Basin Research - Volume 37, Issue 6, 2025

Deep gorges with abrupt river elbows and high‐elevation, low‐relief interfluves containing fluvial sedimentary rocks characterize southeastern Tibet. This transient landscape reflects Eocene to present drainage divide migrations and river captures, reshaping catchment boundaries through episodic exchanges of drainage area between neighboring basins, notably the Jinsha (upper Yangtze) and Yalong Rivers.

The geometry and evolution of the rivers originating from the Tibetan Plateau have been influenced by topography and climate changes during the India–Asia collision. One notable example is the Jinsha (upper Yangtze) River, which expanded its drainage area at the expense of other rivers through several river captures, the timing of which remains controversial. This study focuses on the Yalong River, a major tributary of the Jinsha River, characterised by deep gorges, sharp elbows, where the river exhibits abrupt changes in channel orientation, and interfluves with high‐elevation, low‐relief areas that contain riverine sediments. One such area north of the Yalong–Jinsha confluence is the Yanyuan Basin, which is filled with mainly Eocene alluvial fan deposits and Pliocene fluvial conglomerates that preserve part of the detrital history of the Yalong River. We use detrital rutile U–Pb, muscovite ⁴⁰Ar/³⁹Ar, zircon U–Pb, and fission‐track double dating to constrain the provenance of the Cenozoic detritus of the Yanyuan Basin. Our combined data suggest that the Eocene clastic infill of the Yanyuan Basin was mainly supplied by the Paleo‐Yalong River, which, like the modern Yalong, originated from the Yidun Arc but flowed southward into the Yanyuan Basin, in contrast to the river's current course that flows around the basin and then southward. In the Pliocene, the presence of a small population of young (Cenozoic) zircon grains alongside a dominant population of Neoproterozoic zircons, rutiles, and muscovites shows that the Paleo‐Yalong catchment expanded eastward, including a river originating from the Gongga batholith that flowed southwestward into the Yanyuan Basin. The absence of Cenozoic and Late Cretaceous detrital ages in the modern Yalong River, alongside the presence of the Late Cretaceous ages in the modern Jinsha River, indicates that between the Pliocene and the Present, the Yalong basin experienced a reduction in area on both its western and eastern margins. Finally, during this time, drainage reorganisation resulted in the isolation of the Yanyuan Basin from distant sediment sources, as the Yalong entrenched into its modern gorge.

The Meso‐Neoproterozoic eras witnessed critical transitions in supercontinental cycles that shaped global tectonic regimes and paleogeographic configurations. This study presents LA‐ICP‐MS zircon U–Pb geochronology analyses of thirteen sandstone samples from the Yan‐Liao rift zone along the northern North China Craton (NCC) margin to constrain regional tectonic evolution and basin development. Detrital zircon populations exhibit multiple age clusters, with pre‐1800 Ma grains derived from NCC basement terranes and younger populations (< 1.8 Ga) correlating with Mesoproterozoic magmatic events. Systematic younging of Maximum Depositional Age (MDA), determined through robust statistical treatment of the multi‐MDA method, reveals spatial–temporal depositional patterns controlled by source‐to‐sink relationships across the rift system. Provenance analysis demonstrates that evolving rift morphology progressively modified zircon transport mechanisms and age distributions, defining four distinct stages of basin evolution between 1.8 and 0.9 Ga. These evolutionary phases exhibit temporal correlations with global supercontinent cycles—initial rifting phases correspond to Columbia breakup (1.8–1.4 Ga), while later tectonic reorganization aligns with Rodinia assembly (1.4–0.9 Ga). Our integrated approach provides critical constraints on NCC margin evolution during Precambrian supercontinental transitions, offering new insights into cratonic responses to global‐scale geodynamic processes.

Integrated detrital zircon U–Pb ages (1.6–2.7 Ga) and a four‐stage rift evolution model with hybrid MDA methods reveal the North China Craton's dual responses to Columbia–Rodinia supercontinent cycles and resolve tectonic‐sedimentary dynamics, highlighting localized provenance isolation within the Yan–Liao rift zone during Rodinia assembly.

