Sequence Stratigraphic Principles Research Articles

Implications of Timanian thrust systems in the Barents Sea and Svalbard on using paleontological constraints for plate tectonics reconstructions.

The Svalbard Archipelago is commonly believed to have been located at comparable latitude and, possibly, to have been attached to Laurentia in the early Paleozoic (500-420 Ma) based on trilobite assemblage similarities. Trilobite assemblage differences and lack of mixing between Laurentia-Svalbard and Baltica were further used to propose that these continents were separated by the Iapetus Ocean at that time. However, recent structural correlation of Timanian (650-550 Ma) thrust systems throughout the Barents Sea show that Svalbard was already attached to Baltica in the latest Neoproterozoic and remained so during the Phanerozoic. The present study presents a new interpretation of seismic reflection data from the DISKOS database, which were tied to nearby exploration wells. The study uses recently acquired knowledge of the seismic facies of intensely deformed pre-Caledonian rocks and principles of sequence stratigraphy to interpret the data. The present study reconciles the proximity of Svalbard and Laurentia with the early accretion of Svalbard to Baltica in the latest Neoproterozoic. It also describes the influence of Timanian thrust systems on paleoenvironments and possible effects on trilobite assemblages, e.g., the lack of mixing between those of Laurentia-Svalbard and Baltica. The results suggest that paleontological constraints are robust markers to discuss continent amalgamation but should be considered with greater care when discussing continent separation since other factors, such as major thrust systems, may create major, linear, topographical boundaries, which may act as major faunal barriers within a single tectonic plate. Other factors to consider include paleoclimatic belts.

Sequence stratigraphic model as a modern tool for seismic data interpretation

The sequence stratigraphic models for the clinoform part of the section in the territory studied by production drilling within the Nadym-Pur oil and gas region of Western Siberia are constructed. The purpose of study was to identify patterns in the distribution of reservoir properties of the Achimov objects and substantiate a systematic approach to the correlation of reflecting horizons. The main task is to identify the characteristic features of systemic tracts based on core data from a well-studied field. To solve the problem, a classification of sediments studied by core in wells was carried out within the framework of a sequence model. To confirm theoretical concepts about the formation of improved reservoir zones in system tracts, an analysis of filtration and capacitance parameters (porosity, permeability) was performed. There is the relationship between the reservoir properties and the type of system tract in which the deposits were formed. The seismic section requires the interpretation according to the principles of sequence stratigraphy, and criteria for tracing reflecting horizons. An algorithm for constructing a model is proposed that provides a forecast of zones with improved reservoir properties. A number of advantages for the unsystematic approach to correlating reflecting horizons are given.

An integrated sequence stratigraphic analysis of the early Marsdenian substage of the Millstone Grit Group, Central Pennines, UK

The early Marsdenian substage (Millstone Grit Group) of the Pennines comprises repeated deltaic cycles separated by ammonoid-bearing marine bands. This cyclicity, controlled by the combined forces of glacio-eustasy and modulations in sediment supply, provides an important outcrop area for the application of sequence stratigraphic principles. A new correlation framework is presented where two orders of sequence are identified: (1) a low-order sequence, within which marine bands (R 2a 1, R 2b 1, R 2b 2 and R 2b 3) represent a maximum flooding surface, and (2) high-order sequences nested within the low-order sequences. By integrating and correlating key exposures, historic well boreholes and field mapping, lateral changes in facies and facies association are observed, and palaeogeographic trends mapped. This allows the variation in sequence and systems tract stacking patterns to be interpreted. Three orders of Milankovitch cyclicity are inferred to control the sequence stacking patterns; long-duration ( c. 400 ka) eccentricity oscillation controlling maximum flooding events represented by the R 2a 1 and R 2b 2 marine bands, sub-100 ka obliquity oscillations (controlling the R 2b 1, R 2b 2 and R 2b 3 marine bands and intervening low-order sequence boundaries), and precessional frequencies ( c. 25 ka) which may control the periodicity of the high-order sequences. Supplementary material: Locality details, including lithostratigraphic units observed, gross and sand thicknesses within sequences, and palaeocurrent data measured are available at https://doi.org/10.6084/m9.figshare.c.6408203

