Octavian Catuneanu | University of Alberta (original) (raw)

Papers by Octavian Catuneanu

REGIONAL GEOLOGY AND TECTONICS Volume 2: Phanerozoic Rift Systems and Sedimentary Basins, 2024

Marine and Petroleum Geology, 2023

The analysis of high-resolution images provided by the Perseverance rover indicates the presence ... more The analysis of high-resolution images provided by the Perseverance rover indicates the presence of a Gilbert type deltaic complex in the western part of the Jezero crater, which includes fluvial topsets, as well as subaqueous clinoforms. While previously considered to be genetically related, the topsets and the foresets are separated by subaerial unconformities and belong to different sedimentation cycles (depositional sequences) and systems tracts. Based on the stratal stacking patterns observed at Kodiak butte, the clinoforms belong to fallingstage systems tracts, as indicated by the downstepping trajectory of the clinoform rollovers, the occasional preservation of offlap, and the sharp-based nature of the clinoforms. In contrast, the topsets are part of the lowstand systems tracts of the overlying depositional sequences, and are separated from the underlying foresets by truncation surfaces (i.e., subaerial unconformities). The possible environments for the deposition of clinoforms in the Jezero crater range from lacustrine to marine. In the latter case, a connection between the Jezero Basin and a northern ocean can be inferred, allowing for the possibility of tidal processes influencing the patterns of deposition within the deltaic complex. This may explain the rhythmites observed in the deltaic foresets, although other explanations for the cyclic changes in lithology and energy conditions, such as seasonal variations in fluvial discharge and sediment load, are also possible. The location of the Jezero crater in the shoreline area of the Isidis Basin, which is a bay of the northern ocean, may have created a configuration of interconnected embayments able to amplify the otherwise small tidal range expected from the two moons of the planet. Clarification of the paleogeography at the time of deltaic progradation (c. 3.6-3.8 Ga) has major implications for the strategy of exploration for early life forms on Mars. The acquisition of rock samples from the Jezero Basin and the northern ocean are essential to gain further insight into the early land-ocean interaction and possible co-evolution of life and environments on Mars.

Earth-Science Reviews, 2020

Parasequences were introduced as the building blocks of seismic-scale systems tracts in the conte... more Parasequences were introduced as the building blocks of seismic-scale systems tracts in the context of low-resolution seismic stratigraphy. Pitfalls of this concept relate to the definition of parasequence boundaries as lithological discontinuities that mark episodes of abrupt water deepening. With this general meaning, 'flooding surfaces' may be facies contacts within transgressive deposits, or may coincide with different types of sequence stratigraphic surfaces (maximum regressive, transgressive ravinement, or maximum flooding). In all cases, flooding surfaces are allostratigraphic contacts restricted to coastal and shallow-water settings, where evidence of abrupt water deepening can be demonstrated. Flooding surfaces may also be absent from the shallow-water systems, where conformable successions accumulate during gradual water deepening. It follows that (1) para-sequences have smaller extent than systems tracts, and (2) systems tracts do not always consist of stacked parasequences. These limitations prevent the dependable use of the parasequence concept in sequence strati-graphy. Advances in high-resolution sequence stratigraphy show that the scales of sequences and parasequences are not mutually exclusive; the two types of units define different approaches to the delineation of stratigraphic cycles at high-resolution scales. Sequences that develop at parasequence scales provide a more reliable alternative for correlation, both within and outside of the coastal and shallow-water settings, rendering para-sequences obsolete. Every transgression that affords the formation of a flooding surface starts from a maximum regressive surface and ends with a maximum flooding surface observed at the scale of that transgression. These systems tract boundaries are invariably more extensive than any facies contacts that may form during the transgression. Flooding surfaces remain relevant to the description of facies relationships, but their stratigraphic meaning needs to be assessed on a case-by-case basis. The use of sequences and systems tracts in high-resolution studies provides consistency in methodology and nomenclature at all stratigraphic scales, irrespective of geological setting and the types and resolution of the data available.

Marine and Petroleum Geology, 2020

Confusions between methodology and modeling created a false premise to question the 'future of se... more Confusions between methodology and modeling created a false premise to question the 'future of sequence stratigraphy'. In reality, the future is already here in terms of a standard methodology. Despite the variability of the stratigraphic architecture, there are only a few stacking patterns that are diagnostic to the definition of stratal units and bounding surfaces, which can be observed at all stratigraphic scales. The identification of the diagnostic stacking patterns, at scales defined by the purpose of the study or by the resolution of the data available, provides the guiding principle of the sequence stratigraphic methodology. The modeling of the possible controls on sequence development plays no role in the methodological workflow, and can continue indefinitely after the construction of a sequence stratigraphic framework. Therefore, it is important to separate methodology from modeling in sequence stratigraphy. The standard methodology does not prevent future developments in the field of stratigraphic modeling. Uncalibrated modeling can 'demonstrate' any stratigraphic scenario, whether realistic or not. While the methodology evolved from a model-driven to a data-driven approach, uncalibrated modeling has become the new 'triumph of interpretation over facts and common sense'. The latest trend in forward modeling is the shift from an overemphasis on accommodation to an overemphasis on sediment supply, to the point that all aspects of the stratigraphic architecture are explained by variations in sediment supply or even solely by autocyclicity. In reality, it is always a combination of accommodation and sedimentation, and both elements of this 'dual control' contribute in discernible ways to the architecture and makeup of the sequence stratigraphic framework. The methodology does not require an interpretation of the underlying controls on accommodation and sedimenta-tion, but only the observation of stratal stacking patterns and stratigraphic relationships that result from their interplay. Muddling the distinction between methodology and modeling leads to unnecessary confusion and a reversal of the progress made in the development of sequence stratigraphy as a data-driven methodology.

