Sequence Stratigraphy, Basin Analysis, Fundamental framework and database

1. Method of the
Sequence Stratigraphic
Analysis
By Group A
Roll No.: 1 to 7
M.Sc. 1st Semester, 2078
Central Department of Geology
Kritipur, Nepal
1. Nagesh Rijal
2. Krishna Pd. Niraula
3. Binod Dhakal
4. Pradip Devkota
5. Sujan Raj Pandey
6. Upendra Poudel
7. Arun Shrestha

2. Sequence Stratigraphy
• Sequence stratigraphy (Posamentier and Allen, 1999): the analysis of cyclic
sedimentation patterns that are present in stratigraphic successions, as they
develop in response to variations in sediment supply and space available for
sediment to accumulate.
• Sequence stratigraphy (Embry, 2001a): the recognition and correlation of
stratigraphic surfaces which represent changes in depositional trends in
sedimentary rocks. Such changes were generated by the interplay of
sedimentation, erosion and oscillating base level and are now determined by
sedimentological analysis and geometric relationships.
• Simplest, and that preferred by the authors, is 'the subdivision of sedimentary
basin fills into genetic packages bounded by unconformities and their correlative
conformities‘.
• Sequence stratigraphy is generally used to resolve and explain issues of facies
cyclicity, facies associations and relationships, and reservoir
compartmentalization, without necessarily applying this information for larger-
scale correlations.
• Sequence stratigraphy is commonly regarded as only one other type of
stratigraphy, which focuses on changes in depositional trends and their
correlation across a basin.

3. • The sequence stratigraphic approach has led to improved understanding of
how stratigraphic units, facies tracts, and depositional elements relate to each
other in time and space within sedimentary basins.
• The process of interpreting the origins of sequence stratigraphic surfaces, the
depositional setting and gross sedimentary geometry of the rocks enclosed
within the sequence stratigraphic framework involves Niels Steno‘s Laws of
Superposition and Walther's Law.

4. Sequence Stratigraphic Framework

5. Methods of Sequence Stratigraphic Analysis
• Facies and facies model
• Facies analysis
• Concept of depositional system
• Classification of depositional environment
• Walther‘s law
• Paleocurrent direction
• Pedology
• Iconology
• Well log
• Seismic data
• Age of determination techniques
• Workflow of sequence stratigraphy analysis

6. Facies, Facies Association & Facies model
Facies:
• It is a body of rock with specified characteristics. Ideally, a facies is a distinctive
rock unit that forms under certain condition of sedimentation, reflecting a
particular process or environment.
• It is sum total characteristics of a rock including its chemical, physical and
biological features that distinguishes it from adjacent rock.
• Facies (Bates and Jackson, 1987): the aspect, appearance, and characteristics
of a rock unit, usually reflecting the conditions of its origin; esp. as differentiating
the unit from adjacent or associated units.
•Lithology, grain size, sedimentary structure, color, composition, biogenic content
are the fundamental of facies studies.
• Generally facies are distinguished by what aspect of the rock or sediment is
being studied;
• Lithofacies: facies based on petrological characteristics such as grain size and
mineralogy.
• Bio facies: facies based on fossil content (flora and fauna)
• Ichnology: facies based on trace fossil.

7. Facies
• Facies are controlled by sedimentary processes that operate in particular areas of
the depositional environments. Hence, the observation of facies helps with the
interpretation of syn-depositional processes.
• Sedimentary Facies are bodies of sediment that are recognizable distinct from
adjacent sediments that result from different depositional environment. They are
either terrigenous, biogenic or chemical.
• As condition change with time, so
different depositional site may change
their shape and characteristics.
• The deposition environment includes:
a) Fluvial environment – Siwalik
b) Oceanic environment- different facies
within the ocean (Continental shelf,
submarine fan-turbidite, deep marine
deposits)
c) Glacial environment.
d) Lacustrine environment. Figure 2.1: Showing Sedimentary Facies in different
depositional basin and environment

8. Facies Association & Facies Model
• Constitute several facies that occur in combination and typically represent one
depositional environment.
• Facies Association (Collinson, 1969): groups of facies genetically related to one
another and which have some environmental significance.
• The understanding of facies associations is a critical element for the
reconstruction of paleo-depositional environments. In turn, such reconstructions
are one of the keys for the interpretation of sequence stratigraphic surfaces.
• Facies succession: A progressive change in certain facies properties in a specific
direction (vertical or horizontal).
• Facies model (Walker, 1992): a general summary of a particular depositional
system, involving many individual examples from recent sediments and ancient
rocks.
• A facies model assumes predictability in the morphology and evolution of a
depositional environment, inferring ―standard‖ vertical profiles and lateral
changes of facies.

