Abstract Application of Modern Stratigraphic Techniques: Theory and Case Histories - Much has been written and debated about the various methodologies applied to modern stratigraphic analysis and the ever increasing complexity of terminologies. However, there exist numerous stratigraphic techniques that are reliant upon precise, quantitative, reproducible data, rather than qualitative interpretive stratigraphic methodologies. Such stratigraphic techniques are applied in an entirely pragmatic non-biased manner within the petroleum industry to provide enhanced stratigraphic understanding of petroleum systems. The petroleum industry is a key driver behind the development of new stratigraphic techniques and a major provider of new stratigraphic data, which has resulted in several of these new techniques having been developed as a requirement to the industry. Furthermore, because techniques, such as isotope chemostratigraphy, elemental chemostratigraphy, magnetic susceptibility stratigraphy, numerical biostratigraphy and heavy mineral stratigraphy are based around precise, quantified and reproducible analytical data, they provide an independent means to test the more interpretive stratigraphic methodologies. This volume attempts an overview of stratigraphic methodologies, but largely focuses on data-generative stratigraphic techniques such as chemostratigraphy, magnetic susceptibility stratigraphy, numerical biostratigraphy and heavy mineral stratigraphy. Where appropriate, each paper discusses data generation methods including sample preparation and analytical methods as well outlining data interpretation methods. This is followed by case histories that demonstrate how those data are used to resolve stratigraphic problems, commonly using material derived from petroleum basins around the World.

Abstract Since the mid 20 th century, numerous “sequence” methodologies (sequences, depositional sequences, genetic sequences, T–R sequences, plate sequences, and megasequences) have been proposed. Since all of these methodologies use distinctly different hiatal surfaces as unconformities, define depositional cyclicity in unique ways, and were initially designed to operate at different temporal and spatial scales, it is easy to understand why there is great confusion in the literature as to what actually constitutes an unconformity, a sequence boundary, or a sequence. The sequence stratigraphy family tree contains a robust portfolio of methodologies based on the concept of correlating unconformities and their correlative conformities. In this paper, an unconformity is simply defined as a regionally mappable surface that displays stratal terminations below and/or above. Thus, discordance between the underlying and overlying depositional fabrics or a subaerial hiatal origin is not a requirement. Angular unconformities are unconformities that display angular discordance between the underlying and overlying depositional fabrics, and are characterized by stratal terminations both below (structural truncation) and above (typically onlap). Nonconformities are unconformities underlain by igneous and metamorphic rocks and overlain by onlapping sedimentary strata. Disconformities are unconformities characterized by stratal terminations both below (toplap and stratigraphic truncation) and above (typically onlap) but display no angular discordance between the underlying and overlying depositional fabrics. Paraconformities are unconformities which display stratal terminations above (typically downlaps or distal marine onlaps) but no stratal terminations below. The depositional fabrics above and below a paraconformity are essentially concordant. Conformities are mappable surfaces which lack stratal terminations both above and below. In terms of hiatal type and the depositional cyclicity associated with the various types of unconformities and sequence methodologies, angular unconformities and disconformities represent subaerial hiatal breaks which bound regressive–transgressive (R–T) depositional cycles, while paraconformities represent submarine hiatal breaks which bound regressive– transgressive (R–T) depositional cycles. While depositional cyclicity and hiatal type are important factors for differentiating sequence methodologies, they are actually secondary factors within the family tree. It is the temporal and spatial scales of various sequence stratigraphic approaches which form the backbone for understanding and utilizing the sequence stratigraphy family tree. At the top of the family tree is the overall concept of unconformity-bounded depositional cycles. From this starting point three main sequence stratigraphic branches emanate: (1) methodologies which define the fundamental large-scale unconformity-bounded depositional cycles (sequences, plate sequences, and megasequences); (2) methodologies which define the basic small-scale unconformity-bounded depositional cycles (cyclothems, depositional sequences, and depositional episodes); and (3) methodologies that define mesoscale unconformity-bounded depositional cycles (genetic sequences and TR sequences). Thus the sequence stratigraphy family tree offers a robust portfolio of unconformity-bounded methodologies for subdividing the stratigraphic record into surface-bounded stratigraphic units. The correct sequence approach, in terms of which methodology to utilize, is dependent primarily on the temporal and spatial scale of the interval and area under investigation. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 5–33.