Marine and Petroleum Geology, 2020

Stratigraphic cyclicity in the deep-water setting reflects the interplay of accommodation and sed... more Stratigraphic cyclicity in the deep-water setting reflects the interplay of accommodation and sedimentation on the shelf, which controls shoreline trajectories, sediment supply to the shelf edge, and the timing of all elements of the sequence stratigraphic framework. Stratigraphic trends defined by changes in the types, volume, and composition of gravity flows during the shoreline transit cycles on the shelf provide the diagnostic criteria for the identification of deep-water systems tracts and bounding surfaces. Non-diagnostic variability in the sedi-mentological makeup of systems tracts reflects the unique tectonic and depositional settings of each sedimentary basin, and needs to be rationalized on a case-by-case basis. Contour currents may further modify the sedi-mentological makeup of deep-water sequences, but do not provide diagnostic elements for the definition of systems tracts and bounding surfaces. The application of sequence stratigraphy to the deep-water setting relies on the construction of composite profiles that illustrate the relative chronology of the different types of gravity-driven processes at regional scales. The cyclicity relevant to the definition of sequences is described by the composite rather than local profiles. The place of accumulation of depositional elements depends on the location of sediment entry points along the shelf edge, the types of gravity-driven processes, and the seafloor morphology. The allocyclic and/or autocyclic lateral shifts of deep-water depositional elements further enhance the offset between local trends and the regional composite profile in terms of timing and frequency of cycles, timing of coarsening-and fining-upward trends, and timing of the coarsest sediment. The sedimentological cycles defined by local trends must not be confused with the stratigraphic cycles defined by regional composite profiles.

Marine and Petroleum Geology, 2019

Stratigraphic cyclicity can be observed at different scales. At each scale of observation (i.e., ... more Stratigraphic cyclicity can be observed at different scales. At each scale of observation (i.e., hierarchical level), the building blocks of the sequence stratigraphic framework are represented by sequences and their component systems tracts and depositional systems. At the smallest stratigraphic scales, systems tracts and component depositional systems consist solely of sedimentological cycles (i.e., beds and bedsets). At any larger scales, systems tracts and depositional systems consist of lower rank stratigraphic cycles (i.e., sequences). The stacking pattern of sedimentological cycles defines the lowest rank systems tracts, which are the smallest stratigraphic units of a sequence stratigraphic framework. The scale of the lowest rank systems tracts at any location defines the highest stratigraphic resolution that can be achieved, and the limit between sedimentology and stratigraphy sensu stricto. The formation of depositional systems, and implicitly of systems tracts, requires typically minimum timescales of 10 2 yrs, and it may be sustained for as long as the defining environments are maintained as dominant sediment fairways. Within the transit area of a shoreline, where changes in depositional environment are most frequent, only the lowest rank depositional systems consist strictly of process-related facies accumulated in specific environments; these depositional systems sensu stricto develop commonly at scales below the resolution of seismic stratigraphy. At larger scales (higher hierarchical ranks), depositional systems sensu lato reflect dominant depositional trends, but may record higher frequency changes in depositional environment. The distinction between depositional systems sensu stricto and sensu lato becomes less meaningful outside of the shoreline transit area, where stratigraphic cyclicity may develop without changes in depositional environment. High-frequency sequences are commonly observed at scales of 10 0-10 1 m and 10 2-10 5 yrs, which defines the scope of high-resolution sequence stratigraphy. The stacking pattern of high-frequency sequences defines de-positional systems and systems tracts of higher hierarchical ranks in lower resolution studies.

A B S T R A C T Stratal stacking patterns provide the basis for the definition of all units and s... more A B S T R A C T Stratal stacking patterns provide the basis for the definition of all units and surfaces of sequence stratigraphy. The same types of stacking patterns may be observed at different scales, in relation to stratigraphic cycles of different magnitudes. At each scale of observation, stacking patterns define systems tracts, and changes in stacking pattern mark the position of sequence stratigraphic surfaces. The construction of a framework of systems tracts and bounding surfaces fulfills the practical purpose of sequence stratigraphy. Beyond this framework, model-dependent choices with respect to the selection of the 'sequence boundary' may be made as a function of the mappability of the various types of sequence stratigraphic surface within the studied section. Sequence stratigraphic frameworks are basin-specific in terms of timing and scales of the component units and bounding surfaces, reflecting the interplay of global and local controls on accommodation and sedi-mentation. A stratigraphic sequence corresponds to a cycle of change in stratal stacking patterns, defined by the recurrence of the same type of sequence stratigraphic surface in the rock record. Sequences, as well as component systems tracts and depositional systems, can be observed at all stratigraphic scales. Sequences of any scale may include unconformities of equal and/or lower hierarchical ranks, whose identification depends on the resolution of the data available. The relative ranking of sequences of different scales is defined by their strati-graphic relationships, as lower rank sequences are nested within higher rank systems tracts. Despite this nested architecture, the stratigraphic framework is not truly fractal because sequences of different scales may differ in terms of underlying controls and internal composition of systems tracts. A scale-independent approach to methodology and nomenclature is key to the standard application of sequence stratigraphy across the entire range of geological settings, stratigraphic scales, and types of data available.