Olduvai's oldest Oldowan

Previously, Olduvai Bed I excavations revealed Oldowan assemblages <1.85 Ma, mainly in the eastern gorge. New western gorge excavations locate a much older ∼2.0 Ma assemblage between the Coarse Feldspar Crystal Tuff (∼2.015 Ma) and Tuff IA (∼1.98 Ma) of Lower Bed I, predating the oldest eastern gorge DK assemblage below Tuff IB by ∼150 kyr. We characterize this newly discovered fossil and artifact assemblage, adding information on landscape and hominin resource use during the ∼2.3–2.0 Ma period, scarce in Oldowan sites. Assemblage lithics and bones, lithofacies boundaries, and phytolith samples were surveyed and mapped. Sedimentological facies analysis, tephrostratigraphic and sequence stratigraphic principles were applied to reconstruct paleoenvironments and sedimentary processes of sandy claystone (lake), sandstone (fluvial), and sandy diamictite (debris flow) as principal lithofacies. Artifacts, sized, weighed, categorized, were examined for petrography, retouch, and flake scar size. Taxonomic classifications and taphonomic descriptions of faunal remains were made, and phytoliths were categorized based on reference collections. Lithics are dominantly quartzite, mainly debitage and less frequently simple cores, retouched pieces, and percussors. Well-rounded spheroids and retouched flakes are rare. Identifiable taxa, Ceratotherium cf. simum (white rhinoceros) and Equus cf. oldowayensis (extinct zebra), accord with nearby open savanna grasslands, inferred from C3 grass, mixed and/or alternating with C4 grass-dominated phytolith assemblages. Palms, sedges, and dicots were also identified from phytoliths. Diatoms and sponge spicules imply nearby freshwater. The assemblage accumulated at the toe of a Ngorongoro Volcano-sourced fan-delta apron of stacked debris flows, fluvials, and tuffs, preserving fossil tree stumps and wooded grassland phytoliths farther upfan. It formed after the climax of Ngorongoro volcanic activity during a Paleolake Olduvai lowstand and was then buried and preserved by lacustrine clays, marking the first of two lake transgressions, signifying wetter climates. Orbital precessional lake cycles were superposed upon multimillennial (∼4.9 kyr) lake fluctuations.

Sedimentary evolution of the Neogene-Quaternary Crotone Basin (southern Italy) and relationships with large-scale tectonics: A sequence stratigraphic approach

Abstract The Crotone Basin is a Neogene-Quaternary depocenter developed along the Ionian margin of Calabria, southern Italy. The basin opening was concomitant with the onset of spreading of the Tyrrhenian backarc Basin during late Serravallian and the subduction of the Ionian lithosphere below the Calabrian Arc. The adoption of modern sequence stratigraphic principles to subdivide the basin fill into stratigraphic sequences of different rank, bounded by subaerial unconformities, has allowed cycles of creation and loss of accommodation mainly related to tectonics to be recognized. In particular, an alternation between phases of basin subsidence, concomitant with spreading of the Tyrrhenian backarc Basin and forward migration of the Arc, and phases of compressional or transpressional tectonics, accompanied by basin uplift and stopping of Arc migration, are well recognizable in the basin fill, in particular for the late Messinian to late Pleistocene part of the succession. The present study highlights the effectiveness of the sequence stratigraphic method in basin analysis to decipher the effects of large-scale tectonic events on sedimentation and ultimately to reconstruct the geodynamic evolution of the central Mediterranean.

