Post-Last Glacial Maximum seismic stratigraphy and sediment dynamics of the southernmost Central Vietnam shelf

The continental margin of SE New Zealand is strongly influenced by the Southland Current and associated water masses. This new seismic stratigraphic study of the margin has revealed a range of depositional mounds and erosional channels that document the close interaction of turbidity and bottom currents in shaping the margin from the Mid‐Eocene onward. Bottom‐current influence was initiated with the onset of the Antarctic Circumpolar Current, following the opening of the Tasmanian Gateway. Following this event, four stages of evolution are identified: (1) the Mid‐Eocene saw the onset of the first mixed depositional system with a series of levee‐drifts adjacent to downslope channels, alongslope‐oriented contourite‐dominated drifts, and an alongslope contourite moat; (2) the Early to Late Oligocene saw the continued vertical growth and incision of these mixed depositional and erosional elements; (3) the Late Oligocene to Mid‐Miocene saw a significant change to a more turbidite‐dominated mixed system, with a weakened bottom‐current influence; and (4) the Mid‐Miocene to Recent saw a resumption in bottom‐current activity, and development of a more contourite‐dominated system. The changes observed in margin evolution reflect variations in tectonic activity and source area uplift, variation in continental slope topography, and evolving bottom‐current systems.

Late Quaternary seismic stratigraphy and evolution of the shelf-incised Krka river valley on the Eastern Adriatic coast, Croatia

ABSTRACT The Cretaceous petroleum system beneath the volcanic rocks in the deep offshore Indus Basin presents a challenging yet potentially significant frontier for hydrocarbon exploration. This study utilises new 2D seismic reflection data to explore the stratigraphy and structural complexities within the basin, which is predominantly influenced by extensive magmatic activity. Key findings highlight the presence of significant stratigraphic discontinuities and potential hydrocarbon reservoirs below a regionally extensive basalt unit. Through detailed seismic stratigraphy and sequence analysis, integrating data from boreholes and seismic data, this study delineates five seismic facies units grouped into Lower and Upper Cretaceous megasequences, identifies features such as saucer‐shaped sill complexes and hydrothermal vent complexes, and assesses the post‐Cretaceous depositional environments. The complex interplay between tectonics, sedimentary and magmatic processes has been mapped, providing insights into the potential hydrocarbon system. Upper Cretaceous sequences show lateral variations with a northeast to southwest fining trend and differential thickness across the volcanic units, thinning northward and thickening southeastward towards the Saurashtra High. Lower Cretaceous sequences reveal lithologic composition and thickness variability, with the Sembar and Goru formations locally exceeding 2000 m in thickness on the shelf before thinning basinwards. Quantitative thermal modelling indicates that magmatic intrusions impacted source rock maturation, raising sediment temperatures by 50°C–100°C and affecting approximately 15%–20% of the Cretaceous Sembar Formation source rock, thereby potentially generating an additional 10%–15% hydrocarbons beyond burial maturation alone. Our quantification shows magmatic heating accelerated Sembar Formation maturation by 8%–18%, facilitating hydrocarbon generation in this sub‐basalt system. The timing of this magmatism (~70–60 Ma, just before and during Deccan volcanism) was favourable, coinciding with organic‐rich shales entering the peak oil window and favouring hydrocarbon generation and migration. These findings provide insights into the geological history and hydrocarbon potential of the offshore Indus Basin's Cretaceous units and offer analogues for other volcanic passive margins worldwide.

ABSTRACT The Rio del Rey Basin, situated at the easternmost extension of the Niger Delta in the Gulf of Guinea, remains one of the least explored deep‐water provinces, despite its proven petroleum system and structural affinity with the prolific neighboring basins. This study integrates well‐log interpretation, petrophysical evaluation, and seismic stratigraphy to assess the depositional architecture and hydrocarbon prospectivity of slope‐to‐basin‐floor turbidite systems within two exploratory wells (Idabato and Ifiari East) and regional 2D seismic profiles. Petrophysical analysis using Interactive Petrophysics software indicates that middle Miocene sand‐rich intervals exhibit favorable reservoir properties, with effective porosity ranging from 20% to 35% and permeability locally exceeding 400 mD. Total organic carbon (TOC) values derived from log‐based ΔlogR modeling range between 1.6 and 8.4 wt%, confirming the presence of organic‐rich shales capable of sourcing hydrocarbons. Cross‐plot analyses (neutron–density and sonic–density) reveal three dominant lithofacies: clean turbiditic sands, shaly sands, and marine shales organized into low‐stand and high‐stand system tracts within fault‐bounded mini‐basins. Seismic interpretation identifies growth faults, rollover anticlines, and shale diapirs as key structural controls on sand distribution and trapping geometry. These findings confirm the presence of a fully functional petroleum system comprising source, reservoir, and seal elements within deep‐water turbidite complexes. Exploration potential remains high in stratigraphic traps at channel‐lobe transitions and in structural closures adjacent to shale diapirs. This study provides a predictive framework for hydrocarbon exploration in the Rio del Rey Basin and analogous Atlantic passive margins globally.