A B S T R A C T Foreland systems on overriding plates (i.e., retroarc settings) form through the ... more A B S T R A C T Foreland systems on overriding plates (i.e., retroarc settings) form through the deflection of the lithosphere in response to a combination of supra-and sublithospheric loads. Supracrustal loading by orogens leads to the partitioning of foreland systems into foredeep, forebulge, and back-bulge flexural provinces. Thrusting in the orogenic belt results in foredeep subsidence and forebulge uplift, and the reverse occurs as orogenic load is removed by erosion or extension. This pattern generates out-of-phase ('reciprocal') stratigraphies across the flexural hingeline that separates the foredeep from the forebulge. Coupled with flexural tectonics, accommodation is also modified by dynamic (sublithospheric) loading. The latter mechanism operates at larger, continental scales, with rates controlled by the velocity and the angle of subduction. The interplay of accommodation and sediment supply during the lifespan of a foreland system controls the long-term shift from underfilled to overfilled accommodation conditions, which defines the first-order foreland cycle. Predictable shifts in the balance between flexural tectonics and dynamic loading during the evolution of a foreland system allow the subdivision of the first-order foreland cycle into early and late stages dominated by flexural tectonics, separated by an intermediate stage dominated by system-wide dynamic subsidence. The early stage is defined by an underfilled foredeep that hosts a deep-water environment, and an exposed forebulge whose progradation and erosion generates the 'forebulge unconformity' at the base of the first-order foreland sequence. Submergence of the forebulge during the intermediate stage establishes an interior seaway across the entire foreland system. The late stage marks a shift to a system-wide continental setting, which defines the overfilled phase of the foreland cycle.

High-frequency sequences composed of mixed siliciclastic-carbonate deposits may exhibit either ve... more High-frequency sequences composed of mixed siliciclastic-carbonate deposits may exhibit either vertical or horizontal changes between siliciclastics and carbonates. Vertical facies shifts occur between systems tracts and define a 'reciprocal sedimentation' pattern, typically consisting of transgressive/highstand carbonates and forced regressive/lowstand siliciclastics, although variations from this rule are common. Mixed systems with lateral facies change, usually typifying transgressive and/or highstand systems tracts, may exhibit proximal siliciclastics and distal carbonates or vice-versa, although variations may also occur along depositional strike. The marked variability of mixed siliciclastic-carbonate sequences makes the definition of a universal sequence stratigraphic model impossible, as the composition and geometries of systems tracts may change considerably, and sequence stratigraphic surfaces and facies contacts may vary in terms of occurrence and physical expression. However, some resemblance exists between sili-ciclastic sequences and mixed sequences showing lateral facies changes between siliciclastics and car-bonates. In particular, these mixed sequences display 1) a stratal architecture of the clastic part of the systems tracts that is comparable to that of siliciclastic deposits, 2) a dominant role of the inherited physiography and of erosional processes, rather than carbonate production, in shaping the shelf profile, and 3) a local lateral juxtaposition of siliciclastic sandstones and carbonate bioconstructions due to hydrodynamic processes. These observations are helpful in predicting the location of porous and potential sealing bodies and baffles to fluid flow at the intra-high-frequency sequence scale, and ultimately they are useful for both petroleum exploration and production.

The Kachchh sedimentary basin in the western continental margin of India is a peri-cratonic rift ... more The Kachchh sedimentary basin in the western continental margin of India is a peri-cratonic rift basin which preserves a nearly complete rock record from Middle Jurassic to Recent, punctuated by several stratigraphic breaks. The Cenozoic sediments exposed in the western part of the Kachchh mainland extend offshore into the present-day continental shelf. The unique feature of the outcropping area is a nearly complete, richly fossiliferous and easily accessible Cenozoic succession. Detailed field mapping and litho-biostratigraphic studies have made it possible to identify the chronostratigraphic units, map them in the field and extend the correlation into the offshore, aided by the development of continuously recognizable key biostratigraphic horizons and time boundaries. Detailed field mapping of key sections integrated with the litho-biostratigraphic information has helped in working out a sequence strati-graphic framework for the Cenozoic succession in the basin. The succession comprises a first-order passive margin sequence. Excellent biostratigraphic control has enabled identification of un-conformities of various magnitudes which in turn have helped in mapping 5 second-order and four third-order sequences. Each sequence is discussed with respect to its extent, nature of sequence boundaries, sedimentary fill, key sequence stratigraphic surfaces and depositional setup, to understand the Cenozoic sequence stratigraphic architecture of the basin.

High-frequency clastic shelf sequences deposited in high-latitude settings display marked differe... more High-frequency clastic shelf sequences deposited in high-latitude settings display marked differences, in term of facies and stratigraphic architecture, with respect to their lower latitude counterparts. This is due to the presence of ice which (1) leads to the accumulation of glacigenic and glacimarine deposits; (2) provides an additional control on accommodation; and (3) determines the position of the shoreline. Transgressions and regressions in glaciated settings are controlled respectively by the retreat and advance of the 'ice' shoreline (i.e., the water/ice contact) irrespective of relative sea-level changes; once the ice retreats across the land, the traditional 'land' shoreline is exposed and the control on sequence architecture is exerted by the interplay between relative sea-level changes and sediment supply as in low-and middle-latitude settings. A general model that includes both glacial and non-glacial climatic regimes is provided by this paper. In this frame, the classic sequence stratigraphic model represents one (ice-free) end member, which is opposed to an ice-permanent end member. Between these end members , sequences may accumulate in part under ice-free conditions and in part under conditions dominated by ice on the shelf. The main implication of this is that the classic sequence stratigraphic model may be viewed as only a possible scenario in the stratigraphic record rather than the rule.