Abstract: Sequence stratigraphy is based, for the most part, on the recognition and correlation of a variety of stratigraphic surfaces that collectively can be characterized as representing changes in depositional trend. Five such surfaces, which are material-based and potentially of regional extent, have been defined and are called a subaerial unconformity, a regressive surface of marine erosion, a shoreline ravinement, a maximum regressive surface, and a maximum flooding surface. Each of these surfaces has one or more specific relationships to time, including being in part, or entirely, an approximate time barrier, a low diachronous surface, or a highly diachronous one. The sequence stratigraphic surfaces that are useful for the construction of a regional correlation framework are: subaerial unconformity (approximate time barrier), unconformable shoreline ravinement (approximate time barrier), maximum regressive surface (low diachroneity), and maximum flooding surface (low diachroneity). All of these surfaces are available for use in correlation in shallow marine clastic successions that include intercalations of nonmarine to brackish marine strata. In nonmarine strata subaerial unconformities and maximum flooding surfaces are usually present, with maximum regressive surfaces being much less common. All of these surfaces can be hard to identify with confidence in successions of fluvial strata. In slope and basin settings maximum regressive and maximum flooding surfaces are the only regional sequence stratigraphic surfaces present. These can be delineated mainly by changes in grain-size trends, although their recognition in many instances is either very difficult or equivocal. Correlation throughout a basin can often be accomplished by tracing individual maximum flooding surfaces from deep marine settings, up the slope, across the shelf, and into the coastal-plain setting. In many cases, basin-flank unconformities consist of a combination of a subaerial unconformity and an unconformable shoreline ravinement (SR-U). The basinward termination of the shoreline ravinement adjoins the landward termination of the maximum regressive surface (MRS), and this relationship can facilitate correlation between the basin flank and the basin center. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 35–53.

Abstract Biostratigraphy has been an integral part of hydrocarbon exploration for much of the last century. The basic concepts and methods of using fossils to characterize coeval strata remain unchanged from the pioneer studies of the late 18 th century. This paper describes major developments in biostratigraphic techniques that have occurred during the last twenty years. Advances in deep-water drilling and exploitation technology have promoted a shift from deltaic and shelf reservoirs to slope and basin-floor-fan reservoir targets. This has resulted in a greater emphasis on open marine, planktonic fossils, such as nannofossils and planktonic foraminifera, and lesser emphasis on terrestrial and shallow-water fossils such as benthic foraminifera, pollen, and spores. The development of deviated and horizontal production wells has stimulated the need to monitor the path of wells in real time at the wellsite. The resulting “biosteering” is the quantitative bed-by-bed study of a vertical pilot well, and the subsequent monitoring of the fossil content of the horizontal well, which enables the drill path to stay in the target strata. The Ocean Drilling Program and its predecessor the Deep Sea Drilling Project led to the construction of more refined geologic time scales that integrate biostratigraphy with magnetostratigraphy, isotope stratigraphy, and astronomical cycles. These time scales allow the allocation of numeric ages to increasing amounts of biostratigraphic datums, which aids in the automation of correlation using computers. The concepts and methods of sequence stratigraphy refined in the last twenty years placed biostratigraphy at the heart of geological models, closely integrating it with well-log and seismic stratigraphy. The concepts of sequence stratigraphy stimulated further biostratigraphic research and changed the way biostratigraphic data are used in correlations. Computational power has made it possible to rapidly record, manipulate, and display biostratigraphic data. This has led to the development of programs that automate the process of correlation, paleobathymetric interpretation, construction of expert systems for the identification of fossils, and compilation of databases of text and digital images. These advances have led to more information being extracted from the raw biostratigraphic data. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 57–80.