SISMOESTRATIGRAFIA CORRELATIVA ENTRE AS BACIAS DE TUCANO SUL E RECÔNCAVOo

A estratigrafia de sequências, aplicada a bacias do tipo rifte, consiste em uma adaptação do modelo clássico que se encontra em plena fase de consolidação. Os fundamentos norteadores da estratigrafia de sequências se aplicam em qualquer contexto de sedimentação e são fundamentais para entender a história deposicional de uma bacia. O presente trabalho teve como objetivo estudar o arcabouço sismoestratigráfico de Tucano Sul, sob o viés da estratigrafia de sequências aplicada a bacias rifte, a fim de correlacionar esse estudo com a bacia do Recôncavo. A partir da integração das seções sísmicas compostas associadas a dados de perfis geofísicos e litológicos de 15 poços, foi realizado o tratamento desses dados no software de interpretação sísmica IHS Kindle. A análise sismoestratigráfica de Tucano Sul aqui desenvolvida, envolveu a interpretação das terminações de refletores, definição das unidades sismoestratigráficas a partir do mapeamento de superfícies-chaves, além da caracterização das principais sismofácies. Como resultado, foram individualizadas cinco unidades sismoestratigráficas, segundo o modelo aqui adotado: unidade Pré-rifte, Rifte 1, Rifte 2, Rifte 3 e unidade Pós-rifte. Foram definidas cinco sismofácies, SF1 a SF5, cada qual com seus parâmetros característicos. Ao fim, propôs-se uma discussão acerca da correlação sismoestratigráfica com a bacia do Recôncavo. Para o intervalo rifte, Tucano Sul apresentou uma sequência sismoestratigráfica a menos comparada com a bacia do Recôncavo, indicando importante evento erosivo durante o seu desenvolvimento.&#x0D; Palavras-chave: Estratigrafia de sequências, sismoestratigrafia, rifte.

Depositional style changes during the Permo‐Carboniferous–Early Jurassic evolution of the Central Kalahari Karoo Sub‐basin, Botswana

The Permo‐Carboniferous–Lower Jurassic Karoo succession in the Central Kalahari Karoo Sub‐basin of Botswana is largely confined to the subsurface, and contains coal, coalbed methane and groundwater resources, similar to other Karoo strata throughout southern Africa. Characterization of the stratigraphic architecture (i.e., spatiotemporal stacking character of sedimentary facies) is essential for various aspects of subsurface resource prediction (e.g., resource parameters; reservoir architecture; mining feasibility). This study uses sedimentary facies analysis on borehole cores from central Botswana and sequence stratigraphic principles to resolve large‐scale depositional style changes during the evolution of the greater Kalahari Karoo Basin in southwestern Gondwana. The results show that changes in the Karoo stratigraphic architecture define two, large‐scale overall fining‐upward depositional sequences (i.e., Lower and Upper Karoo) that are marked by regional subaerial unconformities. These regionally mappable depositional sequences contain pairs of high‐ to low‐amalgamation units, which are typified by stacked, multistorey sandstone bodies, succeeded by finer grained units that are sometimes rich in coal (e.g., the Dukwi‐Makoro‐Kamotaka vs. the Morupule‐Serowe‐Tlhabala formations in the Lower Karoo; the lower versus upper Mosolotsane‐Ntane formations in the Upper Karoo). The large‐scale depositional style changes, reflecting base‐level fluctuations and variation in the balance between accommodation and sediment supply, resulted from climatic changes (e.g., Permo‐Carboniferous deglaciation), tectonic events (e.g., regional pre‐Mosolotsane uplift event), and marine incursions. The latter is documented, for the first time, via the marine‐influenced ichnofauna in the uppermost Ecca Group. Further refining this initial sequence stratigraphic framework for the Botswanan Karoo will require acquisition of radioisotopic dates (e.g., U–Pb zircon ages) and modern seismic reflection data.

Intergrated Seismic Stratigraphic and Structural Analysis of the Songo Songo Gas-Field, Shallow Offshore Tanzania, Using Seismic and Well Data

