Principles of Sequence Stratigraphy

By Octavian Catuneanu

Principles of Sequence Stratigraphy, Second Edition presents principles to practical workflow that guide applications in a consistent manner that is independent of model, geological setting and the types and resolution of the data available. The book explains the points of agreement and difference between the various approaches to sequence stratigraphy, while also defining the common ground that affords the standard application of the method. This enables the practitioner to avoid nomenclatural and methodological confusions and apply sequence stratigraphy. The text is richly illustrated with hundreds of full-color diagrams and examples of outcrop, borehole and seismic data.

The book's balanced approach helps students and professionals acquire a sound understanding of the concepts and methodology. It will appeal to geologists, geophysicists and engineers with interest in basin analysis, stratigraphy and sedimentology, as well as in all economic applications that concern the exploration and production of natural resources, including water, hydrocarbons, coal and sediment-hosted mineral deposits.

• Updates the award-winning first edition in all aspects of sequence stratigraphy, from the underlying theory to the practical applications
• Presents the standard approach to sequence stratigraphic methodology, nomenclature, and classification; the role of modeling in sequence stratigraphy, and the difference between modeling and methodology
• Discusses the roles of scale and stratigraphic resolution in sequence stratigraphy, and the workflow that affords a consistent application of the method irrespective of the types of data available
• Describes the three-dimensional nature of the stratigraphic architecture, and the variability of stratigraphic sequences with the tectonic setting, depositional setting, and the climatic regime
• Illustrates all concepts with high-quality, full-color diagrams, outcrop photographs, and subsurface well data and seismic images

• Language: English
• Publisher: Elsevier Science
• Release date: Jul 22, 2022
• ISBN: 9780080885131

Octavian Catuneanu

Octavian Catuneanu is a Professor in the Department of Earth and Atmospheric Sciences at the University of Alberta, with PhD degrees from the University of Toronto and the University of Bucharest. He is the recipient of several distinctions in the field of Geology, including the W.W. Hutchison Medal of the Geological Association of Canada for exceptional advances in earth science research, and best paper awards from the European Association of Geoscientists and Engineers, the Geological Society of America, and the Romanian Academy of Sciences. Octavian Catuneanu served as the Editor-in-Chief of the journal of Marine and Petroleum Geology, Chair of the Task Group on Sequence Stratigraphy of the International Subcommission on Stratigraphic Classification, Chair of the North American Commission on Stratigraphic Nomenclature, and member of the editorial board of several journals in North America, Europe, and Africa. He is the editor of several books and special issues, author of numerous publications in the fields of sedimentology, stratigraphy, and basin analysis, and instructor of sequence stratigraphy and related disciplines for universities, conferences, and companies worldwide. The first edition of his “Principles of Sequence Stratigraphy” textbook (Elsevier, 2006) received the 2007 “Outstanding Academic Title” Choice Award from the American Library Association and remains a best-selling title.

Book preview

Principles of Sequence Stratigraphy

Second Edition

Octavian Catuneanu

Professor, University of Alberta, Edmonton, Alberta, Canada

Table of Contents

Cover image

Title page

Copyright

Preface to second edition

Chapter 1. Introduction

1.1. Overview of sequence stratigraphy

1.2. Development of sequence stratigraphy

Chapter 2. Data in sequence stratigraphy

2.1. Geological data

2.2. Well-log data

2.3. Seismic data

Chapter 3. Controls on sequence development

3.1. Allogenic processes

3.2. Autogenic processes

3.3. Accommodation vs. sedimentation

3.4. Concept of base level

3.5. Allogenic vs. autogenic controls

Chapter 4. Stratal stacking patterns

4.1. Stratal terminations

4.2. Stacking patterns in downstream-controlled settings

4.3. Stacking patterns in upstream-controlled settings

Chapter 5. Stratal units

5.1. Depositional systems

5.2. Systems tracts

5.3. Stratigraphic sequences

5.4. Parasequences

Chapter 6. Stratigraphic surfaces

6.1. Surfaces of sequence stratigraphy

6.2. Within-trend facies contacts

Chapter 7. Sequence stratigraphic framework

7.1. Scale in sequence stratigraphy

7.2. Hierarchy in sequence stratigraphy

7.3. Time in sequence stratigraphy

Chapter 8. Variability of stratigraphic sequences

8.1. Variability with the tectonic setting

8.2. Variability with the depositional setting

8.3. Variability with the climatic regime

Chapter 9. Discussion

9.1. Architecture of the stratigraphic record

9.2. Sequence stratigraphy and geological time

9.3. Methodology and nomenclature

9.4. Workflow of sequence stratigraphy

Chapter 10. Conclusions

10.1. Stratigraphic framework

10.2. Standard approach to sequence stratigraphy

10.3. Summary of key points

References

Glossary of terms

Author index

Subject index

Copyright

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Preface to second edition

Sequence stratigraphy provides a process-based approach to stratigraphic analysis that enables insights into the patterns of sediment distribution during the evolution of sedimentary basins, as well as facies predictions in areas away from data control points. These applications appeal to a wide segment of the stratigraphic community, from academia to the industry. The methodology improved significantly since the 1970s, from a model-driven approach underlain by assumptions regarding the dominant role of eustasy on sequence development, with consequent assertions of global correlations, to a data-driven approach that promotes the use of local data and unbiased geological reasoning. The latter approach affords realistic constructions of local stratigraphic frameworks, which prove to be highly variable, not only from one sedimentary basin to another, but also between subbasins of the same sedimentary basin. The construction of basin-specific stratigraphic frameworks is a major breakthrough and departure from the early models.

The evolution of sequence stratigraphy involved advances in the understanding of the array of possible controls on sequence development, improvements in stratigraphic resolution, revisions to the definition and classification of sequences, and ultimately the emergence of a standard approach to methodology and nomenclature. Most significant to the conceptual developments and practical applications, the increase in stratigraphic resolution prompted a complete overhaul of the early principles of low-resolution seismic stratigraphy, and presented the opportunity to improve our insights into key areas such as the definition, the scales, and the classification of sequences. Old myths of seismic stratigraphy have been debunked in light of high-resolution data, making way for realistic principles that honor the stratigraphic variability generated by the interplay of local and global controls on accommodation and sedimentation. All in all, a new look at the principles of sequence stratigraphy, from the basic concepts to the field criteria that enable the application of the method, is timely.

A number of developments arose since the publication of the first edition of this book in 2006. Undoubtedly the most significant development was the endorsement of sequence stratigraphy by the International Commission on Stratigraphy in 2011, along with the publication of guidelines on methodology and nomenclature (Catuneanu et al., 2011). This concluded decades of work on the definition of a standard approach to sequence stratigraphy, following the failed attempts of two previous working groups led by A. Salvador (1995–2003) and A.F. Embry (2004–2007). The standard methodology relies on the observation of stratal stacking patterns in a manner that is independent of scale and the interpretation of the underlying controls. This ensures maximum flexibility and objectivity, and a consistent application of the method irrespective of geological setting and the types of data available. Once a sequence stratigraphic framework is constructed, the interpretation and testing of the underlying controls on sequence development may continue indefinitely.

