Detailed Seismic Interpretation Research Articles

Structural Variation between the Western and Eastern Kuqa Fold‐and‐thrust Belt, China: Insights from Seismic Interpretation and Analog Modeling

AbstractThe Kuqa fold‐and‐thrust belt exhibits apparent structural variation in the western and eastern zone. Two salt layer act as effective decollements and influence the varied deformation. In this study, detailed seismic interpretations and analog modeling are presented to construct the suprasalt and subsalt structures in the transfer zone of the middle Kuqa and investigate the influence of the two salt layers. The results reveal that the relationship of the two salt layers changes from separated to connected, and then overlapped toward the foreland in the transfer zone. Different structural models are formed in the suprasalt and subsalt units due to the interaction of the two salt layers. The imbricate thrust faults form two broomlike fault systems in the subsalt units. The suprasalt units develop detached folds terminating toward the east in the region near the orogenic belt. Whereas, two offset anticlines with different trends develop at the frontal edge of the lower salt layer and the trailing edge of the upper salt layer, respectively. According to exploration results in this region, the relationship between suprasalt and subsalt structures has an influence on hydrocarbon accumulation. We believe that the connected deformation contains high‐risk plays while the decoupled deformation contains well‐preserved plays.

Challenges for seismic velocity modelling of rafts and impacts for pre-salt depth estimations

Seismic velocity models have significant importance in subsurface studies, notably when applied in structurally challenging areas. In some parts of the Campos Basin, offshore Brazil, the pre-salt reservoir's overburden shows complex structures, mainly due to raft tectonism that positions laterally, resulting in interspersed salt domes, carbonate rafts and siliciclastic sediments. This work used an extensive well database in the Marlim Complex to analyse the raft seismic velocities and their related impacts on pre-salt reservoir models. Based on well data, in combination with detailed seismic interpretation, seven alternative velocity scenarios were proposed for the rafts. The geological motivations for each scenario are discussed with the aim of developing constrained depth models for pre-salt reservoirs. The depth forecast results could be tested by drilled wells, and the resulting models are quantitatively compared in terms of depth predictions and gross-rock volumes. The results show that the topography of the target pre-salt reservoirs can vary considerably, even in scenarios where well and geological constraints are considered. This can impact pre-salt geological characterization and field development.

Extensional deformation of a shale‐dominated delta: Tarakan Basin, offshore Indonesia

AbstractDeformation on shale‐rich continental margins is commonly associated with thin‐skinned extension above mobile shales. Normal faulting and shale mobilization are widespread on such margins, being associated with and controlled by progradation and gravitational failure of deltaic sedimentary wedges. However, due to uncertainties in seismically imaging mobile shales, our understanding of problems like how base mobile‐shale controls deformation, and the shape, size, and distribution of shale structures remains poorly understood. Here, we use 3D seismic reflection data from the platform region of the Tarakan Basin, offshore eastern Indonesia to investigate the temporal and spatial evolution of thin‐skinned deformation of the Neogene sedimentary section. Our detailed seismic interpretation reveals up to 74 km long, concave‐ and convex‐into‐the‐basin normal faults, dipping both basinward (eastwards) and locally landward (westwards), which detach downwards on a basal mobile shale (Early‐Middle Miocene). The base of the mobile‐shale unit dips gently (<17°) seaward, although older (Eocene‐Early Miocene), rift‐related normal faults originate local structural highs deforming the base of mobile shales. Our isochore (thickness map) analysis shows that supra‐shale normal faulting commenced in the Middle Miocene and was accompanied by the formation of hanging‐wall rollover folds and associated crestal grabens, with the subsequent along‐ and across strike migration of the deformation related to the nucleation, lateral linkage and reactivation of individual fault systems. Updip growth normal faulting was also accompanied by the downslope flow of mobile shale, accompanied by parallel and perpendicular variations of the differential loading in the delta system, and local contraction and mobile‐shale upbuilding, resulting in the growth of large, margin‐parallel shale anticlines further downdip. The growth faults and anticlines are locally overlain by up to 5 km tall mud pipes and volcanoes. We suggest that variations in the rate of sedimentary loading, mobile‐shale flow, fault growth and gravitational failure of the delta system above a seaward‐dipping, but locally rugose base mobile‐shale surface, controlled Neogene deformation in the Tarakan Basin. We also demonstrate how variations in the trend and dip of the base mobile‐shale surface influence the position, timing of formation and evolution of supra‐shale normal faults and their associated depocentres along shale‐rich, deltaic margins.