Basement strucrures divide the Essaouira Basin into five structural domains, each displaying distinct salt thicknesses and deformation styles.

We integrate high‐quality 3D seismic reflection surveys and well data to investigate the influence of basement architecture on salt tectonics in the Essaouira Basin, offshore Morocco. Seismic interpretation and base salt mapping reveal previously undocumented rift‐related structures offsetting the base of salt, including the prominent Cap Ghir Graben and the South Cap‐Sim Fault. These features help define the boundaries between salt‐tectonic domains in the area, each characterised by unique salt thicknesses and structural styles. Thin depositional salt is associated with salt‐cored anticlines, punctuated by occasional diapirs. Conversely, the areas with thick depositional salt are characterised by thick salt withdrawal basins in places overlain by salt sheets and canopies. Salt province mapping in the Essaouira Basin illuminates the profound control exerted by inherited rift‐related salt structures on subsequent basin development. While subject to refinement with new data, this understanding provides a critical framework for future exploration and analysis within this structurally complex basin.

Salt tectonics exerts a fundamental control on both the storage potential for CO2 and hydrogen and the formation of hydrocarbon traps across numerous basins, including the North German Basin. Here, we investigate salt dynamics within the basin, uncovering a previously unrecognised link between deep‐seated and supra‐salt faulting and diapirism along its margin. Much of the North German Basin has a simple structural outline characterised by few faults and Zechstein salt mobilised into large salt pillows. In contrast, the northern basin rim is characterised by a complex fault belt and by salt diapirism. Seismic data show that the Lolland‐Falster Fault Zone is part of this fault belt. Detachment faulting over a decollement of Zechstein salt occurred here in the latest Middle to early Late Triassic triggered by mild deep‐seated faulting and furthered by gravitational gliding and local loading from infill of rift depressions. Contemporaneous diapirism took place locally within this fault zone utilising faults as conduits. While from ~300 m to +2 km thick Zechstein halite buffered deep‐seated fault break‐through, and thus hampered diapirism in the central part of the basin, the modest salt thicknesses of around 250–300 m at the outer basin margin permitted fault break‐through, such that diapirism became limited to the basin outskirts despite lesser salt volumes. These mechanisms are applicable in epicontinental salt basins elsewhere. Near basin centres, ductile deformation of thickly developed salt layers inhibits mechanical break‐through of deep‐seated faults into the overlying supra‐salt section. Triggering of salt diapirism here requires strong faulting. In contrast, salt attains a critical thickness on the outer basin margin bordering the basin centre, thin enough for small‐offset deep‐seated faulting to pierce through and thick enough for salt to mobilise into diapirs within fault zones. In Lolland‐Falster, following a pause in salt motion and faulting, renewed differential salt movement and faulting took place during the Mid‐Cimmerian uplift in Middle Jurassic through Early Cretaceous time reactivated by regional tectonism and instability. Salt motion and faulting ceased during the Early Cretaceous with tectonic tranquillity persisting into the Late Cretaceous. The most recent episode of salt motion and detachment faulting occurred sometime during the Cenozoic, deforming the Chalk Group and overlying Palaeocene sediments. Investigations of the near‐surface geology through shallow seismic interpretation, review of SkyTEM data and interpretation of the present‐day landscape based on DEM maps document surface and near‐surface expressions of deeper faults and salt structures caused by either differential erosion or very young salt motion.

Thick salt in basinal areas forms a mechanical boundary that inhibits basement‐rooted faults from breaking through. More anhydrite/carbonate‐rich, brittle Zechstein lithologies at the outer basin margin allow break‐through, which triggers supra‐salt gliding and detachment faulting. Salt intrudes supra‐salt faults and diapirs form at the outer basin margin, while the salt‐rich basin centre is characterised solely by salt pillows.

