Catuneanu O. Principles of Sequence Stratigraphy

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using a consistent terminology regardless of scale is that

jargon is kept to a minimum, which makes sequence

stratigraphy more user-friendly and easier to under-

stand across a broad spectrum of readership. These

issues are tackled in more detail in Chapter 8, which

deals with the hierarchy of sequences and sequence

boundaries.

Among the key concepts shown in Fig. 1.9, the term

depositional system is a general (conventional) notion

defined on the basis of depositional setting and environ-

ment. The terms systems tract and sequence are specific

sequence stratigraphic terms, defined in relationship to

the base-level and the transgressive–regressive curves. A

systems tract includes a sum of laterally correlative

depositional systems (hence, the use of plural: systems).

A sequence includes two or more systems tracts,

depending on the model of choice (Fig. 1.7). The actual

scale for sequence stratigraphic work is highly variable,

depending on the problem in hand, ranging from depo-

sitional system scale (also highly variable) to the entire

fill of the basin, and beyond. When applied to the

analysis of a depositional system, e.g., an ancient delta

(Fig. 1.10), sequence stratigraphy is mainly used to

resolve the nature of contacts and the details of facies

relationships. Such studies are often performed to

describe the degree of reservoir compartmentalization

in the various stages of oil field exploration and produc-

tion. When applied to the scale of depositional system

associations, the issue of stratigraphic correlation

becomes a primary objective, and provides the frame-

work for the larger scale distribution of facies.

The principles outlined above provide a general

idea about the range of potential outcomes and objec-

tives of sequence stratigraphy as a function of scope

and scale of analysis. There is a common misconcep-

tion that sequence stratigraphy is always related to

regional, continental, or even global scales of observa-

tion (sub-basins, basins, and global cycles)—this does

not need to be the case, as sequence stratigraphy can be

applied virtually to any scale. A good example of this is

the study of the ‘East Coulee Delta’ (Posamentier et al.,

1992a), where an entire range of sequence stratigraphic

elements (including ‘classic’ systems tracts) have been

documented at a centimeter to meter scale (Fig. 1.11). In

recent years there have been numerous flume-based

studies where sequences have been created under

controlled laboratory conditions (e.g., Wood et al., 1993;

Koss et al., 1994; Paola, 2000; Paola et al., 2001). Such

studies have provided valuable insight as to variations

on the general sequence model.

Sequence Stratigraphy vs. Lithostratigraphy

and Allostratigraphy

Almost any type of study of a sedimentary basin fill

requires the construction of cross sections. The lines we

draw on these two-dimensional representations are of

10 1. INTRODUCTION

(m)

Fluvial

Shallow marine

direction of progradation

regressive facies

transgressive facies

maximum flooding surface

GR 2 GR 3 GR 4 GR 5 GR 6 GR7 GR 8 GR 9

lower-order (higher-frequency) MFS

coastal to fluvial facies contact

maximum regressive surface

transgressive ravinement surface

(km)

GR 1

FIGURE 1.10 Example of sequence stratigraphy applied to understand the reservoir compartmentalization of

a deltaic depositional system (case study illustrating the regression of the Late Cretaceous Bearpaw seaway,

central Alberta). Abbreviations: GR—gamma ray logs; CH—fluvial channel fill; CS—crevasse splay; MFS—

maximum flooding surface. Note that maximum flooding surfaces are associated with the finest-grained sedi-

ments, and their position reveals the overall progradation and geometry of the delta. The reservoir includes

at least five separate hydrodynamic units, each corresponding to a stage of delta front progradation.

two main types: (1) lines that build the chronostrati-

graphic or time framework of the studied interval, and

(2) lines that illustrate lateral changes of facies or

lithology. The chronostratigraphic framework is

constructed by the correlation of surfaces of sequence

stratigraphic significance, or true time markers such

as bentonites or magnetic polarity boundaries. This is

where some confusion can arise. Strictly speaking,

sequence stratigraphic surfaces commonly are not true

time lines but in fact are to some degree time transgres-

sive, or diachronous. However, because true time lines

are not commonly observed, the geoscientist is rele-

gated to using these surfaces as proxies for time lines,

being pragmatic and accepting the notion that in most

instances, within the confines of most study areas they

are at least very close to being time lines and therefore,

are fundamentally useful. The degree of diachroneity

of sequence stratigraphic surfaces, as well as of other

types of stratigraphic surfaces, is discussed in more

detail in Chapter 7.