A standard methodology does not imply a freeze on developments. While a standard approach to sequence stratigraphy is now in place, future developments are still needed to refine and diversify the criteria that afford the identification of systems tracts and bounding surfaces in the sedimentary record (e.g., the emerging trends of using geochemical and paleontological proxies in sequence stratigraphy, in conjunction with information derived from other independent datasets). Parallel progress in stratigraphic modeling will also continue in order to improve the accuracy of testing of sedimentary responses to the variety of possible controls on sequence development. However, methodology and modeling remain two distinct lines of stratigraphic research, with different goals and underlying data-driven vs. model-driven principles. Therefore, it is important to separate methodology from modeling in sequence stratigraphy. A standard methodology does not prevent future developments in the field of stratigraphic modeling.

Advances in computing power enhanced the ability to test the results of various combinations of controls on the stratigraphic architecture. While this can provide useful insights under realistic boundary conditions, uncalibrated simulations and overreaching conclusions can be misleading and even counterproductive. A dangerous extreme is to think that virtual reality (the outcome of numerical modeling) is more meaningful than the reality described by actual data. Software enthusiasts seem to assume so when ‘demonstrating’ stratigraphic scenarios that have little in common with the real world, due to the unrealistic selection of input parameters. Proposals that numerical simulations should become part of the sequence stratigraphic workflow are not only impractical, but a setback as they bring confusion between modeling and methodology. This undermines the progress made in the development of sequence stratigraphy as a data-driven method with an objective workflow that relies on observations rather than model-driven assumptions. While useful to test the possible controls on the stratigraphic architecture, modeling requires validation with real data and plays no role in the sequence stratigraphic methodology.

The separation of modeling and methodology is an important ‘first amendment’ in sequence stratigraphy. Mixing the methodology with the interpretation of controls on sequence development was a pitfall since the inception of sequence stratigraphy, which took decades of work to correct. The early models favored eustasy as the dominant control, which led to the assumption of global correlations in the 1970s and the 1980s, while the role of sediment supply on par with accommodation was only fully recognized since the 1990s (i.e., the ‘dual control’ of Schlager, 1993). Between these end members, the relative contributions of processes that control accommodation and sedimentation vary with the tectonic and depositional settings and are often difficult to quantify. Linking the methodology to any specific control on sequence development is ultimately misleading, as it is always an interplay of multiple controls that defines the stratigraphic architecture. For this reason, the methodology must remain neutral with respect to the interpretation of underlying controls, and any reference to a specific control (e.g., ‘tectono-sequence stratigraphy’) should be avoided.

The latest trend in numerical modeling is the shift from an overemphasis on accommodation to an overemphasis on sediment supply, which is equally deceptive. Beyond interpretations, the methodology remains grounded on field data and the model-independent observation of stratal stacking patterns and stratigraphic relationships. The stratigraphic record is highly variable in terms of the architecture and composition of sequences, and it includes a mix of diagnostic and nondiagnostic elements with respect to the definition and identification of systems tracts and bounding surfaces. Variability rather than orderly patterns is the stratigraphic norm. This means that the methodology needs to follow an objective data-driven workflow that is independent of model assumptions, in which the construction of the sequence stratigraphic framework is guided by data rather than the model. An important part of this process is the distinction between the diagnostic stacking patterns that afford the identification of systems tracts and the nondiagnostic variability that can accompany the formation of any systems tract.

This second edition updates all key aspects of sequence stratigraphy, from the theoretical principles to the practical workflow. The book provides new insights and an in-depth analysis of all elements of the sequence stratigraphic framework, along with examples that illustrate the concepts and applications of sequence stratigraphy in all geological settings. Long-standing inconsistencies and ‘grey areas’ (e.g., the difference between depositional and geometrical trends in sequence stratigraphy; the scale of sequences and component systems tracts and depositional systems; the difference between high-frequency sequences and parasequences; the role of global vs. local, and allogenic vs. autogenic controls on sequence development; the role of various types of clinoform rollovers in the definition of the sequence stratigraphic framework) are addressed and clarified in a systematic manner. The result is a state-of-the-art presentation of the principles and guidelines that afford a consistent application of sequence stratigraphy across the entire range of geological settings, stratigraphic scales, and types of data available.

Acknowledgments

This work benefitted from the joint effort that led to the publication of formal guidelines on sequence stratigraphic methodology and nomenclature by the International Subcommission on Stratigraphic Classification (ISSC) of the International Commission on Stratigraphy (Catuneanu et al., 2011). I thank William E. Galloway, Christopher G.St.C. Kendall, Andrew D. Miall, Henry W. Posamentier, Andre Strasser, and Maurice E. Tucker for their contributions and support as members of the ISSC task group on sequence stratigraphy. Additional insights were provided by many experts over the years, including V. Abreu, J.P. Bhattacharya, M.D. Blum, I. Csato, R.W. Dalrymple, A.F. Embry, P.G. Eriksson, C.R. Fielding, W.L. Fisher, P. Gianolla, M.R. Gibling, K.A. Giles, W. Helland-Hansen, J.M. Holbrook, R. Jordan, D.A. Leckie, B. Macurda, O.J. Martinsen, J.E. Neal, D. Nummedal, L. Pomar, B.R. Pratt, J.F. Sarg, W. Schlager, B.C. Schreiber, K.W. Shanley, R.J. Steel, A.R. Sweet, C. Winker, and M. Zecchin. I am grateful to Steven Holland for contributing most of the section on Body Fossils in Chapter 2, and to James A. MacEachern, Luis A. Buatois, and Murray K. Gingras for their contributions to the section on Trace Fossils in Chapter 2.

These interactions helped clarify the confusions that plagued sequence stratigraphy for decades. Over the course of my career I worked with professionals embracing different models with respect to the selection of the sequence boundary and the delineation of systems tracts, and yet collaboration was never a problem. This is because all models have a common ground that transcends any arbitrary or nomenclatural differences. In practical terms, each sequence model originated from the observation of specific datasets; therefore, all schools have merits, and the choice between models is not a matter of right or wrong, but a function of the types of data available and the geological setting. This fact ultimately enabled the identification of the core principles that afford a unified approach to sequence stratigraphy. Perhaps the most pertinent advice I give people taking my courses is to forget about models, and let the data guide them to the actual architecture of the stratigraphic record, however imperfect that may be.

Octavian Catuneanu

University of Alberta

Edmonton, 2022

Chapter 1: Introduction

Abstract

Sequence stratigraphy developed informally for more than three decades after the emergence of seismic stratigraphy in the 1970s, leading to the proposal of several alternative approaches to sequence stratigraphic analysis. None of these approaches can be adopted as a standard practice, but common ground does exist in terms of the types of stacking patterns that can be observed in the sedimentary record. The solution to a standard approach rests with the definition of model-independent principles that emphasize the common ground, to provide a simple and robust platform for the consistent application of the method irrespective of geological setting, scale of observation, and the types and resolution of the data available. Formal guidelines for a standard methodology and nomenclature have been sanctioned by the International Commission on Stratigraphy in 2011. Despite this progress, confusion still persists with respect to a number of issues including the scale of sequences and component systems tracts and depositional systems; the role of global vs. local, and allogenic vs. autogenic controls on sequence development; and the classification of sequence stratigraphic units and bounding surfaces. Some of these issues are rooted in the historical development of the method and the resolution of the data used to define the concepts; e.g., in seismic stratigraphy, the scale of sequences, systems tracts, and depositional systems had to exceed the vertical seismic resolution, leading to bias in the perception of scales that typify these stratal units. Chapter 1 introduces the first principles of sequence stratigraphy, which lay the foundation for tackling all aspects of the method in the following chapters.