The Pearl River Mouth Basin (PRMB), located on the northern margin of the South China Sea, contains a significant volume of early Miocene (17.25–14.8 Ma) deltaic strata. The characteristics of these deposits, including their facies, thickness and distribution, are influenced primarily by geomorphology and sea-level fluctuations within the relatively shallow Zhu-1 Depression. Based on newly acquired 3D seismic data and 37 pre-existing wells, we identify positive and negative landforms that developed in the early Miocene between the Southern Enping Sag and the Eastern Yangjiang Sag. The study identified and correlated maximum flooding surfaces and 3rd-order sequence boundaries in study area wells. Integration of well picks with 3D data allowed extensive sequence correlations in seismic to better statistically define differing sand body characteristics of lowstand systems tracts (LST), transgressive systems tracts (TST) and highstand systems tracts (HST) in seismic facies analysis. We show that (1) channels in positive landforms are primarily deltaic, frequently avulsive and linked to sequence boundaries, typically within low-accommodation LST and late HST, forming laterally extensive thick sand bodies; and (2) channels in negative landforms are mainly estuarine, stable and linked to marine flooding surfaces, typically within high-accommodation TST and early HST, forming narrower, vertically stacked thin–medium sand bodies. We assess the reservoir potential of >10 m thick distributary channel sand bodies in positive landforms using wide-frequency interval RGB colour-blending slices, and 2–10 m tidal bars in negative landform units using narrow-frequency interval RGB-colour blending slices. By integrating the principles and techniques of a comprehensive sedimentological–geophysical analysis, our study predicts stratigraphic targets within delta front reservoirs, considering geomorphological and stratigraphic changes. This study not only improves the understanding of reservoir characteristics in the PRMB but also provides valuable insights for future exploration in similar deltaic geological settings.

ABSTRACT This study focuses on the Çandarlı Trough and its surrounding area, located between the Çandarlı Bay and Plomari Basin, which represents a key but understudied sector of the northeastern Aegean Sea. The interaction between sedimentation and tectonics in this region has been largely overlooked, despite its potential to provide valuable insights into regional tectonic processes. By integrating multibeam bathymetry data, seismic reflection profiles, lithostratigraphic and sonic log data from the Foça‐1 exploration well, earthquake focal mechanisms and GPS velocities, this study defines five Miocene‐Quaternary seismic stratigraphic units and reconstructs the tectonic evolution of the study area. The seismic succession documents (i) Burdigalian‐Serravallian volcanoclastic rocks, (ii) Tortonian terrestrial clastics, (iii) Messinian evaporites, (iv) Pliocene sandstones and limestones and (v) Quaternary sediments. Homogeneous thickness during the Tortonian‐Messinian period indicates reduced tectonic activity, whereas renewed Plio‐Quaternary deformation is expressed by active NW‐SE‐striking normal faults and uplifted shelf margins. Earthquake focal mechanisms and GPS vectors confirm ongoing transtension and right‐lateral shear, positioning the Çandarlı Trough as a transitional zone between the westward‐moving Anatolian Block and the Aegean back‐arc system. These results refine the regional tectonic framework by linking local basin development to the wider tectonic evolution of the northeastern Aegean extensional system.

