A Simplified Guide For Sequence Stratigraphy:

Nomenclature, Definitions and Method

SEPM – Society for Sedimentary Geology

Vitor Abreu

President - SEPM

Abstract All attempts to “codify” Sequence Stratigraphy have failed, mostly because:

- perception of cumbersome nomenclature;

- conflicting or obscure causing mechanisms;

- disagreement on basic definitions;

- … or simply that Sequence Stratigraphy is a “young” science

Biostratigraphy has the same set of challenges as Sequence Stratigraphy:- it has a cumbersome nomenclature classification of fossils;

- driving mechanisms for rate of evolution of different taxa is debatable;

- there is strong disagreement as how to classify different species and genera;

- and it is a relatively young science.

Yet, Biostratigraphy has a set of rules and terminology (code) followed by all.

Biostratigraphy is codified as a method, not as a science, based on simple criteria

that can be directly observed from available data.

Implications for interpretation, in terms of causal mechanisms, follow after initial

interpretation, and are not part of the code.

Why do Sequence Stratigraphers have such difficulty agreeing on basic rules for

identifying surfaces and systems tracts based on direct observational criteria?

Conflicting Nomenclature:

Highstand – Transgressive – Lowstand…

Why Not:

Highstand – Midstand(!?!) – Lowstand

Or…

Lower Regressive – Transgressive – Upper Regressive??

At First, A Contradiction…

Posamentier Van Wagoner80’s

Plint

Tucker

Catuneanu

Galloway

Uliana

M Blum

Embry

80’s

To

Today

Community

Eustasy Basic Observations

Peter Vail Bob Mitchum70’s Exxon

A Bit of History

The close association between base-level changes, the formation of surfaces, and

specific stratal stacking that define systems tracts is at the heart of the confusion.

Highstand and Lowstand conflict with terms that are related to shoreline

translation, or attributes that can be directly observed from the geologic record,

such as "transgression", "regression", "progradation", and “retrogradation".

We propose a back-to-basics approach, emphasizing five key observations that can

be made from any geologic data:

lithofacies, lithofacies association, vertical stacking, stratal geometries, and

stratal terminations

Key observations – shoreline position and shoreline trajectory

Terms like highstand, lowstand, and falling stage should be replaced by

observation-based terms like "aggradation-progradation", "progradation-

aggradation", and "degradation", respectively.

Finally, much basic research remains to be done on the relations between stratal

stacking and various controls, and on the formation and chronostratigraphic

significance of key surfaces that demarcate changes in stacking.

Introduction

Parasequence — A relatively conformable succession of genetically related beds and

bedsets bounded by surfaces of flooding, abandonment, or reactivation and their

correlative surfaces (modified from Van Wagoner, 1988).

Sequence —a relatively conformable succession of genetically related strata bounded

by unconformities and their correlative surfaces (modified from Mitchum, 1977).

Parasequences

Sequence

Shoreline Trajectory

Definitions: Parasequence and Sequence

Sequence Boundary — a regional unconformity and its correlative surface

characterized by a downward shift in coastal onlap and across which distinctive

changes in vertical stacking occur.

It is the surface that commonly separates parasequences with aggradational-

progradation-degradation stacking from those with progradation-aggradation or

retrogradation stacking.

Definitions: Stratigraphic Surfaces

Transgressive Surface (Maximum Regressive Surface) – a regional surface

characterized as the first parasequence boundary atop the basinward-most position

of the shoreline.

Parasequence stacking patterns across this surface commonly change from

progradation-aggradation to retrogradation. AKA: Maximum Regressive Surface

(Embry,1995) or Maximum Progradation Surface (Emery and Myers,1996).

Definitions: Stratigraphic Surfaces

Maximum Flooding Surface (Maximum Transgressive Surface) – a regional surface

characterized as the first parasequence boundary atop the landward most position of

the shoreline.

Parasequence stacking patterns across this surface commonly change from

retrogradation to aggradation-progradation-degradation. In seismic, this surface can

be identified as the shelfal downlap surface.

Definitions: Stratigraphic Surfaces

Surface definitions, translation terms, and

recognition criteria.