Keywords

Concept of sequence; Scope of sequence stratigraphy; Sequence models; Standardization of sequence stratigraphy; Types of stratigraphy; Types of unconformities; Unconformity-bounded units

1.1. Overview of sequence stratigraphy

1.1.1. Scope of sequence stratigraphy

Sequence stratigraphy is a type of stratigraphy that relies on stacking patterns for the definition, nomenclature, classification, and correlation of stratal units and bounding surfaces. The method examines the stratigraphic cyclicity and the related changes in sedimentation regimes that can be observed at the scales afforded by the resolution of the data available. Stratal stacking patterns are at the core of the sequence stratigraphic methodology, as they provide the criteria for the definition of all units and surfaces of sequence stratigraphy (Fig. 1.1); i.e., sequence stratigraphic units are bodies of sediment or sedimentary rocks defined by stratal stacking patterns and their bounding surfaces, and sequence stratigraphic surfaces are stratigraphic contacts which mark changes in stratal stacking pattern. The correlation of strata based on their stacking patterns sets sequence stratigraphy apart from other correlation methods that rely on similarities of units in terms of lithology (i.e., lithostratigraphy), fossil content (i.e., biostratigraphy), magnetic polarity (i.e., magnetostratigraphy), geochemical signatures (i.e., chemostratigraphy), or geological age (i.e., chronostratigraphy). Sequence stratigraphic units may or may not coincide with other types of stratigraphic units.

Figure 1.1  Construction of the sequence stratigraphic framework, based on the integration and mutual calibration of independent datasets. The meaning of stratal geometries and vertical profiles is best constrained within a paleo-depositional context. The reliability and the resolution of the constructed framework depend on the type(s) of data available. Where only seismic data are available, stratal stacking patterns are observed at scales above the seismic resolution, on the basis of seismic reflection terminations and architecture (i.e., seismic stratigraphy). Outcrop and well data afford the construction of higher resolution sequence stratigraphic frameworks at sub-seismic scales. Age data enhance the reliability of correlations, but the lack thereof (e.g., in most Precambrian and many Phanerozoic case studies) does not prevent the application of sequence stratigraphy. In the absence of age data, physical stratigraphic markers (e.g., volcanic ash beds, regional coal seams, or regional maximum flooding surfaces) can be used to aid the correlations. Stratal stacking patterns provide the basis for the definition of all units and surfaces of sequence stratigraphy.

The sequence stratigraphic methodology enables the construction of stratigraphic frameworks based on the observation of stratal stacking patterns at scales defined by the purpose of study or by the resolution of the data available. Interpretations in sequence stratigraphy have different degrees of relevance to the methodology. Intrinsic to the method is the rationalization of the sedimentary processes that generate the observed stacking patterns, by placing the data in the correct tectonic and depositional settings (steps 1 and 2 of the sequence stratigraphic workflow; details in Chapter 9). This affords predictions with respect to the sedimentological nature of seismic facies or stratal units in areas away from data control points such as outcrops or wells, within the paleogeographic context of linked depositional systems. The observations that afford the construction of sequence stratigraphic frameworks are independent of the interpretation of underlying controls on sequence development (e.g., the relative contributions of tectonism, sea-level changes, climate, and autogenic controls on stratigraphic cyclicity). The latter defines the scope of stratigraphic modeling (Fig. 1.2).

The correct understanding of sequence stratigraphy requires a clear distinction between the observational workflow of the methodology and the interpretations derived from stratigraphic modeling (Fig. 1.2). Case in point, the modeling and testing of the possible controls on sequence development can continue indefinitely after the construction of a sequence stratigraphic framework. Confusion between the two lines of research undermines the progress made in the development of sequence stratigraphy as an objective, data-driven methodology. Uncalibrated numerical models can generate unlimited results, which, in the absence of reality checks, remain an undifferentiated mix of realistic and unrealistic stratigraphic scenarios. The methodology restores the value of natural processes and facts, by outlining the field criteria that enable the identification of all elements of the sequence stratigraphic framework. The construction of a framework of sequences and component systems tracts explains the genetic relationships between same-age depositional systems, which afford insights into the patterns of sediment distribution across the basin.

Sequence stratigraphy provides the means to rationalize the stratigraphic relationships that develop at different scales within sedimentary basins placed in all tectonic settings, depositional settings, and climatic regimes. While the methodology is independent of geological setting, the sequence stratigraphic framework is variable in terms of timing, scales, and the systems-tract composition of sequences, reflecting the unique accommodation and sedimentation conditions of each sedimentary basin. For this reason, the methodology must be applied objectively, without any a priori assumptions, with the data rather than the model leading to the construction of the sequence stratigraphic framework. The sequence stratigraphic methodology integrates all available datasets that can be derived from surface (e.g., outcrops, modern environments) and subsurface (e.g., borehole, seismic) data sources, and combines insights from all geosciences that contribute to basin analysis (e.g., sedimentary geology, geophysics, geomorphology, and all absolute and relative dating techniques; Fig. 1.1). The reliability of the sequence stratigraphic framework depends on the amount and quality of the data available. Sequence stratigraphic frameworks are typically work in progress as they are constantly improved and refined with the acquisition of more and higher resolution data.

Figure 1.2  Methodology vs. modeling in sequence stratigraphy. The construction of a sequence stratigraphic framework is based on the observation of stratal stacking patterns, irrespective of the interpretation of the underlying controls. In contrast, modeling tests the possible controls on sequence development (e.g., the relative contributions of tectonism, sea/lake-level changes, climate, and sediment supply). The observed stacking patterns can be rationalized in terms of depositional processes by placing the data in the proper paleogeographic context (see workflow of sequence stratigraphy in Chapter 9 ). In downstream-controlled settings, diagnostic stacking patterns relate to shoreline trajectories, whereas non-diagnostic stacking patterns refer to depositional trends that can accompany the formation of any systems tract (e.g., the aggradation of fluvial topsets). In upstream-controlled settings, diagnostic stacking patterns relate to the dominant depositional elements (e.g., channels vs. floodplains in fluvial systems), irrespective of fluvial styles and the interpreted accommodation conditions at syn-depositional time (details in Chapter 4 ). Modeling has no bearing on the methodology, and calibration with field data is required for realistic results (details in Chapter 9 ).

Seismic stratigraphy, which is the precursor of modern sequence stratigraphy, set the early standards for the scales and applications of the methodology (Payton, 1977). Subsequently, the scope of sequence stratigraphy was expanded to include applications to all scales and datasets (from low-resolution seismic stratigraphy to high-resolution sequence stratigraphy at sub-seismic scales afforded by borehole and outcrop data; Amorosi et al., 2005, 2009, 2017; Catuneanu and Zecchin, 2013; Zecchin and Catuneanu, 2013, 2015, 2017; Magalhaes et al., 2015; Zecchin et al., 2017a,b; details in Chapters 2–7), depositional settings (from eolian to deep-water; Kocurek and Havholm, 1993; Catuneanu, 2020a; details in Chapter 8), tectonic settings (from passive to active basins; Bastia et al., 2010; Martins-Neto and Catuneanu, 2010; Maravelis et al., 2016, 2017; details in Chapter 8), and climatic conditions (from icehouse to greenhouse regimes; Bartek et al., 1991, 1997; Kidwell, 1997; Naish and Kamp, 1997; Saul et al., 1999; Fielding et al., 2000, 2001, 2006, 2008; Naish et al., 2001; Cantalamessa et al., 2005; 2007; Di Celma and Cantalamessa, 2007; Isbell et al., 2008; Csato and Catuneanu, 2012; Zecchin et al., 2015; details in Chapter 8), from Precambrian to Phanerozoic successions (Eriksson et al., 1998; 2004, 2005a,b, 2006, 2013; Catuneanu and Biddulph, 2001; Catuneanu et al., 2005; 2012; Sarkar et al., 2005; details in Chapter 9).