Structure and formation mechanism of the Pearl River Mouth Basin: Insights from multi-phase strike-slip motions in the Yangjiang Sag, SE China

• The Pearl River Mouth Basin experienced two stages of strike-slip motions along the ENE and WNW directions. • The partial reactivation of the intrabasement faults controlled the evolution of intrabasin faults. • The formation of the basin resulted from the joint effect of oblique Pacific-Eurasian subduction and the Indo-Eurasian collision. The Pearl River Mouth Basin (PRMB) experienced multi-phase rifting and complex tectono-sedimentary evolution during the Cenozoic, and is a topic of many studies regarding the basin-forming mechanism. In the present study, detailed seismic interpretation and tectonic analysis based on the 3D seismic reflection data of the Yangjiang Sag in the northwestern PRMB were carried out, to provide clues to its tectonic evolutionary history. The qualitative-quantitative analysis of fault strikes and migration of depocenter in the Yangjiang Sag indicated the dextral transtensional setting during the Paleocene to Miocene. Meanwhile, the horsetail and en echelon structures on plane view and negative flower structures in cross-section are exhibited, indicating the successive occurrence of strike-slip motions in ENE and WNW directions respectively after initial rifting combined with the structural analysis of Huizhou Sag and Baiyun Sag. In addition, thrust fault systems trending in WNW and ENE were identified in the basement. Their partial and selective reactivation in strike-slip character during the Cenozoic restricted the faults developed in the basin with differential properties. Geometrically, rhombic-shaped sags with cross-basin fault zones were formed, implying the formation of pull-apart structures along with multi-phase strike-slip motions. The pull-apart mechanism could be accounted due to the joint effect of the oblique Pacific-Eurasian subduction and the Indo-Eurasian collision during the Cenozoic.

Processes controlling volcanic and epiclastic reservoir formation in a buried polygenetic stratocone

Abstract Understanding the formation of volcanic and epiclastic reservoirs is pivotal for exploring geoenergy resources such as geothermal energy, hydrocarbons, and new CO 2 sequestration and hydrogen storage opportunities. This paper examines the processes controlling the quality of pyroclastic and epiclastic reservoirs of the Kora volcano, an extinct stratocone presently buried in the offshore Taranaki Basin, New Zealand. We conduct detailed seismic reflection interpretation, drillcore lithofacies and wireline-log description, petrographic analysis, and analytical tests to generate a unified framework that explains the formation of volcaniclastic reservoirs from basin to pore-scale. Each stage of construction and degradation of the Kora volcano is associated with particular processes that increase or reduce reservoir quality. Primary processes include quench fragmentation, deuteric mineral dissolution, and epiclastic sedimentation. Secondary processes comprise mineral alteration (mainly meteoric; minor hydrothermal and diagenetic), mechanical stress fracturing (mainly tectonic; minor magmatic and burial deformation), and pervasive biogenic cementation. Epiclastic conglomerates present the highest reservoir quality (average 23% porosity and up to 997 mD permeability), followed by lapilli-tuffs and tuff-breccias. In contrast, bioclastic epiclastic sandstones are typically cemented by carbonates and pyrite. Our models and interpretations will increase understanding of the formation of volcaniclastic reservoirs and aid exploration of geoenergy resources in volcanic terrains.