Sequence stratigraphic surfaces are not necessarily

easier to observe than the more diachronous contacts

that mark lateral and vertical changes of facies.

Consequently the practitioner can be faced with the

dilemma of where to begin a stratigraphic interpreta-

tion; in other words, what lines should go first on a

cross-section. The sequence stratigraphic approach

yields a genetic interpretation of basin fill, which

clarifies by time increment how a basin has filled with

sediment. To accomplish this, a chronostratigraphic

framework is first established, and sequence strati-

graphic surfaces are interpreted. Subsequently, the

sections between sequence stratigraphic surfaces are

interpreted by recognizing facies contacts. These two

types of surfaces (i.e., ‘time lines’ and ‘facies contacts’)

define sequence stratigraphy and lithostratigraphy,

respectively (Fig. 1.12).

The inherent difference between lithostratigraphy

and sequence stratigraphy is important to emphasize,

as both analyze the same sedimentary succession but

with the focus on different stratigraphic aspects or

rock properties. Lithostratigraphy deals with the

lithology of strata and with their organization into

units based on lithological character (Hedberg, 1976).

SEQUENCE STRATIGRAPHIC APPROACH 11

Transgressive Systems Tract

Wave-Cut Bevel

Unconformity

Incised Valley

Highstand Systems Tract

Lowstand Systems Tract

Active Deposition

20 cm

FIGURE 1.11 East Coulee Delta (approxi-

mately 1 m wide; modified from Posamentier

et al., 1992a; image courtesy of H.W. Posamentier),

demonstrating the applicability of sequence

stratigraphic concepts at virtually any scale. In

this example, the highstand systems tract was

left behind, and it was subsequently incised as a

result of the fall in the local (pond) base level

during the progradation of the lower elevation

lowstand delta. See Posamentier et al. (1992a) for

a more detailed interpretation.

The boundaries between lithostratigraphic units are

often highly diachronous facies contacts, in which

case they develop within the sedimentary packages

bounded by sequence stratigraphic surfaces. Sequence

stratigraphy deals with the correlation of coeval stratal

units, irrespective of the lateral changes of facies that

commonly occur across a basin, and which are

bounded by low diachroneity (i.e., nearly synchronous)

surfaces (Fig. 1.12). It is also important to note that

facies analyses leading to the interpretation of pale-

oenvironments are much more critical for sequence

stratigraphy than for lithostratigraphy, as illustrated in

Figs. 1.13 and 1.14. These figures show that even along

1D vertical profiles, sequence stratigraphic units are

often offset relative to the lithostratigraphic units

due to their emphasis on different rock attributes.

Understanding what constitutes a reasonable vertical

and lateral relationship between facies within a time

framework assists in correlating the same time lines

through varying lithologies.

An example of a sequence stratigraphic—as

contrasted with a lithostratigraphic—interpretation

based on the same data set is illustrated in Fig. 1.15.

The interpretation of sequence stratigraphic surfaces is

based on two fundamental observations: the type of

stratigraphic contact, conformable or unconformable;

and the nature of facies (depositional systems) which

are in contact across each particular surface. The recon-

struction of paleodepositional environments is there-

fore a critical pre-requisite for a successful sequence

stratigraphic interpretation. In contrast, the lithostrati-

graphic cross-section does not require knowledge of

paleoenvironments, but only mapping of lithological

contacts. Some of these contacts may coincide with

sequence stratigraphic surfaces, others may only reflect

diachronous lateral changes of facies. As a result, the

lithostratigraphic units (e.g., formations A, B, and C in

Fig. 1.15) provide only descriptive information of litho-

logic distribution, which in some instances could

combine the products of sedimentation of various

depositional environments. Thus a simple map of litho-

logic distribution may give little insight as to the

general paleogeography, and as a result be of little use

in predicting lithologies away from known data points.

