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Sedimentary Geology 1

Research paper

Precambrian sequence stratigraphy

O. Catuneanua,T, M.A. Martins-Netob, P.G. Erikssonc

aDepartment of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, Alberta, Canada T6G 2E3bGeology Department, Federal University of Ouro Preto, Caixa Postal 173, 35400-000, Ouro Preto/MG, Brazil

cDepartment of Geology, University of Pretoria, Pretoria 0002, South Africa

Received 3 May 2004; received in revised form 22 October 2004; accepted 20 December 2004

Abstract

Sequence stratigraphy studies the change in depositional trends in response to the interplay of accommodation and sediment

supply, from the scale of individual depositional systems to entire sedimentary basin-fills. As accommodation is controlled by

allogenic mechanisms that operate at basinal to global scales, the change in depositional trends is commonly synchronized

among all environments established within a basin, thus providing the basis for the definition of systems tracts and the

development of models of facies predictability. All classical sequence stratigraphic models assume the presence of an interior

seaway within the basin under analysis and are centered around the direction and types of shoreline shifts, which control the

timing of all systems tracts and sequence stratigraphic surfaces. In overfilled basins, dominated by nonmarine sedimentation,

the definition of systems tracts is based on changes in fluvial accommodation, as inferred from the shifting balance between the

various fluvial architectural elements.

The method of sequence stratigraphy requires the application of the same set of core principles irrespective of the age of

strata under analysis, from Precambrian to Phanerozoic. The study of Precambrian basins is often hampered by poorer stratal

preservation and by a general lack of time control. However, where sedimentary facies are well preserved, the lack of time

control may be partially compensated by a good knowledge of facies architecture and relationships, as well as by paleocurrent

data. The latter are particularly important to understand the stratigraphic record of tectonically active basins, where abrupt shifts

in paleoflow directions allow one to infer tectonic events and map the corresponding sequence-bounding unconformities.

Arguably the most important contribution of Precambrian research to sequence stratigraphy is the better understanding of the

mechanisms controlling stratigraphic cyclicity in the rock record, and hence of the criteria that should be employed in a system

of sequence stratigraphic hierarchy. There is increasing evidence that the tectonic regimes which controlled the formation and

evolution of sedimentary basins in the more distant geological past were much more erratic in terms of origin and rates than

formerly inferred solely from the study of the Phanerozoic record. In this context, time is largely irrelevant as a parameter in the

classification of stratigraphic sequences, and it is rather the stratigraphic record of changes in the tectonic setting that provides

the key criteria for the basic subdivision of the rock record into basin-fill successions separated by first-order sequence

boundaries. These first-order basin-fill successions are in turn subdivided into second- and lower-order sequences that result

from shifts in the balance between accommodation and sedimentation at various scales of observation, irrespective of the time

0037-0738/$ - s

doi:10.1016/j.se

T Correspondi

E-mail addr

76 (2005) 67–95

ee front matter D 2005 Elsevier B.V. All rights reserved.

dgeo.2004.12.009

ng author.

ess: octavian@ualberta.ca (O. Catuneanu).

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9568

span between two same-order consecutive events. Sequences identified in any particular basin are not expected to correlate to

other first- and lower-order sequences of other basins that may be similar in age but may have different timing and duration.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Precambrian; Sequence stratigraphy; Depositional trends; Cyclicity mechanisms

1. Introduction

1.1. Overview

Sequence stratigraphy is a modern interdisciplinary

approach in the broad field of sedimentary geology

that revamps geological thinking and the methods of

facies and stratigraphic analyses. Modern research

trends show that staying within the boundaries of

conventional disciplines brings little opportunity for

significant progress—it is rather the integration of

various approaches, data sets, and subject areas that

generates potential for breakthrough advances in

science. This is exactly the main theme of sequence

stratigraphy, which integrates the methods of several

disciplines with the purpose of providing improved

and reliable models on how sedimentary facies form

and relate to each other within sedimentary basins

(Fig. 1).

As opposed to other, more conventional types of

stratigraphy, such as biostratigraphy, lithostratigraphy,

chemostratigraphy or magnetostratigraphy, sequence

stratigraphy has an important built-in interpretation

component that addresses issues such as (1) the

reconstruction of the allogenic controls at the time

of sedimentation, and (2) predictions of facies

architecture in yet unexplored areas. The former issue

Integrated disciplines:- Sedimentology- Stratigraphy- Geophysics- Geomorphology- Isotope Geochemistry- Basin Analysis

Integrated- outcrops- modern a- drill core- well logs- seismic d

Sequence Stra

Academic applications: genesis and internal aIndustry applications: exploration for hydroca

Fig. 1. Sequence stratigraphy in the context of interdisciplinary research—m

sparked an intense debate, still ongoing, regarding the

relative importance of eustasy and tectonism on

sedimentation, which is highly important to the

understanding of Earth history and fundamental Earth

processes. Beyond sea level change and tectonism, the

spectrum of controls on stratigraphic patterns is

actually much wider, including additional subsidence

mechanisms (e.g., thermal subsidence, sediment com-

paction, isostatic and flexural crustal loading), orbital

forcing of climate changes, sediment supply, basin

physiography and environmental energy (Fig. 1). The

second issue, on the economic aspect of facies

predictability, provides the industry community with

a new and powerful analytical and correlation tool for

exploration of natural resources.

As with any modeling efforts, the reliability of the

sequence stratigraphic model depends on the quality

and variety of input data, and so integration and

mutual calibration of as many data sets as possible are

recommended. The most common data sources for a

sequence stratigraphic analysis include outcrops, core,

well logs, and seismic data (Fig. 1). In addition to the

facies analysis of the strata themselves, sequence

stratigraphy also places a strong emphasis on the

geological contacts that separate packages of strata

characterized by specific depositional trends. Such

contacts may represent event-significant bounding

Main controls:- sea level change- subsidence, uplift- climate- sediment supply- basin physiography- environmental energy

data:

nalogues

ata

tigraphy

rchitecture of sedimentary basin fillsrbons, coal, and mineral resources

ain controls, integrated data sets and subject areas, and applications.

Basin

marginBasin

center

A

B

C

D

E

F

G

unconformity sequencesA-G

Fig. 2. The concept of the unconformity-bounded sequence of Sloss

et al. (1949). As many unconformities are potentially restricted to

the basin margins, the number of sequences mapped in the basin

center is often lower than the number of sequences present in an

age-equivalent succession along the rim of the basin.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 69

surfaces that mark changes in sedimentation regimes,

and may be important both for regional correlation, as

well as for understanding the facies relationships

within the confines of specific depositional systems.

The success and popularity of sequence stratigra-

phy stems from its widespread applicability in both

mature and frontier exploration basins, where data-

driven and model-driven predictions of lateral and

vertical facies changes can be formulated respectively.

These predictive models have been proven to be

particularly efficient for hydrocarbon exploration,

although there is an increasing demand to employ

the sequence stratigraphic method for coal and

mineral resource exploration as well.

1.2. Historical development of sequence stratigraphy

Sequence stratigraphy is generally regarded as

stemming from the seismic stratigraphy of the 1970s.

In fact, major studies investigating the relationship

between sedimentation, unconformities and changes in

base level, which are directly relevant to sequence

stratigraphy, were published prior to the birth of

seismic stratigraphy (e.g., Grabau, 1913; Barrell,

1917; Sloss et al., 1949; Sloss, 1962, 1963; Wheeler

and Murray, 1957; Wheeler, 1958, 1959, 1964; Curray,

1964; Frazier, 1974). Even before the 20th century, the

periodic repetition through time of processes of

erosion, sediment transport and deposition was recog-

nized by James Hutton (18th century), setting up the

foundation for what is known today as the concept of

the dgeological cycleT. Hutton’s observations may be

considered as the first account of stratigraphic cyclic-

ity, where unconformities provide the basic subdivi-

sion of the rock record into repetitive successions. The

link between unconformities and base-level changes

was explicitly emphasized by Barrell (1917), who

stated that bsedimentation controlled by base level will

result in divisions of the stratigraphic series separated

by breaksQ.The term bsequenceQ was introduced by Sloss et al.

(1949) to designate a stratigraphic unit bounded by

subaerial unconformities. Sloss emphasized the

importance of such sequence-bounding unconform-

ities, and subsequently subdivided the entire Phaner-

ozoic succession of the interior craton of North

America into six major sequences (Sloss, 1963). Sloss

also emphasized the importance of tectonism in the

generation of sequences and bounding unconform-

ities, an idea which is widely accepted today, but was

largely overlooked in the early days of seismic

stratigraphy.

The unconformity-bounded sequences promoted

by L. Sloss and H. Wheeler in the pre-sequence

stratigraphy era provided the geological community

with informal mappable units that could be used for

stratigraphic correlation and the subdivision of the

rock record into genetically related packages of strata.

One limitation on this method of stratigraphic analysis

is the lateral extent of sequence-bounding uncon-

formities, which in many instances are restricted to

basin margins. Hence, the number of sequences

mapped within a sedimentary basin may significantly

decrease down dip, from the basin margins toward the

basin center (Fig. 2). This limitation required a

refinement of the early ideas by finding a way to

extend sequence boundaries across an entire sedimen-

tary basin. The definition of bcorrelative con-

formitiesQ, which are extensions towards the basin

center of basin-margin unconformities, marked the

birth of modern seismic and sequence stratigraphy

(Fig. 3). The advantage of modern model sequences,

which are bounded by composite surfaces, consists in

their basin-wide extent—hence, the number of

sequences mapped at the basin margin equals the

number of sequences that are found in the basin

center. Due largely to conceptual disputes regarding

Basin

marginBasin

center

A A

B B

C C

D D

unconformity correlative conformity

Fig. 3. The concept of sequence as defined in seismic and sequence

stratigraphy. The correlative conformities allow tracing of sequences

across an entire sedimentary basin. A–G—sequences.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9570

the timing of the correlative conformity relative to the

base-level cycle, this new concept of a sequence

bounded by unconformities or their correlative con-

formities is yet to be ratified by either the European or

the North American commissions on stratigraphic

nomenclature. The concept of bunconformity-

bounded unitQ (i.e., SlossT bsequenceQ) was only

formalized by the European bInternational Strati-

graphic GuideQ in 1994.