Shallow vs. Deep Subsurface Structures of Central Luconia Province, Offshore Malaysia Reveal by Aeromagnetic, Airborne Gravity and Seismic Data

Across the Luconia continental shelf, the nature and structures of the crust are lacking geological understanding and precise characterization. Newly acquired, aeromagnetic, and airborne gravity data were used to assess deep and shallow sub-surface signals within the Central Luconia Province, off the coast of Sarawak, offshore Malaysia. Regional aeromagnetic anomalies appear to primarily reflect deep crustal features while depth (Z) tensors of airborne gravity anomalies evidence shallow subsurface structures. Strike directions of the interpreted structural trend on aeromagnetic and airborne gravity anomalies maps are measured and plotted into rose diagrams to distinguish the structural orientations for all datasets. Signature patterns extracted from the depth profiles were correlated with parallel seismic lines and nearest exploration wells and coincide well with the top of carbonate for Cycle IV/V and structures seen within the Cycle I and II sediments. The orientation of faults/lineaments at shallower depth is dominated by a NW-SE orientation, similar with the faults extracted from two recently published structural maps. Deeper subsurface sections yielded E-W to NWW-SEE dominant directions which were never presented in the published literature. The E-W oriented anomalies are postulated to represent the remnants of the accretion between the Luconia crustal block and southern boundary of the Palawan block. The NW-SE trend follows the same direction as prominent faults in the region. The insight into shallow and deep subsurface structures in Central Luconia Province imaged through airborne gravity and aeromagnetic data should provide guidelines and complementary information for regional structural studies for this area, particularly in combination with detailed seismic interpretation. Further evaluation on the response of Air-FTG® gravity and aeromagnetic could lead to the zonation of potential basement highs and hydrocarbon prospects in this area.

Unlocking flow pathways in complex carbonate reservoirs: Benefits of an integrated subsurface study from the Cretaceous Mauddud Formation, North Kuwait

Despite its long production history (since 1958) and extensive reservoir stimulation by water injection, the Mauddud reservoir of the Sabiriyah field (SAMA) in northern Kuwait has been plagued by relatively disappointing oil production increase, low oil-by-water replacement ratios, and early water-breakthrough observations. The work described in this paper indicates that reservoir complexity and associated permeability heterogeneity are at the root cause of this and are the result of the interplay between sedimentology, diagenesis and the structural evolution of the area.A multi-disciplinary study involving structural geology, sedimentology, diagenesis, reservoir engineering and geomechanics identified the geological processes responsible for the development of principal high-permeability (High-K) elements in SAMA. Their 3D distribution has been characterized and reservoir property ranges have been established, based on integrated evaluation of static (e.g., seismic, core, borehole image, wireline logs, and drilling information such as losses) and dynamic information (e.g., production and injection logging tools, well test information, pressure data, historical production data and tracer information). Feedback loops between geological realizations and dynamic simulations allowed the testing of various concepts and property ranges with learnings implemented in updates of the geological realizations. This approach increases the confidence level in the conceptual geological models.Three principal plumbing elements contribute to the reservoir and property heterogeneity in the SAMA reservoir. Firstly, relatively thin (one to several decimeters) cemented zones characterized by low matrix porosity but significant secondary vuggy and fracture porosity with high permeability occur in two distinct stratigraphic intervals in the reservoir. These intervals occur near sequence boundaries when the carbonates likely experienced brief periods of exposure. They are interpreted to be cemented cycle tops formed during meteoric diagenesis and represent key flow zones for the initial hydrocarbon production as well as for later high-rate production of formation water and injected water, as identified by production/injection logging tools. Faults and associated fault (damage) zones with abundant fractures are the second key plumbing element. Core recovery and observations from wells located closely to a fault zone identified from detailed seismic interpretation highlight the occurrence of abundant fractures. Tracer information clearly identifies faults as preferential migration pathways between injector and producer wells. Thirdly, induced fracture growth near injectors is an important process in the context of High K development. Hall plots identified that injectivity often increases near injectors after a certain period of injection. Geomechanical analysis suggests that induced fracture growth is plausible due to reduction in total horizontal stress due to the combined effect of depletion and water-injection-induced cooling of the reservoir.Reservoir simulations validate the requirement of presence of these three key elements in the plumbing diagram. Yet, dynamic sensitivity testing shows that the three processes each have a variable impact on flow in the reservoir, depending on local factors such as the nearby presence of faults and the development of the cemented cycle tops. Dynamic simulations further indicate that (1) porosity in the cemented cycle tops is likely low, in line with core observations and out of sync with upscaled porosities and (2) lateral extent of individual cemented cycle tops is in the order of few hundred meters, but final connectivity is enhanced by the stacking of different cemented cycle tops and their concentration in two distinct zones in the Mauddud.Armed with the insight from core analyses and dynamic model results, recommendations are made to improve oil production in SAMA: (1) inject away from the zones and faults, and (2) reduce the injection pressure, thus limiting the likelihood of “new” induced fractures and faults forming that may connect to “old” geologic fracture and faults and cause early-water-breakthrough and thus ineffective oil sweep. Reservoir stimulation via matrix injection, rather than under fracturing conditions, may reduce the initial oil production boost but will most likely lead to significantly better ultimate recovery over the long life of SAMA.