Seismic stratigraphy and structural analysis of seismic data, when combined with wireline data, provides vital information for hydrocarbon exploration in a prospective basin. These techniques were employed in the Songo Songo shallow coastal basin, southern Tanzania to determine stratigraphic setting, trapping mechanism, reservoirs zones. Suites of well logs from two wells (AA-1 and BB-5) and 2-D seismic data was obtained from TPDC in the study area. Lithologic interpretation and well correlation were carried out using the well log suites. Stratigraphic analysis was carried out with the well logs and 2D seismic data by using principles of sequence stratigraphy while structural interpretation was done with aid of the seismic data to produce polar plots for the different structural trends. The lithology was dominated by sand, shale, and limestone. Five sequence boundaries (SB); SB1 (Albian), SB2 (base of Coniacian-Early Campanian), SB3, (Middle Eocene), SB4 (Late Miocene) and SB5 (Quaternary)) and three maximum flooding surfaces (MFS); MFS1-(Early Cretaceous), MFS2, (Late Cretaceous), MFS3-(Early Eocene) were identified. Three main normal faulting systems (Jurassic faults, active during the Jurassic rifting phase of Madagascar, Neogene faults that occurred during Neogene east African rifting and reactivated faults which mostly were Jurassic fault reactivated by east African rifting) of NNW-SSE were recognized in the study area. The structural interpretation reveal that the gas field is dominated by normal faults that occur in the upper and lower part of Songo Songo suggesting two phases of deformation prior to development of the field. The main reservoir is developed in the Neocomian and Albian sandstones, and capped by Jurassic faults and Wami (Formation) overlying rocks. The gas is sourced from Jurassic shale known as Mtumbei Formation and stored at the main reservoir developed in the Lower Cretaceous aged Neocomian sandstone known as Kipatimu Formation, sealed by high pressured shale of upper Cretaceous known as Wami Formation. This study shows that deposition of sediment occurs in the NW – SE direction, with the thinning of sediments thickness towards well BB-5 while the stratigraphic sections show that the horizons are laterally continuous and are being strongly affected by tectonic events.

Depositional environments and sequence stratigraphy of Tertiary sediments of Oleum Field, Eastern Niger Delta Basin, Nigeria

Understanding the stratigraphic framework of Oleum field is critical to hydrocarbon exploration and production success, owing to the alternating nature of organic-rich shale envelopes and porous sand sheets of the field. This research is aimed at studying the sequence stratigraphic framework and depositional environments of sedimentary facies of Oleum field, onshore (swamp) Niger Delta. This aim was achieved using sequence stratigraphic principles based on the integration of biostratigraphic, paleobathymetric, seismic and wireline log data of two wells (i.e. Oleum-001 and Oleum-002). This has led to the delineation of two maximum flooding surfaces (? Ma MFS and 13.6 Ma MFS) at 8182 ft and 9080 ft respectively. Each MFS is associated with depositional sequence and systems tracts. The first depositional sequence consists of two systems tracts; transgressive system tract (TST) and highstand system tract (HST), while the second depositional sequence consists of all the three systems tracts; lowstand system tract (LST, TST and HST). The 13.6 Ma MFS was delineated based on the occurrence of Bolivina 29a / Cassidulina 7 fossils. Additionally, the well logs sequence stratigraphy revealed two sequence boundaries which occur at 7255 ft and 8865 ft of Oleum-001, and 7033 ft and 8770 ft of oleum-002. The lithofacies are predominantly sand and shale displaying different kinds of log motifs. The sedimentological log motif shows a coarsening upward and blocky sands of the HST delineated as the system tract with the best reservoir properties. Fining upward and serrated/saw tooth motif of the TST is delineated as the facies with the best seal properties. The result indicates that the stratigraphic framework of Oleum Field is fluvio-deltaic to marine setting.

