Stratigraphic Principles
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Types of Stratigraphy
Focus on Modern Stratigraphy is Sequence-based
History of Sequence Stratigraphy
Terminology of Sequence Stratigraphy
Examples from Permian Basin
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Steno’s Laws
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It was recognized in the 1600's that in a sedimentary sequence, the older
beds are on the bottom, and the younger beds are on the top. This has
come to be called the Principle of Superposition. You can visualize how
this occurs if you imagine a stack of newspapers in the corner of a room.
Every day you put another newspaper on the pile. After several weeks
have passed, you have a considerable stack of newspapers, and the oldest
ones will be on the bottom of the pile and the most recent ones will be on
the top. This fairly obvious, but very important fact about layering was
first noted by Nicholaus Steno, and is the first of three principles which
have come to be known as Steno's Laws.
Steno's second law is the Principle of Original Horizontality, which
states that sediments are deposited in flat, horizontal layers. We can
recognize this easily if we consider a sedimentary environment such as the
sea floor or the bottom of a lake. Any storm or flood bringing sediment to
these environments will deposit it in a flat layer on the bottom because of
the sedimentary particles settling under the influence of gravity. As a
result, a flat, horizontal layer of sediment will be deposited.
Steno's third law is the Principle of Original Lateral Continuity. If we
consider again the sediment being deposited on the seafloor, the sediment
will not only be deposited in a flat layer, it will be a layer that extends for
a considerable distance in all directions. In other words, the layer is
laterally continuous.
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Types of Stratigraphy
Classical branches
• Lithostratigraphy
• Chronostratigraphy
• Biostratigraphy
Newer subdisciplines
• Seismic stratigraphy
• Cyclostratigraphy
• Magnetostratigraphy
• Chemostratigraphy
• Integration of disciplines in Sequence Stratigraphy
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Terminology of Lithostratigraphic Units
• Supergroup
– Group
• Formation
– Member
» Bedset
» Bed
• Types of unconformities
– Angular unconformity
– Disconformity
– Paraconformity
– Nonconformity
– hiatus
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History of Sequence Stratigraphy: Unconformities
• James Hutton (17261797): Father of Modern
Geology
• First described
unconformity at Siccar
Point in northern Scotland
• In a paper entitled
“Theory of The Earth”
(1785) Hutton recognized
the importance of
unconformities
• Also recognized
stratigraphic nature of
igneous rocks and believed
came from molten material
within Earth
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History of Sequence Stratigraphy: Uniformitarianism
Principles of Geology (1833)
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History of Sequence Stratigraphy
William Smith measured and
described outcrop stratigraphy
during excavation of transport
canals in England beginning in 1791
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History of Sequence Stratigraphy: Facies
Johannes Walther (1892)
proposed what is now
known as “Walther’s Law
of Facies Succession”
"Facies adjacent to one another in a
continuous vertical sequence also
accumulated adjacent to one another
laterally".
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History of Sequence Stratigraphy: Time-significant
surfaces
1909: Eliot Blackwelder published use
of unconformities as time markers;
introduced concept of time
represented by surfaces (erosional
removal and sedimentary hiatus)
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History of Sequence Stratigraphy: Cyclicity
1916: Amadeus Grabau proposed
the pulsation theory.
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History of Sequence Stratigraphy: Base Level
1917: Joseph Barrell stated the
most fundamental events in
geologic history--the time-space
distribution of deposition and nondeposition: the alternating rise
and fall of Base-level.
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What Really Happened: New Concepts from New
Technology
1951 John L. Rich proposes the
concept of clinoforms…
…recognition of seismic
reflection geometries
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History of Sequence Stratigraphy: Time Stratigraphy
1958
Harry Wheeler produced first chronostratigraphic chart
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History of Sequence Stratigraphy: Time Stratigraphy
1963 Lawrence Sloss recognized 6 major sequences in
North America controlled by eustatic sea level changes
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Official Birth of Sequence Stratigraphy
1977 Peter Vail and Robert Mitchum coordinated the publishing of AAPG Memoir
#26 based on the assumption that a
seismic relection surface represents a time
line
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A Definition of Sequence Stratigraphy
•A framework of genetically related stratigraphic facies
geometries and their bounding surfaces used to determine
depositional setting
•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), systems tracts
•Flooding (trangressive surfaces [TS] &/or maximum
flooding surfaces [mfs]); require that relative sea-level is
known
•This framework used to predict the extent of sedimentary
facies geometry, lithologic character, grain size, sorting &
reservoir quality
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A Simpler, More Useful Definition of Sequence
Stratigraphy
A method to impose the dimension of time on the
relationships of rock units in space (area and depth)
To do this we first describe
facies…
…Then we observe the
geometric relationships
among facies
By understanding how rock units are related
in time and space, we can better interpret how they are
connected as oil and gas reservoirs
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How is “Facies” Used In Sequence Stratigraphy
• Facies: the total textural,
compositional and structural
characteristics of a
sedimentary deposit resulting
from accumulation and
modification in a particular
environment:
– Grain size, sorting,
rounding
– Lithology
– Sedimentary structures
– Bedding type
• In other words, the simplest
description of the genetically
related vertical and lateral
succession
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The Problem of Preservation Potential
Sedimentary facies models are useful to explain spatial
relationships of co-eval facies in the modern
But what will be preserved in the stratigraphic record?
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Original Sequence
Stratigraphic Approach
(seismic stratigraphy) was
based on recognition of
unconformity-bound
sequences using geometry and
termination patterns of seismic
reflectors.
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A critical assumption of the
seismic stratigraphic approach,
illustrated in this diagram
from Vail et al (1977), is that
seismic reflectors follow time
surfaces rather than facies
impedance boundaries.
Note the regional scale of this
illustration.
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The Classic Slug Exxon Model
SB – sequence boundary
LST – lowstand systems tract
TST – transgressive systems tract
HST – 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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Sequence Boundary
• The unconformity or correlative conformity
that bounds a sequence
• Not always a major physical feature
• Not ever exposure surface is a sequence
boundary!
• Commonly (but not always) represents a
significant change in stratal arrangements
and therefore reservoir properites
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Maximum Flooding Surface
• Surface that marks the turn-around from
landward-stepping to seaward stepping strata
• Farther out on platform coincides with the
downlap surface (depending on the degree of
condensation of clinoform toes)
• Recognition of the MFS is important for
separating TST and HST, which in turn is
important for other stratigraphic analysis, but on
the platform top (where 99% of carbonate
reservoir facies occur) this can be difficult to pin
down precisely. Don’t get hung up on this. Try to
pick it as closely as possible, knowing that your
colleague will disagree in order to appear
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enlightened.
Transgressive Systems Tracts
• Bounded below by underlying sequence
boundary and above by maximum flooding
surface
• Generally more mounded in geometry
• Sets of high-frequency cycles show upward
thickening and upward deepening trends
• Typically less grainstone prone, more
diverse skeletal assemblages
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Highstand Systems Tracts
• Bounded below by maximum flooding surface and
above by overlying sequence boundary
• Generally shingled or offlapping (clinoformal)
stratal geometry
• Sets of high-frequency cycles show upward
thinning and upward shallowing trends
• Typically grainstone prone, less diverse skeletal
assemblages
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Terminology of Stratigraphic Hierarchies
Composite sequence
High-frequency
sequence
High-frequency cycle
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Transgressive sequence set = retrogradational sequence set
Highstand sequence set = progradational sequence set
Lowstand sequence set
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Can we do sequence
stratigraphy in carbonates
with just logs?
Does anyone here work for
Schlumberger?
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Indicator facies analysis
Walther’s Law Model
development
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