Using seismic spectral blueing for enhancing seismic resolution: a case study from a mature field in a rift basin, southwestern Gulf of Suez, Egypt

Abstract Seismic resolution plays a key role in oil exploration and development. An increase of the seismic frequency content can improve resolution and imaging quality significantly, revealing the presence of minor structures that may highlight geologic features of interest. This can be particularly important during the production phase of mature oil fields with thin producing reservoir(s). The presented workflow has resulted in a more detailed seismic interpretation of an oil field in the Gulf of Suez basin, Egypt. Applying seismic spectral blueing solved the resolution limitation for interpreting minor faults, and allowed better well positioning and improved reserve estimation. In this workflow, the seismic attributes are interpreted and integrated with the geological datasets available for improved structural modelling.

Facies analysis and depositional setting of the upper pliocene Akchagyl Formation in southeastern Caspian Basin, NE Iran

Pliocene deposits of the Cheleken and Akchagyl Formations constitute the most important hydrocarbon reservoirs in the Caspian Basin of Iran and other adjacent countries. In this study, facies characteristics and depositional setting of these sequences were examined using detailed field observations, petrographical studies, wireline-log and 2D seismic interpretations. Three outcrop sections were measured as the oldest and thickest Paleogene–Neogene units in the southeastern part of the Caspian Sea. Based on macroscopic and microscopic investigations, eleven sedimentary facies were identified in the studied sequence. These facies indicate deposition in alluvial fan, mud-flat, foreshore, shoreface and offshore of a wave-dominated lacustrine environment. The Akchagyl Formation is mainly composed of foreshore and shoreface facies with low gamma-ray values, which grades into offshore facies towards southwestern parts of the basin. The presence of marine biota such as Globigerinoides fistulosus, Ammonia becccarii, Pullenia praecursor, Cardium dombra and nanoplanktons (Discoaster brouweri and Discoaster pentaradiatus) demonstrate that this lacustrine setting was periodically connected to the global oceans, particularly in the Late Pliocene–Pleistocene. The stratigraphic correlation of the studied sections shows significant changes in lithology, facies and thickness of the Pliocene deposits. These changes were controlled by tectonic subsidence and clastic sediment supply during the Early-to-Middle Pliocene along with sea-level fluctuation as a consequence of the Akchagylian transgression episode in the Late Pliocene. Lateral changes in the geological parameters of the Akchagyl deposits indicate a more stable condition within the most part of the study area, especially towards the South Caspian Basin.

Presalt reservoirs of the Santos Basin: Cyclicity, electrofacies, and tectonic-sedimentary evolution

Presalt reservoirs of the Santos Basin accounted for more than 50% of Brazilian hydrocarbon production in the first two months of 2019. Its most important reservoirs are found in the Barra Velha Formation; thus understanding its genesis and geologic history is essential. This formation is composed of carbonates deposited in an alkaline lacustrine environment with a multiplicity of facies from boundstones and grainstones to mudstones. We have performed a sedimentary analysis based on the integration of sidewall core (SWC) samples and well logs from two wells coupled with seismic patterns discrimination to characterize the tectonic and depositional evolution of the Barra Velha Formation in a sector of the Outer High of the Santos Basin in this study. Our method initially consisted of the evaluation of well logs, aiming to identify shallowing and flooding upward cycles of the second and third orders for the paleoenvironmental conceptualization upper rift and sag phases. Then, we defined electrofacies through the integration of SWCs, gamma ray, and acoustic impedance logs using the crossplot approach. Finally, we described seismic patterns throughout the study area and correlated with results from well data analysis. Therefore, the Barra Velha Formation was subdivided into three zones: the lower, intermediate, and upper zones. Well 1 has a facies association characteristic of a proximal and stable environment during deposition, whereas well 2 initially presents in a distal environment sedimentation that evolves to a more proximal setting. This fact evidenced differences with respect to base-level variations indicating compartmentalization within the lacustrine environment of the upper rift and sag phase that corroborated with the detailed seismic pattern interpretation of the study area.

