Introductory presentation for a professional field course titled: THE BOOK CLIFFS: A CASE STUDY IN COASTAL SEQUENCE STRATIGRAPHY, offered annually through W.W. LITTLE GEOLOGICAL CONSULTING (also offered by SCA). See details at: HTTP://LITTLEWW.WORDPRESS.COM.

1. William W. Little
Principles of Sequence Stratigraphy
© 2015 by W.W. Little Geological Consulting, LLC Photo by W. W. Little

2. Unless otherwise noted:
• Photos and figures by William W. Little
• Drafting by Daniel W. Little
• Many credited figures obtained from the SEPM Strata website
© 2015 by W.W. Little Geological Consulting, LLC Photo by W. W. Little

3. Stratigraphy is the study of temporal relationships in sedimentary rock
bodies and reflects changes in the balance between rates at which space
is produced and filled. Stratigraphy can be considered the history of past
geological events, particularly base-level fluctuations, and adds the
dimension of time to sedimentology.
Stratigraphy
Photo by W. W. Little

4. Accommodation space is the volume below base level (more properly
the graded profile) and above the basin floor available for sediment
accumulation and can increase or decrease on global (eustatic), regional
(e.g. foreland subsidence), or local (e.g. delta lobe switching) scales.
Basic Concepts: Accommodation Space

5. Basic Concepts: Preservation Potential
Eustatic sea level rises and falls within a
limited range, meaning that most space
produced will subsequently be destroyed.
+
=
Relative base-level is the cumulative result of rates and direction of eustatic base-
level fluctuation and basin subsidence or uplift, leading to creation or destruction of
accommodation space.
Under constant basin subsidence coupled
with eustatic fluctuation, four points of
significance to sequence stratigraphy are
identified:
A: Highstand
B: Maximum rate of fall
C: Lowstand
D: Maximum rate of rise
For long-term preservation, space
production must include tectonic
subsidence.

6. Sedimentation rate reflects the volume of material eroded from a source
region and transported to a basin over a specified period of time.
Sediment supply can increase or decrease depending upon rates of
uplift in the source region, changes to the nature of materials exposed at
the surface, and climatic conditions.
Basic Concepts: Sediment Supply

7. Effects of Variable Accommodation
and Sediment Supply
The relationship between
accommodation production
(A) and sedimentation rates (S)
determines the stacking pattern
of progradational “wedges.”
S > A = Forward stepping
S = A = Vertical stacking
S < A = Backstepping

8. Basic Concepts: Base Level
Base level is the horizon below which continents cannot erode and
above which basins cannot fill (or, more correctly, to which both
will grade).

9. Base Level: Graded Profile
A stream naturally adjusts its gradient so as to barely transport the
available load, producing a profile that flattens toward the basin. This
profile can be modified as it is lengthened or shortened by base level
fluctuations that create and destroy accommodation space and by uplift
and erosion in the source region that affect sediment supply.

10. Eustasy (global base level)
From SEPM Strata (sepmstrata.org)
Base-level fluctuations that can be
identified to have occurred simultaneously
in many localities across the earth have
been combined in terms of time, direction,
and magnitude to establish a global sea
level curve.

11. Regional/local Base Level
Base-level fluctuations for a particular locality can vary from the global
(eustatic) standard due to tectonic uplift/subsidence, sediment
compaction, and variations in sedimentation rates.
Tectonic subsidence provides
the same effect as a eustatic
rise in base level, in that it
produces new accommodation
space.

12. Relative Base Level
Because of the common difficulty of distinguishing between global,
regional, and local effects, we often simply refer to relative base-level.
Photo by W. W. Little

13. Important Terms: Rise vs. Fall
Base level rise and fall refer to the vertical movement of a plane with
respect to the basin floor.

14. Important Terms:
Transgression vs. Regression
Transgression and regression refer to the lateral movement of a line
forming the boundary between land and sea. It is important to note
that regression can occur during either a base level fall (forced) or a
base level rise (normal), depending upon the relative rates of rise
and sedimentation. Transgressions occur only during a base level
rise.
Regression
Transgression
Land
Se
a

15. Important Terms: Progradation,
Retrogradation, and Aggradation
All deposition is progradational, meaning that a volume of sediment
always builds in a basinward direction; however, progradational
wedges (parasequences) can stack in progradational, aggradational, or
retrogradational patterns (sets).
Retrogradation

16. Photo by W. W. Little
Basic Concepts: Deposition is
Progradational (Walther’s Law)
Because sediment always moves basinward, facies that accumulate in more
proximal environments prograde over facies in more distal environments, creating a
vertical facies succession that represents environments which were once adjacent.