1.3. Precambrian vs. Phanerozoic sequence

stratigraphy

The principles of sequence stratigraphy are inde-

pendent of the age of strata under analysis. Similarly,

Precambrian

Time span c. 88% of Earth ’s hist

Facies preservationRelatively poor (due topost-depositional tectondiagenesis, metamorph

Time controlRelatively poor (basedon marker beds and lowresolution radiochrono

Basin-formingmechanisms

Competing plume tecand plate tectonics, merratic regime

Fig. 4. Main contrasts between Precambrian and Phanerozoic

the scope and the step-by-step routine of the sequence

stratigraphic model development are the same irre-

spective of the age of the studied sedimentary basin.

Both Precambrian and Phanerozoic case studies share

the common goal of elucidating the history of

sedimentation in response to base-level changes, but

often with different dammunitionT in terms of data

available for analysis. The basic contrasts between

Precambrian and Phanerozoic, in terms of aspects

relevant to sequence stratigraphy, are summarized in

Fig. 4.

The amount and quality of data tend to deteriorate

with increasing stratigraphic age, due to factors such

as post-depositional tectonics, diagenesis and meta-

morphism, which hamper Precambrian case studies

relative to the Phanerozoic counterparts. Both the

preservation potential and the available time control

for facies correlations are superior in the case of

younger sequences, and hence the resolution of

sequence stratigraphic models that can be constructed

for Phanerozoic successions is usually significantly

better relative to what can be achieved for Precam-

brian deposits. For this reason, the method of

sequence stratigraphy has been developed essentially

based on the study of Phanerozoic successions, being

subsequently expanded to the study of Precambrian

sedimentary basins as well.

In spite of the limitations imposed by data

availability and quality, the application of sequence

stratigraphy to the Precambrian should not be

regarded simply as the low-resolution equivalent of

Phanerozoic sequence stratigraphy. The Precambrian

Phanerozoic

ory c. 12% of Earth’s history

ics,ism)

Relatively good

erlogy)

Relatively good (markerbeds, biostratigraphy ,magnetostratigraphy ,radiochronology)

tonicsore

Plate tectonics, morestable regime

, in terms of aspects relevant to sequence stratigraphy.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 71

offers not only challenges, but also unique opportu-

nities, because its time window into the Earth’s

geological history is vastly wider relative to the

duration of the Phanerozoic (Fig. 4). This greater

time span provides the opportunity for observing

Earth’s processes at a broader scale, and thus gaining

an improved understanding on issues such as the

mechanisms governing stratigraphic cyclicity and the

variability thereof. The study of the Precambrian

therefore provides better insights into some key issues

of sequence stratigraphy, for which the time span of

the Phanerozoic is simply too short to allow for any

meaningful generalizations.

The Precambrian record, which encompasses

nearly 90% of Earth’s history, allows one to see that

the tectonic regimes leading to the formation of

sedimentary basins were, for the greater part of

geological time, not as stable or uniform as one might

infer from Phanerozoic case studies. This has pro-

found implications on the selection of criteria that

should be used to classify stratigraphic sequences, and

helps to resolve existing debates generated from the

study of the Phanerozoic record. This paper provides a

set of core principles of sequence stratigraphy that are

valid irrespective of stratigraphic age. It also explores

the unique insights offered by the Precambrian record,

especially in terms of allogenic controls on sedimen-

tation and their relevance to the various aspects of

sequence stratigraphy.

2. Basic principles of sequence stratigraphy

The principles of sequence stratigraphy have been

summarized in several recent volumes, including

Emery and Myers (1996), Miall (1997), Posamentier

and Allen (1999) and Catuneanu (2003). The essential

aspects of the sequence stratigraphic method are

presented below.

2.1. Controls on sedimentation and stratigraphic

architecture

Sedimentation is generally controlled by a combi-

nation of authigenic and allogenic processes, which

determine the distribution of depositional elements

within a depositional system, as well as the broader

scale stacking patterns of depositional systems within

a sedimentary basin. Authigenic processes (e.g., self-

induced avulsion in fluvial and deep water environ-

ments) are particularly important at sub-depositional

system scale, and are commonly studied using the

methods of conventional sedimentology and facies

analysis. Allogenic processes, on the other hand, are

directly relevant to sequence stratigraphy, as they

control the regional-scale architecture of the basin-fill.

Allogenic controls provide the common platform

that connects and synchronizes the depositional trends

recorded at any given time in all environments

established within a sedimentary basin, thus allowing

for sequence stratigraphic models to be developed at

the basin scale. This in turn is the key for the facies

predictability applications of sequence stratigraphy,

which are so much praised by both academic and

industry practitioners. The basic allogenic controls on

sedimentation include the climate, tectonics and sea

level changes; their relationships with sediment

supply, accommodation and depositional trends are

summarized in Fig. 5. Eustasy and tectonics both

control directly the amount of space (accommodation)

that is available for sediments to accumulate. Climate

mainly affects accommodation via eustasy, as for

example during glacio-eustatic falls and rises in sea

level. The effect of climate is also reflected in the

amount of sediment supply, by modifying the

efficiency of weathering, erosion, and sediment trans-

port processes. This is why eustasy, tectonics and

climate are all invoked when discussing the controls

on sedimentation, but only eustasy and tectonics are

usually accounted for when dealing with the controls

on accommodation (Fig. 5).

It is important to note that the allogenic controls

are dexternalT relative to the sedimentary basin, but not

necessarily independent of each other (Fig. 5).

Eustatic fluctuations of global sea level are controlled

by both tectonic and climatic mechanisms, over

various time scales. Climatic fluctuations are primar-

ily controlled by orbital forcing (Milankovitch

cycles), but at more local scales may also be triggered

by tectonic processes such as the formation of thrust-

fold belts that may act as barriers for atmospheric

circulation. Tectonism is primarily driven by forces of

internal Earth dynamics, which are expressed at the

surface by plume- or plate-tectonic processes. Criteria

to differentiate between the signatures of eustasy,

tectonics and paleoclimate have been summarized in

Tectonics

Eustasy

Climate

Allogenic

controls

Accommodation,

sedimentation

Accommodation

(space available for

sediments to fill)

Sediment supply

Transport capacity

vs.

(water, wind)

uplift

subsidence

rise

fall

uplift,

tilt

Sedimentation

(depositional trends,

shoreline shifts)

Sediment supply

Fig. 5. Allogenic controls on sedimentation, and their relationship to sediment supply, accommodation and depositional trends (modified from

Catuneanu, 2003). Note that the depositional trends (aggradation vs. erosion, progradation vs. retrogradation) represent the end result of this

complex interplay between the allogenic controls on sedimentation.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9572

numerous publications (e.g., Aspler and Chiarenzelli,

2002; Aspler et al., 2001; Eriksson et al., 2001a,b;

Martins-Neto et al., 2001; Ojakangas et al., 2001a,b;

Strand, 2002; Young et al., 2001; Catuneanu, 2003).

There is increasing evidence that the tectonic

regimes which controlled the formation and evolution

of sedimentary basins in the more distant geological

past were much more erratic in terms of origin and

rates than formerly inferred solely from the study of

the Phanerozoic record (e.g., Catuneanu, 2001;

Eriksson et al., 2004, this volume, a,b,c; Eriksson

and Catuneanu, 2004b). The more recent basin-

forming processes seem to be largely related to a

rather stable plate-tectonic regime, whereas the for-

mation of Precambrian basins reflects a combination

of competing mechanisms, including magmatic-ther-

mal processes (dplume tectonicsT) and a more erratic

plate-tectonic regime (Fig. 4; Eriksson et al., this

volume, a,b). These insights offered by the Precam-

brian record are critical for extracting the essence of

how one should categorize the stratigraphic sequences

that can be observed within a sedimentary succession

at different scales. This issue is discussed in more

detail in the section dealing with the sequence-

stratigraphic hierarchy.

2.2. Sediment accommodation

The concept of daccommodationT describes the

amount of space that is available for sediments to fill,

being measured by the distance between base level

and the depositional surface (Jervey, 1988). As the

base level itself is a conceptual and dynamic surface

of equilibrium between deposition and erosion,

largely dependent on fluctuations in environmental

energy, the precise quantification of accommodation

at any given time and in any given location is rather

difficult. For this reason, proxies and approximations

are generally required for workable visualizations of

the available accommodation. At first approximation,

sea level is a proxy for base level (Jervey, 1988;

Schumm, 1993), and so the available accommodation

in a marine environment may be measured as the

distance between the sea level and the sea floor. Both

the sea level and the sea floor may independently

change their position with time relative to the center

of Earth in response to various controls, and therefore

the amount of available accommodation fluctuates

accordingly. Sea level is one of the primary allogenic

controls on sedimentation, and it is in turn controlled

by climate and tectonism, as discussed in the previous

section (Fig. 5). The upward and downward shifts in

the position of the sea floor relative to the center of

Earth depend on two main parameters, namely the

magnitude of total subsidence or uplift, and sedimen-

tation. The amount of available accommodation at any

given time and in any given location therefore equals

the balance between how much accommodation is

created (or destroyed) by factors such as tectonism

and sea level change, and how much of this space is

consumed by sedimentation at the same time. The

separation between these two members of the

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 73

accommodation equation (creation/destruction vs.

consumption) is one of the key themes of sequence

stratigraphy, which allows one to understand the

fundamental mechanisms behind the formation of

systems tracts and sequence stratigraphic surfaces.