Możliwość uszczegółowienia interpretacji sejsmicznej w utworach miocenu zapadliska przedkarpackiego na podstawie interpretacji pomiarów geofizyki otworowej

Możliwość uszczegółowienia interpretacji sejsmicznej w utworach miocenu zapadliska przedkarpackiego na podstawie interpretacji pomiarów geofizyki otworowej

Tectonostratigraphic framework and depositional history of the deepwater Ulleung Basin, East Sea/Sea of Japan

AbstractThe Ulleung Basin, East Sea/Japan Sea, is a Neogene back‐arc basin and occupies a tectonically crucial zone under the influence of relative motions between Eurasian, Pacific and Philippine Sea plates. However, the link between tectonics and sedimentation remains poorly understood in the back‐arc Ulleung Basin, as it does in many other back‐arc basins as well, because of a paucity of seismic data and controversy over the tectonic history of the basin. This paper presents an integrated tectonostratigraphic and sedimentary evolution in the deepwater Ulleung Basin using 2D multichannel seismic reflection data. The sedimentary succession within the deepwater Ulleung Basin is divided into four second‐order seismic megasequences (MS1 to MS4). Detailed seismic stratigraphy interpretation of the four megasequences suggests the depositional history of the deepwater Ulleung Basin occurred in four stages, controlled by tectonic movement, volcanism, and sea‐level fluctuations. In Stage 1 (late Oligocene through early Miocene), syn‐rift sediment supplied to the basin was restricted to the southern base‐of‐slope, whereas the northern distal part of the basin was dominated by volcanic sills and lava flows derived from initial rifting‐related volcanism. In Stage 2 (late early Miocene through middle Miocene), volcanic extrusion occurred through post‐rift, chain volcanism in the earliest time, followed by hemipelagic and turbidite sedimentation in a quiescent open marine setting. In Stage 3 (late middle Miocene through late Miocene), compressional activity was predominant throughout the Ulleung Basin, resulting in regional uplift and sub‐aerial erosion/denudation of the southern shelf of the basin, which provided enormous volumes of sediment into the basin through mass transport processes. In Stage 4 (early Pliocene through present), although the degree of tectonic stress decreased significantly, mass movement was still generated by sea‐level fluctuations as well as compressional tectonic movement, resulting in stacked mass transport deposits along the southern basin margin. We propose a new depositional history model for the deepwater Ulleung Basin and provide a window into understanding how tectonic, volcanic and eustatic interactions control sedimentation in back‐arc basins.

Superposed tectonic regimes in west Beni Suef basin, Nile Valley, Egypt: Implications to source rock maturation and hydrocarbon entrapment

The present study contributes to the knowledge of the structural architecture and kinematic evolution of the West Beni Suef basin, by means of detailed seismic interpretation. This basin is one of several in a NW–SE oriented Early Cretaceous basin system occurring at the northeast corner of the African plate. We used the patterns of growth sedimentation above the limbs of growth folds, and in the downthrows of normal faults as kinematic indictors. Two phases of strike slip tectonics during the Santonian and Campanian–Maastrichtian superposing an Early Cretaceous rifting are verified in this basin. The Santonian and Campanian–Maastrichtian strike slip tectonics are represented by an E–W strike slip fault zone associated with NE growth folds and NW growth normal faults as well as ENE, WNW and E–W strike slip fault segments. The Early Cretaceous rifting facilitates the maturation of the deeper source rocks such as Lower Cretaceous shales of the Kharita Formation. Moreover, the strike slip tectonic events played a major role in the maturation of the shallow depth Cenomanian–Turonian Abu Roash “F” Member through entrapment in a releasing bend at the central part of the study area. The structures associated with the two tectonic regimes include, horsts, normal fault propagation folds and strike slip related anticlines, which formulated the main structural traps in the study area.