Beyond the fundamental research of the basin-fill architecture, sequence stratigraphy also provides a genetic framework to rationalize and predict the distribution of economic deposits that relate to sedimentary processes. The cyclicity, geographic extent, and the physical and temporal relationships of mineral placers, aquifers, coal beds, and petroleum systems guide the exploration and subsequent production development of natural resources. These natural-resource industries employ and benefit from the sequence stratigraphic methodology. The development and distribution of the various types of mineral placers, aquifers, petroleum reservoirs, and coal beds depend on the sequence stratigraphic surfaces and systems tracts with which they are associated (e.g., Hamilton and Tadros, 1994; Banerjee et al., 1996; Bohacs and Suter, 1997; Diessel et al., 2000; Catuneanu and Biddulph, 2001; Ketzer et al., 2003a,b; Fanti and Catuneanu, 2010). The emphasis on depositional processes also led to a shift in the focus of petroleum exploration from structural traps to combined or purely stratigraphic traps (e.g., Bowen et al., 1993; Brown et al., 1995; Posamentier and Allen, 1999). An entire range of new types of petroleum plays thus emerged, and is now defined in light of the sequence stratigraphic concepts.

1.1.2. Sequence stratigraphy—a revolution in sedimentary geology

Sequence stratigraphy is the third of a series of major revolutions in sedimentary geology (Miall, 1995). Each revolution resulted in quantum paradigm shift that changed the way geoscientists understand sedimentary strata. The first breakthrough was marked by the development of the flow regime concept and the associated process/response facies models in the late 1950s and early 1960s (Harms and Fahnestock, 1965; Simons et al., 1965). This first revolution provided a unified theory to explain, from a hydrodynamic perspective, the genesis of sedimentary structures and their predictable associations within the context of depositional systems. Beginning in the 1960s, the incorporation of plate tectonics and geodynamic concepts into the analysis of sedimentary processes at regional scales, marked the second revolution in sedimentary geology. Ultimately, these first two revolutions led to the development of Basin Analysis in the late 1970s, which provided the scientific framework for the study of the origins and depositional histories of sedimentary basins. The conceptual breakthroughs in the fields of process sedimentology and basin analysis paved the way for the emergence of sequence stratigraphy as an interdisciplinary method and genetic approach to stratigraphic analysis.

As the most recent revolutionary paradigm in the field of sedimentary geology, sequence stratigraphy started in the late 1970s with the publication of AAPG Memoir 26 (Payton, 1977), even though its roots can be traced much further back in time as explained below. The concepts embodied by this discipline have resulted in a fundamental change in geological thinking and in particular, the methods of facies and stratigraphic analyses. Over the past few decades, this approach has been embraced by geoscientists as the preferred style of stratigraphic analysis, which has served to tie together observations from many disciplines. In fact, a key aspect of the sequence stratigraphic approach is to encourage the integration of datasets and research methods. Blending insights from a range of disciplines invariably leads to more robust interpretations and, consequently, scientific progress. Thus, the sequence stratigraphic approach has led to improved understanding of how stratigraphic units, facies tracts, and depositional elements relate to each other in time and space within sedimentary basins (Fig. 1.3). The applications of sequence stratigraphy range widely, from predictive exploration for natural resources to improved understanding of Earth's geological record of local to global changes.

Figure 1.3  Sequence stratigraphy in the context of interdisciplinary research. The range of natural resources that can be rationalized in the context of sequence stratigraphy includes hydrocarbons, water, coal, and mineral deposits.

The conventional disciplines of process sedimentology and classical stratigraphy are particularly relevant to sequence stratigraphy (Fig. 1.4). The sedimentological component emphasizes on the processes that lead to the formation of facies and facies contacts within the confines of individual depositional systems. Some of these contacts represent event-significant stratigraphic surfaces that mark changes in stratal stacking patterns and associated sedimentation regimes, which are important for regional correlation. The study of stratigraphic contacts may not, however, be isolated from the facies analysis of the strata they separate, as the latter often provide the criteria for the identification of specific bounding surfaces. Owing to the genetic nature of the sequence stratigraphic approach, process sedimentology is an important prerequisite that cannot be separated from, and forms an integral part of sequence stratigraphy. At the smaller scales of depositional systems, sequence stratigraphy can be used to resolve and explain issues of facies cyclicity, facies associations and relationships, and reservoir compartmentalization, without necessarily applying this information for larger-scale correlations.

The importance of process sedimentology in sequence stratigraphy becomes evident in the workflow of identification of sequence stratigraphic surfaces in the rock record. Basic criteria for the identification of stratigraphic surfaces relate to the conformable vs. unconformable nature of the contact, as well as the nature of the juxtaposed facies across the contact under analysis. Insights of process sedimentology are critical to understanding the origin of the various types of unconformity that may form in nonmarine, coastal, or marine environments, as well as the facies characteristics and variability across systems tracts. The stratigraphic component of sequence stratigraphy relates to its applicability to correlations, both within and beyond the confines of individual depositional systems, in spite of the lateral changes of facies that are common in any sedimentary basin. In addition to its sedimentological and stratigraphic affinities, sequence stratigraphy also brings a component of facies predictability which is particularly appealing to industry-oriented research (Fig. 1.4).

The success and popularity of sequence stratigraphy following the 1970s stems from its widespread applicability in both frontier and mature hydrocarbon basins, where lower and higher resolution predictions of facies development can be formulated, respectively. These predictive models have proven to be particularly effective in reducing lithology-prediction risks for hydrocarbon exploration and production, and have been subsequently employed for the exploration and production of other natural resources as well, including aquifers, coal beds, and mineral placers. In addition to its economic applications, sequence stratigraphy is also employed to resolve issues of fundamental research related to the evolution and stratigraphic architecture of sedimentary basins.

Figure 1.4  Sequence stratigraphy at the limit between process sedimentology and conventional stratigraphy (definitions modified from Bates and Jackson, 1987). Sequence stratigraphy makes use of the principles and methods of both process sedimentology and conventional stratigraphy, in addition to which it brings a new element of facies predictability.

1.1.3. Sequence stratigraphy—an integrated approach

The roots of sequence stratigraphy can be traced far back in the classic principles of sedimentary geology, which established the fundamental guidelines of sedimentological and stratigraphic analyses. These first principles set up the ground rules for the physics of flow and sediment motion, and the processes of sediment accumulation, bypass or erosion in relation to a shifting balance between sediment supply and the energy of the transporting agent (Fig. 1.5). These principles still represent the scientific backbone of sequence stratigraphy, which allows old and modern concepts to blend into a new way of looking at the sedimentary rock record. With this background, sequence stratigraphy emerged as an interdisciplinary approach that relies on the integration of multiple research methods and datasets (Fig. 1.3). At the same time, sequence stratigraphy also provides support for other lines of research such as basin analysis and source-to-sink modeling, which require a multidisciplinary approach.