Fig. 6 helps to define some of the basic concepts

involved in the accommodation equation, such as

eustasy (sea level relative to the center of Earth),

relative sea level (sea level relative to a datum that is

independent of sedimentation), and water depth (sea

level relative to the sea floor). A change in relative sea

level is a proxy for how much accommodation was

created or lost during a period of time, independent of

sedimentation, whereas water depth is a proxy for

how much accommodation is still available after the

effect of sedimentation is also taken into account. The

datum in Fig. 6 monitors the total amount of

subsidence or uplift (including the effects of sediment

compaction) recorded at any location within the basin

relative to the center of the Earth. This datum

reference plane is placed as close to the sea floor as

possible in order to capture the entire subsidence

component related to sediment compaction, but its

actual position is not as important as the change in the

distance between itself and sea level. This is because

we are more interested in the changes in relative sea

level, which reflect how much accommodation is

~~

Eus

tasy

(2)

CENTOF EA

Sedimentsource area Fluvial profile (2)

Lowest level ofcontinental denudation(extension of sea levelbeneath the landscape)

Continent

Shoreline (2)

Shoreline (1)

KEY:

aggradationerosion

Fig. 6. Eustasy, relative sea level, and water depth as a function of sea level

et al., 1988). The datum is a subsurface reference horizon that monitors th

corresponds to the ground surface (subaerial and subaqueous) at time (1).

created or lost during a period of time, rather than the

actual height of relative sea level at any given time.

The separation between relative sea level changes

and sedimentation is a fundamental approach in

sequence stratigraphy, which allows for the compar-

ison between their rates as independent variables. The

balance between these rates (creation/destruction of

accommodation vs. consumption of accommodation)

controls the direction and type of shoreline shifts, and

implicitly the timing of all sequence stratigraphic

surfaces and systems tracts. This approach is therefore

key to a proper understanding of sequence strati-

graphic principles. Failure to do so may result in

confusions between relative sea level changes, water

depth changes, and the directions of shoreline shift.

The above discussion on the controls on accom-

modation is based on the assumption that sea level is a

proxy for base level. This is true at first approxima-

tion, but in reality base level is commonly below the

sea level, due to the energy flux brought about by

waves and currents. As noted by Schumm (1993), this

is also supported by the fact that at their mouths,

rivers erode slightly below the sea level. The actual

distance between base level and sea level depends on

environmental energy, as for example the base level is

lowered during storms relative to its position during

fair-weather. Such energy fluctuations usually take

Sea level (2)

Sea level (1)

Sea floor(2)

DATUM

Waterdepth(2)Relative

sea level (2)

ERRTH

Sediment accumulatedfrom time (1) to time (2)

, sea floor, and datum reference surfaces (modified from Posamentier

e amount of total subsidence or uplift. In this diagram, the DATUM

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9574

place at seasonal to sub-seasonal time scales, at a

frequency that is higher than most highest-frequency

cycles investigated by sequence stratigraphy. Longer-

term shifts in base level, at scales relevant to sequence

stratigraphy, are generally controlled by the interplay

of eustasy and total subsidence. In other words, the

proxies used in the above discussion (i.e., sea level for

base level, and relative sea level changes for changes

in accommodation) are acceptable in a sequence

stratigraphic analysis. The most complete scenario

that illustrates the interplay of the controls on

accommodation and shoreline shifts in a marine

environment is presented in Fig. 7.

The contrast between the rates of change in

accommodation and the sedimentation rates in loca-

tions placed in the vicinity of the shoreline allows one

to understand why the shoreline may shift either

landward or seaward during times of relative sea level

(base level) rise. Accommodation outpacing sedimen-

tation generates transgression (i.e., accommodation is

created faster than it is consumed by sedimentation),

whereas an overwhelming sediment supply may result

in shoreline regression (i.e., accommodation is con-

Eustasy Tectonics Energy flux

Sea levelchanges

Base levelchanges

Relativesea levelchanges

waves, currents

base levelrelative toDATUM

sea levelrelative toDATUM

sea level DATUM

relative to the center of Earth

Marine environment

Fig. 7. Controls on accommodation and shoreline shifts in a marine environ

lacustrine environments by substituting sea level with lake level. See Fig.

level via the effects of waves, wave-generated currents, tidal currents, conto

sub-seasonal time scales) are accounted for under energy flux, whereas the

eustasy.

sumed more rapidly than is being created). In either

situation, the river mouth moves accordingly, land-

ward or seaward, connecting the continuously adjust-

ing fluvial profile to the shifting base level. In the case

of a delta that progrades during a stage of base level

rise, for example, the newly created space is not

sufficient to accommodate the entire amount of

sediment brought by the river, and as a result the

river mouth shifts seaward. This shift triggers a

change in depositional regimes from prodelta and

delta front environments, where sedimentation is

limited to the space between the sea floor and the

base level, to delta plain and alluvial plain environ-

ments (landward relative to the shoreline), where

depositional trends (aggradation, bypass, or erosion)

are governed by the relative position between the

fluvial graded profile and the actual fluvial profile.

The fluvial graded profile is the conceptual

equivalent of the marine base level in the nonmarine

realm, as it describes the imaginary and dynamic

surface of equilibrium between deposition and erosion

in the fluvial environment. This equilibrium profile is

achieved when the river is able to transport its

Sedimentation

Transgressionsand

Regressions

sea floorrelative to DATUM

base level relativeto sea floor

Accommodation

creationor

destruction

consumption

shoreline shifts

ment (modified from Catuneanu, 2003). This diagram also applies to

6 for the definition of the DATUM. The energy flux lowers the base

ur currents or gravity flows. Short-term climatic changes (seasonal to

longer-term climatic changes (e.g., Milankovitch type) are built into

Energy fluxBase level changes

Changes influvial graded profile

Sedimentation

Fluvialaccommodation

Fluvial system connected to a marine environment

river dischargeand velocity

river bed relativeto DATUM

graded profile relativeto ground surface

base level relativeto DATUM

graded profilerelative to DATUM

creationor

destruction

consumption

Fig. 8. Controls on fluvial accommodation in the distal reaches of

a fluvial system. See Fig. 6 for the definition of the DATUM. The

energy flux is mainly controlled by short- to longer-term climatic

changes (especially the discharge component), but also by

tectonic tilt.

Tectonics

Changes influvial graded profile

Sedimentation

Fluvialaccommodation

Fluvial system isolated from marine influences

Energy flux

river bed relativeto DATUM

graded profile relativeto ground surface

DATUM relative tocenter of Earth

graded profilerelative to DATUM

creationor

destruction

consumption

river dischargeand velocity

Fig. 9. Controls on fluvial accommodation in the proximal reaches

of a fluvial system. See Fig. 6 for the definition of the DATUM

The energy flux is mainly controlled by short- to longer-term

climatic changes (especially the discharge component), but also by

tectonic tilt.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 75

sediment load without aggradation or degradation of

the channels (Leopold and Bull, 1979). In this

context, the amount of fluvial accommodation is

defined as the space between the graded profile and

the actual fluvial profile (Posamentier and Allen,

1999). If we compare this definition with the concept

of marine accommodation, discussed above, the

graded profile is the equivalent of the base level,

and the actual fluvial profile is the counterpart of the

sea floor in the marine environment. If we follow this

comparison even further, we notice that the sea level,

which is used as a proxy for base level, does not have

an equivalent in the fluvial realm, which makes the

visualization of fluvial accommodation rather difficult

as there is no physical proxy for the fluvial graded

profile. The only observable surface is the actual

fluvial landscape, whose position relative to an

independent datum changes in response to surface

processes of aggradation or erosion (Fig. 6). In turn,

these surface processes are triggered by an attempt of

the river to reach its graded profile.

The graded profile is danchoredT to the base level atthe river mouth, and as the base level rises and falls this

anchoring point moves either landward or seaward, or

up or down, triggering an in-kind response of the

graded profile (Posamentier and Allen, 1999). There-

fore, base-level changes exert an important control on

graded profiles, and implicitly on fluvial accommoda-

tion, especially in the distal reaches of the fluvial

system (Shanley and McCabe, 1994; Fig. 8). The

position of graded profiles also depends on fluctua-

tions in energy flux, which are mainly attributed to the

effects of climate on a river’s transport capacity (Blum

and Valastro, 1989; Blum, 1990; Fig. 8). Such energy

fluctuations may be recorded over different time

scales, from seasonal climatic changes that may occur

with a frequency higher than the highest-frequency

cycles studied by sequence stratigraphy, to Milanko-

vitch-scale orbital forcing.

The effect of base-level changes on fluvial

processes (aggradation vs. erosion) is only dfeltT by

rivers within a limited distance upstream relative to

the river mouth, which is usually in a range of less

than 200 km (Miall, 1997). Beyond the landward limit

of base-level influences, rivers respond primarily to a

combination of tectonic and climatic controls (Fig. 9).

Tectonism dictates the overall geometry of fluvial

sequences, as the creation of fluvial accommodation

follows the patterns of regional subsidence. For

example, the rates of subsidence induced by flexural

loading in a foreland basin increase in a proximal

direction, toward the center of loading, whereas the

rates of thermal and mechanical subsidence in an

extensional basin increase in a distal direction. These

.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9576

patterns are reflected by the geometry of fluvial

sequences that may fill the basin. Superimposed on

these general trends, the climatic control on runoff and

discharge also affect the position of graded profiles, as

discussed above (Fig. 9).

The role of climate as a control on accommodation

is always difficult to quantify because it operates via

other variables such as eustasy and environmental

energy flux. In a marine environment, the short-term

climatic changes (seasonal to sub-seasonal time scale)

translate into fluctuations in energy flux, whereas the

longer-term changes are accounted for under eustasy

(Fig. 7). In the case of fluvial environments, both

short- and longer-term climatic changes are reflected

in the fluctuations in energy flux because there is no

physical proxy for the graded profile that could be

related to the longer-term climate shifts (Figs. 8 and

9). Climate is also relevant to the dsedimentationT boxin all cases (Figs. 7–9) because the amount of

sediment supply transferred from source areas to the

sedimentary basin depends on the efficiency of

weathering and sediment transport processes, both of

which are partly dependent on climate.

A significant debate still persists regarding the

relationship between base level and the fluvial graded

profile. One school of thought argues that the term

dbase levelT should apply to both concepts, as the

same definition can describe them both (i.e., a

dynamic surface of equilibrium between deposition

and erosion; Barrell, 1917; Sloss, 1962; Cross, 1991;

Cross and Lessenger, 1998). A second school of

thought restricts the term dbase levelT to the level of

the body of water into which the river debouches (sea

level, lake level, or even another river), as used in this

paper (Powell, 1875; Davis, 1908; Bates and Jackson,

1987; Schumm, 1993; Posamentier and Allen, 1999;

Catuneanu, 2003). Terminology is trivial to some

extent, but we find value in keeping the concepts of

graded fluvial profile and base level separate because

they are in a process–response relationship—i.e., the

position in space of the fluvial graded profile is in part

a function of the elevation of the base level, and

changes with time thereof.