Allostratigraphy is a stratigraphic discipline that is

intermediate in scope between lithostratigraphy

12 1. INTRODUCTION

SEQUENCE

systems

tract

Time

Formation A - e.g., a fluvial system

Formation B - e.g., a coastal system

Formation C - e.g., a shallow-marine system

sequence stratigraphic surfaces

lithostratigraphic surfaces

FIGURE 1.12 Conceptual contrast between lithostratigraphy and sequence stratigraphy. Sequence strati-

graphic surfaces are event-significant, and mark changes in depositional trends. In this case, their timing is

controlled by the turnaround points between transgressions and regressions. Lithostratigraphic surfaces are

highly diachronous facies contacts. Note that the system tract and sequence boundaries cross the formation

boundaries. Each systems tract is composed of three depositional systems in this example, and is defined by

a particular depositional trend, i.e., progradational or retrogradational. A sequence corresponds to a full cycle

of changes in depositional trends. This example implies continuous aggradation, hence no breaks in the rock

record, with the cyclicity controlled by a shifting balance between the rates of base-level rise and the sedimen-

tation rates.

and sequence stratigraphy. The North American

Commission on Stratigraphic Nomenclature (NACSN)

introduced formal allostratigraphic units in the 1983

North American Stratigraphic Code to name discon-

tinuity-bounded units. As currently amended, ‘an

allostratigraphic unit is a mappable body of rock that

is defined and identified on the basis of its bounding

discontinuities’ (Article 58). Allostratigraphic units, in

order of decreasing rank, are allogroup, alloformation,

and allomember—a terminology that originates and is

modified from lithostratigraphy. The fundamental

unit is the alloformation (NACSN, 1983, Art. 58). The

bounding discontinuities which define the allostrati-

graphic approach are represented by any mappable

lithological contact, with or without a stratigraphic

hiatus associated with it. Basically, any type of strati-

graphic contact illustrated in Fig. 1.16 may qualify as

an allostratigraphic boundary. In this approach, all

lithostratigraphic and sequence stratigraphic surfaces

that are associated with a lithological contrast may be

used for allostratigraphic studies (e.g., Bhattacharya

and Walker, 1991; Plint, 2000).

Whereas allostratigraphy provides the means to

take lithostratigraphy to a higher level of genetic inter-

pretation of paleodepositional histories, because of the

use of time-significant surfaces, its pitfall rests with

the vague definition of ‘discontinuities.’ NACSN

deliberately left the definition of ‘discontinuity’ to the

practicing geologist who wishes to define or use

allostratigraphic units, so the actual meaning of such

units is largely equivocal. Because a stratigraphic unit

is as well or poorly defined as its bounding surfaces,

the formalization of allostratigraphic units in the

North American Stratigraphic Code remains a half

realized achievement until discontinuity surfaces are

also defined and formalized. Between the European

and the North American commissions on stratigraphic

nomenclature, efforts are being made to clarify both

the degree of overlap and the outstanding differences

between the ‘unconformity-bounded units’ of the 1994

International Stratigraphic Guide (i.e., the pre-

sequence stratigraphy ‘sequences’ of Sloss et al., 1949)

and the ‘discontinuity-bounded units’ of the 1983

NACSN (i.e., allostratigraphic units). Because the

SEQUENCE STRATIGRAPHIC APPROACH 13

LITHOSTRATIGRAPHY SEQUENCE STRATIGRAPHY FACIES

Formation A

Member 1

Member 2

Formation B

Formation C

LST

HST

TST

HST

LST and/or TST

Sequence

facies contacts

subaerial unconformity

wave ravinement surface

maximum floodin

surface

Fluvial

Marine

Fluvial and/or estuarine

Marine

100 m

1B-28-19-16W3

Joli Fou Fm.