FACIES HETEROGENEITIES IN A RAMP CARBONATE RESERVOIR ANALOGUE: A NEW HIGH‐RESOLUTION APPROACH FOR 3D FACIES MODELLING

In contrast to the conventional view that facies distribution patterns on carbonate ramps are relatively simple, outcrop analogue studies point to a high degree of internal facies complexity. Depending on the diagenetic overprint, this complex pattern may result in reservoir compartmentalization due to the presence of interflow baffles. The often subseismic scale heterogeneities may not be included in conventional reservoir modelling. In order to evaluate how facies heterogeneities in shoal reservoirs can be modelled realistically, this paper presents a facies modelling workflow which includes a new approach to the design of training images for multiple‐point statistics (MPS). The workflow was developed in the course of a reservoir outcrop analogue study of a Ladinian (Middle Triassic) coquinadominated shoal complex in SW Germany which was deposited on an epicontinental, gently inclined carbonate ramp. The data set was based on an intensive field study and includes 3D facies and sequence stratigraphic analyses of the largest shoal complex in the Quaderkalk Formation (Upper Muschelkalk). This several metre thick shoal complex represents a subseismic scale, bioclast‐rich reservoir analogue and has a very heterogeneous facies pattern.Integrating 1D facies logs and sequence stratigraphic trends from tens of outcrop sections and cores, two nested 3D geocellular facies models were produced: (i) a large‐scale (30 × 30 km) model based on truncated Gaussian simulation (TGS); this formed the basis for (ii) a smaller‐scale (10 × 10 km), more detailed model based on multiple point statistics. In addition, a new approach for training image design was developed to honour small‐scale sequence stratigraphic trends and lateral facies patterns observed in modern analogues. Compared to facies patterns in modern analogues, the large‐scale model presents geologically‐feasible facies distribution patterns and geometries, and in addition shows a vertical facies distribution which is similar to the observed sequence stratigraphic architecture of the outcrop data‐set used. Due to the new training image design, the final small‐scale model has a distribution pattern of facies heterogeneities which looks similar to modern facies distributions in the offshore UAE and thus represents a valuable method of producing realistic reservoir facies models.The modelling workflow and the new approach for training image design presented will help to reduce uncertainties in the understanding and modelling of subsurface reservoirs by using a systematic combination of outcrop data and modern analogues, with the consistent application of sequence stratigraphic principles. In addition, this study emphasises the importance of careful training image design, derived from modern analogues, which can be used as realistic inputs in order to optimize multiple point simulations, and which may be applied to producing bioclastic reservoirs such as those located on the Arabian Plate or offshore Brazil.

Back To Basics of Sequence Stratigraphy: Early Miocene and Mid-cretaceous Examples from the New Jersey Paleoshelf

Abstract Many sequence stratigraphic approaches have used relative sea-level curves that are dependent on models or preconceived notions to recognize depositional sequences, key stratal surfaces, and systems tracts, leading to contradictory interpretations. Here, we urge following basic sequence stratigraphic principles independent of sea-level curves using seismic terminations, facies successions and stacking patterns from well logs and sections, and chronostratigraphic data to recognize sequence boundaries, other stratal surfaces, parasequences, and systems tracts. We provide examples from the New Jersey siliciclastic paleoshelf from the: 1) early Miocene using academic-based chronostratigraphic, seismic, core, downhole, and core log data, and 2) mid-Cretaceous using commercial well-log, seismic, and biostratigraphic data. We use classic criteria to identify sequence boundaries on seismic profiles by reflection terminations (onlap, downlap, erosional truncation, and toplap), in cores by surfaces of erosion associated with hiatuses detected using biostratigraphy and Sr-isotope stratigraphy and changes in stacking patterns, and in logs by changes in stacking patterns. Maximum flooding surfaces (MFSs) are major seismic downlap surfaces associated with changes from retrogradational to progradational parasequence stacking patterns. Systems tracts are identified by their bounding surfaces and fining- (generally deepening) and coarsening- (generally shallowing) upward trends in cores and well-log stacking patterns. Our Miocene examples of sequences m5.4 (17.7–16.1 Ma) and m5.8 (20.1–19.2 Ma) illustrate how basic sequence stratigraphic techniques reveal higher-order sequences within Myr scale composite sequences. Our mid-Cretaceous examples from the New Jersey shelf provide a paleoshelf transect spanning the Great Stone Dome to the outer continental shelf to identify parasequences, sequences, and systems tracts. This sequence stratigraphic framework provides insights into Myr scale coeval depositional environments across the paleoshelf and reservoir continuity, and highlights the application of basic sequence stratigraphic criteria to reservoir-scale evaluation, not only for oil and gas resources, but also for carbon storage.