High-frequency clastic shelf sequences contain porous deposits, consisting of coastal to shallow-... more High-frequency clastic shelf sequences contain porous deposits, consisting of coastal to shallow-water sandstones and conglomerates, which may represent very good reservoirs, and therefore critical targets for exploration and production, as well as for fluid (hydrocarbon, water or CO 2) storage. The study of these reservoirs, following a sequence stratigraphic approach, is essential to predict their features and distribution within systems tracts forming high-frequency sequences, which in turn compose higher-rank systems tracts and sequences. A critical aspect to improve the exploitability of the reservoirs is their heterogeneity, which directly affects the volume of the reservoirs and determine internal compartmentalization. The heterogeneity can be primary, related to depositional processes influencing grain size and facies distribution, and secondary, related to diagenesis. In particular, the primary het-erogeneity is referred to the facies variability from distal to proximal settings, to the accumulation of condensed shell beds, and to facies characteristics of bedsets, whereas the secondary heterogeneity derives from diagenetic processes at sequence stratigraphic surfaces and facies contacts, and within sandbodies. Both the distribution of reservoirs and their heterogeneity can be predicted following a high-resolution sequence stratigraphic approach. Ultimately, the integration of subsurface data with the analysis of outcrop analogs is essential to better understand the features of clastic shelf reservoirs and to develop 3D models of fluid migration.

Both allogenic and autogenic processes may contribute to the formation of sequence stratigraphic ... more Both allogenic and autogenic processes may contribute to the formation of sequence stratigraphic surfaces, particularly at the scale of fourth-order and lower rank cycles. This is the case with all surfaces that are associated with transgression, which include the maximum regressive surface, the transgressive ravinement surfaces and the maximum flooding surface, and, under particular circumstances, the subaerial unconformity as well. Not all autogenic processes play a role in the formation of sequence stratigraphic surfaces, but only those that can influence the direction of shoreline shift. Any changes in shoreline trajectory, whether autogenic or allogenic in origin, influence the stratal stacking patterns in the rock record which sequence stratigraphic interpretations are based upon. The discrimination between the allogenic and autogenic processes that may control changes in shoreline trajectory is a matter of interpretation and is tentative at best in many instances. For this reason, the definition and nomenclature of units and bounding surfaces need to be based on the observation of stratal features and stacking patterns rather than the interpretation of the controlling mechanisms. In this light, we extend the concept of 'sequence' to include all cycles bounded by recurring surfaces of sequence stratigraphic significance, irrespective of the origin of these surfaces. The updated sequence concept promotes a separation between the objective observation of field criteria and the subsequent interpretation of controlling parameters, and stresses that a sequence stratigraphic unit is defined by its bounding surfaces and not by its interpreted origin. The use of high-frequency sequences eliminates the need to employ the concepts of parasequence or small-scale cycle in high-resolution studies, and simplifies the sequence stratigraphic methodology and the nomenclature.

The sequence stratigraphic architecture includes a complex array of stratal geometries with diffe... more The sequence stratigraphic architecture includes a complex array of stratal geometries with different degrees of stratigraphic significance. The 'non-unique' variability of the sequence stratigraphic framework (i.e., stratal geometries which are not diagnostic for the definition of systems tracts and bounding surfaces) is irrelevant to the workflow of sequence stratigraphy. What is relevant is the observation of the 'unique' stratal geometries that are diagnostic for the definition of units and surfaces of sequence stra-tigraphy. In downstream-controlled settings, these unique stratal stacking patterns relate to the forced regressive, normal regressive, and transgressive shoreline trajectories. Multiple controls interact during the formation of each type of stacking pattern, including accommodation, sediment supply, and the energy of the sediment-transport agents. This interplay explains the non-unique variability, but does not change the unique criteria that afford a consistent application of sequence stratigraphy. The distinction between unique and non-unique stratal geometries is critical to the sequence stratigraphic methodology. Failure to rationalize the non-unique variability within the context of unique stratal geometries is counterproductive, and obscures the simple workflow of sequence stratigraphy. This is the case with uncalibrated numerical modeling, which may overemphasize non-unique or even unrealistic strati-graphic scenarios. While useful to test the possible controls on stratigraphic architecture, modeling requires validation with real data, and plays no role in the sequence stratigraphic methodology.

... Michael J. Pyrcz (mpyrcz@ualberta.ca) Department of Civil & Environmental Engineering Uni... more ... Michael J. Pyrcz (mpyrcz@ualberta.ca) Department of Civil & Environmental Engineering University of Alberta ... Pyrcz, MJ and CV Deutsch, 2003, Stochastic surface modeling in mud rich, fine-grained turbidite lobes: AAPG Annual Meeting, May 11-14, Salt Lake, Utah. Page 12. ...