2.3. Types of shoreline shifts

The interplay of base-level changes and sedimen-

tation controls the available accommodation, as well

as the transgressive and regressive shifts of the

shoreline (Fig. 7). The types of shoreline shifts are

critical in a sequence stratigraphic framework, as they

determine the formation of packages of strata with

specific stacking patterns, known as systems tracts.

Three types of shoreline shifts may be recorded, as

outlined below.

2.3.1. Transgressions

Transgressions take place when accommodation is

created more rapidly than it is consumed by sed-

imentation, i.e., when the rates of base-level rise

outpace the sedimentation rates at the shoreline. This

results in a retrogradation (landward shift) of facies.

The scour surface cut by waves during the shoreline

transgression (wave ravinement surface) is onlapped

by the aggrading and retrograding shoreface deposits

(Fig. 10). The combination of wave scouring in the

upper shoreface and deposition in the lower shoreface

is required to preserve the concave-up shoreface

profile that is in equilibrium with the wave energy

during transgression (Bruun, 1962; Dominguez and

Wanless, 1991). The onlapping deposits that accumu-

late in the lower shoreface dhealT the bathymetric

profile of the seafloor that is oversteepened as a result

of the transgressive shoreline shift, which is why they

are known as dhealing phaseT deposits (Posamentier

and Allen, 1993; Fig. 10).

The rise in base level at the shoreline promotes

coastal aggradation in estuarine (river mouth) or beach

(open shoreline) environments. However, the ten-

dency of coastal aggradation is counteracted by the

wave scouring in the upper shoreface, as the latter

gradually shifts in a landward direction. The balance

between these two opposing forces, of sedimentation

vs. erosion, determines the overall type of trans-

gressive coastline (Fig. 10). Coastlines dominated by

aggradation lead to the preservation of estuarine or

backstepping beach facies in the rock record. Coast-

lines dominated by erosion are associated with

unconformities in the nonmarine part of the basin,

whose stratigraphic hiatuses are age-equivalent with

the transgressive marine facies. Regardless of the

overall nature of coastal processes, the wave ravine-

ment surface is onlapped by transgressive shallow

marine (dhealing phaseT) deposits, which provides a

clue for understanding the transgressive nature of

some subaerial unconformities.

incision

progradation & offlap

fluvial erosionmarine erosion

fluvial erosion

fluvial scourmarine scourconformable clinoforms

fluvial scourconformable clinoforms

(1)

(1)

(1)

(1)

HST=(1)

HST=(1)

(2)

(2)

(3)

(3)

(3)

(3)

(4)

(4)

(4)

(4)

(4)

(4)

erosion at time (2), etc.

forced regressiveshoreface deposits

forced regressiveshoreface deposits

sedimentation at time (2), etc.

sedimentation at time (2), etc.

onset of base level fall

onset of base level fall

Forced regressions: shoreline shift

(2)

(2)

1. Wave-dominated coastline (open shoreline, wave-dominated delta)

2. River-dominated delta

Fig. 11. Shoreline trajectory in forced regressive settings (modified

from Catuneanu, 2003). Forced regressions are driven by base leve

fall, irrespective of sediment supply, and the rates of progradation

are generally high. Wave-dominated subtidal settings are charac

terized by shallow gradients of the seafloor, which is subject to

wave scouring in order to preserve a profile that is in equilibrium

with the wave energy. River-dominated deltas generally have delta

front clinoforms that are steeper than the wave equilibrium profile

and therefore no wave scouring takes place during forced

regression. HST—highstand systems tract.

shoreface aggradation & onlapretrogradation

wave scouring

(1)(2)

(2)

shoreface sedimentation

“healing phase” deposits

“healing phase” deposits

shoreface erosion

wavescour

wave scour

coastal aggradation(estuary or backstepping beaches)

estuarine or beach facies

fluvial facies

base level rise

Transgressive shorelines:shoreline shift

A. Coastal aggradation

B. Coastal erosion

(1)(2)

(2)

shoreface sedimentationshoreface erosion

coastal erosion

coastal erosion (receding cliff)

receding coastline

newgraded profile

fluvial erosion

subaerial erosion

Fig. 10. Shoreline trajectory in transgressive settings (from

Catuneanu, 2003). Transgressions are driven by base level rise,

where the rates of base level rise outpace the sedimentation rates in

the shoreline area. The balance between the opposing trends of

aggradation (in front of the shoreline) and wave scouring (behind

the shoreline) determines the type of transgressive coastline. In

addition to this, shallow-gradient coastal plains are prone to coastal

aggradation, whereas steeper coastal plains are prone to coastal

erosion. In both cases, the gradients may be shallower than the

average shoreface profile (ca. 0.38).

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 77

2.3.2. Forced regressions

Forced regressions occur during stages of base-

level fall, when the shoreline is forced to regress by

the falling base level, irrespective of sediment supply.

In wave-dominated coastal settings, such as open

shorelines or wave-dominated deltas, the preservation

of the concave-up sea floor profile that is in

equilibrium with the wave energy requires coeval

deposition and erosion in the upper and lower parts of

the subtidal area, respectively (Bruun, 1962; Plint,

1988; Dominguez and Wanless, 1991; Fig. 11). As the

shoreline shifts basinward, the upper subtidal forced

regressive deposits downlap the scour generated in the

lower subtidal zone (Fig. 11). At the same time, the

subaerially exposed area is subject to sediment

starvation, as well as fluvial and wind degradation.

The amount of nonmarine downcutting is proportional

to the magnitude of base-level fall (see Posamentier,

2001, for a discussion of incised vs. unincised fluvial

bypass systems).

In the case of river-dominated deltas, the angle of

repose of delta front clinoforms is generally steeper

l

-

,

2 km

2 km

100 ms

100 ms

1. Uninterpreted seismic line

2. Interpreted seismic line

Fig. 12. A seismic example of an incised valley filled with fluvial

(lower large arrow) and estuarine (higher large arrow) deposits. The

smaller arrows indicate onlap of estuarine facies.

aggradationprogradation

(1)(1)

(2) (3) (4)(4)base level rise

Normal regressions: shoreline shift

shoreface/delta frontaggradation and progradation

fluvial/delta plain/strandplain

lateral changesof facies

Fig. 13. Shoreline trajectory in normal regressive settings (from

Catuneanu, 2003). Normal regressions are driven by sedimen

supply, where the rates of base level rise at the shoreline are

outpaced by sedimentation rates. Normal regressions occur during

early and late stages of base level rise, when the rates of base leve

rise are low. Progradation rates are generally lower relative to

forced regressions. Aggradation occurs in coastal environments

(delta plains in river mouth settings, or strandplains along open

shorelines), which triggers fluvial aggradation on the adjacen

alluvial plain.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9578

than the gradient required to balance the energy of the

waves, so there is no reason for wave scouring in the

lower delta front area (Fig. 11). Therefore, the marine

scour surface that forms in shallow marine wave-

dominated settings during forced regression is missing

from the stratal architecture of forced regressive river-

dominated deltas. In the former case, a vertical profile

through the shallow marine forced regressive succes-

sion shows an abrupt shift of facies from offshore

muds to subtidal sands, whereas this facies shift is

gradational in the river-dominated deltas.

Stages of forced regression are generally charac-

terized by a significant increase of sediment supply to

the deep-water depositional systems. This is due to (1)

a lack of accommodation in the fluvial to shallow

marine environments, and therefore the terrigenous

sediment tends to bypass these settings and be

delivered to the deep-water environment; and (2)

additional sediment may be supplied by erosional

processes in the fluvial and lower shoreface environ-

ments. On continental shelves, forced regressions may

result in the formation of incised valleys, which are

filled during subsequent dlowstandT normal regres-

sions and transgressions with fluvial, estuarine, and

even shallow marine deposits (Fig. 12).

2.3.3. Normal regressions

Normal regressions occur in the early and late

stages of base-level rise, when the sedimentation rates

outpace the low rates of base-level rise at the

shoreline. In this case, sedimentation totally fills the

newly created accommodation, sediment bypass

accompanies aggradation (the surplus of sediment

for which no accommodation is available), and facies

prograde (Fig. 13).

The process of coastal aggradation, in response to

rising base level, is an important diagnostic feature

that separates normal regressive from forced regres-

sive deposits (Figs. 11 and 13). As a result, a topset

package of delta plain (in river mouth settings) or

beach/strandplain (in open shoreline settings) sedi-

ments accumulates and progrades over the shallow

marine delta front/shoreface facies. The preservation

potential of this topset package is higher in the case of

the early rise (dlowstandT) normal regressive deposits

because the late rise (dhighstandT) normal regressive

strata are potentially truncated by subaerial uncon-

formities (Fig. 11).

2.4. Sequence stratigraphic models

The concept of a dsequenceT is only as good, or

acceptable, as the boundaries that define it. As a

t

l

t

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 79

matter of principle, it is useless to formalize a unit

whose boundary definitions are left to the discretion

of the individual practitioner. The dsequenceT definedby Sloss et al. (1949) as an unconformity-bounded

unit, was widely embraced (and formalized in the

1994 International Stratigraphic Guide) because the

concept of unconformity was also straightforward

and surrounded by little debate. Modification of the

original concept of sequence, by the introduction of

correlative conformities as part of its bounding

surfaces, triggered both progress and debates at the

onset of the seismic and sequence stratigraphy era.