The Central Arabian Basin is a sedimentary basin that contains a significant number of hydrocarbon reserves. In addition, the Mesozoic succession has the most petroleum system elements. However, publicly available subsurface data for the Central Arabian Basin are scarce. Therefore, our study successfully utilizes wellbore and 2D seismic reflection data from the Central Arabian Basin to reveal the sedimentary processes, depositional environment, and evolution of Mesozoic deposits. Six horizons with onlap and truncation seismic reflection termination, hummocky, subparallel, onlap fill, and chaotic structures with recognizable stratal pattern seismic reflection configurations are interpreted. The lithologies of the Mesozoic deposits are limestone, dolomite, anhydrite, sandstone, and shales. The Mesozoic deposits in the study area were deposited in the shallow marine environment of an intrashelf basin with tidal channels, reefs and transgressive shale depositional elements. Our workflow provides an interpretation of the stratigraphic evolution and depositional environment of Mesozoic deposits in the Central Arabian Basin and could also be applied to a basin with a similar geological setting worldwide.

The Sequoia Pliocene channel reservoirs within the West Delta Deep Marine (WDDM) concession, located offshore of the Nile Delta, pose significant challenges due to their complex stratigraphy and variable reservoir properties. This study employs an integrated approach, combining seismic data interpretation with comprehensive petrophysical analysis, to characterize these reservoirs and assess their hydrocarbon potential. Seismic data interpretation revealed a complex depositional environment, characterized by an upward-fining sequence of sandstones and mudstones. High seismic amplitudes were associated with gas sands, while lower amplitudes indicated background shale. The seismic stratigraphy indicates that the Sequoia channel system evolved from an initial high-energy erosional phase to a more subdued depositional environment, leading to significant heterogeneity in the reservoir quality. Petrophysical analysis demonstrated that effective porosity values within the reservoir range from 18 to 30%, with water-saturation levels of between 38 and 68%, reflecting the variability in reservoir properties across different zones. The calculated gas initially in place (GIIP) for the Sequoia channel ranges from 724.1 to 4158.71 Bcf, highlighting the substantial hydrocarbon potential within this complex system. This study underscores the importance of integrating seismic and petrophysical data to develop a comprehensive understanding of the Sequoia channel reservoirs. The results provide a robust framework for optimizing field development strategies, which is crucial for maximizing hydrocarbon recovery. The findings also offer valuable insights into the geological complexities of the WDDM concession, serving as a reference for future exploration and production efforts in similar deep-water environments.

This study presents a high-resolution seismic stratigraphic and structural interpretation of the Esenköy offshore which is located at the northern margin of the Armutlu Peninsula in the Sea of Marmara. Four distinct seismic units (U1–U4) were identified based on variations in reflection characteristics, continuity, depositional and truncation geometries. Unit U1 is characterized by weak, parallel reflections, thinning northward, while U2 displays sigmoid clinoforms that thicken in the same direction. Unit U3 shows parallel to semi-parallel reflections and is marked by high-amplitude boundaries, whereas the lowermost unit, U4, exhibits chaotic to discontinuous reflectors indicative of older or tectonically influenced deposits. Seismic profiles reveal marked changes from south to north, including the development of canyon head structures that incise into the upper surface of U3 without affecting deeper units. Depth structure and thickness maps indicate that tectonic activity, sediment input variability, and slope morphology play key roles in controlling the distribution and deposition of these units. The results highlight the combined influence of tectonic structuring, sedimentary processes, and morphological evolution in shaping the stratigraphy of this tectonically active marine margin.

The Guinea Plateau contains an ∼200 Myr stratigraphic record, encompassing the mid-Cretaceous opening of the Equatorial Atlantic Gateway (EAG). Here we present new 2D seismic data to constrain the structural and stratigraphic evolution of the plateau. Seismic stratigraphic analysis reveals five megasequences of ∼25–65 Myr duration: M1, a Jurassic synrift sequence with prominent seaward-dipping reflections; M2, a late Jurassic–Early Cretaceous post-rift carbonate platform; M3, a late Early Cretaceous transform clastic-dominated sequence; M4, an Albian–Maastrichtian ocean–continent transform to post-transform sequence; and M5, a Maastrichtian–recent passive margin sequence with low sedimentation rates. These megasequences also contain prominent transgressive–regressive cycles of 5–10 Myr duration, interpreted to be the result of dynamic topography. The boundary between M3 and M4 is a major erosional unconformity documenting the final continental break-up during the opening of the EAG. Above this, a pronounced Albian to Cenomanian/Turonian marine transgression resulted in marine inundation of the plateau. Structural deformation continued into the early Cenomanian along the Guinea Marginal Ridge, a potential structural barrier that restricted marine connection across the EAG. Bulk geochemical data from the shallow Guinea Plateau indicate that enhanced carbon burial in this setting was primarily driven by the deposition of reworked, oxidized organic matter during an oceanic anoxic event, independent of gateway opening.

