The outcrops of the Panoche and Tumey Giant Injection Complexes in California have been instrumental in refining the interpretation of the sandstone intrusion reservoirs in the Volund Field, Norway. Insights from the outcrops enhanced the subsurface team's confidence and understanding of reservoir presence and connectivity during field production. This led to more accurate estimates of hydrocarbon reserves. Learnings from the Volund Field show that historical reservoir models underestimate net reservoir volume and reservoir connectivity. Outcrop data reveal step-like geometry in some intrusions, which potentially explains the lack of seismic resolution of sandstone intrusions in some areas of the field. Failure to recognise this leads to misinterpretation of parts of the field as non-reservoir. In some intervals, well logs interpreted as non-reservoir mudstone-rich units are actually mudstone-clast breccia, which, because of good connectivity within the sandstone matrix, can comprise significant reservoir volumes. The rationale for including sandstone intrusions as reservoirs, although unresolved by seismic or borehole log data in static models, is validated by reference to outcrop data and from recent drilling in the adjacent Kobra Field. Observations of outcrop analogues enhance the interpretation of subsurface data, and the knowledge acquired from outcrops helped justify the drilling of more production wells in areas where reservoir presence and quality were difficult to predict, but almost nearly doubled the hydrocarbon reserves.
Jurassic and Early Cretaceous times were marked by significant changes in Earth's climate and tectonics, most notably the breakup of the supercontinent Pangaea, which led to the opening of the Atlantic Ocean. In Southwest Britain, one of the most prominent features of this time is the Base Cretaceous unconformity representing widespread erosion and non-deposition separating Cretaceous strata from underlying rocks. Despite its widespread presence in Southwest Britain, Iberia, Ireland and conjugate North Atlantic basins, the origin and nature of this unconformity remains enigmatic. To better understand its nature, seismic data was used to map the extent of the unconformities and to establish their relationships with onlapping Jurassic and Cretaceous stratigraphy. We reveal that the Base Cretaceous unconformity is a composite of at least three—Middle Jurassic, Late Jurassic to Early Cretaceous and Mid-Cretaceous—unconformities likely generated by erosion and non-deposition. The Mid-Cretaceous unconformity is often assumed to be responsible for the majority of erosion, but our findings suggest otherwise. Onlap patterns of the Lower Cretaceous Wealden Formation on truncated Jurassic units indicate that the Jurassic to Early Cretaceous unconformity was the most significant. Amplitudes of uplift across different basins in SW Britain are shown to be variable. The most substantial denudation occurred following Berriasian uplift, likely linked to shortening associated with North Atlantic opening. The Mid-Cretaceous unconformity is more subtle, primarily observed at basin margins and linked to the rift-drift transition of the Bay of Biscay. Subsidence histories differ across basins; some (e.g., Brittany Basin) can be explained by simple post-rift thermal cooling models, while others (e.g., Melville and South Celtic Sea Basins) require more complex explanations due to substantial missing stratigraphy, including reactivation of Variscan thrusts and sub-plate support. Our results emphasise that spatially and temporally distinct tectonic and denudation events can combine to generate large-scale composite unconformities.
This study presents a detailed 3D lithofacies model of the Upper Pleistocene–Holocene Tiber Depositional Sequence (TDS) within the alluvial plain of Rome, Italy, developed using an integrated approach. A deterministic framework was used to establish 1D lithofacies constraints, while geostatistical algorithms, particularly indicator kriging, were employed to reconstruct the stacking patterns and interfingering of lithofacies within systems tracts. This methodology allows for the realistic depiction of depositional trends and stratigraphic architecture while addressing challenges posed by limited data density in unsampled locations. The resulting 3D model demonstrates its ability to honour observed data while enabling meaningful extrapolation of subsurface features. The model captures key evolutionary trends and aligns with the conceptual 2D stratigraphic reconstruction developed in this study and the sequence-stratigraphic framework of the TDS derived from previous studies. Stratigraphic cross-sections and 2D correlation profiles extracted from the 3D model reveal the depositional architecture and constrain the thickness and extent of primary lithofacies associations. Key findings include the identification of braided and meandering channel-belt complexes associated with poorly and well-drained floodplain deposits. The lowstand systems tract (LST) is characterised by extensive braided channel belts with high width-to-thickness ratios, while the transgressive systems tract (TST) exhibits vertically stacked meandering channels associated with poorly drained floodplains. The highstand systems tract (HST) shows increased channel clustering and lateral expansion of meandering channel belts, associated with well-drained floodplain deposits displaying pedogenic features. The findings highlight the strengths and limitations of two-point geostatistical algorithms, with indicator kriging outperforming traditional methods like Truncated Gaussian Simulation and Sequential Indicator Simulation in maintaining geological coherence and lateral continuity. The 3D model enhances our understanding of the Tiber alluvial basin evolution and provides a robust framework for urban geological applications. It serves as a pivotal tool for managing subsoil resources, mitigating geohazards, and preserving cultural heritage in densely populated areas. This approach demonstrates the feasibility of applying efficient, scalable techniques to model sedimentary successions in similar urbanised alluvial settings worldwide.