The main source of contention relates to the nature

and timing of these correlative conformities, and

consequently a number of different models are now

in use, each promoting a unique set of terms and

bounding surfaces. This creates unnecessary jargon

and confusion, and hampers communication of ideas

and results. A few reasons for this variety of

approaches in sequence stratigraphy include: (1)

the underlying assumptions regarding the primary

controls on stratigraphic cyclicity; (2) the type of

basin from which models were derived; and (3) the

gradual conceptual advances that allowed for alter-

native models to be developed. Present-day sequence

stratigraphy can thus be described as a still devel-

oping field that takes the science of Sedimentary

SequencesSloss (1949, 19

Depositional Sequ(Seismic StratigrMitchum et al. (1

Depositional Sequence IIHaq et al. (1987)

Posamentier et al. (1988)

Depositional SequVan Wagoner et al. (1

Christie-Blick (1

Genetic SequencesGalloway (1989)

Frazier (1974)

Sequence Stratig

Fig. 14. Family tree of sequence stratigraphy (modified from Donovan, 20

style of conceptual packaging of strata into sequences, i.e., with respect t

Geology in an exciting new direction of conceptual

and practical opportunities, even though along a

bumpy road punctuated by disagreements and

controversy.

Early work on seismic and sequence stratigraphy

published in the AAPG Memoir 26 (Payton, 1977)

and the SEPM Special Publication 42 (Wilgus et al.,

1988) resulted in ddepositional sequenceT being

defined as the primary unit of a sequence strati-

graphic model. This stratigraphic unit is bounded by

subaerial unconformities on the basin margin and

their correlative conformities toward the basin

center. The depositional sequence was subdivided

into lowstand, transgressive and highstand systems

tracts on the basis of internal surfaces that corre-

spond to changes in the direction of shoreline shift

from regression to transgression and vice versa.

Variations on the original depositional sequence

theme resulted in the publication of several slightly

modified versions of the depositional sequence

model (Figs. 14 and 15).

Soon after the SEPM Special Publication 42,

Galloway (1989), based on Frazier (1974), proposed

that maximum flooding surfaces, rather than subaerial

unconformities, be used as sequence boundaries. This

unit was termed a bgenetic stratigraphic sequenceQ,also referred to as a regressive–transgressive (R–T)

63)

ence Iaphy)977)

ence III988,1990)991)

Depositional Sequence IVHunt and Tucker (1992, 1995)Plint and Nummedal (2000)

T-R SequencesEmbry (1993, 1995)

Curray (1964)

raphy

01). The various sequence stratigraphic models mainly differ in the

o where the sequence boundaries are picked in the rock record.

DepositionalSequence II

DepositionalSequence III

DepositionalSequence IV

GeneticSequence

T-RSequence

end ofbase level fall

end ofregression

end oftransgression

onset ofbase level fall

Events

Sequencemodel

early HST(wedge)

early HST

early LST(fan)

early LST(fan)

late LST(wedge)

late LST(wedge)

late HST(fan)

HST HST

HST HST

TST TST

LST

TST TST TST

RST

RST

FSST

HST

HST

LST

sequence boundaryin a marine successionin a nonmarine successionsystems tract boundarywithin systems tract surface

Time

onset ofbase level fall

end ofbase level fall

end ofregression

end oftransgression

(*)

(*)

(**)

(**)

Fig. 15. Timing of systems tract and sequence boundaries for the sequence models currently in use. Abbreviations: LST—lowstand systems

tract; TST—transgressive systems tract; HST—highstand systems tract; FSST—falling stage systems tract; RST—regressive systems tract; T–

R—transgressive–regressive. Note that the conformable portion of the sequence boundary of the depositional sequence II was originally

considered to form during early sea level fall (Posamentier et al., 1988), which was later revised to the onset of sea level fall (Posamentier et al.,

1992), as represented in this table.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9580

sequence. Finally, Embry and Johannessen (1992)

proposed a third type of stratigraphic unit, named a

btransgressive–regressive (T–R) sequenceQ, corre-

sponding to a full cycle of transgressive and regres-

sive shoreline shifts (Figs. 14 and 15).

The various sequence models that are currently in

use differ from each other mainly in the style of

conceptual packaging of the stratigraphic record,

using a different timing for systems tract and sequence

boundaries in relation to a cycle of base-level shifts

(Figs. 14 and 15). Each sequence model may work

best under particular circumstances, and no one model

is universally applicable to the entire range of case

studies (Catuneanu, 2002). The applicability and

practical limitations of each approach are discussed

in detail by Catuneanu (2003).

Irrespective of the model of choice, a common

theme emerges in the sense that a full cycle of base-

level changes records four main stratigraphic events

that signify changes in the type of shoreline shifts; i.e.,

the onset of forced regression, the end of forced

regression, the end of (normal) regression and the end

of transgression (Fig. 16). These events separate

systems tracts, and result in the formation of four

sequence stratigraphic surfaces: the basal surface of

forced regression (=correlative conformity sensu

Posamentier et al., 1988), the correlative conformity

(sensu Hunt and Tucker, 1992), the maximum

regressive surface (=transgressive surface), and the

maximum flooding surface respectively (Fig. 16).

Three more sequence stratigraphic surfaces form

during particular stages of shoreline shift, such as

the subaerial unconformity during forced regression

(fluvial scour in Fig. 11), the regressive surface of

marine erosion during forced regression in wave-

dominated settings (marine scour in Fig. 11), and the

wave ravinement surface during transgression (wave

scour in Fig. 10). The correct identification of these

Tim

e

(-A

)

Maximum flooding surface

Correlative conformity *

Basal surface of forced regression **

Basal surface of forced regression **

Maximum regressive surface

Rise Fall

Full

cycl

eBase level Events Sequence stratigraphic surfaces

*

**Hunt and Tucker (1992)

= correlative conformity Posamentier et al. (1988)sensu

sensu

Onset of forced regressionEnd of transgression

End of regressionEnd of forced regression

Onset of forced regression

}

}Wave ravinement surface

Subaerial unconformityand

Regressive surface of marine erosion

Systems tracts

FR (FSST)

NR (LST)

T (TST)

NR (HST)

Fig. 16. Timing of sequence stratigraphic surfaces relative to the main events of the base level cycle (modified from Catuneanu et al., 1998;

Embry and Catuneanu, 2002; Catuneanu, 2003). Each of these seven surfaces of sequence stratigraphy can serve, at least in part, as systems tract

boundaries. Abbreviations: (�A)—negative accommodation; FR—forced regression; NR—normal regression; T—transgression; FSST—

falling stage systems tract; LST—lowstand systems tract; TST—transgressive systems tract; HST—highstand systems tract. The nomenclature

of systems tracts conforms with the depositional sequence IV model (Fig. 15).

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 81

sequence stratigraphic surfaces is the key for a robust

sequence stratigraphic interpretation, regardless of

how we name the systems tracts between them, or

where we choose to place the sequence boundary (Fig.

15). Criteria for identifying sequence stratigraphic

surfaces are now firmly established, based on the

nature of contacts, nature of facies that are in contact

across the surface, and types of stratal terminations

that are associated with each particular type of surface

(Fig. 17). Catuneanu (2003) discusses these criteria in

detail.

Stratigraphic surfaceNatureof contact Strata below Str

Subaerial unconformity Scoured ortop of paleosol

Variable(where marine, c-u)

Non

Correlative conformity * Conformable Marine, c-u Mar(c-u

Regressive surfaceof marine erosion

Scoured Shelf, c-u Shor

Basal surfaceof forced regression **

Conformableor scoured

Marine, variable(c-u on shelf)

Mar

Maximum regressivesurface

Conformable Variable(where marine, c-u)

Vari(whe

Maximum floodingsurface

Conformableor scoured

Variable(where marine, f-u)

Vari(whe

Wave ravinementsurface

Scoured Variable(where marine, c-u)

Mar

Fig. 17. Diagnostic features of sequence stratigraphic surfaces (modified fro

Tucker (1992); **correlative conformity sensu Posamentier et al. (1988).

3. Sequence stratigraphic hierarchy

3.1. Introduction

A sequence hierarchy assigns different orders to

stratigraphic sequences and bounding surfaces based

on their relative importance. Within a hierarchical

system, the most important sequence is recognized as

of dfirst-orderT and may be subdivided into two or

more dsecond-orderT sequences. In turn, a second-

order sequence may be subdivided into two or more

ata above Temporal attributes

marine Variable hiatus

ineon shelf)

Low diachroneity

eface, c-u High diachroneity

ine, c-u Low diachroneity

ablere marine, f-u)

Low diachroneity

ablere marine, c-u)

Low diachroneity

ine, f-u High diachroneity

Stratalterminations

Truncation, toplap,fluvial onlap, offlap

Downlap

Coastal onlap

Truncation, downlap

Downlap

“Downlap surface”

Downlap,marine onlap

m Embry and Catuneanu, 2002; Catuneanu, 2003). *Sensu Hunt and

Abbreviations: c-u—coarsening-upward; f-u—fining-upward.

high

orde

r

(low

freq

uenc

y)

low

orde

r

(hig

hfr

eque

ncy)

fifthorder

firstorder

secondorder

thirdorder

fourthorder

Fig. 18. Diagrammatic representation of the concept of hierarchy.

This pyramid approach assumes that the events leading to the

formation of the most important sequences and bounding surfaces

(first-order) occurred less frequently in the geological record relative

to the events leading to the formation of lower order sequence

boundaries.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9582

dthird-orderT sequences, and so on (Fig. 18). The more

important sequences are designated as dhigh-orderT (atthe top of the hierarchy pyramid), and generally have

a low frequency in the stratigraphic record. The less

important sequences are of dlower-orderT and are more

common in the rock record (Fig. 18).

The critical element in developing a system of

sequence hierarchy is the set of criteria that should be

used to differentiate between the relative importance

of sequences and bounding surfaces. Two different

approaches are currently in use, based on the study of

the Phanerozoic record: (1) a system based on

boundary frequency (sequence duration), and (2) a

system based on the magnitude of base-level changes

which resulted in boundary formation (independent of

sequence duration). The former system has historical

priority, having being proposed at the dawn of seismic

Hierarchical order Duration (My)

First order 200-400

Second order 10-100

Third order 1-10

Fourth and fifth order 0.01-1

Fig. 19. Tectonic and orbital controls on eustatic fluctuations (modified from

here for orders of stratigraphic sequences (see text for details). Local- or ba

sea level cycles, often with higher rates and magnitudes, and with a rang

and sequence stratigraphy (Vail et al., 1977; Fig. 19).