Mississippian carbonate platforms in the East Irish Sea Basin developed not only on footwalls but also within hanging wall basins, controlled by inherited N–S faults. Seismic interpretation reveals complex growth geometries and platform demise, offering new insights into extensional tectonics and geothermal reservoir potential in structurally complex carbonate systems.

Mississippian‐aged (Lower Carboniferous) syn‐rift carbonate platforms in the UK have been extensively studied in outcrop. They have been interpreted to grow principally on the footwall of faults, with deeper marine sedimentation in the adjacent hanging wall basins. However, the transition from the shelf margin to the basin is often poorly constrained due to a lack of exposure and the scarcity of high‐quality seismic data. With renewed interest in Mississippian carbonate strata as potential geothermal reservoirs in northern Europe, a better understanding of the detailed geometry of these carbonate platforms, and the controls on their growth and demise, is crucial as it provides insights into their occurrence, size and thickness and burial/exposure history. This study uses high‐resolution 3D seismic data from the southern part of the offshore East Irish Sea Basin (EISB), western UK, to identify, characterise and map the platform to basin transition of the North Wales carbonate platform, exposed on the North Wales coastline. The results indicate that there is not a simple platform to basin transition, as has previously been mapped, but that the North Wales platform gives way offshore to numerous small carbonate platforms, the presence of which is predominantly controlled by N‐S‐oriented extensional faults. The fault orientation is not consistent with the regionally interpreted N‐S stress direction during the Mississippian, but fault growth analysis suggests that their orientation most likely reflects the precursor structural grain. These faults facilitated the development of horst‐graben structures, promoting carbonate growth on footwalls within the EISB. Six areas of potential carbonate platform development (A1–A6) were mapped and evaluated. Thicknesses range from ~1 to 2 km. The platforms prograded during the Tournaisian, characterised by low‐angle slopes, followed by a backstepping phase in the Visean, marked by steeper slopes. The platforms significantly shrank in size from the early Tournaisian to the Visean, resulting in the formation of complex, patchy carbonate platforms with diverse shapes and sizes. The results demonstrate that numerous small carbonate platforms grew in the EISB on structural highs but were susceptible to environmental change at the end of the Mississippian, causing them to become increasingly isolated and to eventually drown.

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.

A comprehensive integration of geomorphological, stratigraphic, geophysical, and geodetic datasets is employed to characterise the tectono‐stratigraphic architecture of the Çandarlı Trough and its surrounding area. The synthesis incorporates the morphotectonic map, litho‐stratigraphy and sonic log data from the Foça‐1 well, the marine stratigraphic section, the offshore fault network, the seismic profile crossing Foça‐1, the 3D fault model, and GPS velocity and error maps, together with a tectonic reconstruction of the region. This study provides a refined tectono‐stratigraphic framework, thereby improving the understanding of active fault architecture and regional deformation patterns within the north‐eastern Aegean domain.

Megabeds, also known as ‘megaturbidites,’ are exceptionally large submarine sediment deposits likely formed by catastrophic geohazard events. These deposits are increasingly being identified with modern high‐resolution geophysical data, yet their origins and characteristics remain debated. Five megabeds have been identified in the Marsili Basin of the Tyrrhenian Sea within the upper 70 m of sediment. These deposits are hypothesized to have been triggered by explosive volcanic eruptions of the Campanian Volcanic Province, including the ~39.8 ka Campanian Ignimbrite (CI) super‐eruption, which is among the largest known eruptions, having a volcanic explosivity index (VEI) of 7. These megabeds were intersected by Ocean Drilling Program (ODP) Leg 107 Site 650, where sediment cores were collected in 1986. However, their presence was not recognized at the time due to lack of appropriate geophysical data. To better understand the properties and origins of the Marsili Megabeds, we identified the megabeds within the ODP cores and conducted detailed sedimentological and elemental analyses, along with age dating, to determine their possible sediment provenance, depositional mechanisms, and potential triggering events. Elemental analysis and age dating suggest a potential link between these megabeds and known eruptions from the Campanian Volcanic Province, including the Neapolitan Yellow Tuffs eruption (14.9 ka), the Masseria del Monte Tuff eruption (29.3 ka), and the Campanian Ignimbrite super‐eruption (39.8 ka). A new megabed discovered below the Y‐7 tephra is older than 60,300 years but its triggering event is unknown. The re‐examination of ODP cores reveals that not all megabeds conform to a megaturbidite morphology. In the Marsili Basin, the variety of sedimentological structures differs within and between megabeds, suggesting varying and complex depositional mechanisms. The findings reveal that the megabeds are more internally complex than previously thought, with variations in their depositional processes even in one basin.

