEMENTATION
& DIAGENESIS
Sequence Stratigraphy Defined

18. Elements – Sequence Building Blocks
Definition of element hierarchy
Framework for systematic description & comparison of deposits of a depositional setting (fluvial, deltaic, deepwater etc)
Based on physical organization of strata (geometry) & the surfaces bounding them
Genetically-related stratigraphic elements form the hierarchy
Independent of type of setting
Applicable at all scales & to all sedimentary systems
Purpose
Analysis & comparison of the elements of similar depositional systems
Provide the detailed character of a sequence and/or system tract
Net to-gross, aspect ratio, & connectivity
Lithofacies type & aquifer/reservoir quality
Application
Better defined depositional geometries and so depositional models
More accurate aquifer/resource assessment
Optimize strategy for depletion of aquifer/resource
Sequence Stratigraphy Defined

19. History of Sequence Stratigraphy
Sloss recognized intercontinental-unconformities & related them to eustasy
Vail extrapolated eustatic signals to seismic sequence boundaries
Jervey’s simulations showed seismic sequences product of cyclic sea level (base level) change
Van Wagoner & Posamentier related unconformities, transgressive surfaces & maximum flooding surfaces to boundaries of system tracts in depositional sequences responding to sea level change
Hydrocarbon exploration models & production reservoir models use bounding surfaces, facies assemblages & system tracts as templates for depositional models & lithofacies geometry predictions
Sequence Stratigraphy Defined

20. Sloss Unconformities & Eustasy
After Lowell Thwaite
Sequence Stratigraphy Defined

21. 1st Seismic Sequence Interpretation
Vail et al, 1976
Mesozoic through Tertiary of Offshore Morocco
Sequence Stratigraphy Defined

22. 'Depositional' sequence Vail
Jervey
Posmentier
Van Wagoner
Sequence Stratigraphy Defined

23. Sequence stratigraphy
Analytical protocol marries rules of thumb (heuristics) to conceptual models
Interprets general depositional setting of layered clastic & carbonate sedimentary strata
Models developed to interpret variety of datasets
Work best with combination of outcrop, core, well log, & seismic data
May work with two or more of these data sources but are least reliable for a single data source
Local differences in depositional processes, topography, and tectonics and, base level position, mean a model more appropriate to one setting, than others?
Sequence Stratigraphy Defined

24. Sequence Stratigraphy’s Fuzzy Rules
Lithofacies geometries & confining surfaces transgress time
Different geometries for a specific time interval
Local variations in rates & direction of tectonic movement
Local rates of sediment supply & accumulation
Not all erosional or depositional surfaces are product of base level change
Depositional models successfully predict lithofacies geometry for exploration & reservoirs
Depositional model is refined as data base grows
Sequence Stratigraphy Defined

25. Sequence stratigraphic analysis
Fundamental to sequence stratigraphic analysis:
Strata deposited in order
Surfaces subdivide strata into packages of beds with common depositional origin
Geometric arrangement of strata & packages of strata reflect
Basin filling
Erosional events
Commonly sequence stratigraphiy applied to sediment accumulation at basin margins in continental, marginal marine, and/or down-slope settings
Fill accumulates either as:
Unconfined fill over these settings
Confined within erosional down-cut topography
Sequence Stratigraphy Defined

26. Unconfined geometric architecture
Stacked layers tend to have three
basic patterns:
Aggrading (lie above one another vertically)
Prograding (inclined in order over and beside one another in a seaward direction)
Retrograding (inclined in order over & beside one another in a landward direction)
Sequence Stratigraphy Defined

27. Stacking Patterns - Unconfined
After Van Wagoner
Sequence Stratigraphy Defined

28. Confined geometric architecture
Fill post erosional down-cutting expressed by a geometric architecture of stacked layers in either succession of :
Organized offset bodies and/or
Randomly ordered disorganized offset bodies
Sequence Stratigraphy Defined

29. Confined Sedimentary Fill - Channels
Sequence Stratigraphy Defined

30. Stacking Pattern Rules & Problems
End member stratal stacking patterns reflect interplay of accommodation (space available for sediments to fill) & rates of sediment accumulation
Local vagaries in
Depositional processes
Topography
Tectonics & so base level position
mean stacking styles of geometry may merge with one another but are tied to system tracts
Sequence Stratigraphy Defined