9. Fig.3: Generalized facies model and architecture for a typical
meandering river system.
• Facies models are based
on facies association and
are designed to show the
3D relationship (architecture
between individual facies (
architectural elements for a
depositional system.
• Models can be tailored to
specific stratigraphic unit or
can be generalized to show
an average characteristics
for a typical depositional
system.

10. Facies Analysis
• Facies analysis is a fundamental sedimentological method of characterizing
bodies of rocks with unique lithological, physical, and biological attributes relative
to all adjacent deposits
• Facies analysis is of paramount importance for any sequence stratigraphic study,
as it provides critical clues for paleogeographic and paleoenvironmental
reconstructions, as well as for the definition of sequence stratigraphic surfaces.
• As such that, facies analysis is an integral part of both sedimentology and
sequence stratigraphy.
• In the context of sequence stratigraphy, facies analysis is particularly relevant to
the study of cyclic changes in the processes that form individual depositional
systems in response to base level shifts.
• The facies concept refers to the sum of characteristics of a sedimentary units,
commonly at a fairly small scale(cm-m)
• It includes the analysis of parameter such as the configuration continuity,
amplitude, phase, frequency, interval velocity. These variable give an indication
of the lithology and sedimentary environment of the facies.

11. Importance of Facies Analysis
• Used for hydrocarbon exploration.
• Used for determining paleography.
• Useful for groundwater exploration.
• Understanding climate changes and
subsidence history of depositional
basin.
• The reconstruction of paleo
depositional environments via facies
analysis is an important pre-requisite
for sequence stratigraphic
interpretations.
• Gradational (vertical) transitions from one facies to another indicate original
adjacency and genetic relationship during formation.
• Sharp/erosional (vertical) contacts between the facies provides no evidences of
contemporaneous genetic relationship of depositional environments.

12. Concept of depositional system
• Depositional basin are the region of the earth long term subsidence creates
accommodation space for accumulation of sediments.
• A depositional system is the product of sedimentation in a particular depositional
environment;. hence, it includes the three-dimensional assemblage of strata
whose geometry and facies lead to the interpretation of a specific paleo
depositional environment.
• Convergent boundary creates accretionary wedge and foreland basins through
tectonics compression of oceanic and continental crust during lithospheric
flexure.
• Tectonic extension at divergent boundaries where continental rifting is occurring
can create a nascent ocean basin leading to either an ocean or the failure of the
rift zone.
• In strike- slip settings, accommodation spaces occur as transgressional,
transitional basins according to the motion of the plates along the fault zone and
local topography.

13. Types of Depositional Basin

14. Classification of depositional environment
• A depositional environment is a specific type of place in which sediments are
deposited, such as a stream channel, a lake, or the bottom of the deep ocean.
• Depositional settings may be classified into three broad categories as shown
below:
• In coastal areas, the river-mouth
environments (i.e., sediment entry points
to the marine basin) are separated by
stretches of open shoreline where the
beach environment develops.
• Coastal environments are critical for
sequence stratigraphy, as they record
the history of shoreline shifts and are
most sensitive in providing the clues for
the reconstruction of the cyclic changes
in depositional trends.

15. Fig 5: Depositional environments and sedimentary basin

16. Figure 6: Transition from
marine to nonmarine
environments. The large
arrows indicate the direction
of shoreline shift in the two
river-mouth environments
(R—regressive; T—
transgressive). Between the
river-mouth environments,
the coastline is an open
shoreline. Note that the
character of the shoreline
(transgressive vs.
regressive) may change
along strike due to variations
in subsidence and
sedimentation rates.

17. Figure 7: Dip-oriented profile illustrating the main geomorphic and depositional settings of a
continental shelf: alluvial plain, coastal plain, coastline (including the intertidal and supratidal
environments;), and shallow-marine (shoreface and shelf) environments (modified from Posamentier
et al., 1992b

18. Walther‘s law
• Walther‘s law(1860-1937) states that, the vertical succession of facies reflect
lateral change in environment.
• Conversely, it states that when a depositional environment ―migrates‖ laterally,
sediment of one depositional environment come to lie on top of another.
• Walther‘s Law (Posamentier and Allen, 1999): the same succession that is
present vertically also is present horizontally unless there is a break in
sedimentation.
• This law is applicable only to situations where there is no break in sedimentary
sequences.
• The rock succession that is present vertically is also present horizontally
unless there is a break in the sedimentation.
• The concept was first stated by German geologists Johannes Walther in 1984.
• Golovkinsky (1834-1897). A classic example of this law is a vertical
stratigraphic succession that typifies marine transgressions and regression.