Abstract Valdivia Bank (VB) is an oceanic plateau in the South Atlantic that formed from hotspot‐ridge volcanism during the Late Cretaceous at the Mid‐Atlantic Ridge (MAR). It is part of Walvis Ridge (WR), a quasi‐linear seamount chain extending from offshore Namibia to Tristan da Cunha and Gough Islands. To understand Valdivia Bank evolution, we interpret the seismic stratigraphy from multichannel seismic data paired with coring results from International Ocean Discovery Program (IODP) Expedition 391, which recovered mostly pelagic nannofossil ooze and chalks. The seismic section can be divided into three seismic units (SU), a lower transparent interval which is faulted and conforms to basement, a middle, moderate to high amplitude interval which is thick in local depocenters such as rifts, and an upper, subparallel transparent interval. Notable features include regional unconformities, dipping clinoforms, mass transport and contourite deposits, and volcanic structures. Additionally, three infilled rifts are observed across the plateau. Our analysis implies that following a period of sedimentation in the Campanian, the edifice was faulted through the Paleocene, coinciding with a South Atlantic tectonic reorganization. Local depocenters formed as a result of rifting. Subsequently, the plateau experienced thermal rejuvenation and regional uplift during the Eocene. Volcanic mounds were emplaced atop Cretaceous sediments and intrusives were emplaced within the sediments. During the Cenozoic, sedimentation was punctuated, likely in response to changes in the carbonate compensation depth and bottom current intensification. VB sedimentation was complex and largely influenced by the paleoceanographic context of the plateau, as well as thermal rejuvenation and tectonism.

High amplitude bottom simulating reflections (BSRs) interpreted in seismic reflection data are common proxy indicators for gas hydrates, while the spatial relationship of BSRs with fault systems can provide an indication for the source of gas bound within hydrates. The spatial correlation of fault zones with strong BSRs and thick free gas zones (FGZs) has sometimes been recognised as a common feature of thermogenic hydrate systems. We investigate the seismic stratigraphy and reflectivity of New Zealand’s Chatham Rise northwestern slope (CRNWS), which is a remnant section of the ancient East Gondwana subduction margin’s accretionary wedge. Seismic interpretation indicates the presence of a partially subducted, Cretaceous-aged sedimentary unit beneath the inactive, ∼6 km-thick East Gondwana accretionary wedge. Heat flow estimation and calculation of temperature profiles suggests that the ∼1–2 km-thick downgoing Mesozoic sedimentary sequence (MES) is situated within a thermal window conducive to thermogenic methane generation. As the downgoing MES may contain source rocks similar to the Glenburn Formation, a well-known thermogenic source, which is proposed to span the neighbouring Pegasus and East Coast Basins, we propose the presence of a sub-Gondwanan wedge thermogenic gas zone. Overlying the proposed Gondwanan thermogenic zone by ∼6–8 km, seismically-distinct shallow BSRs and hydrate-related features are interpreted spanning ∼1400 km2 of the CRNWS. BSRs often terminate against and are associated with deeply-rooted CRNWS faults, which penetrate the Gondwana wedge. These BSRs mark previously-undefined hydrate accumulations situated ∼50–100 km SW from the active Hikurangi subduction margin. We interpret the presence of thermogenic methane within the CRNWS hydrate zone, supplied from the ∼8–10 km deep downgoing MES by Gondwanan thrust faults, and BSR-proximal fault asperities. The close association of BSRs with a shallow, unit-bound polygonal fault complex may be further distributing free gas, up-dip across the CRNWS, resulting in concentrated hydrate accumulations and thick (∼100–150 m) FGZs.