Widepsread and thick megabeds occur in the Marsili Basin of the Tyrrhenian Sea. Megabeds are linked to volcanic eruptions. The Marsili megabeds are recorded by thick turbidites to complex and heterogeneous deposits.

• A sequence of 5 megabeds occurs in the upper 60 kyrs of strata in the deepwater Marsili Basin in the Tyrrhenian Sea.
• The Marsili megabeds are more internally complex than previously thought.
• New age‐dates and XRF data aligns the Marsili Megabeds with volcanic eruptions from the Phlegraean Fields of Italy.

The southern Levant Basin, Eastern Mediterranean, has a complex geological history. The separation of Africa from Arabia, and the collision of the latter with Eurasia during the Oligocene–Miocene had significant implications for the tectono‐stratigraphy of the region, as recorded in the thick, siliciclastic‐dominated sequence preserved in the southern Levant Basin. Previous studies mostly focused on either onshore or relatively local offshore areas, with a synthesis of the interplay between plate motions and sedimentation still lacking. Using multiple high‐resolution, 3D seismic reflection surveys, we generated sediment thickness maps, spectral decomposition, and ISO‐proportional slices that document the structural and sedimentological elements shaping the basin during the Oligocene–Miocene. More specifically, our results show that during the Early Oligocene, sedimentation was dominated by an easterly (Arabian) source, whereas the Late Oligocene to Aquitanian witnessed a shift to a southerly (African) source through the evolution of the Nile River. The Burdigalian period marked a significant tectono‐stratigraphic transition period during which large‐scale folding, regional faulting and renewed incision had occurred. The Langhian–Serravallian was followed by widespread carbonate deposition. The Early Tortonian is marked by a thick, extensive, seismically chaotic interval that underlies deposits associated with the Messinian Salinity Crisis. This interval is identified across the basin, being associated with the collision of Cyprus and Eratosthenes, a major tectonic event that affected the entire Southern Levant Basin. The Late Tortonian–Messinian was largely characterised by widespread submarine incision across the southern Levant Basin. Our study reveals how sedimentary systems record important clues as to complex tectonic reorganisations involving rifting, subduction and strike‐slip motion.

• Complex Oligocene‐Miocene tectono‐stratigraphy shaped Levant Basin's sedimentation patterns.
• We used 3D seismic data to document the structural and sedimentological elements in the basin.
• By integrating onshore‐offshore events our findings shed light on the sediment source to the Levant
• A compilation of tectono‐stratigraphic maps was created for a simplified coherent evolutionary model.

Synthesis of Late Burdigalian tectono‐stratigraphic events occurring in and around the southern Levant Basin. Highlighted are the active NW‐Se‐striking normal faults nucleating onshore Sinai and across the southern Levant Basin. The offshore strike‐slip fault networks are also highlighted and are believed to be related to the same event which nucleated the regional normal faulting and the northward propagation of the Dead‐Sea transform. Also highlighted are the renewed incised valley canyons offshore (Green – Afiq, Blue – Ashdod and other regional transport system).

• Sandstones were sampled on the Cretaceous divergent margin of the Demerara Plateau (Buteur Ridge)
• Sedimentary and thermal history evidences two‐rifting stage of the Equatorial Atlantic
• The onset of the first rift stage of the Equatorial Atlantic rift occurred during the Hauterivian
• The second rift stage began during the Cenomanian and likely ended during the Late Cenomanian

Reconstructing the sedimentary, diagenetic, and thermal history of sediments from the Buteur Ridge (tilted block) constrains the evolution of the Demerara Plateau's Cretaceous divergent margin. The results reveal two distinct rifts of the Equatorial Atlantic, the first one starting during Hauterivian, a second rifting occurring during Cenomanian, the latter likely linked to the kinematic reorganisation between Africa and South America.

