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).
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.
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 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.
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.
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.
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.
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.
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.
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：