Relevance. The heterogeneity of the lithological composition (alternation of carbonate, effusive, clay-siliceous and other rocks), steep angles of strata incidence, the neighborhood of ancient rocks with much younger rocks, tectonic activity evidences and metamorphosis processes make it difficult to predict the objects of the Pre-Jurassic depositional complex that are promising from the point of view of the presence of hydrocarbons. Object. Seismic wavefield of the Pre-Jurassic complex of deposits in the southeastern part of the West Siberian oil and gas province (Tomsk and Novosibirsk regions). Aim. Carrying out a morphological description followed by systematization of images of the seismic wave field of lithologically heterogeneous rocks of the Pre-Jurassic complex. Methods. The study of the seismic wave field behavior in various geological formations of the Pre-Jurassic depositional complex. Seismic stratigraphy and seismic formation analysis of time seismic sections. Generalization and systematization of accumulated data. Classification of various typical objects of the Pre-Jurassic complex according to the wave pattern. Results and conclusions. The author has typified the main seismogeological complexes of the Pre-Jurassic deposits of the south-east of Western Siberia (Tomsk and Novosibirsk regions). The considered criteria of seismogeological typification are recommended for assessing and zoning the seismic wave field of Paleozoic objects according to their degree of prospects. The limestones overlain by weathering crust, as well as monocline and submerged blocks of organogenic limestones and dolomites stand out most vividly on the seismic record. The protrusions of igneous rocks are least energetically pronounced. An additional seismogeological class of regular recording was identified. It is characterized by the deflection of the central part of blocks of horizontally layered rocks. This may be characteristic of clustic deposits (volcanogenic sedimentary formations of the Triassic), which may be unpromising in the deposits of the Pre-Jurassic complex in the territory under consideration. The aithor proposed the approaches for further development of the study.

Understanding the sedimentary dynamics of continental shelves is crucial for decoding past high-energy events like tsunamis. Based on data from HSV FISA<acute accent>LIA cruise of the Portuguese Navy, this study investigates the geomorphological features of the southwestern Algarve shelf and the seismo-stratigraphic characteristics of sedimentary units attributed to two tsunamis that occurred in 1755 CE (Lisbon earthquake) and ca. 3600 cal yr BP. Using high-resolution geoacoustic profiling in combination with sedimentological analyses and radiocarbon dating from prior studies, this study is the first to identify an Infralittoral Prograding Wedge on the shallow southwestern Algarve shelf. Furthermore, remnants of an older transgressive prograding wedge-shaped sediment body have been detected on the mid to outer shelf off Portimao. A crucial finding of this study is a high- amplitude reflector which has been associated with the ca. 3600 cal yr BP tsunami deposit. This reflector is particularly strong based on the corresponding deposit's stark compositional contrast with the surrounding sediment. In its distribution, this reflector is restricted to the base of the Infralittoral Prograding Wedge indicating this wedge as the most likely sediment source for the ca. 3600 cal yr BP deposit. On the other hand, the 1755 CE Lisbon tsunami deposit has no clear geophysical signature on the southwestern Algarve shelf due to its vestigial thicknesses and scarce compositional contrast with the surrounding sediment. This divergence raises significant questions about the different triggering mechanisms and transport processes that define both offshore tsunami deposits. Our findings highlight the significance of local bathymetric conditions, sediment sources, as well as triggering mechanisms and transport pathways in shaping offshore tsunami deposits.

Abstract The deep-water Sadewa Field is located about 45 km east-northeast offshore of the Mahakam delta, North Kutai Basin, East Kalimantan Indonesia, at water depths of 1,000 to 2,800 feet. Most of the producing reservoirs in Mahakam delta were the Early Miocene sand reservoirs deposited in shallow water of shelf delta. During Miocene the study area was submerged under shallow sea level and there were multiple small-scale low-stand system-tracts deltas deposited along the Sadewa shelf slope. The coarse-grain clastic sediments were fed the shelf slope onto the channels and local fans of the deltas. The local fans were filled with thicker, cleaner, and more porous sands as they had bigger accommodation space and higher depositional energy than the channels. Seismic stratigraphy analysis, guided by seismic attributes, identifies and maps the channel and fan facies. This research focuses on delineating the Sadewa Miocene net-pay sand reservoirs using seismic attributes and inversion. The post-stack AI inversion is applied to mapping the associated lithology, porosity, and pore fluids. The net-pay sand was calculated based on the stratigraphic thickness between the two top target zones (gross sand) with cut-off values of VCL &lt; 40%, POR &gt; 10%, and SW &lt; 70% for each target reservoir. Based on the cross plot between seismic attributes and net-pay thickness, shows that net-pay thickness is associated with high RMS seismic amplitude and low attribute variance. The result shows that RMS seismic amplitude is related to the presence of hydrocarbon fluid and the variance is related to the facies and reservoir geometry in terms of continuity and reflector alignment. Thus, using the RMS amplitude*1/Variance attribute can provide answers for hydrocarbon production needs and determine which geometry and sediment are more prioritized. Later, this attribute can be used to see the distribution of net-pay sand with facies and reservoir geometries with high thicknesses.