19. • Walther‘s Law is an
important principle upon
which the origin of vertical
rock successions is
explained.
• Sediments are deposited in
environments that change
over time as a result of
relative sea-level
fluctuations.
• As the environments
change, so does the nature
of the sediments deposited
at any one location. The
vertical succession thus
records the lateral changes
in environments over time.
Figure 8: Walther's law model of facies succession 1894.

20. Applications of Walther‘s Law
• This is a fundamental principle of stratigraphy, which allows the geologist to
visualize predictable lateral changes of facies based on the vertical profiles
observed in 1D sections such as small outcrops, core or well-logs.
• Vertical changes in litho and bio facies have long been used to reconstruct
paleogeography and temporal changes in depositional environments and, with
the aid of Walther‘s Law, to interpret lateral shifts of these environments.
• Walther‘s law is a powerful tool for facies modeling.
• The transgression and regression of sea-level causes the sediments in
depositional basin migrate seaward and landward. This causes the sediment
deposition to shift laterally and vertically over a period of time so we can
actually see the horizontal sequence changes in vertical rock sequence
record. Thus, Walther's law is a useful method for sequence stratigraphic
analysis.
• Walther‘s law is equally valuable when applied to system tracts, as the internal
architecture of each tract involves progradational or retrogradational shifts of
the faces which translate into corresponding facies changes along vertical
profile.

21. Paleocurrent direction
• Paleocurrent analysis is performed in order to determine the orientation of
the current (river, stream) responsible for dispersing and depositing a
sedimentary rock unit in a basin.
• In the case of tectonically active basins (graben, rift, foreland), the
paleocurrent direction data may provide strong evidence for sequence
delineation, paleogeographic reconstructions, and stratigraphic correlations.
• The change of paleocurrent direction may be due to tectonic reorganization
of sedimentary basins which changes its tilt direction and can cause major
breaks in stratigraphic records.
• In some past historical cases, in a region where vertical profile of sequences
are ambiguous and do not show any stratigraphic breaks, paleocurrent data
have shown multiple second order depositional sequences separated by
unconformities.

22. • The orientation of the long axes of cobbles, the orientation of cross-bedding,
ripple crests, groove and flute casts can be analyzed for paleocurrent
direction
• But, these kind of analysis can be done only for sedimentary rocks that are at
least in part clastic in origin and coarse grained enough so that they exhibit
noticeable directional structures or easily analyzed textural trends.
• Paleocurrent direction can also be
analyzed from the rose diagram as
shown in figure.
• It is constructed by plotting directional
data and the frequency as a circular
histogram through 360˚
Figure 9: Rose diagram

23. Pedology
Pedology refers to scientific discipline concerned with all aspects of soils, including
their physical and chemical properties, the role of organisms in soil production and
in relation to soil character, the description and mapping of soil units, and the
origin and formation of soils.
Paleosols also called fossil soils are buried soil from geological past.
Pedological studies have various geological applications:
• Interpretations of ancient landscapes, from local
to basin scales.
• Interpretations of ancient surface processes
such as sedimentation, nondeposition, erosion.
• Interpretations of paleoclimates.
• Stratigraphic correlations, and the cyclic change
in soil characteristics in relation to base-level
changes.
All of these applications are related to sequence
stratigraphy.

24. Formation of soil/paleosols
• The soil/paleosol form in varieties of different conditions.
• Paleosols form mostly on non marine settings such as alluvial, palustrine, eolian
and also costal and marginal to shallow marine environment.
• Soils also form in conjunction with different surface process such as sediment
aggradation, sediment bypass (nondeposition), sediment reworking and others.
• Soils formed during sediment aggradation occur within conformable successions,
whereas soils formed during nondeposition or erosion are associated with
stratigraphic hiatus, marking diastems or unconformities in the stratigraphic record.
• These issues are important in sequence stratigraphy to distinguish between
paleosols with significance of sequence boundaries, playing the role of subaerial
unconformities and paleosols that occur within sequences and system tracts.
• From a sequence stratigraphic perspective, paleosols may provide key evidence
for reconstructing the syndepositional conditions (e.g., high vs. low water table,
accommodation, and sedimentation rates, paleoclimate) during the accumulation
of systems tracts, or about the temporal significance of stratigraphic hiatuses
associated with sequence-bounding unconformities.