Sequence stratigraphy has become an essential component of basin analysis. In the context of larger scale source-to-sink numerical models, sequence stratigraphy provides a reality check for the calibration of model results with field data. Beyond the data-based sequence stratigraphic analysis of a basin fill, source-to-sink studies integrate the analysis of sediment sources within numerical simulations of drainage systems and sediment delivery patterns from the provenance to the depocenters. This type of research extends the field of stratigraphic modeling to larger scales, and the reliability of its predictions depends on the calibration of model results with field data (Fig. 1.2). The development of source-to-sink modeling techniques does not change nor replace the need for sequence stratigraphic work. Sequence stratigraphy will continue to provide the means to rationalize the stratigraphic relationships within a basin fill, in a data-driven approach that is independent of model assumptions. The results of sequence stratigraphic analysis can be used to constrain realistic input parameters for the source-to-sink models.

The complexity and accuracy of geological models devised to resolve academic or economic issues improved over time in response to corresponding advances in concepts and technology. Classical geology remains the foundation of everything we know today, by providing the means to understanding the first principles of sedimentary geology (Fig. 1.5). This does not mean that sequence stratigraphy only presents old concepts in a new package, or that it developed as a stand-alone discipline in isolation from other methods. Due to its integrated approach (Fig. 1.3), sequence stratigraphy affords new insights into the genesis and architecture of sedimentary basin fills, which were not possible prior to the introduction of seismic stratigraphic concepts in the 1970s. The issue of facies predictability is a good example of a new insight that was made possible by the sequence stratigraphic approach, which is highly significant on both academic and economic grounds.

Figure 1.5  First principles of sedimentary geology that are relevant to sequence stratigraphy (modified after Middleton, 1973; Posamentier and Allen, 1999).

Technological advances in the fields of three-dimensional seismic data acquisition and processing resulted in the development of seismic geomorphology starting with the 1990s, in parallel with sequence stratigraphy. As defined by Posamentier (2000, 2004), seismic geomorphology deals with the imaging of paleogeographic elements, such as depositional systems and elements thereof, using three-dimensional seismic data. Seismic geomorphology can be performed as a stand-alone technique, but it can also be integrated with sequence stratigraphy for a three-dimensional control of the basin fill that combines 2D section-view insights from seismic stratigraphy (e.g., reflection geometries and terminations, stratigraphic discontinuities, seismic facies) with the 3D plan-view images of seismic geomorphology. This three-dimensional control on the stratigraphic architecture is important at any stage, from frontier exploration to production development, as it provides support and enhances the accuracy of facies predictions, including the interpretation of seismic facies in terms of sedimentary facies.

The resolution of the sequence stratigraphic work will continue to improve in parallel with technological advances in data acquisition and processing. Current efforts aim at reducing the error margin of stratigraphic models and interpretations, during both stages of exploration and production of natural resources, as well as the costs of exploration and production. As with the introduction of seismic geomorphology, technological advances will dictate the next cornerstone that can be achieved. For example, borehole imaging using electric logs (micro resistivity data, which simulate a virtual coring of boreholes) afford insights into process sedimentology (e.g., the visualization of sedimentary structures and paleoflow directions), thus eliminating the costs of mechanical coring. Such techniques and datasets will continue to be integrated into sequence stratigraphy in order to advance our knowledge and understanding of the evolution and architecture of sedimentary basin fills, from sedimentological to stratigraphic scales.

1.1.4. Sequence stratigraphy vs. other types of stratigraphy

Sequence stratigraphy is a type of stratigraphy that is uniquely focused on the identification and correlation of stratal stacking patterns in the sedimentary record (Fig. 1.6). This is fundamentally different from the correlation approaches that are employed by all other types of stratigraphy (Fig. 1.6). The distinction between the different types of stratigraphy is well defined, and yet confusions still arose between sequence stratigraphy and other types of stratigraphy, notably chronostratigraphy and allostratigraphy. Some of these confusions stem from early model assumptions (e.g., the assumption that sequence stratigraphic surfaces are time lines, hence the confusion between sequence stratigraphy and chronostratigraphy) or from faulty definitions of stratal units and bounding surfaces in the early days of sequence stratigraphy (e.g., the definition of parasequences and flooding surfaces, which employed allostratigraphic rather than sequence stratigraphic criteria). Although these confusions have been addressed and resolved, they still occasionally permeate the sequence stratigraphic practice and literature.

Figs. 1.7 and 1.8 present the classic definitions of sequence stratigraphy and of the main stratal units involved in sequence stratigraphic analysis. Subsequent to these developments, the concept of sequence continued to evolve and several types of stratigraphic sequence have been defined, depending on the selection of the sequence boundary and the definition and nomenclature of the component systems tracts (Figs. 1.9 and 1.10). For this reason, and in spite of having been widely embraced by the stratigraphic community, sequence stratigraphy remained the last type of stratigraphy to be endorsed with formal guidelines for methodology and nomenclature by the International Commission on Stratigraphy (Catuneanu et al., 2011). This formal endorsement was made possible by the identification of common-ground principles that enable a standard application of the method in a manner that is independent of model, as explained in this book.

Figure 1.6  Types of stratigraphy, and the rock attributes that they use for correlation. Sequence stratigraphy is a type of stratigraphy which relies on stacking patterns for the definition, nomenclature, classification, and correlation of stratal units and bounding surfaces. Sequence stratigraphic studies highlight the stratigraphic cyclicity that develops in response to changes in relative sea level (accommodation) and base level (sedimentation).

Figure 1.7  Definitions of sequence stratigraphy.

Figure 1.8  Building blocks of the sequence stratigraphic framework.

Figure 1.9  Evolution of sequence stratigraphy (modified from Catuneanu et al., 2011).

Important to note is that the definition and application of sequence stratigraphic concepts are independent of scale. There is no reference to scale in the definition of concepts (Figs. 1.7 and 1.8), and the same terminology can be applied for depositional systems, systems tracts, sequences, and bounding surfaces that develop at different temporal and physical scales. Sequence stratigraphy thus applies to features as small as those produced in an experimental flume, formed in a matter of hours (e.g., Wood et al., 1993; Koss et al., 1994; Paola, 2000; Paola et al., 2001), as well as to those that are continent wide and formed over periods of millions of years. Nonetheless a distinction must be made between larger- and smaller-scale sequences, systems tracts, and stratigraphic surfaces. This is addressed through a hierarchy based on the use of modifiers such as first-order, second-order, third-order, etc., commonly in a relative rather than an absolute sense. Although this terminology is often associated with specific time ranges (Vail et al., 1977a,b, 1991; Krapez, 1996), this has not always been common practice in the scientific literature (see discussions in Embry, 1995; Posamentier and Allen, 1999; Catuneanu et al., 2004, 2005). One reason for this is that we often do not know the scale (especially duration, but also lateral extent or thickness changes across a basin) of the stratal units we deal with within a given study area, so the use of specific names for specific scales may become quite subjective. Another advantage of using a consistent terminology regardless of scale is that jargon is kept to a minimum, which makes sequence stratigraphy more user-friendly and easier to understand across a broad spectrum of readership. These issues are tackled in more detail in Chapter 7.