Abstract Stratigraphic data and interpretations are often presented in written text format with accompanying data charts, stratigraphic summary logs, and well correlations, and as a result only basic stratigraphic information tends to be utilized by geophysicists. In the present-day environment there is a need to streamline data presentation to add value to sequence stratigraphic interpretations by full integration of all stratigraphic and environmental data with the seismic. Stratigraphy to Seismic (StS™) is a technique, developed by FRL, and is a means of providing stratigraphic interpretations in a digital format for integration with seismic data. The interpretations are displayed as a suite of curves which are loaded into seismic software packages for posting on seismic sections. By accessing this information, any interpreter, regardless of scientific background, can distinguish seismic features that are attributable to stratigraphic events or features. In this paper we present the methodologies of the technique and show the application through specific examples from Brazil, North Africa, and East Africa. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 81–90.

Abstract Changes in the bulk inorganic geochemical composition of both sandstones and silty mudstones taken from conventional cores are used to subdivide the Lower Cretaceous Mannville Group and the overlying Colorado Group into chemostratigraphic packages and geochemical units. The chemostratigraphic packages are broadly equivalent to lithostratigraphic formations whereas the geochemical units are represent finer-scale informal stratigraphic subdivisions that occur within the formations. The chemostratigraphic packages are equivalent to the Lower Mannville Formation, the Upper Mannville Formation, the Basal Colorado Sandstone (an informal unit at the base of the Colorado Group), and the overlying Joli Fou Formation. The changes, which enable each lithostratigraphic unit, or chemostratigraphic package, to be geochemically fingerprinted, are primarily related to changes in mineralogy, which in turn appear to coincide with changes in sediment provenance and basin architecture. These chemostratigraphic packages, which are broadly equivalent to lithostratigraphic formations, can be considered to result from first-order changes in whole-rock geochemistry. The geochemical units are equivalent to incised-valley-fill sequences within the lithostratigraphic units, and here it is shown that the incised-valley-fill sequences of the Upper Mannville and Basal Colorado Sandstone each have a unique geochemical signature. Three incised-valley-fill sequences are present in the latter intervals, the oldest of which lie within the Upper Mannville Formation. Valleys at the base of the Basal Colorado Sandstone incise Upper Mannville deposits and are termed the lower Basal Colorado sandstones. The youngest valleys lie at the top of the Basal Colorado Sandstone and are termed the upper Basal Colorado sandstones. The sedimentary deposits in each of these incised valleys can be chemically distinguished from one another, even where a sandstone-on-sandstone contact is present in a single wellbore. The geochemical changes that enable each incised-valley fill to be recognized can be considered as second-order variations and are referred to as geochemical units. Stacked valleys observed in the Lower Mannville Formation have been the subject of previous chemostratigraphic work, and all of these have a unique geochemical signature and are also considered here to be geochemical units. The base of each incised-valley-fill succession, or geochemical unit, is a sequence boundary. By enabling clear identification of the geochemical unit above and below a sequence boundary, the technique of chemostratigraphy has direct application to aiding both lithostratigraphic and sequence stratigraphic correlations in low-accommodation basin settings. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 93–107.