The permanent oceanic connection between the Jurassic Central Atlantic and the Cretaceous South Atlantic was only established with the late opening of the Equatorial Atlantic, but the timing of this event remained unclear due to a lack of geological dating. In 2023, the DIADEM oceanographic cruise conducted sampling of the Buteur Ridge, offshore French Guiana, by dredging and during a manned deep submersible (Nautile) dive. The Buteur Ridge belongs to the eastern rifted margin of the Demerara Plateau, formed during the Lower Cretaceous Equatorial Atlantic rift. It is a 7 km‐long and 6 km‐wide tilted block, located at a depth of 3750 m, where sedimentary records of the Equatorial Atlantic are outcropping, making it an ideal location for investigating the timing of this rift.

We integrate petrological observations, biostratigraphy, fission‐track analyses of detrital apatites and zircons, and LA‐ICP‐MS U–Pb dating of authigenic apatites to reconstruct the sedimentary, diagenetic and thermal history of the sediments sampled on the Buteur Ridge.

Our results constrain the tectono‐sedimentary evolution of the divergent margin of the Demerara Plateau, revealing a complex rifting history of the Equatorial Atlantic involving two distinct rifts. The onset of the first rift occurred between 130 and 125 Ma (Hauterivian), which is earlier than the previously proposed Aptian age. A second rifting then occurred during the Cenomanian, likely during the kinematic reorganisation between Africa and South America in the Equatorial Atlantic. This later rifting is evidenced on the Buteur Ridge by terrigenous sedimentation followed by telodiagenesis during basin inversion, likely related to normal fault reactivation and ridge uplift. We interpret the crystallisation of authigenic apatites, dated 93 ± 12 Ma, as a record of the subsequent onset of marine transgression at the end of this second rifting, likely not occurring after the Late Cenomanian (circa 93 Ma).

We present a numerical model of radiolytic H2 generation from a fractured basement in the Taranaki Basin (New Zealand). Based on a conventional exploration approach combining seismic interpretation and a full dataset from two wells reaching the basement, we calculated the potential radiolytic H2 generation rate within the altered basement. The model highlights that H2 mass concentration in water is higher along the faults and in interbedded sand facies, implying that hydrogen in solution could migrate, both by diffusion and advection along these paths. It also indicates that hydrogen‐saturated water could be trapped or experience delayed flow within the possible optimal H2 preservation window (80°C–200°C), potentially leading to the exsolution of supersaturated hydrogen into a gaseous phase. Gas anomalies reported during drilling, comprising a mix of abiotic and thermogenic methane, suggest that such anomalies may serve as proxies for hydrogen exploration in sedimentary basins. CC Zone, chemical consumption zone; MC Zone, microbial consumption zone; TWT, two‐way travel time.

• This work brings key exploration elements to develop the hydrogen sector and ideas to revisit sites that were underexploited at the time of the initial oil exploration.
• This study presents the first basin model of radiolytic hydrogen generation from a granitic basement beneath a sedimentary basin.
• Petroleum system modelling can be effectively adapted for natural hydrogen by adjusting key parameters, providing a practical framework for hydrogen exploration.
• Model outputs shows that potential reservoirs lie within the optimal thermal window (80°C–200°C) for hydrogen preservation.
• Potential hydrogen accumulations coincide with intervals of high CH4 concentrations detected during drilling, suggesting methane may serve as a proxy for natural hydrogen exploration.