Colorado Gp.

Mannville Group

Pense Formation

Cantuar Fm.

(m)

SP Sonic

subaerial unconformity

wave ravinement surface

maximum flooding surface

of higher frequency

fluvial facies

marine facies

Sequence 2

Sequence 1

SEQUENCE

STRATIGRAPHY

higher-frequency

T-R cycles

higher-frequency

T-R cycles

FIGURE 1.14 Relationship between depositional environments,

lithostratigraphy, and sequence stratigraphy (wireline logs from the

Western Canada Sedimentary Basin). Note that facies analysis (inter-

pretation of paleodepositional environments) is more critical to

sequence stratigraphy than to lithostratigraphy. Several higher

frequency transgressive–regressive cycles can be noted within each

sequence. The most prominent maximum flooding surface of each

sequence, corresponding to the peak of finest sediment, belongs to

the same hierarchical order as the sequence itself. These maximum

flooding surfaces separate the transgressive and highstand systems

tracts of sequences 1 and 2. Abbreviations: SP—spontaneous poten-

tial; T–R—transgressive–regressive.

FIGURE 1.13 Lithostratigraphic

and sequence stratigraphic interpreta-

tions of a gamma ray (GR) log (modi-

fied from Posamentier and Allen,

1999). Lithostratigraphy defines rock

units on the basis of lithology, often

irrespective of the depositional envi-

ronment. Sequence stratigraphy

defines rock units based on the event-

significance of their bounding surfaces.

Abbreviations: LST—lowstand sys-

tems tract; TST—transgressive systems

tract; HST—highstand systems tract.

Fluvial system

(meandering)

Fluvial system

(meandering)

Fluvial system

(meandering)

Fluvial system

(meandering)

Fluvial system

(meandering)

Fluvial system

(meandering)

Fluvial system

(meandering)

Fluvial system

(meandering)

Fluvial system

(meandering)

Fluvial system

(meandering)

gravel lags

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Braided system

gravel lag

Central estuary

Delta plain

Delta front

Estuary mouth

1. Data: vertical profiles and paleo-environments

2. Sequence stratigraphic framework

10 m

10 Km

subaerial unconformity

wave ravinement surface

maximum flooding surface

maximum regressive surface

higher frequency maximum regressive surfaces

(deltaic clinoforms, ~time lines)

3. Sequence stratigraphic framework, facies contacts, and paleo-depositional environments

4. Cross-section emphasizing lithostratigraphic units

FIGURE 1.15 Sequence stratigraphic vs. lithostratigraphic frameworks, starting from the same set of facies

data. 1. The reconstruction of paleodepositional environments via facies analysis is an important pre-requisite for

sequence stratigraphic interpretations. The nature of stratigraphic contacts (scoured, conformable) also needs to

be assessed via sedimentological analysis. 2. The sequence stratigraphic framework is constructed by correlating

the key sequence stratigraphic surfaces. All sequence stratigraphic surfaces shown on the cross section are good

chronostratigraphic markers (low diachroneity), with the exception of the transgressive wave-ravinement surface

which is highly diachronous. 3. Sequence stratigraphic cross section, showing key surfaces, within-trend facies

contacts, and paleodepositional environments. Within-trend facies contacts, marking lateral changes of facies, are

placed on the cross-section after the sequence stratigraphic framework is constructed. Facies codes: A—meander-

ing system; B—braided system; C—estuary-mouth complex; D—central estuary; E—delta plain; F—upper delta

front; G—lower delta front—prodelta. 4. Lithostratigraphic cross-section. Three main lithostratigraphic units

(e.g., formations) may be defined: A—a sandstone-dominated unit; B and C – mudstone-dominated units, with

silty and sandy interbeds. Formations B and C are separated by Formation A. Additional lithostratigraphic units

(e.g., members—subdivisions of units A, B, C) may be defined as a function of variations in lithology and color.