Among the key concepts shown in Fig. 1.8, the term depositional system defines the largest stratal unit of sedimentology, and predates modern sequence stratigraphy. In contrast, systems tract and depositional sequence are specific sequence stratigraphic terms, introduced with the advent of seismic stratigraphy in the 1970s. A systems tract is a sum of laterally correlative depositional systems (hence, the use of plural: systems), which forms during a specific stage of a stratigraphic cycle (e.g., a transgressive systems tract forms during shoreline transgression). A sequence includes two or more systems tracts, depending on the number of stratal stacking patterns that develop during a stratigraphic cycle. The actual scale for sequence stratigraphic work is highly variable, ranging from depositional system scale (also highly variable) to the entire fill of a sedimentary basin, and beyond. When applied to the analysis of a depositional system (e.g., an ancient delta; Fig. 1.11), sequence stratigraphy is mainly used to resolve the details of facies relationships. Such studies are often performed to describe the degree of reservoir compartmentalization in the various stages of oil field exploration and production. When applied to the scale of depositional system associations, the issue of stratigraphic correlation becomes a primary objective, and provides the framework for the larger scale distribution of facies.

Figure 1.10  Approaches to sequence stratigraphy: nomenclature of systems tracts and timing of sequence boundaries (from Catuneanu et al., 2011 ). While the concept of systems tract was introduced in the 1970s ( Brown and Fisher, 1977), its usage in sequence stratigraphy only started in the 1980s ( Posamentier and Vail, 1985). Abbreviations: CC∗—correlative conformity in the sense of Posamentier et al. (1988), herein referred to as the basal surface of forced regression; CC∗∗—correlative conformity in the sense of Van Wagoner et al. (1988), herein referred to as the correlative conformity; FR—forced regression; FSST—falling-stage systems tract; HNR—highstand normal regression; HST—highstand systems tract; LNR—lowstand normal regression; LST—lowstand systems tract; MFS—maximum flooding surface; MRS—maximum regressive surface; R—regression; RSL—relative sea level; RST—regressive systems tract; T—transgression; T–R—transgressive-regressive; TST—transgressive systems tract. See Fig. 1.9 for the proponents of the different models.

The principles outlined above provide a general idea about the range of potential outcomes and objectives of sequence stratigraphy as a function of scope and scale of analysis. There is a common misconception that sequence stratigraphy is always related to regional, continental, or even global scales of observation (sub-basins, basins, and global cycles). This does not need to be the case, as sequence stratigraphy can be applied virtually to any scale. A good example of this is the study of the East Coulee Delta (Posamentier et al., 1992a), where an entire range of sequence stratigraphic elements (including systems tracts) have been documented at a centimeter to meter scale (Fig. 1.12). In recent years there have been numerous flume-based studies where sequences have been created under controlled laboratory conditions (e.g., Wood et al., 1993; Koss et al., 1994; Paola, 2000; Paola et al., 2001). Such studies have provided valuable insight as to variations on the general sequence model.

Almost any type of study of a sedimentary basin fill requires the construction of cross sections. The lines we draw on these two-dimensional representations are of two main types: (1) lines that build the chronostratigraphic or time framework of the studied interval, and (2) lines that illustrate lateral changes of facies or lithology. The chronostratigraphic framework is commonly constructed by the correlation of surfaces of sequence stratigraphic significance, or true time markers such as bentonites or magnetic polarity boundaries. This is where some confusion can arise. Strictly speaking, sequence stratigraphic surfaces are not true time lines but in fact are to some degree time transgressive, or diachronous. However, because true time lines are not commonly observed, the geoscientist is relegated to using these surfaces as proxies for time lines, being pragmatic and accepting the notion that within the confines of most study areas they are at least close to being time lines and therefore, are fundamentally useful. The degree of diachroneity of sequence stratigraphic surfaces, as well as of other types of stratigraphic surfaces, is discussed in more detail in Chapters 6 and 7.

Figure 1.11  Stratigraphic architecture of a shallow-water system (Late Cretaceous, Alberta, Canada). Following the transgression of the seaway, the long-term regression is punctuated by higher frequency stages of progradation and retrogradation which delineate clinoforms separated by transgressive shales. This is an example of petroleum reservoir compartmentalization at a production development scale, in which each clinoform is a separate hydrodynamic unit. Abbreviations: GR—gamma-ray log; CH—fluvial channel fill; CS—fluvial crevasse splay.

Figure 1.12  East Coulee Delta (from Posamentier et al., 1992a ; image courtesy of Henry Posamentier), demonstrating the applicability of sequence stratigraphic concepts at virtually any scale. In this example, the highstand systems tract was incised during the fall in the water level (pond evaporation), followed by the progradation of the lower elevation lowstand delta. See Posamentier et al. (1992a) for a more detailed interpretation.

Sequence stratigraphic surfaces are not necessarily easier to observe than the more diachronous contacts that mark lateral and vertical changes of facies. Consequently the practitioner can be faced with the dilemma of where to begin a stratigraphic interpretation; in other words, what lines should go first on a cross section. The sequence stratigraphic approach yields a genetic interpretation of the basin fill, which clarifies by time increment how a basin has filled with sediment. To accomplish this, sequence stratigraphic surfaces are interpreted first, to produce a genetic framework within which other types of surface can be rationalized. Subsequently, the sections between sequence stratigraphic surfaces are interpreted by recognizing facies contacts. These two types of surfaces define sequence stratigraphy and lithostratigraphy, respectively (Fig. 1.13).

The inherent difference between lithostratigraphy and sequence stratigraphy is important to emphasize, as both analyze the same sedimentary succession but with the focus on different stratigraphic aspects or rock properties. Lithostratigraphy deals with the lithology of strata and with their organization into units based on lithological character (Hedberg, 1976). The boundaries between lithostratigraphic units are often highly diachronous facies contacts, in which case they develop within the sedimentary packages bounded by sequence stratigraphic surfaces (Fig. 1.13). The advantage of the sequence stratigraphic approach is that correlation can be carried out despite the lateral changes of facies that commonly occur across a basin, for which reason sequence stratigraphic surfaces are typically more extensive than the facies contacts. It is also important to note that facies analyses leading to the interpretation of paleoenvironments are much more critical for sequence stratigraphy than for lithostratigraphy, as illustrated in Figs. 1.14 and 1.15. These figures show that even along 1D vertical profiles, sequence stratigraphic units are often offset relative to the lithostratigraphic units due to their emphasis on different rock attributes. Understanding what constitutes a reasonable vertical and lateral relationship between facies within a time framework assists in correlating event-significant surfaces that mark changes in stratal stacking patterns through varying lithologies.

An example of a sequence stratigraphic—as contrasted with a lithostratigraphic—interpretation based on the same dataset is illustrated in Fig. 1.16. The interpretation of sequence stratigraphic surfaces is based on two fundamental observations: the type of stratigraphic contact, conformable or unconformable; and the nature of facies (depositional systems) which are in contact across the stratigraphic surface. The reconstruction of paleodepositional environments is critical in sequence stratigraphy. In contrast, the lithostratigraphic cross section does not require knowledge of paleoenvironments, but only mapping of lithological contacts. Some of these contacts may coincide with sequence stratigraphic surfaces; others may only reflect lateral changes of facies. As a result, the lithostratigraphic units (e.g., formations A, B, and C in Fig. 1.16) provide only descriptive information of lithologic distribution, which in some instances could combine the products of sedimentation of various depositional environments. Thus a simple map of lithologic distribution may give little insight as to the general paleogeography, and as a result be of little use in predicting lithologies away from known data points.