Marine and Petroleum Geology, 2016

REGIONAL GEOLOGY AND TECTONICS Volume 2: Phanerozoic Rift Systems and Sedimentary Basins, 2024

Marine and Petroleum Geology, 2023

The analysis of high-resolution images provided by the Perseverance rover indicates the presence ... more The analysis of high-resolution images provided by the Perseverance rover indicates the presence of a Gilbert type deltaic complex in the western part of the Jezero crater, which includes fluvial topsets, as well as subaqueous clinoforms. While previously considered to be genetically related, the topsets and the foresets are separated by subaerial unconformities and belong to different sedimentation cycles (depositional sequences) and systems tracts. Based on the stratal stacking patterns observed at Kodiak butte, the clinoforms belong to fallingstage systems tracts, as indicated by the downstepping trajectory of the clinoform rollovers, the occasional preservation of offlap, and the sharp-based nature of the clinoforms. In contrast, the topsets are part of the lowstand systems tracts of the overlying depositional sequences, and are separated from the underlying foresets by truncation surfaces (i.e., subaerial unconformities). The possible environments for the deposition of clinoforms in the Jezero crater range from lacustrine to marine. In the latter case, a connection between the Jezero Basin and a northern ocean can be inferred, allowing for the possibility of tidal processes influencing the patterns of deposition within the deltaic complex. This may explain the rhythmites observed in the deltaic foresets, although other explanations for the cyclic changes in lithology and energy conditions, such as seasonal variations in fluvial discharge and sediment load, are also possible. The location of the Jezero crater in the shoreline area of the Isidis Basin, which is a bay of the northern ocean, may have created a configuration of interconnected embayments able to amplify the otherwise small tidal range expected from the two moons of the planet. Clarification of the paleogeography at the time of deltaic progradation (c. 3.6-3.8 Ga) has major implications for the strategy of exploration for early life forms on Mars. The acquisition of rock samples from the Jezero Basin and the northern ocean are essential to gain further insight into the early land-ocean interaction and possible co-evolution of life and environments on Mars.

Earth-Science Reviews, 2020

Parasequences were introduced as the building blocks of seismic-scale systems tracts in the conte... more Parasequences were introduced as the building blocks of seismic-scale systems tracts in the context of low-resolution seismic stratigraphy. Pitfalls of this concept relate to the definition of parasequence boundaries as lithological discontinuities that mark episodes of abrupt water deepening. With this general meaning, 'flooding surfaces' may be facies contacts within transgressive deposits, or may coincide with different types of sequence stratigraphic surfaces (maximum regressive, transgressive ravinement, or maximum flooding). In all cases, flooding surfaces are allostratigraphic contacts restricted to coastal and shallow-water settings, where evidence of abrupt water deepening can be demonstrated. Flooding surfaces may also be absent from the shallow-water systems, where conformable successions accumulate during gradual water deepening. It follows that (1) para-sequences have smaller extent than systems tracts, and (2) systems tracts do not always consist of stacked parasequences. These limitations prevent the dependable use of the parasequence concept in sequence strati-graphy. Advances in high-resolution sequence stratigraphy show that the scales of sequences and parasequences are not mutually exclusive; the two types of units define different approaches to the delineation of stratigraphic cycles at high-resolution scales. Sequences that develop at parasequence scales provide a more reliable alternative for correlation, both within and outside of the coastal and shallow-water settings, rendering para-sequences obsolete. Every transgression that affords the formation of a flooding surface starts from a maximum regressive surface and ends with a maximum flooding surface observed at the scale of that transgression. These systems tract boundaries are invariably more extensive than any facies contacts that may form during the transgression. Flooding surfaces remain relevant to the description of facies relationships, but their stratigraphic meaning needs to be assessed on a case-by-case basis. The use of sequences and systems tracts in high-resolution studies provides consistency in methodology and nomenclature at all stratigraphic scales, irrespective of geological setting and the types and resolution of the data available.

Marine and Petroleum Geology, 2020

Confusions between methodology and modeling created a false premise to question the 'future of se... more Confusions between methodology and modeling created a false premise to question the 'future of sequence stratigraphy'. In reality, the future is already here in terms of a standard methodology. Despite the variability of the stratigraphic architecture, there are only a few stacking patterns that are diagnostic to the definition of stratal units and bounding surfaces, which can be observed at all stratigraphic scales. The identification of the diagnostic stacking patterns, at scales defined by the purpose of the study or by the resolution of the data available, provides the guiding principle of the sequence stratigraphic methodology. The modeling of the possible controls on sequence development plays no role in the methodological workflow, and can continue indefinitely after the construction of a sequence stratigraphic framework. Therefore, it is important to separate methodology from modeling in sequence stratigraphy. The standard methodology does not prevent future developments in the field of stratigraphic modeling. Uncalibrated modeling can 'demonstrate' any stratigraphic scenario, whether realistic or not. While the methodology evolved from a model-driven to a data-driven approach, uncalibrated modeling has become the new 'triumph of interpretation over facts and common sense'. The latest trend in forward modeling is the shift from an overemphasis on accommodation to an overemphasis on sediment supply, to the point that all aspects of the stratigraphic architecture are explained by variations in sediment supply or even solely by autocyclicity. In reality, it is always a combination of accommodation and sedimentation, and both elements of this 'dual control' contribute in discernible ways to the architecture and makeup of the sequence stratigraphic framework. The methodology does not require an interpretation of the underlying controls on accommodation and sedimenta-tion, but only the observation of stratal stacking patterns and stratigraphic relationships that result from their interplay. Muddling the distinction between methodology and modeling leads to unnecessary confusion and a reversal of the progress made in the development of sequence stratigraphy as a data-driven methodology.