Forward seismic modeling as a guide improving detailed seismic interpretation of deltaic systems: Example of the Eocene Sobrarbe delta outcrop (South-Pyrenean foreland basin, Spain), as a reference to the analogous subsurface Albian-Cenomanian Torok-Nanushuk Delta of the Colville Basin (NPRA, USA)

Abstract A forward seismic model of the Middle Eocene Sobrarbe delta outcrop (South-Pyrenees, Spain) has been made to investigate its seismic signature. The Sobrarbe delta complex corresponds to a syntectonic sedimentary wedge locally thicker than 1000 m. This 15 km-long, highly-progradational and moderately aggradational sedimentary system presents sigmoid and oblique clinoforms, characterized by slopes ranging from 0.2° to 5.7°. Along the clinoforms, the classical deltaic depositional environments grade progressively from one to the other: alluvial plain, delta plain, delta front and prodelta. Locally, specific carbonate deposits occur, corresponding to transgressive pulses. The transition from delta front to prodelta is locally marked by large slide scars affecting clinoform morphology. A detailed outcrop transect of the Sobrarbe delta was converted to an acoustic impedance model by assigning petrophysical properties to each geological facies. This model was then used to create synthetic seismic lines characterized by various input wavelets. The resulting various peak frequency synthetic seismic lines have been interpreted, and the seismic interpretation compared to the outcrop description to calibrate the seismic interpretation and assess the “limits” of that interpretation. This work shows that the “seismic stratigraphy” methodology is consistent and allows the correct interpretation of most seismic sequences. However, composite reflections from rapid lateral facies transitions and higher-frequency sequence boundaries can clearly lead to seismic interpretation mistakes. The seismic facies of seven facies associations have been described, providing guidelines to recognize them on actual seismic lines. The synthetic seismic image of four selected systems tracts comprising good reservoir bodies has been analyzed to highlight recognition criteria which can be used to interpret analog deltaic systems in the subsurface, and therefore enhance the prediction and characterization of the reservoir bodies that they hold. These guidelines were systematically applied to a direct subsurface analog: the Torok-Nanushuk Delta (Colville Basin, NPRA, USA).

Depositional history of the western Nile Delta, Egypt: Late Rupelian to Pleistocene

The availability of onshore and offshore three-dimensional seismic surveys facilitated detailed seismic sequence-stratigraphic interpretation of a large swath of the western Nile Delta evolution since the late Oligocene. The resulting sequence-stratigraphic framework is calibrated against more than 60 wells. The interpretation of repetitive sequence boundaries, that is, unconformities, on seismic sections was constrained by high-resolution abundance and diversity within biostratigraphic data sets and lithofacies-stacking patterns interpreted from well logs. Our series of depositional facies maps reflect environments of undifferentiated lowstand and transgressive systems tracts, that is, depositional elements interpreted between the lower bounding unconformity surface (sequence boundary) and maximum flooding surface above. These typically constitute terrestrial distributary channels and floodplains landward of strike-aligned lowstand deltas and marine shoreline deposits at and over the relict shelf break area of the underlying sequence boundary. Basinward deep-marine shales, slope channels, splays, fans, and terminal channel lobes define the remainder of the deposition over the rather extensive deep-marine slope apron region of the western Nile Delta. Incised valleys, canyons, and broad slope channels often confine any of the above-mentioned depositional facies at the lower bounding unconformity of each sequence.

Igneous seismic geomorphology of buried lava fields and coastal escarpments on the Vøring volcanic rifted margin