SurfaceTranslation

Terms

Primary

Recognition

Criteria

Secondary Recognition Criteria

(based on limited available data)

Maximum

Flooding

Surface

MFS

Maximum

Transgressive

Surface

MTS

Atop maximum

landward

position of the

shoreline

Downlapss,o. Turn around in stacking pattern

from retrogradation to aggradation or

progradationw,c,o.

Transgressive

Surface

TS

Maximum

Regressive

Surface*

MRS

Atop maximum

basinward

position of the

shoreline

Surface beneath first backstep (landward

step) of shelf-slope breaks. Turn around in

stacking pattern from progradation or

aggradation to retrogradationw,c,o.

Sequence

Boundary

SB

Sequence

Boundary

SB

Beneath abrupt

basinward shift

in shoreline

Surface beneath first increase in

accommodation after progradation or

degradations. Break in shoreline trajectory

‘S’s. Truncation and/or toplap below, onlap

above s. Abrupt occurrence of proximal facies

over distal faciesw,c,o.

*sensu Embry, 2002s=seismic; w=wells; c=core; o=outcrop.

Lowstand Systems Tract (PA) — a linkage of contemporaneous depositional

systems (Brown and Fisher, 1977), characterized by a progradational to

aggradational stacking of parasequences and bounded by a Sequence Boundary

(SB) at the base and a Transgressive Surface (TS or MRS) at the top.

Transgressive Systems Tract (R) — a linkage of contemporaneous

depositional systems (Brown and Fisher, 1977), characterized by retrogradational

stacking of parasequences and bounded at the base by the TS (or MRS) and at

the top by the Maximum Flooding Surface (MFS or MTS).

Highstand Systems Tract (APD) — a linkage of contemporaneous

depositional systems (Brown and Fisher, 1977), characterized by an

aggradational to progradational to degradational stacking of parasequences,

bounded at the base by the MFS (or MTS) and at the top by the SB.

Definitions: Systems Tracts

Systems Tract Stacking Pattern Bounding SurfacesAccommodation/

Sediment Supply Trend

Highstand

Systems Tract

HST

Aggradation to

Progradation to

(possible) Degradation

A-P-(D)

Above: SB

Below: MFS (MTS)

Decreasing, at

increasing rate

Transgressive

Systems Tract

TST

Retrogradation

R

Above: MFS (MTS)

Below: TS (MRS)

Rapidly increasing, to

a maximum

Lowstand

Systems Tract

LST

Progradation to

Aggradation

P-A

Above: TS (MRS)

Below: SB

Increasing, at

increasing rate

System Tract definitions, stacking patterns, and

recognition criteria.

4. Use Systems Tracts and Surfaces to define depositional sequences

The sequence stratigraphy method can be summarized in 4 steps:

1. Define lithofacies and vertical lithofacies successions to identify

vertical stacking trends and stratal terminations

2. Use vertical stacking patterns and stratal termination patterns to define 3

surfaces:

• Sequence Boundary

• Transgressive Surface (Maximum Regressive Surface)

• Maximum Flooding Surface (Maximum Transgressive Surface)

3. Use Surfaces, vertical stacking, and stratal geometries to define 3 systems

tracts:

• Lowstand Systems Tract (PA)

• Transgressive Systems Tracts (R)

• Highstand Systems Tract (APD)

Method

Then: make maps, find resources, seek to explain by various mechanisms,…

Step 1: a) Identify bedset stacking patterns;

b) Interpret high- and moderate-confidence candidate flooding surfaces;

c) Identify parasequence stacking patterns;

d) Select datum on candidate maximum flooding surface above interval of interest.

Defining Surfaces: Well Logs

Step 2: Correlate lower-confidence bedset surfaces and sequence boundary as constrained by flooding &

bedset surfaces, truncation & onlap, and reservoir quality changes, and connect lithofacies within

parasequences.

Step 3: Use parasequence stacking patterns & stratal geometry to interpret systems tracts, using criteria

on previous page. Note the relation of rock properties (e.g., porosity) to systems tracts.

Defining Surfaces: Well Logs

HST

(A-P-D)

LST

(P-A)

TST (R)

HST

A resulting motif in a depositional succession starting with negative

accommodation rates on the shelf, to maximum accommodation and to

negative again is of: progradational to aggradation (PA or LST), followed by

retrogradation (R or TST), followed by aggradation to progradation to

degradation (APD or HST).