Marine and Petroleum Geology, 2020

Stratigraphic cyclicity in the deep-water setting reflects the interplay of accommodation and sed... more Stratigraphic cyclicity in the deep-water setting reflects the interplay of accommodation and sedimentation on the shelf, which controls shoreline trajectories, sediment supply to the shelf edge, and the timing of all elements of the sequence stratigraphic framework. Stratigraphic trends defined by changes in the types, volume, and composition of gravity flows during the shoreline transit cycles on the shelf provide the diagnostic criteria for the identification of deep-water systems tracts and bounding surfaces. Non-diagnostic variability in the sedi-mentological makeup of systems tracts reflects the unique tectonic and depositional settings of each sedimentary basin, and needs to be rationalized on a case-by-case basis. Contour currents may further modify the sedi-mentological makeup of deep-water sequences, but do not provide diagnostic elements for the definition of systems tracts and bounding surfaces. The application of sequence stratigraphy to the deep-water setting relies on the construction of composite profiles that illustrate the relative chronology of the different types of gravity-driven processes at regional scales. The cyclicity relevant to the definition of sequences is described by the composite rather than local profiles. The place of accumulation of depositional elements depends on the location of sediment entry points along the shelf edge, the types of gravity-driven processes, and the seafloor morphology. The allocyclic and/or autocyclic lateral shifts of deep-water depositional elements further enhance the offset between local trends and the regional composite profile in terms of timing and frequency of cycles, timing of coarsening-and fining-upward trends, and timing of the coarsest sediment. The sedimentological cycles defined by local trends must not be confused with the stratigraphic cycles defined by regional composite profiles.

Marine and Petroleum Geology, 2019

Stratigraphic cyclicity can be observed at different scales. At each scale of observation (i.e., ... more Stratigraphic cyclicity can be observed at different scales. At each scale of observation (i.e., hierarchical level), the building blocks of the sequence stratigraphic framework are represented by sequences and their component systems tracts and depositional systems. At the smallest stratigraphic scales, systems tracts and component depositional systems consist solely of sedimentological cycles (i.e., beds and bedsets). At any larger scales, systems tracts and depositional systems consist of lower rank stratigraphic cycles (i.e., sequences). The stacking pattern of sedimentological cycles defines the lowest rank systems tracts, which are the smallest stratigraphic units of a sequence stratigraphic framework. The scale of the lowest rank systems tracts at any location defines the highest stratigraphic resolution that can be achieved, and the limit between sedimentology and stratigraphy sensu stricto. The formation of depositional systems, and implicitly of systems tracts, requires typically minimum timescales of 10 2 yrs, and it may be sustained for as long as the defining environments are maintained as dominant sediment fairways. Within the transit area of a shoreline, where changes in depositional environment are most frequent, only the lowest rank depositional systems consist strictly of process-related facies accumulated in specific environments; these depositional systems sensu stricto develop commonly at scales below the resolution of seismic stratigraphy. At larger scales (higher hierarchical ranks), depositional systems sensu lato reflect dominant depositional trends, but may record higher frequency changes in depositional environment. The distinction between depositional systems sensu stricto and sensu lato becomes less meaningful outside of the shoreline transit area, where stratigraphic cyclicity may develop without changes in depositional environment. High-frequency sequences are commonly observed at scales of 10 0-10 1 m and 10 2-10 5 yrs, which defines the scope of high-resolution sequence stratigraphy. The stacking pattern of high-frequency sequences defines de-positional systems and systems tracts of higher hierarchical ranks in lower resolution studies.

A B S T R A C T Stratal stacking patterns provide the basis for the definition of all units and s... more A B S T R A C T Stratal stacking patterns provide the basis for the definition of all units and surfaces of sequence stratigraphy. The same types of stacking patterns may be observed at different scales, in relation to stratigraphic cycles of different magnitudes. At each scale of observation, stacking patterns define systems tracts, and changes in stacking pattern mark the position of sequence stratigraphic surfaces. The construction of a framework of systems tracts and bounding surfaces fulfills the practical purpose of sequence stratigraphy. Beyond this framework, model-dependent choices with respect to the selection of the 'sequence boundary' may be made as a function of the mappability of the various types of sequence stratigraphic surface within the studied section. Sequence stratigraphic frameworks are basin-specific in terms of timing and scales of the component units and bounding surfaces, reflecting the interplay of global and local controls on accommodation and sedi-mentation. A stratigraphic sequence corresponds to a cycle of change in stratal stacking patterns, defined by the recurrence of the same type of sequence stratigraphic surface in the rock record. Sequences, as well as component systems tracts and depositional systems, can be observed at all stratigraphic scales. Sequences of any scale may include unconformities of equal and/or lower hierarchical ranks, whose identification depends on the resolution of the data available. The relative ranking of sequences of different scales is defined by their strati-graphic relationships, as lower rank sequences are nested within higher rank systems tracts. Despite this nested architecture, the stratigraphic framework is not truly fractal because sequences of different scales may differ in terms of underlying controls and internal composition of systems tracts. A scale-independent approach to methodology and nomenclature is key to the standard application of sequence stratigraphy across the entire range of geological settings, stratigraphic scales, and types of data available.