By means of seismic interpretations, this study provides improved constraints on a major Tournaisian (lowermost Carboniferous) tectonic phase with faulting across the Campine Basin, northeastern Belgium. Faults are normal with throws below 100 m, except for some larger intra-rift horst and graben structures with throws up to 300 m. In an asymmetric graben structure in the southern study area, an estimated average of 1000 m of Tournaisian sediments accumulated. Outside the graben, Tournaisian thicknesses are in the order of 300–500 m, which agrees with the limited available well data outside the study area of the Campine Basin. There is an uncertainty on fault strikes since the individual fault segments are short compared to the spacing between the seismic lines, but we estimate it to vary between SW–NE and WNW–ESE. The wide range of fault strikes can be related to the reactivation of pre-existing faults in the Cambro-Silurian basement. The SW–NE and WNW–ESE directions of the Tournaisian fault strikes have been identified as lineaments on gravimetric and aeromagnetic maps of the lower Palaeozoic Brabant Massif to the southeast and southwest of the study area, respectively. Such fault strikes imply a roughly NNW–SSE to N–S extensional stress field prevailing in the area during the Tournaisian. The range of fault strikes is very similar to the strike of contemporaneous faults in Ireland and the United Kingdom, which suggests that the NNW–SSE to N–S extensional stress field occurred throughout much of northwestern Europe. The Tournaisian succession of the Campine Basin includes numerous mound-shaped complexes, interpreted as buildup structures. We show examples of major buildup complexes that developed in graben structures. One of them reaches a height of 750 m and is 3 km wide. Given the similarity in timing of formation and size of the buildup complexes in the Campine Basin with buildup complexes in southern Belgium and Ireland, we consider it likely that the buildup complexes in the Campine Basin represent Waulsortian mudmounds.
Three-dimensional seismic imaging combined with offshore well data analyses is used to interpret inverted faults underlying a thick Layered Evaporite Sequence in the Southern North Sea. By observing changes in evaporite volume above and away from an inversion structure, we infer that reactivation of thick-skinned normal faults induced multi-layered, trans-structural flow in the overlying evaporites. This flow acted to decouple deformation and prevent stress transmission from below to above the salt. The induced salt flow is layer-dependent, occurring mainly within the halite lithologies of the Layered Evaporite Sequence between a folded anhydrite stringer. This stringer folding predates inversion, which later induced stringer fold amplification and deflection nearer to the top of the evaporite sequence. These findings provide insights into the complexities of stratified evaporite rheologies and the timing of basin deformation, with wider implications for contractional salt tectonics wherever thick- and thin-skinned deformation may be coeval.
For nearly three decades, Equinor's Sleipner Carbon Capture and Storage project has demonstrated how the application of geological principles, modelling techniques and analysis of repeated time-lapse (4D) seismic data has helped to characterise the CO2 plume migration within the late Miocene–early Pliocene Utsira Formation. However, the influence of stratigraphic complexity on fluid migration has been rather poorly understood. This has resulted in a significant degree of uncertainty in the geological characterisation of the storage formation, including the distribution of mudstone-rich elements, which may serve as baffles and barriers for migration of fluid, and elements that allow for their bypass. Our study, utilising high-quality 3D seismic data integrated with wireline-logs, time-lapse seismic and regional contextual information, has shown that the Utsira Formation in the South Viking Graben represents a confined, channelized submarine fan system characterised by a complex stratigraphic architecture. The study has highlighted that the intricate interplay between fan lobes, channel erosion, channel infill and draping of lobes, lobe-complexes and channel incision surfaces by mud-rich layers, provides a first-order control on CO2 storage compartments and exerts a substantial influence on vertical and lateral fluid flow pathways. The latter is well expressed by the morphology of several mapped CO2-filled layers. Both generally discontinuous channel-base mud-rich drapes and more continuous lobe-complex and fan mudstone drapes have been locally compromised by processes linked to channel erosion and sand injection, in some cases combined with faulting and fracturing. This complex stratigraphic pattern has probably been exacerbated by post-depositional deformation that triggered fluid and sediment expulsion from the Utsira Formation and the underlying early-Miocene Skade Formation. These factors allowed for increased vertical connectivity between originally disconnected sandstone bodies and fluid migration from deeper to shallower layers, prior to injection of CO2, thus serving as preferred pathways post-injection.