Background. The hydrocarbon potential of the Zykh-Hovsan area is predominantly associated with the Lower Pliocene deposits of the Productive Series. However, at present, the main hydrocarbon-bearing unit in the Zykh-Hovsan field is the Qala Suite (QaS). The Miocene deposits underlying the Qala Suite have also been of particular interest in recent years. The present seismic studies were conducted in the view of new 3D seismic survey data. The purpose of the studies was to detail the geological models of the Zykh structure, to identify and trace the zones of development of faults and to identify oil and gas prospects of both the Qala Suite and Miocene. Methods. Seismic stratigraphy and sequence stratigraphy methods were chosen as the main research methods. Attribute analysis was also carried out. Results. In order to expand the resources of the Zykh field, recommendations were prepared for drilling of exploratory and appraisal well №2 based on 3D seismic survey data. Geological and geophysical materials were prepared and analyzed to justify the selection of the location of exploratory wells. After analyzing the seismic cubes, 3 location points of the project prospecting wells were selected, from which the first priority well – Zykh-2 – was selected and recommended for drilling. The recommended exploratory well Zykh-2 is located on the eastern steep slope of the Zykh uplift, in an area where prospective seismic facies in the Qala Suite intervals and prospective targets in the Miocene section are reliably and confidently identified in the section. The presence of well-defined seismic attributes as well as seismic classes in the predicted part of the section all indicate the presence of probable traps here. The well solves the task of both searching for the lower part of the sedimentary cover not explored by drilling and exploring the peripheral (eastern) part of the reservoir of the Sub Kirmaky Suite. Сonclusions. The studies have shown that the prerequisites for oil and gas bearing capacity on the eastern slope of the Zykh uplift are the existing favorable regional conditions of petroleum system development, and also local favorable conditions, which consist in the presence of a screening formation elongated in the submeridional direction. The negative factors include the steep eastern slope of the Zykh uplift. Taking into account the results obtained and analytical data, the Zykh-2 exploratory well is recommended for drilling in the project location.

A reappraisal of Mesozoic-Cenozoic sequence stratigraphy in Offshore Indus Basin, Pakistan

Seismic stratigraphy and petroleum prospectivity in the Northern Rovuma Basin, offshore Tanzania

This review aims to present an updated lithostratigraphic framework of the northern Danube Basin in Slovakia, consistent with recent shifts in geochronology and depositional system redefinitions based on sedimentology and seismic stratigraphy. Several transgressive–regressive sequences are distinguished: The Lower Badenian (Middle Miocene), represented by the Špačince Fm, mainly occurred in peripheral Blatné and Želiezovce sub-basins. The central part of the Danube Basin formed an elevation during this period, coinciding with the onset of intermediate volcanic activity. The Upper Badenian (Middle Miocene), encompassed within the Pozba Fm, saw the flooding of the central Danube Basin, signifying a change in transport direction. The inception of this cycle is well constrained by recently published multiple 40 Ar/ 39 Ar dating to c. 13.8 Ma. The Sarmatian deposition (Middle Miocene), characterized by the Vráble Fm, also occurred in newly significantly deepened Komjatice and Rišňovce sub-basins, coinciding with a gradual cessation of calc-alkaline volcanism, observed only at the basin's eastern edge. The Pannonian (Upper Miocene) deposition includes lacustrine Ivanka, deltaic Beladice and alluvial Volkovce formations, representing interconnected depositional systems prograding towards Lake Pannon. The subsequent evolution entails a post-rift stage (9.5–6 Ma), primarily marked by the alluvial Volkovce Fm deposition, and basin inversion, with alluvial deposition mostly confined to the basin centre and differentially eroded basin margins (from 6 Ma to the present).