Abstract Important gas reservoirs occur in the Upper Carboniferous coal measures and red beds of the Southern North Sea. The thick red beds of the Boulton and Ketch formations are difficult to correlate, due to poor internal seismic definition, repetitive e-log signatures, and their barren nature. Although the underlying coal measures of the Westoe, Cleaver, and Caister Formations have better seismic resolution and contain palynomorphs, coals that die out laterally and the lack of diagnostic taxa over certain intervals contribute to their correlation being problematical. However, the application of chemostratigraphy to more than sixty wells from numerous fields in UK Quadrants 44 and 49, as well as from Dutch sector Blocks E, F, and K, allows the establishment of an independent, robust, detailed correlation framework for the aforesaid red beds and coal measures. Presented in this paper are correlative chemostratigraphic reference sections for the Caister, Westoe, Cleaver, Ketch, Boulton, and Step Graben formations. The chemostratigraphic zonations erected for these formations are based on variations in silty claystone geochemistry that can be tied to changes in provenance, climate, and depositional environment. In addition, the zonations are supported by stratigraphic changes in sandstone and coal geochemistry, the geochemical correlation of tonsteins and marine bands, and the recognition of different types of paleosol in the above formations. The chemostratigraphic correlation framework enables specific broad intervals (“packages”) to be correlated between fields and is also used to constrain seismic correlations with a view to highlighting potential exploration targets. Furthermore, the same framework allows much thinner intervals (“units” and “subunits”) to be correlated within fields: these smaller-scale correlations enhance reservoir correlations with respect to the development of fields such as Boulton, Schooner, Tyne, Ketch, and Topaz. In addition to using inorganic geochemical data to characterize and correlate sedimentological packages, data can also used to identify and correlate marker horizons and surfaces (tonsteins, coals, marine bands, major paleosols), which may be highly correlative low-diachrony surfaces, which greatly enhance the overall validity of the stratigraphic correlation scheme. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 109–127.

Abstract This article outlines the history, theory, and application of Sr-isotope stratigraphy, and provides an outline of some recent uses of the method that may be of interest to readers. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 129–142.

Abstract The Strathclyde and Clackmannan Groups comprise the Lower Carboniferous successions exposed in the eastern Midland Valley of Scotland (MVS) and adjacent areas of northern England. They form a thick succession (2–3 km in thickness) of similar-appearing shallow-marine to shoreline and fluvial–deltaic sandstones and shales punctuated by thin (typically < 1–2 m thick) shallow-marine carbonate rocks. This study obtained stable-isotope data on the carbonate units in order to assess the utility of C isotopes as an independent means of testing and refining stratigraphic correlations. The δ 13 C carbonate data: (1) corroborate most of the lithostratigraphic correlations determined previously using other stratigraphic methodologies; (2) diagnose miscorrelations based on markedly different C-isotope profiles exhibited by carbonate units originally thought to be correlative; and (3) help discern patterns of varying rates of sediment flux and accommodation-space genesis across the eastern MVS basin. These results prove the utility of C-isotope profiles in helping construct and evaluate the stratigraphic framework of a sedimentary basin and highlight their usefulness as a tool that could be applied relatively quickly and inexpensively in areas of lesser-known geology and when time and financial investment are at a premium. The data also show that the Strathclyde Group has mostly negative C-isotope values (ca. -1 to -5‰) that shift abruptly to consistently positive values (0 to 2‰) at the contact with and into the overlying Clackmannan Group. Radiometric ages on volcanic rocks in the MVS constrain the negative interval to between ca. 343–335 Ma and that the shift to positive values occurred close to ca. 335 Ma. This trend coincides with a decline and recovery in δ 13 C trends documented in Visean rocks elsewhere and likely records a widespread (global?) shift in the isotopic composition of Early Carboniferous oceans. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 143–151.

Abstract Magnetic susceptibility (MS) measurements of marine rocks provide an underutilized but powerful high-resolution tool in stratigraphy. In ideal circumstances and when combined with other stratigraphic techniques, the method can yield resolution to 10,000 years or less. This paper applies the MS method to solving a Cretaceous global correlation problem. Because of the active global processes that drove significant evolutionary changes during this time, the Upper Cretaceous is important in Earth history. However, correlations among geological sequences are difficult, in part because Earth’s magnetic polarity was essentially non-varying from the Aptian to the Santonian. Here we present high-resolution correlations for Upper Cretaceous marine sedimentary successions spanning all or part of the Santonian Stage from the Western Interior Seaway (U.S.A.) and the Western Sinai Peninsula (Egypt). To do this we have integrated the results of magnetic susceptibility (MS) measurements of unoriented samples from lithified marine rocks (in outcrop and from core) and biostratigraphic data sets from these sequences. In this study a MS zonation for the Santonian Stage has been developed and graphic comparison has been used for correlation. In the main, correlation between the U.S. and Egyptian sequences is excellent. Third order T/ R cycles (> 100 kyr) observed in this high-resolution data set for the Santonian Stage indicate significant similarities between the U.S. and Egyptian sections and allow correlation among sequences. We interpret these correlations to result from cyclicities caused by climate-controlled continental erosion and deposition of detrital components, mainly clay, in the marine realm. Second-order cycles (> 1 Myr) are also observed in these data sets but show distinctive differences between the U.S. and Egyptian sequences. We interpret these second-order differences to result from local synsedimentary tectonic controls on sediment erosion and deposition. Also observed are two distinct, short-term MS marker events that can be correlated globally. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 155–166.