The search for natural hydrogen (H2) in sedimentary basins is gaining increasing recognition due to its environmental friendliness. Therefore, as an alternative energy source, natural hydrogen could address the issue of environmental challenges and participate in the energy mix necessary for the energy transition. Despite ongoing research, many uncertainties remain in H2 exploration, which is still at an early stage. In this work, we provide, for the first time, a numerical model of radiolytic natural H2 generation from the fractured basement based on the Taranaki Basin example (New Zealand). This approach uses conventional hydrocarbon exploration techniques, with some adjustments to properly reproduce the subsurface natural H2 behaviour. We calculated the potential radiolytic H2 generation rate to be approximately 10.3 mg/g/Ma. This value was used as a constant rate input in the model. Potential reservoirs within the possible optimal H2 preservation window (80°C–200°C) include the Tane formation sandstone, as well as the Taimana and Tikorangi carbonate formations. The model highlights that H2 mass concentration in water is higher along the faults and in interbedded sand facies of the Rakopi and Wainui formations, implying that hydrogen in solution could migrate both by diffusion and advection along these paths. The density inversion of the seal and the underlying reservoirs began at 9.4 Ma and 6.8 Ma in the Witiora and Taranga boreholes respectively, due to the northwestward progradation of the Mohakatino Formation. This inversion indicates a period during which hydrogen‐saturated water could be trapped or experience delayed flow, potentially leading to the exsolution of supersaturated hydrogen into a gaseous phase. The Tane formation gas anomaly reported during the drilling could be due to the conversion of CO2 into abiotic CH4 via the Sabatier reaction at higher temperatures (> 200°C). Consequently, abiotic CH4 could be an accurate proxy for depicting natural H2 generation.

• A stratigraphic framework is presented of Middle to Lave Devonian shelfal marine strata of Western Canada.
• Outcrop studies are extrapolated to subsurface frameworks using well and seismic data.
• The results allow understanding between carbonate, clastic and mud deposition in low latitude settings.
• Predictive models can be used for subsurface predictions for basin architecture and resource exploitation.

Middle to Upper Devonian strata preserved in the Mackenzie Mountains and adjacent basins in the Northwest Territories, Canada, record a transgressive sequence set of shelfal marine deposits in a low latitude basin margin transitioning from drift to convergence basin phase. The interplay between shallow‐water carbonate and clastic depositional systems and offshore organic‐matter‐rich mudstone deposits is described within a chronostratigraphic and sequence stratigraphic framework. Relative rise of sealevel resulted in backstepping and flooding of a carbonate ramp by biosiliceous and organic‐matter‐rich mudstones. Steep isolated stromatoporoid carbonate platforms show rapid lateral facies transitions associated with these transgressions. At times of tectonically induced relative falls in sea level and exposure of updip carbonate deposits, clastic sediment was transported across the basin margin, resulting in the deposition of mud‐rich subaqueous clinothems. Transgression of these clinothems led to the deposition of onlapping wedges of organic‐matter‐rich mudstones. Three main sequences are developed within this overall transgressive sequence set, and these three sequences can be correlated from outcrop to subsurface, both in the adjacent Peel and Mackenzie Valley Basins as well as into the subsurface strata of the Horn River and Liard Basins, which are prolific hydrocarbon basins to the south. Each depositional system develops distinct seismic geomorphologies and allows for the mapping of favourable lithofacies belts with regard to identifying carbonate deposits (aquifers and petroleum reservoirs) and organic‐matter‐rich mudstones (source rocks and unconventional reservoirs). The workflows and regional chronostratigraphic framework may be applied to coeval deposits along the divergent and convergent margins of Laurentian and Gondwanan cratons preserved across the globe.

The spatial interplay between updip clastic and carbonate depositional systems and downdip detrital and biogenic mud dominated depositional systems are mapped temporally using the sequence stratigraphic method to predict the occurrence of aquifers, petroleum reservoirs and organic‐rich deposits.