This time-based hierarchy emphasizes eustasy as the

main driving force behind stratigraphic cyclicity,

which in turn is controlled by a combination of plate

tectonic and orbital mechanisms. As eustasy is global

in nature, the philosophy behind this hierarchy system

led to the construction of global cycle charts (Vail et

al., 1977), whose validity is currently under intense

scrutiny (Miall, 1992, 1997).

3.2. Hierarchy system based on boundary frequency

In addition to the controversy brought about by

global cycle charts, the application of the hierarchy

system based on sequence duration poses an impor-

tant practical problem, which is the fact that good time

control is required to ensure that a dthird-orderTsequence falls indeed within the 1–10 My duration

bracket (Fig. 19; Vail et al., 1977), and so on. Such

time control is often difficult to acquire even for

Phanerozoic successions, and it becomes more and

more unrealistic with increasing stratigraphic age. In

spite of this practical limitation, the hierarchy system

based on sequence duration, which was originally

developed based on Phanerozoic case studies (Vail et

al., 1977), was eventually extrapolated to the Precam-

brian as well (Krapez, 1996, 1997). Krapez (1996)

provides average durations for sequence orders as

follows: fourth=90–400 ky, third=1–11 My, sec-

ond=22–45 My, and first=approximately 364 My.

Each of these orders of stratigraphic cyclicity is

genetically related to particular tectonic (and to a

much lesser extent climatic) controls whose perio-

dicity is assumed to be more or less constant during

geological time. For example, the 364 My duration of

Cause

Formation and breakupof supercontinents

Volume changes inmid-oceanic spreading centers

Regional plate kinematics

Orbital forcing

Vail et al., 1977; Miall, 2000). These hierarchies are NOT proposed

sin-scale tectonism is superimposed and independent of these global

e of time scales.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 83

first-order cycles is calculated based on the assump-

tion that nine equal-period global tectonic (Wilson)

cycles of supercontinent assembly and breakup took

place during the 3500–224 Ma interval (Krapez, 1993,

1996). The need for a hierarchy system based on

sequence duration is based on the argument that

bThere are no physical criteria with which to judge the

rank of a sequence boundary. Therefore, sequence

rank is assessed from interpretations of the origin of

the strata contained between the key surfaces, and of

the period of the processes that formed these strataQ(Krapez, 1997, p. 2).

More important than the current practical limita-

tions related to the availability of time control, or the

lack thereof, which may be resolved in the future as

the resolution of dating techniques improves, is the

fundamental question of whether or not the nature and

periodicity of tectonic mechanisms controlling strati-

graphic cyclicity were indeed constant throughout the

Earth’s history, as assumed by the proponents of time-

based hierarchy systems. The Phanerozoic time

window into the geological past is simply too small

to provide an unequivocal answer to this question, and

therefore the study of the Precambrian most likely

holds the key to this debate. The hierarchy systems

based on sequence duration are fundamentally pre-

dicated on the assumption that the controls on

cyclicity at specific hierarchical orders are predictable,

repetitive, and unchanged during the evolution of

Earth. This implies that the controls on stratigraphic

cyclicity are governed by the law of uniformitarianism

throughout the Earth’s history, allowing equal perio-

dicity for stratigraphic cycles of the same hierarchical

order, irrespective of age. However, recent work on

Precambrian geology (Catuneanu and Eriksson, 1999;

Eriksson et al., 2004, this volume, a,b) points to very

different conclusions, emphasizing that the mecha-

nisms controlling the formation and evolution of

sedimentary basins, for the greater part of geological

time, were far more diverse and erratic in terms of

activity rates than originally inferred from the study of

the Phanerozoic record (Fig. 4). This means that time

is the last, or at least not the primary, variable that one

should employ in designing a universally applicable

hierarchy system. Instead, alternative criteria need to

be identified for a more flexible conceptual frame-

work that can be used irrespective of basin type and

stratigraphic age.

3.3. Hierarchy system based on the magnitude of

base-level changes

A hierarchy system based on the magnitude of

base-level changes that resulted in boundary forma-

tion provides a classification in which the order of a

sequence depends on the physical attributes of its

bounding surfaces, and is independent of sequence

duration (Embry, 1995; Fig. 20). Six attributes have

been chosen to establish the boundary classification:

the areal extent over which the sequence boundary

can be recognized; the areal extent of the uncon-

formable portion of the boundary; the degree of

deformation that strata underlying the unconformable

portion of the boundary underwent during the

boundary generation; the magnitude of the deepening

of the sea and the flooding of the basin margin as

represented by the nature and extent of the trans-

gressive strata overlying the boundary; the degree of

change of the sedimentary regime across the boun-

dary; and the degree of change of the tectonic setting

of the basin and surrounding areas across the

boundary. Five different orders of sequence bounda-

ries have been defined on the basis of these character-

istics (Embry, 1995; Fig. 20).

Two potential pitfalls with this classification

scheme have been discussed by Miall (1997, pp.

330–331). One is that it implies tectonic control in

sequence generation. Sequences generated by glacio-

eustasy, such as the Upper Paleozoic cyclothems of

North America and those of Late Cenozoic age on

modern continental margins, would be first-order

sequences in this classification on the basis of their

areal distribution, but lower-order on the basis of the

nature of their bounding surfaces. The second prob-

lem is that this classification requires good preserva-

tion of the basin margin in order to properly assess the

areal extent of the unconformable portion of the

boundary or the degree of deformation across the

boundary. Beyond its practical limitations, the hier-

archy system based on the magnitude of base-level

shifts has the advantage of employing physical criteria

for boundary delineation, irrespective of the time span

between sequence boundaries that show similar

attributes. This represents a major advantage in the

case of Precambrian case studies, where the lack of

time control is generally the norm. This approach also

bypasses the problem of the erratic nature and

1 orderst

2nd order

3rd order

4th order

5th order Subaerialunconformity

Maximum regressivesurface

2

2

2

2nd order

2nd order

3

3

3

3

4

4

4th order

4th order

4th order

3rd order

3rd order

3rd order

3rd order

3rd order

3rd order

1. 2.BASINMARGIN

BASINCENTRE

Fig. 20. Hierarchy system based on the magnitude of base level changes that resulted in the formation of bounding surfaces (modified from

Embry, 1993, 1995). (1) Schematic depiction of five orders of sequence boundaries determined from boundary characteristics that reflect base

level changes. (2) Principles of determining the order of a sequence: a sequence cannot contain within it a sequence boundary of equal or greater

magnitude than its lowest magnitude boundary; the order of a sequence is equal to the order of its lowest magnitude boundary.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9584

periodicity of the controls on stratigraphic cyclicity

manifest throughout Earth’s history, as discussed

above.

3.4. Discussion

Because the sequence hierarchy systems that are

currently in use present conceptual and/or practical

limitations, the practitioner of sequence stratigraphy

still faces the dilemma of how to deal with the variety

of sequences that are more or less important relative to

each other. As argued by Catuneanu (2003), the

easiest solution to this problem is to deal with the

issue of hierarchy on a case-by-case basis, assigning

hierarchical orders to sequences and bounding surfa-

ces based on their relative importance within each

individual basin. This approach is an adaptation of

Embry’s (1995) method of sequence delineation, and

requires the partitioning of the stratigraphic record

into successions that are the product of sedimentation

in discrete sedimentary basins. In this context, the

most important sequence boundaries in the strati-

graphic record are genetically related to shifts in the

tectonic setting that led to changes in the type of

sedimentary basins.

This working methodology places the emphasis on

the nature of the tectonic setting and changes thereof.

As a result, the most fundamental events in the rock

record that led to changes in tectonic setting and basin

type are marked as first-order sequence boundaries,

irrespective of the time span between two such

consecutive events. In this context, first-order sequen-

ces correspond to entire sedimentary basin-fills,

regardless of the origin and life span of each particular

basin. Within this framework, second-order cycles

provide the basic subdivision of a first-order sequence

(basin-fill) into packages with unique character that

reflect overall shifts in the balance between accom-

modation and sedimentation, and so on as we decrease

the scale of observation. These sequences are not

expected to correlate to other first- and lower-order

sequences of other, separate basins, which most likely

have different timing and duration. This method may

prove to be more flexible and realistic given the fact

that each basin is unique in terms of formation,

evolution and history of base-level changes.

Our conclusions are supported by statistical sur-

veys of the duration and thickness of stratigraphic

sequences, which demonstrated that there is no

evidence for a hierarchy in the rock record that can

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 85

be linked to the periodicity of recurrence of the same-

order bounding surfaces (Algeo and Wilkinson, 1988;

Carter et al., 1991; Drummond and Wilkinson, 1996).

As pointed out by Drummond and Wilkinson (1996),

bdiscrimination of stratigraphic hierarchies and their

designation as nth-order cycles [based on cycle

duration] may constitute little more than the arbitrary

subdivision of an uninterrupted stratigraphic continu-

umQ. The link between hierarchical orders and

temporal durations is artificial and meaningless to a

large extent, as multiple sequence-generating mecha-

nisms that do not readily fall into simple temporal

classifications may interact and contribute to the

architecture of sequences in the rock record (Miall,

1997). The combination of such independent controls

often results in sequences whose durations and

thicknesses have log-normal distributions that lack

significant modes (Drummond and Wilkinson, 1996).

Similar conclusions are reflected by the work of

Algeo and Wilkinson (1988), as well as that of Peper

and Cloetingh (1995), who demonstrated that calcu-

lated periodicities of stratigraphic cycles may have

random distributions relative to any given sequence-

forming mechanism.

An added bonus of this case-by-case basin

approach is the simplification of terminology because

modifiers such as first-order, second-order, etc., have

straightforward meanings, reflecting relative impor-

tance independent of time connotations. In contrast,

the time-based hierarchy systems are permeated by

unnecessary and sometimes conflicting jargon. For

example, the bsupersequenceQ of Krapez (1996) is

referred to as a bsequenceQ by Vail et al. (1977); the

bsequenceQ of Krapez (1996) corresponds to the

bmesothemQ of Ramsbottom (1979), or to the

bmegacyclothemQ of Heckel (1986); the bparacycleQof Krapez (1996) is equivalent to the bmajor cycleQ ofHeckel (1986), etc. Further, the term dparacycleT (andits corresponding dparasequenceT) is particularly con-

fusing, because parasequences (as bounded by

dflooding surfacesT) may not even technically be a

type of sequence, depending on what the flooding

surface actually is (see discussion in Catuneanu,

2003). Beyond the terminology issue, which may be

trivial to some extent, the real danger consists of the

fact that each of these terms (e.g., megasequence,

supersequence, parasequence, etc.) is associated with

a specific time connotation (sequence duration),

which requires a time control that is unavailable in

many Precambrian (and even Phanerozoic) case

studies.