Sedimentary basins in the distal Cenozoic Andean retroarc yield an important geological archive that provides crucial insights into the tectonic and sedimentary processes associated with the different stages of mountain building. At 33° S, the tectonic and sedimentary processes that have operated during the Neogene and Quaternary periods of Andean orogenesis are well documented, whereas information on the Paleogene period remains fragmentary and partly enigmatic. The Paleogene sedimentation in the distal retroarc at this latitude is represented by the Divisadero Largo Formation, a 70-m-thick sedimentary unit that has been extensively studied for its fossil content, leading to the controversial definition of the late Eocene Divisaderan South American Land Mammal Age (SALMA). New zircon U–Pb geochronological data provide a valuable age constraint for Paleogene tectonic and sedimentary processes in the Southern Central Andes. Furthermore, we present the first detailed facies analysis of the Divisadero Largo Formation, combined with a sedimentary provenance study and a seismic subsurface characterisation of this unit. Our results indicate that the age of the Divisadero Largo Formation is Palaeocene to early Eocene (~65–41 Ma). Deposition of this unit occurred in a shallow, lacustrine depositional environment with variable water depths and was characterised by a low accumulation rate of 3 m/Myr. During this time, the sediment source was predominately located in the Andean magmatic arc; however, no conclusive evidence of significant Paleogene deformation exists. These characteristics (age, depositional environment, low accumulation rate and provenance) enable a regional correlation with Paleogene deposits farther south in the Neuquén Basin. In addition, based on U–Pb geochronology and sedimentary features, a 20 Myr hiatus could be defined between the Divisadero Largo Formation and overlying synorogenic deposits, as has been proposed farther south, reflecting the northernmost record of this hiatus. Taken together, these new observations help to refine a tectono-sedimentary model for the evolution of the Southern Central Andes retroarc basin at 33° S that comprises four stages preceding the well-documented Miocene contraction phase: (i) Late Jurassic–Early Cretaceous extension; (ii) Late Cretaceous contraction; (iii) Palaeocene–middle Eocene tectonic quiescence; and (iv) a renewed phase of late Eocene–Oligocene extension.
Subduction trenches receive sediment from sediment gravity flows sourced from transverse pathways and trench parallel axial transport pathways. Understanding the interplay between axial and transverse sediment transport in shaping stratigraphic architectures is hindered by the episodic nature of sedimentary gravity flows and limited datasets, yet such insights are crucial for reconstructing sedimentary flow pathways and interpreting sedimentary records. We investigate sediment routing pathways to the northern Hikurangi Trough of New Zealand using a combination of multibeam, 2D and 3D seismic reflection and International Ocean Discovery Program core data from Site U1520. Site U1520's location downstream of axial and transverse conduits of sediment delivery makes it an excellent location to observe how these processes interact in deep marine settings. We characterise regional basin floor geomorphology and sub-surface architecture of the upper ~110 m siliciclastic sequence of the Hikurangi Trough deposited over the past ~42 ka (Seismic Unit 1; SU1). Sediment delivery to the trough is fed by sediment gravity flows sourced from both the shelf-incising transverse Māhia Canyon to the south-west and the axial Hikurangi Channel to the south. Flows sourced from these systems have a strong influence on the geomorphology of the region and are responsible for forming large-scale bathymetric features such as erosional scours and sediment waves. Sedimentary features identified within SU1 indicate that sediment transport via the transverse Māhia Canyon was more significant than that of the axial Hikurangi Channel throughout the last 42 ka, particularly during the last glacial period when sea levels were lower, and sedimentation rates were extremely high (up to ~20 m/kyr). This study emphasises the need for a nuanced consideration of transverse and axial systems and how they may influence sediment records and the geomorphic characteristics of trench systems.
Downstream changes of fluvial styles and related grain size triggered by localised tectonically-induced changes in riverbed gradient are still poorly understood, especially in terms of their impact on the accumulation of alluvial successions. In this study, we analyse the morpho-sedimentary response of rivers crossing multiple fault-controlled subsiding areas, by using field data from the age-constrained, fluvial deposits of the Pleistocene Dandiero Basin (Eritrea) to create scaled, controlled laboratory experiments performed at the Eurotank Stratigraphic Analogue Modelling Facility (Utrecht University, NL). With this experimental series, we quantified the impacts of degradational/aggradational fluvial dynamics showing that stream bed degradation occurs upstream of subsiding depocenters following the localised increase in river slope. Following a tectonic-induced decrease in river slope, aggradation occurs downstream of the fault zones, and marked in-channel aggradation promotes the branching of major river trunks into minor channels and the development of unchannelised tabular bodies. Experiments also show that highly subsiding areas promote the accumulation of fine-grained deposits, but their accumulation zones shift downstream following localised bed aggradation. We show that where multiple subsiding areas occur along a river, localised depocenters separated by degradational areas occur, causing general starvation in the downstream subsiding reaches, where lacustrine deposition became common. These findings suggest that the role of active faults could have been significantly overlooked when studying how changes in allogenic forcings impact alluvial strata. The results obtained in this study offer a solid basis for creating a predictive model for facies distribution in river dynamics, providing insights into detecting neotectonic signatures in active rivers and identifying tectonic imprints on ancient fluvial successions.
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：