- (“Transgressive” Stacking)

(“Highstand” Stacking) (“Lowstand” Stacking)

Depositional Sequence

Neal and Abreu, 2009

Accommodation Succession

Sequence Stratigraphic methods are amenable to experimental stratigraphy

because stratal terminations are geometric, scale-independent features.

Stratigraphic section comes from the Experimental EarthScape Facility (XES)

located at Saint Anthony Falls and was recently published (AAPG Bulletin)

Martin et al., 2009

Experimental Stratigraphy

Interpretation – applying the sequence stratigraphic method…

Experimental Stratigraphy

Interpretation – applying the sequence stratigraphic method…

Experimental Stratigraphy

Modified from Roberts (2005)

Coastal onlap

PA

APD

SB

Quaternary Example

Uninterpreted and interpreted seismic line through the Lagniappe delta. LST, lowstand systems tract; HST, highstand

systems tract; sb, sequence boundary. Modified from Roberts et al. (2004) and Sydow and Roberts (1994)

unconformable

relatively

conformable

Coastal onlap

SB

PAAPD

Sequence Boundary Expresssion

modified from Mitchum and Van Wagoner, 1991

Composite Sequence: A relatively conformable succession of one or more sequence setsoverlain by a regional drape complex and bounded by regional (100's to 1000's of km2) unconformities or their correlative conformities (called composite sequence boundaries; Mitchum and Van Wagoner, 1991).

Sequence Sets and Composite Sequences

Nested Stratigraphic Hierarchy of the Neogene (Pelotas Basin, Brazil)

0 10 20 30 km

multiple

Early

Miocene

Early to

Middle

Miocene

PlioceneMiddle to Late

Miocene

PASS

RSS

APDSS

Composite SB

Sequence

Boundary (SB)

Termination

Multiple

PA-SS

APD-SS

R-SS

Modified from Abreu (1998)

Pelotas Basin, South Atlantic (Brazil)

24

Kunin and Segalovich, 1996

Sequence Sets and Composite Sequences

25

Kunin and Segalovich, 1996

West Siberia – Kunin and Segalovich (1996)

Sequence Sets and Composite Sequences

26

Modified from Kunin and

Segalovich, 1996APSS

PASS Composite Sequence Boundary

Sequence Sets and Composite Sequences

Fluvial

Floodplain

Coal

Delta Front

Prodelta

Shelfal Muds

Modified from Li and Bhattacharya, 2013

… Or, better… sea level changes cannot be

directly observed from the geologic record. Shoreline trajectory can.In the minds of men and women!!

So, Where is Sea Level in all of this???

Relative movement of sea level is not used and is very misleading to

define systems tracts and surfaces. For example, all Systems Tracts

are at least, in part, deposited during a relative rise of sea level.

PAHST - APD

CSBBasiward shift in coastal onlap

Offlap break observed in seismic profiles is interpreted as the position of the

shoreline and vertical stacking of lithofacies in cores, well-logs and outcrops

indicate changes from proximal to distal shelfal environments.

Systems Tract bounding surfaces are defined at the changes in direction of a

shoreline trajectory during an accommodation succession.

Transgressive Surface (or Maximum Regressive Surface) is defined at the

basinward-most position of the shoreline within an accommodation succession

Maximum Flooding Surface (or Maximum Transgressive Surface) is defined at the

landward-most positions of the shoreline during an accommodation succession,

The Sequence Boundary is defined by the basinward shift in coastal onlap

High-resolution, Quaternary inner-shelf to slope data sets and tank experiments

clarified these processes and are of unique importance to further advance the

understanding of sequence stratigraphic architecture prediction

Conclusions: Objective Criteria

Understanding sequence hierarchy is an important part of seismic sequence

stratigraphy at several spatial and temporal scales

Placing your observations into a stratigraphic hierarchy will put local

interpretations into a regional context for prediction away from well control

Regional thinking is required – even for prospect-scale (or outcrop-scale)

problems

Regional mapping guided by composite surfaces – key for play elements

presence and distribution prediction

Our method:

Conclusions 2: A Practical & Useful Approach

Successions of accommodation change and sediment fill,

observed from stratal patterns and facies stacking

relative to key bounding surfaces,

not defined by time duration or relative sea level position,

placed into a hierarchy framework,

& calibrated with age control