25. • Compound, composite
and cumulative
paleosols occur within
conformable
successions, hence
within depositional
sequences.
• ‗Truncated‘ paleosols
are associated with
stratigraphic hiatuses,
and therefore mark
diastems or
unconformities.
Figure: 11: Interplay of pedogenesis and surface processes (modified from
Morrison, 1978; Bown and Kraus, 1981; Marriott and Wright, 1993; Kraus, 1999).

26. Ichnology
• Ichnology is the study of traces made by organisms,
including their description, classification and interpretation
(pembertonetal.,2001).
• Ichnofossils are the geological records of biological activity.
• Such traces may be paleoichnology or neoichnology and
generally reflects basic behavior patterns.(e.g., resting,
locomotion, dwelling or feeding).
Importance of ichnology in sequence stratigraphy:
a) Represents both sedimentological and paleontological entities.
b) Helps in recognition of various types of discontinuities and their genetic
interpretation.
c) Assists on the identification and interpretation of bounding surface of stratal
units.
d) Ichnology may be employed to resolve surfaces of sequence stratigraphy mainly;
through the recognition of substrate-controlled ichnofacies and through careful
analysis of vertical ichnological successions.
Figure 12:Trace fossils of annelid.

27. Classification of Ichnofacies
Figure 13: Classification of ichnofacies based on substrate type and consistency, as well as
depositional environment (modified from Bromley et al., 1984, and Pemberton et al., 2001).

28. Well Log
• Well logs represent geophysical recording of various rock properties in bore holes.
• The process of extracting the detailed records of geologic formations made by a
well or a borehole is called well logging.
• One major advantage of geophysical logs over outcrops is that they provide
continuous information from relatively thick successions, often in a range of
kilometers. This type of profile (log curves) allows one to see trends at various
scales, from the size of individual depositional elements within a depositional
system, to entire basin fills. For this reason, data provided by well logs may be
considered more complete relative to the study of outcrops.
Types of well logging and geological form ( modified from Cant, 1992)

29. Figure 14: Types of well logs, properties they measure, and their use for geological interpretations
(modified from Cant, 1992).

30. Seismic Data
• Seismic data are collected along a grid of linear profiles, that results 2D seismic
lines(two way travel time vs. horizontal distance).
• Then raw seismic information are processed further before using it for
geological interpretation.
• Then the seismic lines provide continuous subsurface information over distance
of 10s of km and depth in range of kms.
• The continuous character of seismic data shows major advantages over other
methods of stratigraphic analysis.
• Seismic data provide the fundamental means for the preliminary evaluation of a
basin fill in the subsurface, usually prior to drilling, in terms of overall structure,
stratigraphic architecture, and fluid content.
• The seismic data analysis are analysed in a workflow of ; Reconnaissance
Studies, Interval Attribute Maps, Horizon Attribute Maps and 3D Perspective
Visualization

31. • Seismic surveys are an integral part of hydrocarbon exploration, as they allow;
(1) assess the tectonic setting and the paleo depositional environments;
(2) identify potential hydrocarbon traps (structural, stratigraphic, or combined);
(3) evaluate potential reservoirs and seals;
(4) evaluate source rocks and estimate petroleum charge in the basin;
(5) Evaluate the amount and the nature of fluids in individual reservoirs;
(6) develop a strategy for borehole planning based on all of the above; and
(7) significantly improve the risk management in petroleum exploration.
 Reconnaissance Studies: initial scrolling through the data (side to side ,front to back, top to
bottom) in order to assess the overall structural and stratigraphic styles (Hart,2000).
 Interval Attribute Maps: then, the intervals bracketing sections of geologic interest can be evaluated
in more detail by constructing interval attribute maps.
 Horizon Attribute Maps: Enhances the visualization of geomorphologic and depositional elements
of specific paleodepositional surfaces by picking the geological horizon of interest within the seismic
window.
 3D Perspective Visualization: illustrates surfaces extracted from 3D seismic data.

32. Figure 15 : Sample of a three-dimensional seismic volume showing a prograding Permian shelf
margin from the Delaware Basin (from Hart, 2000

33. Age Determination Techniques
• Evaluation of geological age Involves relative abundance of radioactive
isotopes.
• Age Determination Technique is one of the important methods of sequence
stratigraphic analysis.
• Age data are useful to have, and particularly useful to correlate at larger scales
which are controlled by;
Biostratigraphy (on the basis of available fossils and biological succession).
Magneto stratigraphy(based on the polarity of remanent magnetism of rock strata ).
Isotope Geochemistry (based upon the study of natural variations in the relative
abundances of isotopes of various elements. )
Chrono stratigraphy (deals with the relative time relations of rocks)
Marker Horizons (Oolitic Hematite of Bhainskati Fm)