Secondary rock structures and the regional hydrogeology of claystone-rich cretaceous strata, Williston Basin, Saskatchewan, Canada

The geometry and spatial distribution of a polygonal fault system (PFS) and collapse features within Cretaceous strata (predominantly mudstones and claystones) were investigated using three high-resolution three-dimensional seismic datasets of the Williston Basin, Saskatchewan, Canada. Mapping of the planform geometry and fault throw distributions (throw–depth (T–z) profiling) shows that the PFS present in the Colorado Group and Pierre Fm has a vertical extent of 200–330 m. Variation in the lateral planform geometry is attributed to the relative rates of stress accumulation during early development of the planar faults and is constrained using sequence stratigraphic principles. The mean fault dip is 60° ± 12° (number of measurements, n = 225). The T–z profiles appear as partial C-type profiles, demonstrating that at least half of the total height of the PFS was removed during post-Cretaceous erosion. The presence of polygonal faults in equivalent strata of the Western Interior Sedimentary Basin (WISB) suggests the PFS described in the current study (1510 km2) may be present across the WISB. Collapse features, formed in response to dissolution cavities within underlying strata, crosscut the entire Cretaceous sequence and are subcircular in plan view with typical diameters of 350–450 m. These features are present in each of the datasets at a rate of 0.02–0.11 collapses/km2. The prevalence of collapses in areas where faults display modified throw distributions may suggest post-Cretaceous fault reactivation associated with Pleistocene glacial periods. Although these secondary rock structures likely affect groundwater and solute transport at the basin scale, the impact remains to be determined.

Lower To Mid-Cretaceous Sequence Stratigraphy and Characterization of CO 2 Storage Potential In the Mid-Atlantic U.S. Coastal Plain

Abstract: The Mid-Atlantic U.S. Coastal Plain (New Jersey, Delaware, Maryland, and northern Virginia) contains thick (> 500 m) mid-Cretaceous sand–sandstone reservoirs confined by thick clay–shale confining units and thus has high potential for storage of CO 2 captured from nearby point sources. The predictability of the continuity of the reservoir and confining units can be improved by applying principles of sequence stratigraphy, including integration of lithostratigraphy, biostratigraphy, paleoenvironmental proxies, and a novel application of fluvial aggradation cycles (FACs). We evaluate the storage and confinement potential for the Lower Cretaceous Waste Gate Formation and mid-Cretaceous Potomac Formation/Group in New Jersey and Maryland, which we divide into three major reservoirs (Waste Gate-Potomac Unit I, Potomac Unit II, and Potomac Unit III). We use new core data to ground-truth well-logs and paleoenvironmental changes, sequence stratigraphic stacking patterns (including FACs), and pollen biostratigraphy to update previous well-log correlations in New Jersey and extend these correlations into deep holes in Maryland. While individual sand beds are typically local in extent, zones of sands are broadly correlative over distances of 60 km. These regionally traceable sand-prone zones should be useful for carbon storage. Cenomanian Potomac Unit III sands are relatively thick (∼ 70 m) in New Jersey, but generally thin (average of ∼ 50 m) into Maryland; they are near the updip limit for supercritical storage (800 m) in New Jersey and Maryland and may not be suitable due to updip migration above the supercritical level. Potomac Unit II sands (Albian Pollen Zone II) appear to be discontinuous and less suitable in both states. Potomac Unit I (Aptian Pollen Zone I) and Waste Gate Formation sands (?early Aptian to Berriasian pre-Pollen Zone I) are relatively thick (∼ 88–223 m and ∼ 81–288 m, respectively) and confined in New Jersey and appear to be widespread and continuous; the updip confinement of this reservoir in Maryland is less certain. Volume storage estimates for the Potomac I-Waste Gate in the Mid-Atlantic Coastal Plain are 8.4–33.5 Gt CO 2 , adequate to store CO 2 captured from 24–95 GW of natural gas generation for a century.

Sequence stratigraphic evolution of The post-rift MEGASEQUENCE in The northern part of The Nile Delta basin, Egypt