(lithological) ‘discontinuity’ is a much less specific

term, including both unconformities and conformities

(Fig. 1.16), ‘unconformity-bounded units’ remain only

a special case of allostratigraphic units. In this context,

the currently informal concepts of sequence stratigra-

phy may ultimately provide the framework that will

allow previously defined types of stratigraphic units

and surfaces to obtain a clear status in relation to each

other and within the bigger picture of genetic stratig-

raphy. Formalizing sequence stratigraphic concepts is

thus an important next task for all international

commissions on stratigraphy.

SEQUENCE STRATIGRAPHIC APPROACH 15

sedimentary

igneous/metamorphic

A. Unconformity = significant hiatus ± erosion (usually with erosion)

A substantial break or gap in the geological record … It normally implies uplift and erosion with los

of the previously formed record. … Relationship between rock strata in contact, characterized by a

lack of continuity in deposition, and corresponding to a period of nondeposition, weathering, or esp.

erosion (either subaerial or subaqueous) prior to the deposition of the younger beds.

B. Diastem = short hiatus ± erosion (a minor paraconformity)

C. Conformity = no hiatus

A relatively short interruption in sedimentation, involving only a brief interval of time, with little

or no erosion before deposition is resumed; a depositional break of lesser magnitude than a

paraconformity, or a paraconformity of very small time value.

Undisturbed relationship between adjacent sedimentary strata that have been deposited in orderly

uence... True strati

hic continuit

in the se

uence of beds.

STRATIGRAPHIC CONTACTS

1. Disconformity = hiatus + erosion

2. Paraconformity = hiatus ± erosion (no discernable erosion)

3. Angular unconformity = hiatus, erosion, and tilt

4. Nonconformity = top of basement rocks

An unconformity in which the bedding planes above and

below the break are essentially parallel, indicating a significant

interruption in the orderly sequence of sedimentary rocks,

generally by a considerable interval of erosion ..., and usually

marked by a visible and irregular or uneven erosion surface of

appreciable relief.

An obscure or uncertain unconformity in which no erosion

surface is discernable ..., and in which the beds above and

below the break are parallel.

An unconformity between two groups of rocks whose bedding

planes are not parallel or in which the older, underlying rocks

dip at a different angle (usually steeper) than the younger,

overlying strata.

An unconformity developed between sedimentary rocks and

older igneous or metamorphic rocks that had been exposed to

erosion before the overlying sediments covered them.

FIGURE 1.16 Types of stratigraphic contacts (definitions from Bates and Jackson, 1987). Note that any of

these stratigraphic contacts may qualify as an allostratigraphic unit boundary, i.e., a ‘discontinuity,’ as long

as it is associated with a lithological contrast.

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CHAPTER

INTRODUCTION

The roots of sequence stratigraphy can be traced far

back in the classic principles of sedimentary geology,

which established the fundamental guidelines of sedi-

mentological and stratigraphic analyses. These ‘first

principles’, as referred to by Posamentier and Allen

(1999), set up the ground rules for the physics of flow

and sediment motion, and the processes of sediment

accumulation, bypass or erosion in relation to a shift-

ing balance between relative sea-level changes, sedi-

ment supply and the energy of the transporting agent

(Fig. 2.1). These principles still represent the scientific

background of sequence stratigraphy, that allows old

and modern concepts to blend into an evolving new

way of looking at the sedimentary rock record.

It is therefore recognized that sequence stratigraphy

is a fresh approach to analysis of sedimentary succes-

sions rather than a brand new method on its own. One

cannot stress enough that a successful sequence strati-

graphic study requires integration of various data sets

and methods of data analysis into a unified, interdisci-

plinary approach (Fig. 1.1). This is not to say that

sequence stratigraphy simply re-sells old concepts in

a new package—in fact, the sequence stratigraphic

approach allows for new insights into the genesis and

architecture of sedimentary basin fills, which were not

possible prior to the introduction of seismic strati-

graphic concepts in the 1970s. The issues of facies

formation and predictability in both mature and fron-

tier hydrocarbon exploration basins are good exam-

ples of such new insights that were made possible by

the sequence stratigraphic approach, and which are

highly significant on both academic and economic

grounds.