4. Case studies

An increasing number of case studies of Precam-

brian sequence stratigraphy have become available in

recent years, allowing us to see the complexity of the

controlling factors on sedimentation and stratigraphic

cyclicity at a scale larger than originally made

possible by the study of the Phanerozoic record.

More meaningful generalizations can now be formu-

lated as a result of this research. This section

synthesizes the results of some of these case studies,

from the ca. 3.0–2.0 Ga (Late Archean–Early Proter-

ozoic) interval of the Kaapvaal craton of South Africa

to the ca. 1.75–0.65 Ga (late Paleoproterozoic–late

Neoproterozoic) interval of the Sao Francisco craton

and Aracuaı fold belt of eastern Brazil. These case

studies cover more than 2 Gy of Precambrian Earth’s

evolution.

4.1. Kaapvaal craton of South Africa

The stratigraphy and tectonic evolution of the

Kaapvaal craton of South Africa during the ca. 3.0–

2.0 Ga (Late Archean–Early Proterozoic) interval are

presented in detail by Eriksson et al. (this volume, b).

Relevant to this paper is the fact that the ca. 1 Gy

record of Kaapvaal evolution was marked by a

combination of plate tectonic and plume tectonic

regimes, whose relative importance determined the

type of tectonic setting and sedimentary basin

established at any given time. The shifting balance

between these two allogenic controls on accommo-

dation resulted in a succession of discrete basins,

starting with the Witwatersrand (accommodation

provided by subduction-related tectonic loading),

followed by the Ventersdorp (accommodation gener-

ated by thermal uplift-induced extensional subsi-

dence), and lastly by the Transvaal (accommodation

created by extensional and subsequent thermal sub-

sidence). The end of the Transvaal cycle was marked

by a relatively short-lived plume tectonics event,

which led to the emplacement of the Bushveld

igneous complex. The sedimentary fill of these three

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9586

basins, each of which is genetically related to different

tectonic settings, represents an unconformity-bounded

first-order depositional sequence.

The temporal duration of the Kaapvaal first-order

cycles varied greatly with the type of tectonic setting,

from ca. 5 My in the case of the plume-related

Ventersdorp thermal cycle, to N600 My in the case of

the extensional Transvaal Basin. This first-order

cyclicity was independent of the Wilson-type cycles

of supercontinent assembly and breakup, being rather

a reflection of the interplay between plate tectonics

(e.g., extension or subduction-related tectonic loading)

and plume tectonics. It is noteworthy that the first-

order cycles controlled by plate tectonics lasted about

two orders of magnitude longer (ca. 102 My) relative to

the plume tectonics cycles (ca. 100 My). Each of the

Kaapvaal first-order cycles is subdivided into second-

order cycles, whose temporal duration also varies

greatly, from ca. 1 My in the case of the Ventersdorp

plume tectonics-controlled basin to ca. 100 My in the

case of the plate tectonics-controlled basins.

The case study of the Kaapvaal craton suggests that

time, and implicitly the frequency of occurrence of

same-order sequence boundaries in the rock record, are

irrelevant to the hierarchy of stratigraphic cycles. This

is a consequence of the fact that processes controlling

the formation and evolution of sedimentary basins in

the geological past were far more erratic than

originally inferred from the study of the Phanerozoic

record. The extrapolation of principles developed from

Phanerozoic case studies (e.g., Vail et al., 1977; Fig.

19) to the entire geological record based on the law of

uniformitarianism is therefore inadequate for provid-

ing a unified approach to the concept of sequence

hierarchy. This conclusion reinforces the idea that the

classification of sequences and bounding surfaces

should be approached on a case-by-case basis, starting

from the premise that each sedimentary basin-fill

corresponds to a first-order sequence.

4.2. Sao Francisco craton and Aracuaı fold belt of

eastern Brazil

A record of the late Paleoproterozoic to late

Neoproterozoic history of the Sao Francisco craton

and Aracuaı fold belt of eastern Brazil (Fig. 21) is

preserved by sedimentary successions in the Espin-

haco, Macaubas, and Bambuı basins (Martins-Neto et

al., 2001). Each of these major sedimentary succes-

sions represents a first-order depositional sequence,

which is the record of an unconformity-bounded,

single basin-fill cycle (Martins-Neto et al., 2001).

Collectively, these basins track major plate reorgan-

izations that affected the Sao Francisco craton through

a time interval greater than 1 Gy, which marks one

episode of aborted lithospheric stretching, and a

complete cycle of supercontinent breakup and assem-

bly. The Espinhaco Basin records a stage (ca. 1.73–

1.50 Ga) of aborted lithospheric stretching of the Sao

Francisco–Congo continental mass that had amalga-

mated during the Transamazonian–Eburnian orogeny

(ca. 2.2–2.0 Ga; Trompette, 1994; Alkmim and

Marshak, 1998). The Macaubas Basin (ca. 950–700

Ma) comprises rift-to-drift successions that were

deposited during the breakup of the supercontinent

Rodinia and the opening of the Brazilide–Adamastor

ocean (Dalziel, 1997). The Bambuı Basin (ca. 800–

650 Ma) formed as a consequence of thrust loading

related to shortening in the Brasılia fold belt on the

western flank of the Sao Francisco craton (Fig. 21)

during the closing of the Brazilide ocean and the

amalgamation of the Gondwana supercontinent.

Because most deposits of the Espinhaco and Bambuı

basins are well exposed in cratonic areas or in the

weakly deformed external domains of the Aracuaı

orogenic belt, sequence stratigraphy can be applied to

their successions.

4.2.1. Espinhaco Basin

Sedimentologic, paleogeographic, stratigraphic,

structural and tectonic studies in the Paleo/Mesopro-

terozoic metasedimentary Espinhaco first-order

sequence in southeastern Brazil indicate deposition

in a rift-sag basin (Martins-Neto, 2000). The basin

displays a dsteer’s-headT geometry where four basin

evolution stages are recognized (pre-rift, rift, transi-

tional and flexural). These four stages form the basic

subdivision of the first-order basin-fill sequence and

therefore can be equated with unconformity-bounded

second-order sequences. The unconformities are

recognized in the field and are mapped on a regional

scale. The pre-rift and rift second-order sequences of

the Espinhaco Basin consist of nonmarine depositio-

nal systems that were deposited during continental

lithosphere stretching. The recognition of 3rd order

unconformities allowed the recognition and mapping

Fig. 21. Location of the Sao Francisco Basin in the context of the Sao Francisco Craton and its surrounding orogenic belts (modified after

Alkmim and Marshak, 1998).

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 87

of three 3rd order synrift sequences within the rift 2nd

order sequence. The first marine incursion within the

Espinhaco Basin marks the change in the subsidence

regime of the basin from extensional to thermally

driven, and is due to thermal contraction of the

lithosphere during cooling when the transitional and

flexural stages evolved. The transitional stage was

characterized by relatively low subsidence rates.

Higher subsidence rates and a consequent base-level

rise characterize the flexural stage of the Espinhaco

Basin.

At increased detail, the ca. 900-m-thick second-

order flexural (dConselheiro MataT) succession of the

Espinhaco Basin is subdivided into three third-order

transgressive–regressive sequences (Fig. 22). These

third-order sequences were first recognized by

Dupont (1995), each with a transgressive base and

a progradational top. The first sequence (250–400 m

thick) contains transgressive barred nearshore depos-

its and progradational beach to shallow marine

deposits. Its maximum flooding surface marks the

greatest expansion of the Espinhaco sea (Martins-

Transgression

Transgression

Transgression

Progradation

Progradation

Progradation

Max. flooding surface

Max. flooding surface

e

Sequ

ence

3Se

quen

ce 2

Sequ

ence

1Galho do Miguel2nd-order sequence(transitional stage)

Conselheiro Mata2nd-order sequence(flexural stage)

E

Post-Espinhaço

glaciogenic erosion

W

Fig. 22. Schematic stratigraphic cross-section showing the three third-order transgressive–regressive sequences of the Conselheiro Mata

(second-order) succession of the Espinhaco Basin (modified after Dupont, 1995). The eastern section is about 900 m thick.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9588

Neto, 2000). The second sequence (250–350 m

thick) comprises transgressive shelf deposits overlain

by progradational alluvial plain to coastal succes-

sions. The third sequence (200–300 m thick) is

C

SD

Prograding2nd-order sequences

W E

Fig. 23. Stratigraphic chart of the Bambuı first-order sequence (modified af

Note that the three, inverted thin black triangles show the three second-o

defined by transgressive mixed siliciclastic-carbonate

shelf deposits overlain by coastal to fluvial sedi-

ments. The top of the third sequence marks the final

filling of the Espinhaco Basin and therefore corre-

SERRA DA SAUDADEFORMATIONshale, siltstone

TRÊS MARIAS FORMATIONsiltstone, arkose,sandstone, conglomerate

STRATIGRAPHY

SAM

BU

RA

FO

RM

ATI

ON

cong

lom

erat

e, s

ands

tone

, mud

ston

e

CARRANCAS F ORMATION (C)diamictite, conglomerate

SETE LAGOAS FORMATIONdolostone (D), shale,calcarenite, calcilutite(locally with stromatolite -S)

LAGOA DO JACARÉ FM.limestone, calcarenite,

oolitic limestone,siltstone

SERRA DESANTA HELENA FM.shale, mudstone, siltstone

ter Martins-Neto et al., 2001). The succession is about 3000 m thick.

rder sequences within the Bambuı first-order sequence.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 89

sponds to a first-order sequence boundary. Each of

these third-order sequences has an estimated duration

in the range of tens of million years and is

considered to be the product of in-plane stress

variations (Martins-Neto, 2000).