The stratigraphic succession of the subsurface Pliocene-Quaternary post-rift megasequence in the north-central part of the Nile Delta includes the rock units; Kafr El-Sheikh Formation (Early-Middle Pliocene), El- Wastani Formation (Late Pliocene), Mit-Ghamr and Bilqas formations (Quaternary). These rock units were analyzed according to the sequence stratigraphic principles to construct their stratigraphic architecture and discuss the depositional events influencing their evolution. Accordingly, seven 3rd order depositional sequences were encountered, of which six 3rd order seismic depositional sequences (sequences 1–6) are found in the Early–Middle Pliocene Kafr El-Sheikh Formation, whereas sequence-7 includes the Quaternary rock units. Sequences 1 and 7 were further subdivided, on the basis of high-resolution sequence stratigraphy into 8 and 11 4th order subsequences respectively. The results of the sequence stratigraphic analyses suggested that the depositional evolution of the examined Pliocene-Quaternary megasequence represents a complete prograding depositional phase during the Nile Delta history. The lower part of Kafr El-Sheikh Formation (sequences 1, 2, 3 and 4) was deposited as a thick outer marine shelf succession over which the younger rock units were deposited. However, the depositional sequences 5 & 6 of Kafr El-Sheikh Formation and the lower parts of El-Wastani Formations may indicate a deposition within active prograding prodelta sub-aqueous deltaic-subenvironments. The upper parts of El-Wastani Formation were deposited as a constructive delta-front pushing its way northward. The Pleistocene Mit-Ghamr Formation was evolved as a direct result of a huge fluvial input, organized as coalescing laterally extensive sand-rich bars. These were laid-down by active fluvial distributary streams that dominated the delta plain as the final phases of the present deltaic subaqueous environments.

Depositional controls on sediment body architecture in the Eagle Ford/Boquillas system: Insights from outcrops in west Texas, United States

A detailed sedimentological study of the middle Eagle Ford/Boquillas (outcrop analog of subsurface producing strata) units was conducted on numerous roads cut along US Highway 90 in Val Verde County and on outcrops in Big Bend National Park, Brewster County, Texas, using field-based petrographical and high-resolution image capture methods (light detection and ranging and GigaPans). This study demonstrates that vertical and lateral facies distribution is controlled by the interaction of sediment productivity under the influence of bottom currents below storm wave base. Vertical cyclicity is the result of alternating periods of lower primary productivity and relatively low sediment accumulation rates (globigerinid argillaceous wackestones) and shorter periods of high primary productivity and higher accumulation rates (pelagic grainstones), driven by the absence or presence of iron from volcanic ash deposition. Lateral variations are controlled by the deposition and reworking of pelagic sediment under the influence of below–storm wave base bottom currents. Pelagic grainstones accumulated in the form of isolated barchanoid hydraulic dunes, sand ridges, coalesced sand ridges, and sand sheets and less commonly as continuous beds. Detailed measurements show that pelagic grainstones have no more than 50% continuity, and ash beds have 72% continuity. Application of sequence stratigraphic principles needs to be done with caution because the deeper-water depositional setting is affected not by sediment input from a shallow-water benthic carbonate factory but by pelagic sediment from the open-marine environment subject to bottom current reworking. Packages of strata may be more reliable for longer-distance correlations.

Sequence stratigraphy of a mixed siliciclastic-carbonate setting, Scotian Shelf, Canada

During the Jurassic Period, a large-scale carbonate bank (Abenaki Formation) and a siliciclastic (Sable) delta coexisted in North America. Conventionally, carbonate systems (in situ) are separated from siliciclastic systems (transported) because of their contrasting origin. However, we developed a case study to show that the basic principles of sequence stratigraphy remain applicable. We integrated the results obtained from a regional 2D study and a detailed follow-up study using 3D seismic data of the Scotian Shelf, Canada. The results were integrated with the prepared Wheeler diagrams, and a unified sequence stratigraphic framework was proposed. We determined that two second-order sequences were developed on a larger scale during the Jurassic Period. The first sequence developed during the transition from a ramp to rimmed margin. The second sequence developed during the evolution from a rimmed to ramp margin. These sequences formed a distinct stratigraphic style throughout the Scotian Shelf. The siliciclastic supply varied from the northeast to the southwest depending on the studied site; however, the regions close to the siliciclastic supply contained well-defined clinoform patterns. The topsets of such clinoforms were mostly eroded. Their directions were also found to be different than the carbonate-related clinoform geometries. Most of the carbonates were developed; as such, they kept up and prograded toward a backreef margin during the rimming stages. The second-order sequences were further subdivided into four third-order sequences. These were studied using the 3D seismic data and were found to contain several barrier reefs that could have stratigraphic exploration potential in the Penobscot area.