This chapter presents a brief account of the main

methods that need to be integrated into a comprehen-

sive sequence stratigraphic analysis, including facies

analysis of ancient deposits (outcrops, core) and modern

environments; analysis of well-log signatures; analysis

of seismic data; and the achievement of time control

via relative and absolute age determinations. Each of

these methods forms the core of a more conventional

and dedicated discipline, so this presentation only

reiterates aspects that are particularly relevant to

sequence stratigraphy. Following the introduction to

the various methods, a general guideline for a step-by-

step sequence stratigraphic workflow is provided as a

practical approach to the generation of geological

models.

FACIES ANALYSIS: OUTCROPS, CORE,

AND MODERN ANALOGUES

Facies analysis is a fundamental sedimentological

method of characterizing bodies of rocks with unique

lithological, physical, and biological attributes relative

to all adjacent deposits. This method is commonly

applied to describe the sediments and/or sedimentary

rocks observed in outcrops, core, or modern environ-

ments. 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, facies analysis is an

integral part of both sedimentology and sequence stratig-

raphy, which explains the partial overlap between

these disciplines (Fig. 1.2). 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.

Concepts of Depositional System, Facies,

and Facies Models

A depositional system (Fig. 1.9) is the product of

sedimentation in a particular depositional environment;

Methods of Sequence Stratigraphic Analysis

CHAPTER

18 2. METHODS OF SEQUENCE STRATIGRAPHIC ANALYSIS

hence, it includes the three-dimensional assemblage of

strata whose geometry and facies lead to the interpre-

tation of a specific paleodepositional environment.

Depositional systems form the building blocks of

systems tracts, the latter representing an essential

concept for stratigraphic correlation and the genetic

interpretation of the sedimentary basin fill. The study

of depositional systems is intimately related to the

concepts of facies, facies associations, and facies

models, which are defined in Fig. 2.2.

Facies analysis is an essential method for the recon-

struction of paleodepositional environments, as well as

for the understanding of climatic changes and subsi-

dence history of sedimentary basins. The understand-

ing of facies and their associations are also essential for

the correct interpretation of sequence stratigraphic

surfaces, as is explained in more detail in Chapter 4.

Facies analysis is therefore a prerequisite for any

sequence stratigraphic studies.

Classification of Depositional Environments

Depositional settings may be classified into three

broad categories, as follows (Fig. 2.3): nonmarine

(beyond the reach of marine flooding), coastal (inter-

mittently flooded by marine water), and marine

(permanently covered by marine water). An illustra-

tion of the subenvironments that encompass the tran-

sition from nonmarine to fully marine environments

is presented in Fig. 2.4. Note that 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. The

glacial environment is not included in the classification

FIGURE 2.1 Key ‘first principles’ of sedimentary geology that are relevant to sequence stratigraphy

(modified from Posamentier and Allen, 1999).

Principles of flow and sediment motion

Principles of sedimentation

All natural systems tend toward a state of equilibrium that reflects an optimum use of energy.

This state of equilibrium is expressed as a graded profile in fluvial systems, or as a base level

in coastal to marine systems. Along such profiles, there is a perfect balance between sediment

removal and accumulation.

Fluid and sediment gravity flows tend to move from high to low elevations, following pathways

that require the least amount of energy for fluid and sediment motion.

Flow velocity is directly proportional to slope magnitude.

Flow discharge (subaerial or subaqueous) is equal to flow velocity times cross-sectional area.

Sediment load (volume) is directly proportional to the transport capacity of the flow, which

reflects the combination of flow discharge and velocity.

The mode of sediment transport (bedload, saltation, suspension) reflects the balance between

grain size/weight and flow competence.