34. Workflow Of Sequence Stratigraphy Analysis
• The purpose of stratigraphic analysis of an area is to determine lithostratigraphy,
chronostratigraphy, possible reservoir and depositional environment studies.
• Integrate & Interpret as many types of data as possible., derived from the study
of outcrop , core, well logs, and seismic volume.
• The workflow suggests the basic building of systematic sequence stratigraphic
analysis to approach.
• Here, the data interpreter should have a board flexibility in adapting different
geological circumstances (e.g., type of basin, subsidence, and sedimentation
history) and different data.
• An example on how the data are analyzed is discussed here on the basis of
principle that understanding of the larger-scale tectonic and depositional setting
must be achieved first, before the smaller-scale details can be tackled.
• The accuracy of sequence stratigraphic analysis, as with any geological
interpretation, is proportional to the amount and quality of the available data.

35. • Workflow indicates the steps that need to be carried out in order to analyze
the sequence stratigraphic.
• Following approach are taken for sequence stratigraphic analysis as shown
in figure below.
Stage -1
Stage -2
Stage -3
Figure: Workflow of sequence stratigraphic analysis
• Here, workflow
progresses at a gradually
decreasing scale of
observation and
increasing level of detail.

36. Stage 1. Tectonic Setting
• First stage, the type of basin hosts
the sedimentary succession of
different fundamental variables are to
be constrained.
• Tectonic setting is unique in terms of
subsidence patterns stratigraphic
architecture, nature of depositional
systems such that it controls the
formation of basin.
• These pattern represent primary
control on overall geometry and
internal architecture.
• The reconstruction of tectonic setting
must be based on regional data
(obtained from well log, seismic lines,
fossil content, etc.) and the analysis
of these data proceeds. Figure 16: Generalized dip-oriented cross section
through divergent continental margin, illustrating overall
subsidence pattern and stratigraphic architecture
• Example: graben, rift valley, etc having
high subsidence rate in distal direction
and foreland basin in proximal direction.

37. Stage- 2. Paleo-depositional Environment
• Interpretation of paleo depositional environment is another key step in sequence
stratigraphic workflow.
• Each depositional environment has its own geometry and morphology.
• Identification of specific depositional elements evaluate stratigraphic unit.
• Paleoenvironmental reconstruction are important for both inside and outside the
scope of sequence stratigraphy.
• For the workflow 3D seismic data are more useful than 2D seismic data.
• Interpretations depends on integration of multiple data set of seismic, well-log,
core, outcrop.
• Finally, the result of paleo environment is presented in the form of
paleogeographic map.

38. Figure 17 :Azimuth map (top) and structure map (bottom) of the seafloor
relief, offshore east Java, Indonesia, showing the tectonic and depositional
settings during the Late Pleistocene relative sea-level lowstand (images
courtesy of H.W. Posamentier)..
• The detached
shorelines (sediment
ridges) on the
continental shelf
formed during relative
sea-level fall, prior to
the shoreline reaching
its lowstand position.
• The slump scars
indicate instability at
the shelf edge, a
situation that is
common during times
of relative fall.

39. Stage - 3 Sequence Stratigraphic Framework
• It explains the origin of enveloped
erosional and depositional surface
boundaries.
• It provides the genetic context in
which separated strata and
surfaces are placed into a
coherent model for all temporal
and spatial relationship of the
facies filling a sedimentary basin.
• Most efficient exploration
approach for natural resources.
• It proceeds with observation of
stratal termination, identification of
sequence stratigraphic surfaces
and labeling of strata in terms of
system tracts and sequences.
Figure 18: A sequence stratigraphic framework leads to
interpretations of depositional setting and predictions
of lithofacies geometries.

40. 3.1 Stratal Termination
• Refers to the geometric
relationships between
strata and stratigraphic
surfaces.
• Stratal terminations may
also be inferred on well-
log cross-sections of
correlation.
• It provides critical
information regarding the
direction and Syn-
depositional shoreline
shift.
3.2 Stratigraphic Surface
• It helps to build the
chronostratigraphic
framework for the
sedimentary succession
under analysis.
• Can be identified on the
basis of nature of contact,
the nature of depositional
system, types of stratal
termination and
depositional trends.
3.3 Systems Tracts and
Sequences
• Last stage of sequence
stratigraphic workflow.
• Represent the
fundamental mapping until
that contains depositional
systems for
paleogeographic map can
be drawn.
• Once the position and
type of stratigraphic
surfaces are at hand,
identification of systems
tracts on cross-sections is
a straight forward
procedure.

41. Types of data sets to the sequence stratigraphic interpretation.

42. Thank You