17. Important Terms: Parasequence
A parasequence is what was once referred to as a progradational or
clastic wedge. It represents a single progradational episode that
observes Walther’s Law internally but is bound above and below by
discontinuities, primarily flooding surfaces.
Photo by W. W. Little
From SEPM Strata (sepmstrata.org)Photo by W. W. Little

18. Photo by W. W. Little
Shoreface Parasequence

19. A parasequence is a relatively conformable succession of genetically-
related beds or bedsets bounded by marine flooding surfaces or their
correlative “surfaces.”
Parasequence
Flooding surface
Flooding surface
Shallowingupward
Photo by W. W. Little

20. Though parasequences represent progradational pulses of deposition,
internally they can either coarsen or fine upward, depending upon the
depositional system within which they form.
Vertical Trends within a Parasequence
Coarsening-upward Parasequence Fining-upward Parasequence
From SEPM Strata (sepmstrata.org)

21. The type of stacking pattern
is controlled largely by the
relative balance between
rates of accommodation
production (base-level
fluctuation) and basin filling
(sediment supply). E.g.,
progradation can occur
during either a base-level
fall or rise, depending upon
the amount of sediment
delivered to the basin.
Parasequence Stacking Patterns
Forced regression
Transgression
Regression
Aggradation

22. Important Terms: Systems Tracts
A systems tract consists of coeval depositional systems within a given
depositional basin. Systems tracts within a sequence stratigraphic
framework are dependent upon the direction and rate of base level
change with respect to sedimentation rates and are identified by stacking
pattern, position within a sequence, and nature of bounding surfaces.
From SEPM Strata (sepmstrata.org)

23. Sequence stratigraphy is the subdivision of the stratigraphic record on
the basis of bounding discontinuities (allostratigraphy).
Sequence Stratigraphy
From SEPM Strata (sepmstrata.org)
Though diachronous over their
lateral extent, bounding surfaces
have chronostratigraphic
significance, in that everything
above is younger than everything
below the surface. Because events
producing bounding surfaces have
identifiable beginning and ending
points, they represent isochronous
events (e.g. base-level fluctuations).
Time relationships are typically
shown by Wheeler Diagrams.

24. A discontinuity represents a break in deposition, across which there is a
violation of Walther’s Law and can be represented by a large range of
scales.
Types of Discontinuities (scale)

25. Discontinuities can be produced by either a fall or a rise in base level,
the former creating an erosional surface and the latter a surface or
interval of non- to very slow sedimentation.
Types of Discontinuities (process)

26. Photo by W. W. Little
Discontinuities differ in character, mode of formation, and timing from
proximal to distal portions of a basin. Proximal unconformities tend to
be erosional and form through incision during base level fall. Distal
unconformities are more likely to be non-depositional, forming through
sediment starvation during base level rise.
Timing of
Discontinuities

27. Photo by W. W. Little

28. Photo by W. W. Little
Sequence Boundaries
(Discontinuities formed by a drop in base level)
Sequence boundaries are surfaces bounding depositional sequences.
Depending upon whether base-level falls or slowly rises with respect to
rates of basin filling, they can be erosional (type 1) or conformable
(type 2) and are recognized by the abrupt placement of more landward
facies over more basinward facies with missing facies between.
Distal facies
Proximal facies

29. Photo by W. W. Little
Flooding Surfaces
(Discontinuities formed by a rise
in base level)
Flooding surfaces represent relative rises in base-level. They are
recognized by deeper-water (basinward) facies abruptly overlying
shallower-water (landward) facies with missing facies between.
Proximal facies
Distal facies

30. Formal Definitions of a Sequence
• A relatively conformable succession of genetically related strata
bounded at their upper surface and base by unconformities and their
correlative conformities (Vail, et al., 1977).
• A Sequence is composed of a succession of genetically linked
deposition systems (systems tracts) and is interpreted to be deposited
between eustatic-fall inflection points (Posamentier, et al., 1988).
• Study of rock relationships within a time-stratigraphic framework of
repetitive, genetically related strata bounded by surfaces of erosion or
non-deposition, or their correlative conformities (Posamentier et al.,
1988; Van Wagoner et al., 1988).
• The sequences and the system tracts they enclose are subdivided and/or
bounded by a variety of "key" surfaces that bound or envelope these
discrete geometric bodies of sediment. They mark changes in
depositional regime "thresholds" across that boundary (Kendall).

31. Sedimentary deposits related to a single cycle of base level change.
My Definition of a Sequence

32. Litho- vs. Chronostratigraphy
Sediment fills space to base level, then accumulates through basinward
progradation, producing lithostratigraphic units with bounding surfaces
that are time transgressive.

33. According to Walther’s Law, absent an unconformity, facies stacked
vertically were deposited in environments that existed laterally to one
another. Therefore, facies boundaries within a parasequence are
diachronous.
Walther’s Law

34. From SEPM Strata (sepmstrata.org)
Litho- vs. Chronostratigraphy
Lithostratigraphic units (formations, members, groups) are
time transgressive and are different ages in different places.

35. Litho- vs. Sequence Stratigraphy
Sequence stratigraphy correlates rock
bodies on the basis of where they fall
within a cycle of base level fluctuation,
focusing on bounding allostratigraphic
(unconformable) surfaces.
Lithostratigraphy correlates rock bodies
on the basis of physical characteristics and
stratigraphic position.