About this title ‐ Precambrian Basins of India: Stratigraphic and Tectonic Context

This Memoir provides a comprehensive review of the Precambrian basins of the four Archaean nuclei of India (Dharwar, Bastar, Singhbhum and Aravalli-Bundelkhand), encompassing descriptions of the time–space distribution of sedimentary–volcanic successions, the interrelationship between tectonics and sedimentation, and basin histories. Studies of 22 basins within the framework of an international basin classification scheme deepen an understanding of the basin architecture especially for cratonic basins. Most Indian sedimentary successions formed as cratonic to extensional-margin rift and thermal-sag basins, some reflecting mantle plume movement, subcrustal heating or far-field stress. This Memoir shows that Phanerozoic plate-tectonic and sequence stratigraphic principles can be applied to the Precambrian basins of large Archaean provinces. The differences between the stratigraphic architecture of the Indian Precambrian and examples of Phanerozoic basin-fill successions elsewhere are ascribed to variable rates and intensities of the controls on accommodation and sediment supply, and changes inherent in the evolution of the hydrosphere–atmosphere and biosphere systems.

Dynamic stratigraphy of composite peripheral unconformity in a foredeep basin

AbstractThis study employs facies analysis and basic principles of sequence stratigraphy to correlate isolated outcrop sections and reveal the depositional history of the Chmielnik Formation – a prominent mid‐Serravalian clastic wedge formed on the basinward forebulge flank of the Polish Carpathian Foredeep. The coarse‐grained clastic wedge, up to 30 m thick and spanning ca 1·1 Ma within biozone NN6, consists of fluvio‐deltaic, foreshore and shoreface deposits with a range of large littoral sand bars, all enveloped in muddy offshore‐transition deposits. Its dynamic stratigraphy indicates rapid shoreline shifts and environmental changes due to the interplay of forebulge tectonism, sediment supply and third‐order eustatic cycles. A similar interplay of tectonism and eustasy is recognizable in the whole middle Miocene sedimentary succession deposited on the forebulge flank, demonstrating an extreme case of an accommodation‐controlled shelf and indicating tectonic cycles of the forebulge uplift and subsidence spanning ca 800 to 900 ka. The episodes of forebulge uplift correlate with the main pulses of orogen thrusting. The resulting composite peripheral unconformity differs markedly from the idealized model of a ‘steady‐state’ stepwise onlap driven by forebulge continuous retreat. It is concluded that the foredeep peripheral unconformities, instead of being simplified in accordance with this idealized model, should rather be studied in detail because they bear a valuable high‐resolution record of regional events and give unique insights into the local role of tectonics, eustasy and sediment supply.

Sequence stratigraphic principles applied to the analysis of borehole microseismic data

Based on a sequence stratigraphic framework developed using gamma ray stacking patterns, we have identified brittle-ductile couplets, which allow us to better interpret the microseismic response recorded during a single-stage hydraulic fracture stimulation treatment monitored from three strategically located observation wells. We have analyzed and compared hydraulic fracturing results inferred by individual processing of microseismic data acquired from horizontal and vertical sensor arrays, as well as the results from simultaneously processing the signals recorded by all three sensors. Ultimately, we have decided in favor of the triple array simultaneous solution as the most useful data set to interpret the stimulation treatment due to the location of the microseismic events coupled with the theoretical expectation from our sequence stratigraphic framework. The final data set has not only allowed us to better interpret the hydraulic fracturing results, but also helped us improve recommendations in support of the field development campaign.

Historical developments inWheeler diagrams and future directions

AbstractThe Wheeler diagram is a type of chronostratigraphic chart and is one of the fundamental instruments available in the geologists' toolkit that is used to understand spatiotemporal relationships of strata. Over the last four decades, these diagrams have continued to improve due to advances in seismic technology. This article examines the historical developments behind Wheeler diagrams, not only stressing their merits, but also their pitfalls and the role that sequence stratigraphic principles have played in interpreting these diagrams. It is emphasized that the diagrams are only complete if one utilizes the thicknesses of a sequence stratigraphic unit (sequence, systems tracts) – a missing dimension that turns a 3D Wheeler diagram into 4D. The article also argues that the latter 4D diagrams represent the future for Wheeler diagrams.