Figure 1.13  Sequence stratigraphic vs. lithostratigraphic approaches to stratigraphic correlation and the definition of stratal units. Sequence stratigraphic surfaces mark changes in stratal stacking patterns (e.g., from progradation to retrogradation and vice versa ), with or without changes in lithology. Lithostratigraphic surfaces mark changes in lithology, with or without changes in stacking pattern. As they are independent of lithology, sequence stratigraphic units and bounding surfaces are typically mappable over larger areas despite the lateral changes of facies, and therefore provide a superior method of stratigraphic correlation. Facies contacts are also important to map after the construction of the sequence stratigraphic framework, as they are best rationalized within the genetic context of systems tracts. Abbreviations: C–coarsening upward; F–fining upward.

Figure 1.14  Lithostratigraphy and sequence stratigraphy of a facies succession (modified from Posamentier and Allen, 1999 ). Lithostratigraphy defines rock units on the basis of lithology, often irrespective of the depositional system. Sequence stratigraphy defines rock units based on stratal stacking patterns and changes thereof across their bounding surfaces. Lithostratigraphic and sequence stratigraphic surfaces may or may not coincide. The maximum flooding surface, which often provides the best datum for stratigraphic correlation, is commonly placed within undifferentiated lithostratigraphic units. Other sequence stratigraphic surfaces may also be missed within the lithostratigraphic framework if the facies below and above share a similar lithological character. Abbreviations: GR—gamma-ray log; LST—lowstand systems tract; TST—transgressive systems tract; HST—highstand systems tract.

Figure 1.15  Contrast between lithostratigraphy and sequence stratigraphy in the delineation of stratigraphic units (Cretaceous, Western Canada Sedimentary Basin). Knowledge of depositional systems is only critical to sequence stratigraphy. The systems tracts of depositional sequences A and B include lower rank stratigraphic cycles. Abbreviations: SP—spontaneous potential; LST—lowstand systems tract; TST—transgressive systems tract; HST—highstand systems tract.

Allostratigraphy is a stratigraphic discipline with strong affinity to lithostratigraphy, but with emphasis on bounding surfaces rather than stratal units. The North American Commission on Stratigraphic Nomenclature (NACSN) introduced formal allostratigraphic units in the 1983 North American Stratigraphic Code to name discontinuity-bounded units. As currently amended, an allostratigraphic unit is a mappable body of rock that is defined and identified on the basis of its bounding discontinuities (Article 58). Allostratigraphic units, in order of decreasing rank, are allogroup, alloformation, and allomember—a terminology that originates and is modified from lithostratigraphy. The fundamental unit is the alloformation (NACSN, 1983, Art. 58). The bounding discontinuities which define the allostratigraphic approach are represented by any mappable lithological contact, with or without a stratigraphic hiatus associated with it. In this approach, all lithostratigraphic and sequence stratigraphic surfaces that are associated with a lithological contrast may be used for allostratigraphic studies (e.g., Bhattacharya and Walker, 1991; Plint, 2000). However, not all allostratigraphic surfaces are of sequence stratigraphic significance (e.g., flooding surfaces that develop during transgression, with retrogradational stacking patterns below and above, are surfaces of allostratigraphy but not of sequence stratigraphy; Catuneanu, 2019a).

Figure 1.16  Sequence stratigraphic vs. lithostratigraphic frameworks. 1. The reconstruction of depositional systems and the observation of the scoured vs. conformable nature of stratigraphic contacts are important steps in the sequence stratigraphic workflow; 2. Sequence stratigraphic framework based on the observation of stratal stacking patterns; 3. Sequence stratigraphic framework with facies contacts and depositional systems: A—meandering system; B—braided system; C—estuary-mouth complex; D—central estuary; E—delta plain; F—upper delta front; G—lower delta front—prodelta; 4. Lithostratigraphic framework (e.g., formations): A—sandstone-dominated unit; B and C—mudstone-dominated units, with silty and sandy interbeds; units B and C are separated by unit A; additional lithostratigraphic units (e.g., members) may be defined as a function of variations in lithology and color.

1.2. Development of sequence stratigraphy

Modern sequence stratigraphy started as seismic stratigraphy in the 1970s (Payton, 1977), whereby the method was applied specifically to seismic data. This evolved into the more generic sequence stratigraphy in the 1980s as the application of the method was extended to other types of data, such as those provided by wells and outcrops (e.g., Wilgus et al., 1988). Noteworthy, the development of sequence stratigraphy as a new type of stratigraphy in the 1970s and 1980s was preceded by the much earlier publication of several of its key concepts (e.g., Barrell, 1917; Sloss et al., 1949; Wheeler, 1964, Fig. 1.17). Some of these milestones include the concepts of base level (Powel, 1875; Gilbert, 1895; Barrell, 1917), unconformity-bounded sequence (Longwell, 1949; Sloss et al., 1949), correlative conformity (introduced as continuity surface; Wheeler, 1964), and depositional system (Fisher and McGowan, 1967). Building on this foundation, the refinements brought about by seismic stratigraphy include the definition of systems tracts (Brown and Fisher, 1977, Fig. 1.8), seismic-reflection terminations (Mitchum, 1977), a revision to the definition of a sequence (Mitchum, 1977, Fig. 1.8), and the usage of seismic data for a genetic interpretation of the stratigraphic architecture (Payton, 1977). From here, sequence stratigraphy bloomed and diversified in the 1980s and the 1990s, with several models being proposed (Figs. 1.9 and 1.10).

The evolution of sequence stratigraphy involved advances in the understanding of the array of possible controls on sequence development, improvements in stratigraphic resolution, revisions to the definition and classification of sequences, and ultimately the emergence of a standard approach to methodology and nomenclature (Figs. 1.9 and 1.17). The methodology improved significantly since the 1970s, from a model-driven approach underlain by assumptions regarding the dominant role of eustasy on sequence development, with consequent assertions of global correlations (Vail et al., 1977a,b; Haq et al., 1987), to a data-driven approach that promotes the use of local data without any assumptions regarding the underlying controls on sequence development (Miall, 1986, 1991, 1992; Catuneanu et al., 2011). The latter affords realistic constructions of local stratigraphic frameworks, which prove to be highly variable in terms of timing and scales of stratigraphic cycles, not only from one sedimentary basin to another but also among the sub-basins of the same sedimentary basin (Catuneanu et al., 1999, 2002; Miall et al., 2008; Menegazzo et al., 2016). The construction of basin-specific stratigraphic frameworks is a major breakthrough and departure from the early models.