31. Stacking, Surfaces & System tracts!
Geometric architecture of stacked layers are inferred to be related to eustatic events :
Lowstand - Progradation-to-aggradational (PA)
Transgression - Retrogradational geometries (R),
Highstand - Aggradational-to-progradation geometries (AP) system tracts (Van Wagoner et al., 1988; Neil and Abreu, 2008)
As many as five system tracts recognized but above three are most commonly used
Sequence Stratigraphy Defined

32. System Tracts - Reviewed
Sequence Stratigraphy Defined

33. System Tracts - Unconfined
3-D facies assemblages of common genetic origin with unconfined geometric architecture are interpreted to form during phases of relative sea-level cycle (Posamentier, et al, 1988)
System tracts defined by:
Bounding surfaces
Position within a sequence
Geometric stacking pattern
Lowstand - Progradation-to-aggradational (PA)
Transgression - Retrogradational geometries (R),
Highstand - Aggradational-to-progradation geometries (AP) system tracts (Van Wagoner et al., 1988; Neil and Abreu, 2008)
As many as five system tracts recognized but above three are most commonly used
Sequence Stratigraphy Defined

34. Surfaces, System tracts & Sequences
Role of conceptual depositional models:
System tracts are inferred to be related to accommodation generation and fill. This relationship is explained using conceptual models
Sequence Stratigraphy Defined

35. Sequence Stratigraphy Defined
Bounding Surfaces
Identification & interpretation of bounding surfaces that separate layered clastic and carbonate sedimentary strata into genetically related packages, system tracts, a key to Sequence Stratigraphy
Maximum Flooding Surfaces (MFS)
Transgressive Surfaces (TS) (maximum regressive surfaces & transgressive ravinement surfaces)
Sequence Boundaries (SB) (subaerial unconformities, regressive surfaces of marine erosion & correlative conformities).
Sequence Stratigraphy Defined

36. Sequence Stratigraphy Defined
Conceptual Models
Three conceptual models commonly used in sequence stratigraphy are separated from each other on basis of bounding & subdividing boundaries of system tracts:
'Depositional' sequence of Vail et al 1971
'Genetic Stratigraphic' sequence model of Galloway, 1989
'Transgressive-Regressive' (T-R) sequence model of Embry and Johannessen, 1992
Sequence Stratigraphy Defined

37. 'Depositional' Sequence (Vail et al 1971)
Bounded by subaerial unconformities & marine correlative conformities
Bounding surface assumed genetically connected with stratigraphic hiatus associated with subaerial unconformity that is progressively younger in seaward direction
No matter systems-tract terminology used bounding surfaces of this sequence enclose:
Forced regressive
Normal regressive (lowstand and highstand)
Transgressive sedimentary packages
Sequence Stratigraphy Defined

38. 'Genetic Stratigraphic' Sequence Galloway, 1989
Bounded by maximum flooding surfaces.
These surfaces interpreted to form as sea level rises rapidly, sediment supply slows & organic matter accumulates sequestering radioactive materials
Sequence encloses
Forced regressive deposits
Normal regressive (lowstand and highstand) deposits
Transgressive deposits
Sequence Stratigraphy Defined

39. 'Transgressive-Regressive' (T-R) sequence (Embry & Johannessen, 1992)
Composite sequence boundary includes subaerial unconformity & marine portion of maximum regressive surface
‘Normal' & 'forced' regressive deposits are included within the 'regressive systems tract'
Sequence Stratigraphy Defined

40. Boundaries & Conceptual Models
After Catuneanu, 2007
Sequence Stratigraphy Defined

41. Sequence Stratigraphy Model Tree
After Catuneanu, 2002
Sequence Stratigraphy Defined

42. Application & nomenclature of conceptual models subject to debate
Nomenclature of systems tracts & sequence stratigraphic surfaces
Surfaces that should be ranked as 'sequence boundary‘
Framework of surfaces, systems tracts, selection of sequence boundaries may vary with approach, available data sets, & depositional setting
Good news!!
Sequence stratigraphic method determines depositional setting of section
Identification of genetic units & bounding surfaces mostly model independent.
For both non-marine and marine systems, no matter characterization of 'sequence boundary', these boundaries envelope sedimentary section as through-going physical surface from basin margin to depocenter
Sequence Stratigraphy Defined

43. Sequence Stratigraphy Defined
Caveats
Sequence stratigraphic surfaces serve, at least in part, as boundaries between different genetic types of deposit
Not all data lend themselves to identification of all sequence stratigraphic surfaces
Not all sequence stratigraphic surfaces are present in every depositional section
Depositional settings of nearshore to just offshore generate an array of depositional and erosional surfaces, many of incorporated into sequence stratigraphy
In contrast, within either fluvial and/or deep-water systems, conditions favor formation of fewer key bounding sequence stratigraphic surfaces
Sequence Stratigraphy Defined