Voluminous igneous complexes are commonly present in sedimentary basins on volcanic rifted margins, and they represent a challenge for petroleum explorationists. A [Formula: see text] industry-standard 3D seismic cube has recently been acquired on the Vøring Marginal High offshore mid-Norway to image subbasalt sedimentary rocks. This cube also provides a unique opportunity for imaging top- and intrabasalt structures. Detailed seismic geomorphological interpretation of the top-basalt horizon, locally calibrated with high-resolution P-Cable wide-azimuth data, reveals new insight into the late-stage development of the volcanic flow fields and the kilometer-high coastal Vøring Escarpment. Subaerial lava flows with compressional ridges and inflated lava lobes cover the marginal high, with a comparable structure and size to modern subaerial lava fields. Pitted surfaces, likely formed by lava emplaced in a wet environment, are present in the western part of the study area near the continent-ocean boundary. The prominent Vøring Escarpment formed when eastward-flowing lava reached the coastline. The escarpment morphology is influenced by preexisting structural highs, and these highs are locally bypassed by the lava. Volcanogenic debris flows are well-imaged on the escarpment horizon, along with large-scale large slump blocks. Similar features exist in active volcanic environments, e.g., on the south coast of Hawaii. Numerous postvolcanic extensional faults and incised channels cut into the marginal high and the escarpment, and we found that the area was geologically active after the volcanism ceased. In summary, igneous seismic geomorphology and seismic volcanostratigraphy are two very powerful methods to understand the volcanic deposits and development of rifted margins. Our study demonstrates great promise for further understanding the igneous development of offshore basins as more high-quality 3D seismic data become available.

Plio–Quaternary seismic stratigraphy and depositional history of the Ulleung Basin, East Sea: Association with debris-flow activity

We analyzed multi-channel seismic reflection profiles to decipher the Plio–Quaternary stratigraphic architecture and resolve the depositional history of the Ulleung Basin. A detailed seismic stratigraphic interpretation revealed nine seismic units (Units 1–9) separated by unit boundaries in the Plio–Quaternary deposits of the Ulleung Basin. Unit 1 (Pliocene) is dominated by debris-flow deposits (DFDs) throughout the basin. Units 2–9 (Quaternary) are characterized by stacked DFDs interbedded with thin hemipelagic sediments along the southern slope, whereas the northern basin floor is filled with hemipelagic and pelagic sediments. The areal distribution and dimensional characteristics of the DFDs indicate that sedimentation in the Ulleung Basin has been controlled by a combination of tectonic movement, eustatic changes in sea level, and gas hydrates dissolution and dissociation. During the Pliocene (Unit 1), sedimentation was mainly controlled by tectonic movements, causing margin-wide slope failures under the compressional regime. Large sediment deposits were supplied to the basin through mass-transport processes, resulting in an abundance of DFDs throughout the basin. During the Quaternary (Units 2–9), compressive stress decreased sharply, causing the DFDs to retreat landward. At that time, sedimentation was mainly influenced by eustatic changes in sea level and gas hydrates dissolution and dissociation. As the sea fell to the lowstand, slope failures were activated by the generation of high pore-water overpressure and the generation of weak layers in the sediments, resulting in stacked DFDs. However, as the sea level rose to the highstand, sediment was primarily deposited via hemipelagic and pelagic processes due to increased hydrostatic pressure and slope stability.

The development of volcanic sequences at rifted margins: New insights from the structure and morphology of the Vøring Escarpment, mid‐Norwegian Margin

AbstractOn the Vøring Margin offshore mid‐Norway, Paleogene continental breakup was characterized by the extrusion of large volumes of flood basalts erupted in different depositional environments. The transition from subaerial to submarine emplacement environment is marked by the formation of the Vøring Escarpment which records the early encroachment of flood basalt into the basin and the buildup of a lava delta system. The increased availability of new and reprocessed high‐quality seismic data allows a more detailed characterization of the along‐strike and across‐strike continuity and variability of the different volcanic seismic facies units. Detailed seismic interpretation shows that the ~350 km long NE‐SW trending Vøring Escarpment is a prominent feature along the Vøring Margin with a height ranging between 200 and 1600 m. Structurally, the Vøring Escarpment is segmented along strike into five segments (E1–E5) with different controlling factors leading to variation in accommodation space. Relative sea level change and magma supply are the major controlling factors for segments E2 and E4 which are characterized by a well‐developed lava delta system and significant escarpment height. Tectonic movements along the Jan Mayen Fracture Zone resulted in second‐order segmentation of the E1 segment into pseudoescarpments with a very thin lava delta system and limited escarpment height. Segments E3 and E5, situated along the flanks of Cretaceous/Paleocene highs, are controlled by the structural highs, which were possibly reactivated during breakup time. Our mapping results provide crucial information about the paleogeography and yield important information regarding the paleo–water depth and depocenter locations prior to and during the breakup of the Vøring Margin.