A B S T R A C T Foreland systems on overriding plates (i.e., retroarc settings) form through the ... more A B S T R A C T Foreland systems on overriding plates (i.e., retroarc settings) form through the deflection of the lithosphere in response to a combination of supra-and sublithospheric loads. Supracrustal loading by orogens leads to the partitioning of foreland systems into foredeep, forebulge, and back-bulge flexural provinces. Thrusting in the orogenic belt results in foredeep subsidence and forebulge uplift, and the reverse occurs as orogenic load is removed by erosion or extension. This pattern generates out-of-phase ('reciprocal') stratigraphies across the flexural hingeline that separates the foredeep from the forebulge. Coupled with flexural tectonics, accommodation is also modified by dynamic (sublithospheric) loading. The latter mechanism operates at larger, continental scales, with rates controlled by the velocity and the angle of subduction. The interplay of accommodation and sediment supply during the lifespan of a foreland system controls the long-term shift from underfilled to overfilled accommodation conditions, which defines the first-order foreland cycle. Predictable shifts in the balance between flexural tectonics and dynamic loading during the evolution of a foreland system allow the subdivision of the first-order foreland cycle into early and late stages dominated by flexural tectonics, separated by an intermediate stage dominated by system-wide dynamic subsidence. The early stage is defined by an underfilled foredeep that hosts a deep-water environment, and an exposed forebulge whose progradation and erosion generates the 'forebulge unconformity' at the base of the first-order foreland sequence. Submergence of the forebulge during the intermediate stage establishes an interior seaway across the entire foreland system. The late stage marks a shift to a system-wide continental setting, which defines the overfilled phase of the foreland cycle.

High-frequency sequences composed of mixed siliciclastic-carbonate deposits may exhibit either ve... more High-frequency sequences composed of mixed siliciclastic-carbonate deposits may exhibit either vertical or horizontal changes between siliciclastics and carbonates. Vertical facies shifts occur between systems tracts and define a 'reciprocal sedimentation' pattern, typically consisting of transgressive/highstand carbonates and forced regressive/lowstand siliciclastics, although variations from this rule are common. Mixed systems with lateral facies change, usually typifying transgressive and/or highstand systems tracts, may exhibit proximal siliciclastics and distal carbonates or vice-versa, although variations may also occur along depositional strike. The marked variability of mixed siliciclastic-carbonate sequences makes the definition of a universal sequence stratigraphic model impossible, as the composition and geometries of systems tracts may change considerably, and sequence stratigraphic surfaces and facies contacts may vary in terms of occurrence and physical expression. However, some resemblance exists between sili-ciclastic sequences and mixed sequences showing lateral facies changes between siliciclastics and car-bonates. In particular, these mixed sequences display 1) a stratal architecture of the clastic part of the systems tracts that is comparable to that of siliciclastic deposits, 2) a dominant role of the inherited physiography and of erosional processes, rather than carbonate production, in shaping the shelf profile, and 3) a local lateral juxtaposition of siliciclastic sandstones and carbonate bioconstructions due to hydrodynamic processes. These observations are helpful in predicting the location of porous and potential sealing bodies and baffles to fluid flow at the intra-high-frequency sequence scale, and ultimately they are useful for both petroleum exploration and production.

The Kachchh sedimentary basin in the western continental margin of India is a peri-cratonic rift ... more The Kachchh sedimentary basin in the western continental margin of India is a peri-cratonic rift basin which preserves a nearly complete rock record from Middle Jurassic to Recent, punctuated by several stratigraphic breaks. The Cenozoic sediments exposed in the western part of the Kachchh mainland extend offshore into the present-day continental shelf. The unique feature of the outcropping area is a nearly complete, richly fossiliferous and easily accessible Cenozoic succession. Detailed field mapping and litho-biostratigraphic studies have made it possible to identify the chronostratigraphic units, map them in the field and extend the correlation into the offshore, aided by the development of continuously recognizable key biostratigraphic horizons and time boundaries. Detailed field mapping of key sections integrated with the litho-biostratigraphic information has helped in working out a sequence strati-graphic framework for the Cenozoic succession in the basin. The succession comprises a first-order passive margin sequence. Excellent biostratigraphic control has enabled identification of un-conformities of various magnitudes which in turn have helped in mapping 5 second-order and four third-order sequences. Each sequence is discussed with respect to its extent, nature of sequence boundaries, sedimentary fill, key sequence stratigraphic surfaces and depositional setup, to understand the Cenozoic sequence stratigraphic architecture of the basin.

High-frequency clastic shelf sequences deposited in high-latitude settings display marked differe... more High-frequency clastic shelf sequences deposited in high-latitude settings display marked differences, in term of facies and stratigraphic architecture, with respect to their lower latitude counterparts. This is due to the presence of ice which (1) leads to the accumulation of glacigenic and glacimarine deposits; (2) provides an additional control on accommodation; and (3) determines the position of the shoreline. Transgressions and regressions in glaciated settings are controlled respectively by the retreat and advance of the 'ice' shoreline (i.e., the water/ice contact) irrespective of relative sea-level changes; once the ice retreats across the land, the traditional 'land' shoreline is exposed and the control on sequence architecture is exerted by the interplay between relative sea-level changes and sediment supply as in low-and middle-latitude settings. A general model that includes both glacial and non-glacial climatic regimes is provided by this paper. In this frame, the classic sequence stratigraphic model represents one (ice-free) end member, which is opposed to an ice-permanent end member. Between these end members , sequences may accumulate in part under ice-free conditions and in part under conditions dominated by ice on the shelf. The main implication of this is that the classic sequence stratigraphic model may be viewed as only a possible scenario in the stratigraphic record rather than the rule.