Abstract The magnetostratigraphy susceptibility technique is used to establish high-resolution correlation among Paleocene–Eocene boundary sequences in Egypt, Spain, and the U.S.A. This work initially focuses on the Global boundary Stratotype Section and Point (GSSP), defining the base of the Ypresian Stage (lowest Eocene), located in the Dababiya Quarry near Luxor in Upper Egypt. The base of the Eocene represents the beginning of the Paleocene–Eocene Thermal Maximum (PETM) identified by a negative carbon isotope (δ 13 C) excursion. While onset of the CIE is somewhat gradual in most reported Paleocene–Eocene (P–E) sections, at the GSSP it is very abrupt and begins immediately after an unusual lithologic change that magnetic susceptibility (MS) and other data indicate represents a short erosional or nondepositional hiatus. Comparison of MS zones from five well-studied marine sequences (the Dababiya Quarry GSSP, Jebal El Qreiya, also in Upper Egypt, Zumaia in northern Spain, Alamedilla in southern Spain, and the MGS-1 Harrell Core from southeastern Mississippi, U.S.A.) with that from the GSSP site shows a period of reduced sedimentation and nondeposition through the boundary interval in the GSSP. This interval, estimated to have lasted for ~ 10,000 years, is less than the biostratigraphic resolution for the site. Due to the hiatus in the GSSP, we have chosen the P–E section in Zumaia as the MS reference section for the P–E boundary interval. Because the correlation between the Zumaia section in Spain and the MGS-1 Core from the U.S.A. is excellent, and because the MGS-1 data set represents a longer interval of time than does the Zumaia data set, we use the MS data from the MGS-1 Core to extend the MS zones from Zumaia and establish a MS composite reference section (MS CRS) for the P–E boundary interval sampled. Orbital-forcing frequencies for the Zumaia reference section are then identified, via spectral analysis. Extending the MS zones into the MS CRS allows age assignment to MS zones for all five sections with a resolution of ~ 26,000 years. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 167–179.

Abstract The Devonian–Carboniferous Clair Group reservoir succession in the Clair Field, located west of Shetland on the UK continental shelf, comprises over 1000 m of clastic sediment deposited in a range of fluvial, lacustrine, and eolian environments. Owing to the unfavorable depositional conditions, palynomorphs and microfossils are almost entirely absent, precluding development of a high-resolution biostratigraphic framework for reservoir correlation. An alternative approach to reservoir subdivision and correlation is therefore necessary in order to establish a viable reservoir model prior to field development. Heavy-mineral analysis, which subdivides clastic successions on the basis of changes in provenance and sediment transport history, has proved successful in establishing a high-resolution correlation framework for the Clair Field. This paper concentrates on the heavy-mineral stratigraphy of the Lower Clair Group, which is the target for the first phase of the field development. The key parameters that have been used to erect the correlation framework are provenance-sensitive ratios of heavy minerals (notably garnet:zircon, rutile:zircon, and apatite:tourmaline), grain morphology (apatite roundness), and mineral chemistry (garnet composition). The Lower Clair–Upper Clair boundary is a major heavy-mineral event related to a fundamental change in provenance. Six major units (I–VI) and a number of subunits have been recognized within the Lower Clair Group, boundaries being related to more subtle changes in provenance and sediment transport history. The successful application of integrated heavy-mineral analysis in the Clair Field demonstrates that the method can be reliably applied to correlation of clastic hydrocarbon reservoirs. The technique is successful because it generates data that are independent of factors such as hydrodynamics and diagenesis, and therefore directly reflect correlatable geological events such as changes in provenance, sediment transport history, and climate. Furthermore, the method can be used on the full range of geological samples acquired during hydrocarbon exploration, since data are acquired from the constituent components of the sample rather than from the bulk sample, thereby enabling contamination from drilling additives and caving to be filtered out. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 183–199.