4.2.2. Bambuı basin

The carbonate to siliciclastic deposits of the

Bambuı first-order sequence, which are up to 3000

secon

Uninterpreted seismic line

Paranoa/CanastraParanoa/Canastra first-order sequencefirst-orderse

Fig. 24. Reflection seismic profile in the cratonic area of the Sao Francisco

sequence boundaries. The Bambuı first-order sequence is composed of

second-order sequences of the Bambuı succession show siliciclastic depos

Canastra first-order sequence represents passive-margin deposits of the we

Brasılia fold belt.

m thick, overlie much of the Sao Francisco Craton.

They are also exposed in the Brasiliano/Pan

African fold belts surrounding the craton, mainly

in the Brasılia fold belt on its western flank (Fig.

21). Recent studies (e.g., Castro and Dardenne,

2000; Martins-Neto et al., 2001) indicate deposition

in a foreland basin that was generated during

thrusting and crustal loading in the Brasılia fold

belt along the western margin of the Sao Francisco

First-ordersequenceboundaries

Progradingd-order sequences

quence

Bambuífirst-ordersequence}

Basin, showing the seismic expression of first-order sequences and

three prograding second-order sequences. Note that the older two

its at their bases and carbonate deposits at their tops. The Paranoa/

stern flank of the Sao Francisco craton, whose closure generated the

Fig. 25. High-frequency prograding sequence of the Lagoa do Jacare

Formation showing storm-influenced rhythmites at the base and

coastal oolitic calcarenites at the top. The section is approximately

6 m thick.

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9590

Craton, related to the ca. 800 to 650 Ma arc–

continent to continent–continent collision (Pimentel

et al., 2000). Three second-order transgressive–

regressive sequences characterize the fill of the

Bambuı Basin (Dardenne, 1981; Figs. 23 and 24).

Each of these sequences represents the record of

initial flooding of the basin (higher accommodation

relative to sediment supply as a result of flexural

loading and rapid subsidence) and the subsequent

filling of accommodation by a prevailing sediment

supply.

The organic-rich marine shales of the Sete Lagoas

Formation (Fig. 23) were deposited in the central and

western parts of the basin. Distal deposits near an

inferred forebulge consist of a carbonate ramp

succession of limestone (locally with stromatolites),

dolostone and argillaceous limestone. The carbonate

ramp prograded westward over the deeper-water

pelites, and produced the first transgressive–regres-

sive second-order sequence. Dolomitized supratidal

deposits with microbial mats, dissolution structures,

tepees and birds-eye structures as well as mud cracks,

characterize the top of the unit, indicating subaerial

exposure and marking the second-order sequence

boundary.

The second transgressive–regressive second-order

sequence begins with shale and argillaceous limestone

of the Serra de Santa Helena Formation (Fig. 23),

which shows an upward increase in the abundance of

siltstone beds and storm-wave reworking. Limestone,

calcarenite, oolitic limestone and siltstone, which

were deposited in a storm-influenced ramp of the

Lagoa do Jacare Formation, prograded over the Serra

de Santa Helena Formation. Higher frequency pro-

grading deposits occupy the transitional interval

between the deeper-water facies of the Serra de Santa

Helena Formation and the shallower-water facies of

the Lagoa do Jacare Formation. Each sequence

comprises storm-influenced shale-calcilutite rhythmite

at the base, and coastal oolitic calcarenite at the top

(Fig. 25).

The uppermost transgressive–regressive second-

order sequence consists at its base of the marine

shale and siltstone of the Serra da Saudade

Formation, which are overlain by siltstone, sand-

stone, arkose and conglomerate of the Tres Marias

Formation that were deposited in a storm-dominated

shallow marine system, and finally passing upward

to sediments deposited in alluvial environments

(Fig. 23).

5. Discussion and conclusions

The principles of sequence stratigraphy may be

applied at different spatial scales, from individual

depositional systems to entire sedimentary basin-fills.

The common theme, irrespective of scale, is the study

of the sedimentary response to changes in accom-

modation. Within the boundaries of individual depo-

sitional systems, changes in accommodation result in

predictable shifts with time in the types of deposi-

tional elements and lithofacies that accumulate in each

particular environment. As changes in accommoda-

tion are in turn controlled by allogenic mechanisms

that operate at basin scales, such shifts in depositional

trends are synchronized across the basin, allowing the

grouping of depositional systems into systems tracts

characterized by specific stacking patterns and facies

relationships.

Sequence-stratigraphic surfaces and systems tracts

may be identified at particular locations within the

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–95 91

basin, such as boreholes (using core and/or well log

data) or outcrops, or at broader scales involving

mapping and correlations of outcrop and/or surface

(well log, core, seismic) data. The criteria identified

in Fig. 17 for the recognition of sequence strati-

graphic surfaces (and especially the nature of

contacts and juxtaposed facies associated with each

contact) may be applied in any given location,

without requiring time control. The identification of

stratal terminations usually requires a broader scale

of observation, and is best performed on seismic

lines and in large outcrops. Time control is

generally desired for correlation, but the lack

thereof, which is a common theme in Precambrian

case studies, may be compensated for by a good

knowledge of facies architecture and relationships

within the study area.

In tectonically active basins, the most important

breaks in the rock record (e.g., second-order

sequence boundaries that provide the basic subdivi-

sion of the first-order basin-fill) are commonly

associated with stages of tectonic reorganization

within the basin, which usually lead to changes in

tilt directions across the major unconformities. In

such cases, paleocurrent data provide the key to infer

tectonic events during the basin’s evolution and to

map event-significant sequence boundaries across the

basin. This is the case with the Early Proterozoic

Athabasca Basin in Canada, where each second-

order sequence is characterized by unique fluvial

drainage systems, with abrupt shifts in paleocurrent

patterns across the second-order sequence boundaries

(Ramaekers and Catuneanu, 2004). In this basin,

paleocurrent data provide the best evidence to

constrain regional correlations and to compensate

for the general lack of time control in a succession

that is relatively homogeneous from a lithofacies

point of view.

Sequence stratigraphy uses the same set of core

principles irrespective of the age of strata under

analysis. In that respect its application to Precambrian

deposits is no different from the methods applied to

Phanerozoic successions. Where sedimentary basins

are transgressed by interior seaways, the shifts in

shoreline position, which are in turn controlled by the

interplay of accommodation and sediment supply,

represent the fundamental element that constrains the

timing of all systems tracts and sequence stratigraphic

surfaces. All classic sequence-stratigraphic models

(Fig. 15) account for the presence of a shoreline

within the basin under analysis, thus justifying a

systems-tract nomenclature that makes specific refer-

ence to transgressions and regressions. In overfilled

basins, however, the depositional environment may be

entirely nonmarine, and so the application of sequence

stratigraphy must be adapted accordingly. In such

cases, the systems-tract nomenclature makes direct

reference to the amount of available accommodation

(i.e., low vs. high accommodation systems tracts) as

inferred from the ratio between fluvial architectural

elements (e.g., see Eriksson and Catuneanu, 2004a;

Ramaekers and Catuneanu, 2004, for Precambrian

case studies).

Basins related to plume-controlled first-order

cycles (i.e., plume tectonics) are prone to a domi-

nantly nonmarine sedimentation regime because the

net amount of thermal uplift generally exceeds the

amount of subsidence created via extension above the

ascending plume. As plume tectonics was much more

prevalent in the Precambrian relative to the Phaner-

ozoic, the low- and high-accommodation systems

tracts seem to be more commonly applicable with

increasing stratigraphic age. In contrast, basins related

to plate tectonic activity are dominated by subsidence,

and so they are prone to be transgressed by interior

seaways. Even such subsidence-dominated basins,

however, may reach an overfilled state under high

sediment-supply conditions, in which case the recog-

nition of fully fluvial systems tracts (low vs. high

accommodation) becomes the only option for the

sequence-stratigraphic approach. Case studies of such

overfilled plate-tectonic-related basins have been

documented for both Precambrian and Phanerozoic

successions (e.g., Boyd et al., 1999; Zaitlin et al.,

2000, 2002; Wadsworth et al., 2002, 2003; Leckie and

Boyd, 2003; Eriksson and Catuneanu, 2004a; Ram-

aekers and Catuneanu, 2004).

The application of sequence stratigraphy to Pre-

cambrian basins has considerably enlarged the per-

spective of fundamental principles governing the

processes of sedimentary basin formation and the

mechanisms controlling stratigraphic cyclicity in the

rock record. The latter principles are perhaps the most

important contribution of Precambrian research to

sequence stratigraphy because the large time span of

the Precambrian affords a better understanding of the

O. Catuneanu et al. / Sedimentary Geology 176 (2005) 67–9592

allogenic controls on sedimentation and hence of the

criteria that should be used in a system of sequence

stratigraphic hierarchy. At the broader scale of Earth’s

geological history, the tectonic regimes governing the

formation and evolution of sedimentary basins are

shown to have been much more erratic in terms of

nature and rates than originally inferred solely from

the study of the Phanerozoic record. This indicates

that time is largely irrelevant as a parameter in the

classification of stratigraphic sequences; instead, it is

rather the change in the tectonic setting that affects the

key criteria for subdividing the rock record into

genetically related basin-fill successions separated

by first-order sequence boundaries. These first-order

basin-fill successions are in turn subdivided into

second- and lower-order sequences as a function of

the shifts in the balance between accommodation and

sedimentation at various scales of observation. Such

sequences, which may at least in part reflect the

influence of local controls, are not expected to

correlate to other first- and lower-order sequences of

other basins, which most likely have different timings

and durations.

Acknowledgments

Octavian Catuneanu acknowledges support from

the University of Alberta and NSERC Canada. The

research of Marcelo Martins-Neto was supported by

the FAPEMIG—Research Support Foundation of

Minas Gerais State, Brazil, and by the CNPq—

Brazilian National Research Council. Pat Eriksson

acknowledges generous research funding from the

University of Pretoria. We thank the ANP-Brazilian

National Petroleum Agency for permission to use

seismic data in this paper. We are grateful to Charlie

Jefferson and Reg Olson for providing thoughtful and

constructive reviews of earlier drafts of this paper.

Responsibility for the views presented herein, how-

ever, rests with the authors.

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