High-frequency clastic shelf sequences contain porous deposits, consisting of coastal to shallow-... more High-frequency clastic shelf sequences contain porous deposits, consisting of coastal to shallow-water sandstones and conglomerates, which may represent very good reservoirs, and therefore critical targets for exploration and production, as well as for fluid (hydrocarbon, water or CO 2) storage. The study of these reservoirs, following a sequence stratigraphic approach, is essential to predict their features and distribution within systems tracts forming high-frequency sequences, which in turn compose higher-rank systems tracts and sequences. A critical aspect to improve the exploitability of the reservoirs is their heterogeneity, which directly affects the volume of the reservoirs and determine internal compartmentalization. The heterogeneity can be primary, related to depositional processes influencing grain size and facies distribution, and secondary, related to diagenesis. In particular, the primary het-erogeneity is referred to the facies variability from distal to proximal settings, to the accumulation of condensed shell beds, and to facies characteristics of bedsets, whereas the secondary heterogeneity derives from diagenetic processes at sequence stratigraphic surfaces and facies contacts, and within sandbodies. Both the distribution of reservoirs and their heterogeneity can be predicted following a high-resolution sequence stratigraphic approach. Ultimately, the integration of subsurface data with the analysis of outcrop analogs is essential to better understand the features of clastic shelf reservoirs and to develop 3D models of fluid migration.

Both allogenic and autogenic processes may contribute to the formation of sequence stratigraphic ... more Both allogenic and autogenic processes may contribute to the formation of sequence stratigraphic surfaces, particularly at the scale of fourth-order and lower rank cycles. This is the case with all surfaces that are associated with transgression, which include the maximum regressive surface, the transgressive ravinement surfaces and the maximum flooding surface, and, under particular circumstances, the subaerial unconformity as well. Not all autogenic processes play a role in the formation of sequence stratigraphic surfaces, but only those that can influence the direction of shoreline shift. Any changes in shoreline trajectory, whether autogenic or allogenic in origin, influence the stratal stacking patterns in the rock record which sequence stratigraphic interpretations are based upon. The discrimination between the allogenic and autogenic processes that may control changes in shoreline trajectory is a matter of interpretation and is tentative at best in many instances. For this reason, the definition and nomenclature of units and bounding surfaces need to be based on the observation of stratal features and stacking patterns rather than the interpretation of the controlling mechanisms. In this light, we extend the concept of 'sequence' to include all cycles bounded by recurring surfaces of sequence stratigraphic significance, irrespective of the origin of these surfaces. The updated sequence concept promotes a separation between the objective observation of field criteria and the subsequent interpretation of controlling parameters, and stresses that a sequence stratigraphic unit is defined by its bounding surfaces and not by its interpreted origin. The use of high-frequency sequences eliminates the need to employ the concepts of parasequence or small-scale cycle in high-resolution studies, and simplifies the sequence stratigraphic methodology and the nomenclature.

The sequence stratigraphic architecture includes a complex array of stratal geometries with diffe... more The sequence stratigraphic architecture includes a complex array of stratal geometries with different degrees of stratigraphic significance. The 'non-unique' variability of the sequence stratigraphic framework (i.e., stratal geometries which are not diagnostic for the definition of systems tracts and bounding surfaces) is irrelevant to the workflow of sequence stratigraphy. What is relevant is the observation of the 'unique' stratal geometries that are diagnostic for the definition of units and surfaces of sequence stra-tigraphy. In downstream-controlled settings, these unique stratal stacking patterns relate to the forced regressive, normal regressive, and transgressive shoreline trajectories. Multiple controls interact during the formation of each type of stacking pattern, including accommodation, sediment supply, and the energy of the sediment-transport agents. This interplay explains the non-unique variability, but does not change the unique criteria that afford a consistent application of sequence stratigraphy. The distinction between unique and non-unique stratal geometries is critical to the sequence stratigraphic methodology. Failure to rationalize the non-unique variability within the context of unique stratal geometries is counterproductive, and obscures the simple workflow of sequence stratigraphy. This is the case with uncalibrated numerical modeling, which may overemphasize non-unique or even unrealistic strati-graphic scenarios. While useful to test the possible controls on stratigraphic architecture, modeling requires validation with real data, and plays no role in the sequence stratigraphic methodology.

... Michael J. Pyrcz (mpyrcz@ualberta.ca) Department of Civil & Environmental Engineering Uni... more ... Michael J. Pyrcz (mpyrcz@ualberta.ca) Department of Civil & Environmental Engineering University of Alberta ... Pyrcz, MJ and CV Deutsch, 2003, Stochastic surface modeling in mud rich, fine-grained turbidite lobes: AAPG Annual Meeting, May 11-14, Salt Lake, Utah. Page 12. ...

Marine and Petroleum Geology, 2016

Principles of Sequence Stratigraphy - Second Edition, 2022

An up-to-date and comprehensive guide to the theory and practice of sequence stratigraphy KEY FEA... more An up-to-date and comprehensive guide to the theory and practice of sequence stratigraphy KEY FEATURES  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