Abstract Terrestrial sediments are difficult to correlate because they are laterally variable and generally lack easily identifiable chronostratigraphic surfaces. However, we have been able to identify systematic variations in petrographic properties of paralic coal that respond to changes in accommodation. These properties enable us to distinguish two types of paralic peat cycle (transgressive and regressive) characterized by wetting-upward and drying-upward behavior linked to variations in the groundwater table. They also enable recognition of a range of terrestrial stratigraphic surfaces that record responses to changing accommodation, including accommodation reversal surfaces, flooding surfaces, hiatal surfaces, paludification surfaces, and terrestrialization surfaces. A combination of these coal parameters, together with the facies characteristics of the surrounding terrestrial and marginal marine sediments, enables recognition of distinctive high-resolution sequence stratigraphic signatures. This in turn provides a previously unavailable ability to correlate stratigraphic units from their down-slope marine position, through the shoreline zone, and into the terrestrial realm. Results show that earlier concepts of parasequences in marine sediments need to be significantly modified in the terrestrial realm. Sharp hiatal parasequence boundaries in the marine realm such as flooding surfaces and wave or tidal ravinement surfaces may correlate up-slope to packages of sediments that pass gradationally from transgressive to regressive units and preserve the transitions between the two. Terrestrial sediments may accumulate during and following shoreline regression, and prior to and during shoreline transgression. The exact style and preservation of the terrestrial stratigraphic package depends on the local balance between accommodation and sediment flux at the time of deposition. Coals occur in both regressive and transgressive styles and may initiate or terminate parasequences. Coals may also occur as compound coals that span more than one parasequence and contain internal discontinuity surfaces. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 201–219.

Abstract Laterally extensive, thin, eustatically controlled, transgressive marine shale beds that occur within paralic sequences are generally regarded as reliable correlative markers. Such shale beds in the Carboniferous of NW Europe are referred to as marine bands and have been used extensively for stratigraphic correlations, particularly in the petroleum industry, where they are used to construct interwell correlations. True marine bands are represented by black anoxic shales (characterized by high U levels and high gamma API responses) that contain definitive ammonoid assemblages, i.e., demonstrably were deposited in a marine environment. However, not all black shales in the Carboniferous of NW Europe are the product of marine deposition, despite which they are still colloquially referred to as “marine bands” and are used for stratigraphic correlations. The problem of “marine band” recognition and correlation is exacerbated when dealing with well bores, where only wireline-log data and cuttings are available. This study demonstrates how inorganic geochemical data are used as a means to refine the identification of true marine bands and how these data can be used for enhanced stratigraphic correlations. “Marine-band chemostratigraphy” is established using core sections from the onshore Carboniferous Coal Measures sequences encountered in the West Midlands of England. Using variations in U, Mo, Zn, Cu, V, P 2 O 5 , Al 2 O 3 , Th, and Zr concentrations, a geochemically based facies classification scheme is erected, which allows the differentiation of mudstones deposited in marine, freshwater lacustrine, and floodplain environments, and which has been validated by palynological and sedimentological facies data. This scheme is successfully extended to a nearby well from which only cuttings are available. The general concept of marine-band chemostratigraphy can be applied to the sedimentary rocks deposited in any coastal-plain to marginal-marine setting. The methodology provides a robust technique for the identification and correlation of “marine bands” and also demonstrates the importance of inorganic geochemical data in the context of sequence stratigraphy. Application of Modern Stratigraphic Techniques: Theory and Case Histories SEPM Special Publication No. 94, Copyright © 2010 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 221–238.