Seismic stratigraphic interpretation of megasequence and sequence framework in the Upper Cambrian through Devonian formations in the central part of the Darling Basin, western New South Wales, Australia

Upper Cambrian through Devonian formations in the central part of the Darling Basin, western New South Wales were investigated using seismic data, complemented by well and outcrop information. Detailed seismic stratigraphic interpretation of four main second-order seismic megasequence buildups in the central-northern Blantyre and southern Pondie Range sub-basins, shows that they are constructed of seventeen principal third-order seismic sequences. The four seismic megasequences are characterized as follows: Seismic megasequence A corresponds to the Upper Cambrian through Middle Ordovician strata and is equivalent to the Scropes Range Formation or Mutawintji Group, Seismic megasequence B corresponds to uppermost Silurian through Lower Devonian strata and is equivalent to the Winduck Interval, Seismic megasequence C corresponds to upper Lower Devonian through lower Middle Devonian strata and is equivalent to the Snake Cave Interval and Seismic megasequence D corresponds to upper Middle Devonian through Upper Devonian strata and is equivalent to the Ravendale Interval. Five regional seismic-stratigraphic boundaries have been identified in the three seismic sections to show the continuity of the Upper Cambrian through Devonian formations throughout the central-northern Blantyre and southern Pondie Range sub-basins. All seismic-stratigraphic boundaries are based on good continuous markers, with strong amplitudes throughout the whole sub-basins.Detailed sedimentological analysis was applied using lithologic samples, wireline-log and limited biostratigraphic information, to aid in the development of a paleodepositional environment for the Upper Cambrian through Devonian sequence which displays ten different sedimentary facies successions. Seismic facies analysis was also applied to some of the seismic lines, comparing well log observation with reflection configuration and other seismic characteristics for the Upper Cambrian through Devonian successions. The seismic facies patterns show continuous, semicontinuous and discontinuous reflections with moderate amplitude and high to moderate frequency. The sedimentary sequence from the well data can also be recognized in the seismic lines, with features such as subparallel to divergent high amplitude reflections, parallel to subparallel medium to low amplitude reflectors with high-amplitude and high-continuity reflections, sediment waves with hummocky clinoforms and sometimes high-angle clinoforms, indicating fluvial channels complex and shallow channel-fill complex. As a result, a sequence stratigraphic framework was constructed successfully, consisting of nine seismic sequences. Six of these contain three systems tracts (lowstand, transgressive to highstand) and two sequence surfaces (transgressive surface and marine flooding surface). Another seismic sequence is composed of two systems tracts, a transgressive systems tract and a highstand systems tract separated by a maximum flooding surface. The other two, within the Blantyre 1 well and the Pondie Range 1 well, consist of one stratal pattern that has a highstand systems tract capped by a seismic sequence boundary.

Regional magma plumbing and emplacement mechanisms of the Faroe‐Shetland Sill Complex: implications for magma transport and petroleum systems within sedimentary basins

AbstractThe movement of magma through the shallow crust and the impact of subsurface sill complexes on the hydrocarbon systems of prospective sedimentary basins has long been an area of interest and debate. Based on 3D seismic reflection and well data, we present a regional analysis of the emplacement and magmatic plumbing system of the Palaeogene Faroe‐Shetland Sill Complex (FSSC), which is intruded into the Mesozoic and Cenozoic sequences of the Faroe‐Shetland Basin (FSB). Identification of magma flow directions through detailed seismic interpretation of approximately 100 sills indicates that the main magma input zones into the FSB were controlled primarily by the NE–SW basin structure that compartmentalise the FSB into its constituent sub‐basins. An analysis of well data shows that potentially up to 88% of sills in the FSSC are <40 m in thickness, and thus below the vertical resolution limit of seismic data at depths at which most sills occur. This resolution limitation suggests that caution needs to be exercised when interpreting magmatic systems from seismic data alone, as a large amount of intrusive material could potentially be missed. The interaction of the FSSC with the petroleum systems of the FSB is not well understood. Given the close association between the FSSC and potential petroleum migration routes into some of the oil/gas fields (e.g. Tormore), the role the intrusions may have played in compartmentalisation of basin fill needs to be taken fully into account to further unlock the future petroleum potential of the FSB.