Washover fans form during intense storms through barrier breaching and coastal inundation. Despite their importance for understanding coastal response to storms and their potential as stratigraphic traps, ancient washover fans remain poorly documented and underrepresented in subsurface studies, resulting in limited criteria for their recognition. This study investigates the depositional characteristics, controls, and dispersal patterns of a tectonically controlled washover fan succession within the late Eocene Pinghu Formation, Xihu Depression, using 3D seismic, geological and geophysical logs, and petrology. Based on palaeogeography, heavy mineral analysis, seismic‐based provenance analysis, and paleocurrent studies suggest that the Pinghu Formation records a barrier island system. Successions of washover fan deposits are tens of meters thick and comprise stacked 0.5–2.0 m (locally up to 6.6 m) thick, medium‐ to fine‐grained sandstone beds. Individual sandstone beds are generally poorly sorted, normally graded, contain gravel lags, and exhibit parallel stratification. Grain‐size distributions and spatial trends from different wells support a marine‐to‐landward transport process. Petrology shows abundant dolomite crystals and bioclasts. The washover fan deposits are interbedded with thoroughly bioturbated mudstone intervals, which are interpreted as back‐barrier bay deposits. These successions are significantly different from those of river‐dominated deltas and flood‐tidal deltas present in the study area. Washover fan development and preservation are controlled by sea‐level fluctuations, sediment supply, and antithetic faults with associated paleo‐uplifts. The fan dispersal pattern was confined to the syn‐rift period and coincided with rapid sea‐level rise. This study provides criteria for the identification of ancient washover fans and enhances our understanding of their development. Additionally, owing to the succession's significant stratigraphic trap potential, this study is a useful reference for petroleum exploration in the East China Sea Shelf Basin and analogous basins.

Conceptual model of the tectonically controlled washover fan in the Xihu Depression.

• Identification of washover fan deposits in the late Eocene Pinghu Formation, Xihu Depression.
• A comprehensive comparison of the washover fan succession in this study with both modern and ancient analogs.
• Influence of sea‐level rise, sediment supply, and fault‐controlled paleotopography on washover fan preservation.
• Seismic geomorphology reveals distinct sediment dispersal patterns associated with relative sea‐level changes.

The UK Central North Sea Chestnut field was discovered and appraised between 1985 and 1987 and brought online in 2008. The 23‐year delay between discovery and production reflected the modest size of the accumulation combined with a poor understanding of the reservoir sedimentology and challenges associated with seismic imaging of the Eocene‐aged reservoir sandstone. The original reservoir interpretation as a series of discrete turbiditic terminal lobes of depositional origin was disputed when a detailed core re‐interpretation highlighted abundant evidence for sandstone injection. The ramifications of this were profound as the implication was that the reservoir units, which straddled multiple palynologic zones, could represent a well‐connected remobilised sand complex, as was being observed in outcrop analogues, rather than a series of poorly connected discrete lobes. The re‐interpretation was also being corroborated by pre‐production dynamic observations that confirmed good reservoir connectivity despite legacy seismic data showing a patchy, disconnected reservoir system. The field potential was gradually unlocked as subsurface teams embraced this new interpretation and applied new technologies to reservoir evaluation techniques. Enhancement of seismic processing, recognition of the presence and implications of large‐scale sand injection and remobilisation, and integration of these observations with dynamic reservoir data gradually increased confidence in the updated subsurface models. Updated modelling more accurately defined reserves, dynamic behaviour and field potential. The result was that through a better understanding of reservoir architecture, applying learnings from analogue datasets and a focused multidisciplinary approach to field evaluation a poorly understood stranded asset evolved into a highly successful five‐well development recovering 27 Mmstb (million stock tank barrels) of oil—far exceeding even its pre‐development sanctioned reserve base of 7 Mmstb. More fundamentally, the learnings and experience gained from the Chestnut field contributed to the enhanced understanding of the geologic characteristics and dynamic behaviour of injectite reservoirs, which represent a prolific hydrocarbon play and are present throughout the UK and Norwegian Tertiary stratigraphy.

The Chestnut case study highlights how the identification of injectite features on core combined with other multidisciplinary subsurface datasets unlocks a stranded oil field and provides valuable insight into the characteristics of North Sea Eocene remobilised sandstone complexes.