44. Sequence Stratigraphy Defined
Why codify ‘rules’ for sequence stratigraphic nomenclature?
We use common terms and know their meaning
Have a standard hierarchy of subdivisions
Have a uniform methodology
Guidance for revision
Teaching resource: each new generation of students & practitioners have a common understanding
Sequence Stratigraphy Defined

45. Sequence Stratigraphy Defined
Terms to Define
Surfaces
Separate layered clastic and carbonate sedimentary strata into genetically related packages, system tracts
System Tract
Specific three-dimensional facies assemblages of common genetic origin, associated with unconfined geometric architecture & interpreted as formed during phases of a relative sea-level cycle
Conceptual Models
Explains configuration of surfaces and geometries that occur in layered sedimentary record in terms of:
Basinal setting
Rates of sediment supply & erosion (accumulation)
Eustasy
Tectonic movement
Sequence Stratigraphy Defined

46. Terms to Define - Surfaces
Separate layered clastic & carbonate sedimentary strata into genetically related packages, or system tracts
Subaerial unconformity
Correlative conformity (sensu Posamentier, and sensu Hunt and Tucker; the former have renamend Posamentier’s CC as the “basal surface of forced regression”). (Two different surfaces).
Regressive surface of marine erosion
Maximum regressive surface
Maximum flooding surface
Transgressive ravinement surfaces
Sequence Stratigraphy Defined

47. Terms to Define – Systems Tracts
Specific three-dimensional facies assemblages of common genetic origin, associated with unconfined geometric architecture & interpreted as formed during phases of a relative sea-level cycle
Falling Stage Systems Tract (FSST)
Lowstand Systems Tract (LST)
Transgressive Systems Tract (TST)
Highstand Systems Tract (HST)
Regressive System Tract
Low-accommodation systems Tract
High-accommodation Systems Tract
Forced regression
Normal regression
Transgression
Sequence Stratigraphy Defined

48. Terms to Define – Conceptual Models
Models that explain surfaces & geometries of layered sediments in terms of basinal setting, rates of supply & erosion (accumulation), eustasy, and tectonics
Depositional sequence model
Genetic Stratigraphic sequence model
Transgressive-Regressive sequence model
Sequence Stratigraphy Defined

49. Definitions – Points to consider
Alternate terms
Origin of Feature
Absolute time or Fuzzy time significance if any?
Sequence Stratigraphy Defined

50. Sequence Stratigraphy Defined
"What's in a name? That which we call a rose. By any other name would smell as sweet.“ Shakespeare's Romeo and Juliet (II, ii, 1-2)
WHAT, YOU THINK
I’M AN IDIOT?
OF COURSE I WROTE DOWN WHAT WENT WHERE.
OH….. WAIT…… IS THAT AN “H” OR AN “I”
Sequence Stratigraphy Defined

51. Sequence Stratigraphy Defined
The fundamental key to sequence stratigraphic interpretation is the surfaces that subdivide the sedimentary section.
Unfortunately the nomenclature of each of these sequence stratigraphic surfaces is constantly changing as our understanding of sedimentary systems & their interpretation improves
Though changes in nomenclature are well intentioned they add to the confusion to a scientific methodology that is already overlaid with complex multi-syllable terminology
A surface can be given a name that has been used before for a different surface. The innocent, not knowing the terminology has been changed, may lack understanding of the reason for the change, & feel that they are going stark raving mad
Sequence Stratigraphy Defined

52. Sequence Stratigraphy – Conclusions
Subdivision & interpretation of sedimentary record using a framework surfaces seen in outcrops, well logs, & 2-D and 3-D seismic.
Include:
Surfaces of erosion & non-deposition (Sequence Boundaries, Forced Regression Erosion Surface, Regressive Surface of Marine Erosion)
Flooding (Trangressive Surfaces [TS or Max Regressive Surface] &/or maximum flooding surfaces [mfs] Ravinement Surfaces [RS- transgressive )
This template is used to predict the extent of sedimentary facies geometry, lithologic character, grain size, sorting & reservoir quality
Sequence Stratigraphy Defined

53. Sequence Stratigraphy Defined
Which way now?
Paul Dimitri Krynine’s alleged mantra was that:
“Stratigraphy is the triumph of terminology over common sense“
Our collective hope is to circumvent this cynical position & propose a more consistent & practical set of terminology!
Sequence Stratigraphy Defined

54. Sequence Stratigraphy Defined