Abstract Modern estuaries and incised valleys are important depositional settings that have widespread significance for human land use. The deposits of these environments are economically important for hydrocarbon exploration and production. Estuaries and incised valleys are a complex and possibly unique environmental grouping, inasmuch as they represent creation of depositional space by one process (mainly fluvial erosion) and fill of that space by a range of other processes (fluvial, estuarine, and marine deposition). Early investigations of valleys began slowly in Greek and Roman times, but increased in the nineteenth century, when they were used to develop ideas on the age of the earth in uniformitarian debates. Gradual progress was made throughout the nineteenth and twentieth centuries with the introduction of ideas on river grade, fluvial equilibrium profiles, and base level, followed by the development of fluvial facies models in the 1960s. Studies on estuaries began in earnest much later than those on valleys, and major advances were not made until the mid-twentieth century, with development of the first comprehensive facies model in the 1990s. Research on estuaries and incised valleys was energized in the 1980s by the concept of sequence stratigraphy, and work in the field has mushroomed since then. Indeed, the currently used facies models for estuaries and incised valleys were among the first to explicitly take into account the external control on the creation of accommodation and to be presented in a sequence-stratigraphic framework. In line with other sedimentary environments, the facies models for estuary and incised-valley environments have also proliferated, leading to the need for fundamental advances in how facies models are conceived. Estuaries, as defined geologically here, are transgressive in nature. They receive sediment from both fluvial and marine sources, commonly occupy the seaward portion of a drowned valley, contain facies influenced by tide, wave, and fluvial processes, and are considered to extend from the landward limit of tidal facies at their heads to the seaward limit of coastal facies at their mouths. Estuaries can be divided, on the basis of the relative power of wave and tidal processes, into two main types, wave-dominated estuaries and tide-dominated estuaries. Estuarine facies models exhibit generally retrogradational stacking of facies and a tripartite zonation reflecting the interaction of marine and fluvial processes. All estuaries and incised valleys have a fluvial input by definition, but estuarine facies models reflect the balance between wave and tidal processes. Valleys form because the transport capacity of a river exceeds its sediment supply. An incised-valley system is defined as a fluvially eroded, elongate topographic low that is characteristically larger than a single channel, and is marked by an abrupt seaward shift of depositional facies across a regionally mappable sequence boundary at its base. The fill typically begins to accumulate during the next baselevel rise, and it may contain deposits of the following highstand and subsequent sea-level cycles if the accommodation is not filled during the first sea-level cycle. Incised valleys may be formed by either a piedmont or a coastal-plain river and can exhibit a simple or compound fill. The erosion that creates many incised valleys is thought to be linked to relative sea-level fall, although climatically produced changes in discharge and/or sediment supply may independently cause incision, even in areas far removed from the coast. In the case of valleys in coastal areas, fluvial deposition typically begins at the mouth of the incised-valley system when sea level is at its lowest point and expands progressively farther up the valley as the transgression proceeds, producing depositional onlap in the valley. Based on the longitudinal distribution of broad depositional environments, the length of an incised valley can be divided into three segments. Ideally, the fill of the seaward portion of the incised-valley (segment 1) is characterized by backstepping (lowstand to transgressive) fluvial and estuarine deposits, overlain by transgressive marine deposits. The middle reach of the incised valley (segment 2) consists of the drowned-valley estuarine complex that existed at the time of maximum transgression, overlying a lowstand to transgressive succession of fluvial and estuarine deposits similar to those present in segment 1. The innermost reach of the incised valley (segment 3) is developed headward of the transgressive estuarine-marine limit and extends to the point where relative sea-level changes no longer controlled fluvial style (i.e., to the landward limit of sea-level-controlled incision). This segment contains only fluvial deposits; however, the fluvial style changes systematically due to changes in the rate of change of base level. The effect of base-level change decreases inland until eventually climatic, tectonic, and sediment-supply factors become the dominant controls on the fluvial system. In valleys far removed from the sea, the fill consists entirely of terrestrial deposits, but shows changes in fluvial style that are similar to those in segment 3, even though the stacking patterns are controlled more by local tectonics and climate. Recent and future development of estuarine and incised-valley facies models has emphasized the use of ichnology to recognize brackish-water deposits and the ability to subdivide compound valley fills on the basis of sediment composition. Imaging the valley and its fill has been greatly improved with 3D and 4D seismic techniques. Seabed mapping of modern estuaries has enabled detailed distributions of facies and morphology to be compiled, enhancing the ability to predict these features in ancient rocks. Our current set of facies models represents the early classification stage in the development of depositional models. The appropriate way forward appears to be a transformation from qualitative approaches to empirical and quantitative computer-based models with predictive capability, based on a thorough understanding of the dominant processes operating in each environment.