Walther’s Law: within a relatively conformable succession of genetically related strata, vertical

shifts of facies reflect corresponding lateral shifts of facies.

The direction of lateral facies shifts (progradation, retrogradation) reflects the balance between

sedimentation rates and the rates of change in the space available for sediment to accumulate.

Processes of aggradation or erosion are linked to the shifting balance between energy flux and

sediment supply: excess energy flux leads to erosion, excess sediment load triggers aggradation.

The bulk of clastic sediments is derived from elevated source areas and is delivered to

sedimentary basins by river systems.

As environmental energy decreases, coarser-grained sediments are deposited first.

scheme in Fig. 2.3 because it is climatically controlled

and may overlap on any nonmarine, coastal, or marine

setting. Within the nonmarine portion of the basin, a

distinction can be made between the steeper-gradient

alluvial plain, which captures the upstream reaches of

fluvial systems, and the gently sloping coastal plain

that may develop within the downstream reaches of

the fluvial environment (Fig. 2.5). ‘Coastal plain’ is a

geomorphological term that refers to a relatively flat

area of prograded or emerged seafloor, bordering a

coastline and extending inland to the nearest elevated

land (Bates and Jackson, 1987; Fig. 2.5). Figure 2.5 illus-

trates the situation where the coastal plain forms by

processes of progradation of the seafloor, rather than

emergence. In this case, the sediments that accumulate

on the coastal plain during the progradation of the

shoreline are part of the so-called ‘coastal prism’,

which includes fluvial to shallow-water deposits

(Posamentier et al., 1992b; Fig. 2.5). The coastal prism

is wedge shaped, and expands landward from the

coastal environment by onlapping the pre-existing

topography in an upstream direction. The landward

limit of the coastal prism was termed ‘bayline’ by

Posamentier et al. (1992b), and it may shift upstream

when the progradation of the shoreline is accompa-

nied by aggradation.

Coastal environments are critical for sequence

stratigraphy, as they record the history of shoreline

shifts and are most sensitive in providing the clues for

1. Nonmarine environments

2. Coastal (marginal marine) environments

3. Marine environments

- regressive river mouths: Deltas

- transgressive river mouths: Estuaries

- foreshore

- backshore

- shoreface

- inner and outer shelf

- continental slope

- abyssal plain (basin floor)

• Colluvial and alluvial fans

• Fluvial environments

• Lacustrine environments

• Aeolian environments

• River mouth environments

• Open shoreline (beach) environments

• Shallow marine environments

• Deep marine environments

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.

Facies (Walker, 1992): a particular combination of lithology, structural and textural attributes

that defines features different from other rock bodies.

Facies Association (Collinson, 1969): groups of facies genetically related to one another and

which have some environmental significance.

Facies model (Walker, 1992): a general summary of a particular depositional system, involving

many individual examples from recent sediments and ancient rocks.

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.

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 (see more details in Chapter 4).

A facies model assumes predictability in the morphology and evolution of a depositional

environment, inferring “standard” vertical profiles and lateral changes of facies. Given

the natural variability of allocyclic and autocyclic processes, a dogmatic application of

this idealization introduces a potential for error in the interpretation.

FIGURE 2.2 Concepts of facies, facies associations, and facies models.

FIGURE 2.3 Classification of depositional environments, based

on the relative contributions of nonmarine and marine processes.

The coastal/marginal-marine environments, also known as ‘transi-

tional’, are intermittently flooded by marine water during tidal

cycles and storms. Note that both types of coastal environments

(river-mouth or open shoreline) may be transgressive or regressive.

Depositional systems refer to products (bodies of rock in the strati-

graphic record), whereas depositional environments refer to active

processes in modern areas of sediment accumulation. This is similar

to the conceptual difference between cycle and cyclothem, or between

period and system, etc. The boundaries between the various coastal

and shallow-marine environments are defined in Fig. 2.4.

FACIES ANALYSIS: OUTCROPS, CORE, AND MODERN ANALOGUES 19