What is Seqeuence Stratigraphy Introduction

What is Seqeuence Stratigraphy Introduction

1. A framework of genetically related stratigraphic facies geometries and
their bounding surfaces used to determine depositional setting.
or Sequence stratigraphy is 'the sub-division of sedimentary basin
fills into genetic packages bounded by unconformities and their
correlative conformities'.
UpperMiddleLower
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2. What is a sequence?
”A sequence is a succession of geneticallyrelated
strata that can be delineated chronologicallyand
spatially, and which possesses some
characteristic propertythat defines the sequence
as a particularproductof the total geological
history, with respect to eventsand processes”.
Nystuen 1998, p. 33
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3. Sequence Stratigraphy Applications
Academic applications:
Genesis and internal architecture of sedimentary basin fills
Age estimation: First approximation from the Cycle Chart.
Global Correlations: First-order comparisons
Facies Distribution: Prediction of horizontal and vertical migration of
sedimentary facies.
Industry applications:
Exploration for hydrocarbons, coal, and mineral resources
A tool for interpretation of dynamics of basin sediment infill
A tool for predicting sedimentary facies, source rocks and reservoir
rocks
Applies for alltypes of sedimentary basins
Optimal use presupposes knowledge of geological processes in time and
space.
Shale Gas and Tight Gas.
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4. Stratigraphy -Outcrop mapping and definition of sequencesas ‘assemblages of
strata and formations bounded by prominent interregional unconformities’
(Sloss, Krumbein& Dapples 1949).
Very large scale, the succession of rocks bound by unconformities spans c.60-
100Ma, now termed a Megasequence.
Seismic Stratigraphy -1960’s/70’ssaw the development of seismic acquisition .
Allowed imaging of the sub-surfaceand sequence recognition based on
unconformities at seismic scale. A ‘seismic sequence’ was defined by Mitchumet
al.1977).
Various controls on sequence development were emphasised, from eustaticsea-
level change(Vail et al. 1977)to tectonic (Hubbard et al. 1985).
Relativesea-level change is referred to when the causal mechanism of the change
is not constrained.
Brief Historical Review
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5. The meaning of a stratigraphic ‘sequence’ has been subsequently expanded to
include any ‘relatively conformable succession of genetically related strata’
(Mitchum, 1977), irrespective of temporal and spatial scales.
In parallel with the development of the ‘sequence’ concept in a stratigraphic
context, sedimentologistsin the 1960s and 1970s have redefined the meaning of
the term ‘sequence’ to include a vertical succession of facies that are ‘organized
in a coherent and predictable way’ (Pettijohn, 1975),reflecting the natural
evolution of a depositional environment.
The development of seismic and sequence stratigraphyin the late 1970s and
1980s revitalized the use of the term ‘sequence’ in a stratigraphic context, which
remained the dominant approach to date.
The unconformity-bounded sequences promoted by Sloss (1963).
The concept of ‘unconformity-bounded unit’(i.e., Sloss’ ‘sequence’) was
formalized by the European ‘International Stratigraphic Guide’ in 1994.
Brief Historical Review
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6. The introduction of ‘correlativeconformities,’ which are extensions towards
the basin center of basin margin unconformities, marked the birth of modern
seismic and sequence stratigraphy (Fig. 1.3 & 1.4) (Mitchum, 1977).
The advantage of the modern sequence, bounded by a composite surface that
may include a conformable portion, lies in its basin-wide extent -hence, the
number of sequencesmapped at the basin marginequals the number of
sequencesthat are found in the basin center.
Brief Historical Review
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7. Haqetal.’sCycleChart
basedonglobaldata.
Abeakthroughinthe
historyoftheglobal
sequencestratigraphy.
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8. Relative sea level= (f) Eustasy + Tectonic subsidence or uplift +
Compaction
+ Isostasy
Figure1.5Showingbasicconceptoftheeustaticsealevelchangesrelativesealevelchanges.
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9. First order cycle
A sea-level cycle with a duration on the order of hundred of millions of
years. During Phanerozoictime (post –Precambrian), there were twosuch
cycles,
A 300 m.ycycle from the Precambrian to the Triassic, and
A 225 m.y. cycle from Triassic to the present (Fig. 1.6).
Second order cycle
A sea-level cycle generally with duration on the order of 9-10 million years
(Fig. 1.6). Several such cycles are superimposed upon the Phanerozoicfirst-
order cycles shown in Figure 1.5 A.
Third order cycle
A sea level cycle generally with a duration on the order of 1-5 million years
(Figs. 1.6 and 1.9).
Fourth order cycle
A sea-level cycle with a duration generally on the order of 100,000-250,000
years (Fig. 1.6 and 1.9). Several such cycles are superimposed upon the third
order cycles (Fig. 1.9).
Fifth order cycle
A sea-level cycle generally on the order of tensof thousands of years
duration (Fig.1.6).
Sixth order cycle
A sea-level cycle with a duration generally on the order of thousandsof years
(Fig.1.6).
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12. Stacking Patterns
Transgression
Regression
Progradation(regression)
Retrogradation(transgression)
Aggradation (Stillstand)
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13. Sediment Supply > Accommodation = Progradation
 Facies migrate basin wards
 Regression of shoreline
Sediment Supply = Accommodation = Aggradation

 Facies stack vertically
Sediment Supply < Accommodation = Retrogradation
 Facies migrate landward
 Transgression of
shoreline
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14. Basic Units of Sequence Stratigraphy (Vail at.al., 1991)
0.5-5 Ma 0.2-1.0 Ma 0.01-0.5 Ma
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15. The Classic Slug Exxon Model
SB –sequence boundary LST –lowstand systems tract
TST –transgressive systems tractHST –highstand systems tract
SMW –shelf-margin wedge Mfs –maximum flooding surface
Lsw –lowstand wedge Sf –slope fan
Bf –basin-floor fan
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