36. Exercise
Correlate these four cores or measured sections.

37. Lithostratigraphic Solution
Given the similarity in physical characteristics, the most common
solution would be to hang the sections at the top of the first prominent
sandstone.

38. Sequence Stratigraphic Solution
An alternative would be to assume an overall progradational stacking
pattern common to highstand systems tracts and to hang the section on
the first recognizable parasequence.

39. Elements: Sequence Boundary
A sequence boundary (SB) is produced as relative base-level drops.
Erosion begins in landward regions and progresses basinward
(diachronous) with deposition in more basinal areas, producing the falling-
stage systems tract (FSST). The SB separates the highstand systems tract
(HST) below from the FSST or lowstand systems tract (LST) above.

40. Photo by W. W. Little
Sediment bypass
Formation of sequence boundary

41. Elements: Falling-stage Systems Tract
A FSST can form as a downstepping (offlaping) deposit while
relative base level falls (forced regression) and the SB is produced;
however, because of cannibalization, this systems tract is often
missing or poorly developed.

42. Photo by W. W. Little
Falling-stage delta

43. Photo by W. W. Little
Cannibalization during progressive falling stages

44. Lowstand Systems Tract
An LST is produced during the early stages of relative base-level rise.
Erosion continues in landward areas, but preservation potential is
higher than for FSST sediments, as accommodation is produced in a
progressively more landward direction. These are characterized by
onlap onto FSST deposits and/or the sequence boundary.
Parasequence patterns change from progradational to aggradational.

45. Photo by W. W. Little

46. Photo by W. W. Little
LST
HST
SB

47. Photo by W. W. Little

48. Transgressive Surface
The transgressive surface (TS) separates the LST below from the TST above and
forms during the maximum rate of relative base-level rise, as basinal
accommodation development surpasses sediment supply. Stacking patterns change
from aggradational to retrogradational. It is the first significant flooding surface
within a sequence and commonly marks the base of the most prominent onlap
exhibited by the sequence. Erosion often accompanies formation of the TS.

49. Photo by W. W. Little
Possible future transgressive surface
Sequence boundary

50. Both transgressive and regressive events can develop erosional surfaces
associated with reworking at wave base. This commonly occurs as
shoreface erosion during development of the transgressive surface.
Shoreface Ravinement Surface

51. Transgressive Systems Tract
The transgressive systems tract is typically thin in coastal areas, thick in
proximal areas, and characterized by a retrogradational parasequence set
as landward regions become flooded. This systems tract is bounded by
the TS below and the maximum flooding surface (MFS) above.

52. Maximum Flooding Surface
The MFS forms the boundary between the TST and HST and represents
the greatest landward incursion of the sea. Parasequence stacking
patterns change from retrogradational to aggradational. Basinward
regions are characterized by a lack of sedimentation, producing a
starved zone or condensed interval. Typically forms a downlap surface
for the highstand systems tract (HST) deposits.

53. Highstand Systems Tract
The HST is found between the MFS and the upper SB. As
accommodation development slows, parasequence sets change from
aggradational to progradational. Bed terminations are characterized by
onlap in proximal regions and downlap in more basinal areas.

54. Complete Sequence

55. From SEPM Strata (sepmstrata.org)
Variations

56. From SEPM Strata (sepmstrata.org)
Multiple Cycles

57. Chronostratigraphic Significance
By plotting time against space, facies migration, discontinuity
development, and sea-level history can be reconstructed
through use of a Wheeler Diagram.
WheelerDiagram
From SEPM Strata (sepmstrata.org)

58. What it looks like in outcrop
Deltaic
Distal shoreface
Medial shoreface
Proximal shoreface
Proximal shoreface
Coastal plainFluvial
Deltaic (LST)
Distal shoreface (TST)
Medial shoreface
Proximal shoreface
Proximal shoreface
Coastal plainFluvial
Marine (HST)
(SB)
(TS)
(MFS)
(HST)
Photo by W. W. Little

59. Recognition of stratigraphic surfaces in
measured sections can be used as a means
of determining sea-level history for one
area and correlating that history to
litholigically different strata of another.
What it looks like in measured section

60. Seismic sections record changes in impedance across discontinuities;
therefore, unless disrupted by structures, patterns within a seismic
profile reflect parts of a stratigraphic sequence.
What it looks like in a seismic section

61. Truncation
(base level drop & erosion)
Overlying Surface
Toplap
(static base
level)
Concordant
(rising base
level)
Underlying Surface
Onlap
(rising base level &
shoreline transgression)
Downlap (progradation) Offlap
(base level drop &
forced regression)
Bedset Terminations
Bedset terminations are named according to their angular
relationship with underlying and overlying bounding surfaces.

62. Reflector Terminations & Systems Tracts
Bedset terminations can be used to identify systems tracts within
seismic sections.

63. HST
FSST/LST
TST
HST
SB
Seismic sections record changes in impedance across discontinuities;
therefore, unless disrupted by structures, patterns within a seismic
profile reflect parts of a stratigraphic sequence.
What it looks like in a seismic section

64. From SEPM Strata (sepmstrata.org)