Abstract The Viking Formation of the Joffre Field area comprises parts of three discrete sequences. The reservoir facies lies within the lower part of Sequence 3, interpreted to reflect shoreline-attached, marginal marine deposits. Sequence 3 was initiated by a fall of relative sea level with associated subaerial exposure and erosional scour, generating a sequence boundary. This sequence boundary was erosionally modified by ravinement during the ensuing transgression, to form a broad NW-SE trending asymmetric incision at Joffre, referred to as basal discontinuity 2 (BD-2). BD-2 is mantled by conglomeratic lags and biorurbated, glauconitic transgressive sand sheets (Facies A). These are overlain by moderately burrowed, trough and low angle planar cross-stratified sandstone, pebbly sandstone and conglomerate, concentrated along the southern (landward) margin of BD-2, and interpreted to reflect distributary channels (Facies B/C/D). These channels fed sediment to prograding bay-head delta fronts, which coalesced to form broad, NW-SE trending coarse clastic aprons (Facies B/C/D and F). Each bay-head delta apron progressively interfingers with, and ultimately passes into weakly burrowed interbedded sandstone and mudstone (Facies E). These fine-grained deposits contain oscillation ripples, storm-generated wavy parallel laminations, and low diversity trace fossil suites, and are interpreted as brackish-water bay deposits. Fluctuations in the rate of transgression resulted in the shifting of brackish-water bay deposits over channel/bay-head delta complexes, delineating three discrete marginal marine parasequences. Each parasequence trends northwest-southeast, onlaps relief on BD-2 along its landward (southwestern) margin, and offlaps/downlaps to the northeast. Resumed regional transgression generated a flooding surface (FS) with associated ravinement, that terminated brackish-water deposition and returned the study area to fully marine, offshore conditions.

Abstract The study of unconformities has a long and distinguished history, and incised valleys have been recognized for more than 70 years. Early descriptions of incised-valley deposits lacked detail, with fluvial and deltaic interpretations predominating. Estuarine deposits were largely unrecognised until advances in our understanding of estuarine sedimentation permitted more sophisticated treatment of the fluvial-marine transition. Interest in incised-valley systems has increased dramatically in the last decade due to widespread application of sequence-stratigraphic concepts. Following standard definitions, we urge that the term "incised valley" be restricted to fluvially eroded features that are larger than a single channel. A loss of accommodation space and the resulting formation of incised valleys may occur in response to factors unrelated to changes in relative sea level; however, all but one of the examples described in the volume are believed to be associated with a drop of relative sea level. Thus, the model proposed by Zaitlin and others (this volume) for this type of incised-valley system is used to group the papers according to which portion of an incised-valley system the deposits represent: segment 1 —the portion between the mouth of the valley and the initial highstand shoreline, which is transgressed and overlain by marine deposits; segment 2 —the region occupied by the drowned-valley estuary at the time of maximum transgression; and segment 3 —the incised valley landward of the limit of marine/estuarine facies, which contains and is overlain exclusively by fluvial deposits. Each segment displays a predictable succession of environments and stratigraphic surfaces, but differences exist between the examples due to the poorly understood influence of such factors as the rate of sediment input and the magnitude and duration of the relative sea-level fall and rise.