Concomitant with the improvements in methodology, refinements in stratigraphic modeling driven by advances in computing power enhanced the ability to test the response of sedimentary systems to any combinations of possible controls on sequence development. The insights enabled by numerical simulations are particularly useful when calibrated with field data (Euzen et al., 2004; Rabineau et al., 2005, 2006; Csato et al., 2013, 2015; Leroux et al., 2014; Catuneanu and Zecchin, 2016). In light of these advances, a clear distinction is required between methodology and modeling in sequence stratigraphy. The methodology is based on the observation of stratal stacking patterns in a manner that is independent of the interpretation of the underlying controls. Beyond the purpose of the methodological workflow, the modeling and testing of the possible controls on sequence development can continue indefinitely after the construction of a sequence stratigraphic framework. Stratigraphic modeling is an independent line of research that plays no role in, and it does not change the outcome of the methodological workflow (Catuneanu, 2020b, Fig. 1.2).

Most significant to its practical applications, the development of sequence stratigraphy was accompanied by a gradual increase in stratigraphic resolution, from the seismic scales of petroleum exploration (Payton, 1977) to the sub-seismic scales of petroleum production development (e.g., Van Wagoner et al., 1990; Homewood et al., 1992; Homewood and Eberli, 2000; Zecchin and Catuneanu, 2013, 2015; Magalhaes et al., 2015; Catuneanu, 2019b). Sequence stratigraphic frameworks can be constructed at different scales, depending on the scope of the study and the resolution of the data available. Seismic data are typically used to build larger scale, lower resolution frameworks, whereas borehole and outcrop data afford the construction of higher resolution frameworks at sub-seismic scales. The observation of the full spectrum of stratigraphic complexity that develops at intertwining scales relies on the integration of multiple datasets with different resolutions. In the workflow of hydrocarbon exploration, the construction of a stratigraphic framework typically starts with 2D seismic transects. The context provided by seismic data enhances the accuracy of facies predictions in subsequent higher resolution studies.

The development of seismic stratigraphy in the 1970s made use of established sedimentological concepts (e.g., the concept of depositional system as a three-dimensional assemblage of lithofacies linked by a common environment of deposition; Fisher and McGowan, 1967) to define new building blocks of the stratigraphic framework (e.g., systems tracts, as linkages of contemporaneous depositional systems; Brown and Fisher, 1977). Owing to the specific type of data used to develop the methodology (i.e., 2D seismic transects), seismic stratigraphy introduced by default a minimum scale for depositional systems, systems tracts, and sequences, which had to exceed the vertical seismic resolution (i.e., typically in a range of 10¹ m in the 1970s). As a result, the building blocks of the seismic stratigraphic framework are commonly observed at scales of 10¹–10² m. The perception that sequences and their component systems tracts and depositional systems develop typically at scales of 10¹–10² m is an artifact of seismic resolution, but it dominated stratigraphic thinking for decades.

Figure 1.17  Milestones in the development of sequence stratigraphy. Modern sequence stratigraphy, which started as seismic stratigraphy in the 1970s ( Vail, 1975; Payton, 1977), was dominated in the 1970s–1980s by the assumption that eustasy exerted the main control on sequence development; this led to the construction of reference global-cycle charts for stratigraphic cyclicity and correlations worldwide (Vail et al., 1977b; Haq et al., 1987, 1988; Posamentier et al., 1988). Subsequent developments in the 1990s changed the emphasis on tectonism as a major control on sequence development (e.g., Krapez, 1996: The importance of eustasy in sequence stratigraphy should be de-emphasized). The standard methodology that emerged in the 2000s–2010s is decoupled from the interpretation of the underlying controls, and it is based on the observation of stratal stacking patterns in the stratigraphic record.

The reality of sequences, systems tracts, and depositional systems at sub-seismic scales has become evident with the advances in high-resolution sequence stratigraphy (e.g., Tesson et al., 1990, 2000; Lobo et al., 2004; Amorosi et al., 2005, 2009, 2017; Bassetti et al., 2008, Catuneanu and Zecchin, 2013; Nanson et al., 2013; Zecchin and Catuneanu, 2013, 2015, 2017; Csato et al., 2014; Nixon et al., 2014; Magalhaes et al., 2015; Zecchin et al., 2015, 2017a,b; Ainsworth et al., 2017, 2018; Pellegrini et al., 2017, 2018; Catuneanu, 2019a,b). Improvements in stratigraphic resolution demonstrated that unconformities may form over a wide range of scales, both below and above the seismic resolution, and therefore, unconformity-bounded units are not restricted to the scales of seismic stratigraphy (e.g., Miall, 2015; Strasser, 2016, 2018). It is now clear that most commonly, the building blocks of a seismic stratigraphic framework consist of higher frequency sequences that develop at sub-seismic scales; e.g., seismic-scale systems tracts (10¹–10² m) consist typically of sequences of 10⁰–10¹ m scales, which are different from and should not be confused with parasequences (Catuneanu, 2019a).

1.2.1. Unconformities

Sequence stratigraphy started to emerge as a method of stratigraphic analysis ever since the recognition of unconformities in the rock record, which allowed the subdivision of the sedimentary succession into units separated by breaks in deposition (Fig. 1.17). Early depictions of angular unconformities date as far back as the 17th century (Nicolaus Steno, 1669), but their geological meaning was only realized late in the 18th century (James Hutton, 1788, 1795). Hutton presented the concept of unconformity as part of the rock cycle, although he never actually used the term unconformity; instead, he used descriptive phrases in which the expression conjunction of vertical and horizontal strata was widely used (Tomkeieff, 1962). The term unconformity was coined by Robert Jameson in the early 19th century (Jameson, 1805), but it was only widely incorporated into the geological vocabulary following the work of Charles Lyell and Henry De la Beche (De la Beche, 1830; Lyell, 1830).

The term unconformity was synonymous with what we know today as angular unconformity until the beginning of the 20th century, when the term disconformity was proposed for a particular type of erosional unconformity where sedimentary strata above and below the contact are parallel to each other (Grabau, 1905). Other types of unconformities were recognized subsequently, including the contact between basement rocks and the overlying sedimentary rocks (i.e., known today as nonconformity; Blackwelder, 1909) and the non-depositional hiatus that assumes a gap in sedimentation without necessarily involving erosion (i.e., referred to today as paraconformity; Willis, 1910). All these types of unconformity assume a substantial break in the geologic record (Neuendorf et al., 2005), although the actual span of time of what is considered to be substantial (as opposed to brief, as in a diastem) was never quantified.

The spectrum of hiatal stratigraphic contacts was completed with the definition of the diastem by Barrell (1917), essentially as a minor paraconformity. However, the distinction between a paraconformity and a diastem, both in terms of temporal significance and physical expression, remains elusive to the present day. Further discussion and recommendations on the usage of the diastem concept are presented in Chapter 7. The definition of the various types of stratigraphic contacts is summarized in Fig. 1.18.

1.2.2. Unconformity-bounded units

As early as the eighteenth century, Hutton (1788, 1795) recognized the alternation through time of processes of erosion and deposition, setting up the foundation for what is known today as the rock cycle (Fig. 1.17). Hutton's observations may be considered as the first account of stratigraphic cyclicity, whereby unconformities provide the basic subdivision of the rock record into repetitive successions. The link between unconformities and base-level changes was subsequently explained by Barrell (1917), who stated that sedimentation controlled by base level will result in divisions of the stratigraphic series separated by breaks (Fig. 1.19).

Following the recognition of unconformities in the rock record, stratigraphic hiatuses have become natural candidates for correlation and the subdivision of the stratigraphic succession into units characterized by relatively continuous sediment accumulation. The nomenclature of unconformity-bounded units included terms such as rhythms (Barrell, 1917; to