5 - The NE Atlantic conjugate margins
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Deposition of cenomanian – Turonian organic-rich units on the mid-Norwegian margin: Controlling factors and regional implications
2023, Marine and Petroleum GeologyOn the mid-Norwegian margin, extensive rifting and subsequent deposition of thick Cretaceous and Cenozoic sediments have buried the traditional Upper Jurassic organic-rich shales too deep. Consequently, these organic-rich shales are overmature and spent in the deep basins on the mid-Norwegian margin. The absence of well-control, variable seismic quality and in particularly, the great burial depth, makes it difficult to identify alternative Upper Jurassic and Lower Cretaceous organic-rich units. By combining high-resolution 2D seismic data, well logs, and Rock-Eval data, this study documents the presence of alternative organic-rich units in the Cretaceous succession on the Halten Terrace and the Vøring Basin. Multiple seismic horizons which correspond to regional flooding surfaces and define a series of seismic sequences have been mapped across the study area. The regionally extensive upper Cenomanian horizon is associated with wireline log signals and Rock-Eval parameters which imply the presence of a potential source rock unit. Source rock evaluation indicate that this unit contains mainly kerogen Type III on the Halten Terrace, suggesting an organofacies with significant contribution from terrestrial sources. In the Vøring Basin, the unit is sparsely drilled but appears to be mature, thus displaying a relatively limited potential. One well from the Vigrid Syncline demonstrate somewhat higher potential, with Rock-Eval data indicating a kerogen Type II composition. As such, more prolific units seems to exist in the Vøring Basin, albeit exhibiting a patchy distribution. We speculate that the deposition and preservation of this upper Cenomanian organic-rich unit record the development of an extended oxygen minimum zone attributable to increased primary production and sluggish water circulation, linked to the global Oceanic Anoxic Event 2 (OAE 2). However, local physiographic conditions, such as high sedimentation rates, erosion by gravity flows and periodically oxygenated conditions hindered preservation of a significant quantities of organic matter, thus limiting the thickness and quality of the upper Cenomanian organic-rich unit on the mid-Norwegian margin.
The influence of orogenic collision inheritance on rifted margin architecture: Insights from comparing numerical experiments to the Mid-Norwegian margin
2022, TectonophysicsMost rifts and rifted margins around the world developed on former orogens. This implies that the pre-rift lithospheric configuration is heterogeneous in most cases. Here we investigate how collision inheritance in the form of inherited weak thrusts, long-term thermal weakening, compositional changes, and orogenic collapse, could have played into the spatio-temporal evolution and final architecture of rifted margins. We present interpretations of dynamic numerical experiments, including constraints representative of the North Atlantic Mid-Norwegian rift system phases of continental collision, orogenic collapse, and extension, and compare these to interpretations of seismic reflection profiles.
The experiments form rifted margins characterized by basement structures and sedimentary geometries very similar to the Møre and Vøring rifted margins - with onshore collapse-related basins, extensively deformed continental crust with detachments, shear zones, core complexes, rotated thrusts and an offshore succession of distinct structural domains (proximal, necking, hyperextension, exhumation, and outer).
Although extensional models developed on homogeneous lithosphere are a good approximation of rifted margin architecture, our results suggest that models that consider pre-rift orogenic inheritance tend to reproduce more accurately the geometries observed in our natural example.
The North-East Atlantic Mid-Norwegian rifted margin: Insights from the deep imaging Geoex MCG RDI19 dataset
2022, TectonophysicsThe Norwegian Continental Shelf is one of the world's most used laboratories to study rifting processes and rifted margin architecture. Available datasets are dense, various and of good quality. However, since the full basement is rarely imaged, major questions remain unanswered regarding the structural details and nature of rocks at depth. The Geoex MCG Regional Deep Imaging 2019 (RDI19) dataset presents - for the first time - a series of regional long-offset seismic reflection profiles, of high resolution and deep imaging (16 s-twtt). The dataset offers an unprecedented imaging of the entire margin architecture including deep basement units, Moho and upper mantle - from the proximal margin to the outer margin.
This contribution introduces the dataset and proposes an interpretation accompanied by gravity modelling experiments. Focus is set on the identification and seismic facies characteristics of the top basement and Moho core envelopes to discuss the dip and lateral variability of the various basement/crustal units. Basic gravity models are used to develop a discussion on the possible nature of the acoustic basement in the distal margin (crust, magma, mantle, combinations). Based on the observations and interpretation, an updated map of the Møre and Vøring margin structural domains is proposed and discussed.
New insights into the late Mesozoic-Cenozoic tectono-stratigraphic evolution of the northern Lofoten-Vesterålen margin, offshore Norway
2021, Marine and Petroleum Geology2D multi-channel seismic profiles and a 3D seismic survey were utilised together with potential field and available well data to study the late Mesozoic-Cenozoic tectono-stratigraphic evolution of the northern Lofoten-Vesterålen margin, offshore northern Norway. The analysis resulted in an updated structural and stratigraphic framework, together with new and better refined structural elements. Distinct along-margin basin segmentation is evident and is imposed by NW-SE trending curvilinear transfer zones informally named as the Jennegga transfer zone, Vesterålen transfer zone system, and Andøya transfer zone. These divide the study area into three main margin segments, namely the northern Lofoten, Vesterålen, and Andøya segments. Five main rift phases of varying intensity have been recognised and refined, and they are evidenced by eight mapped fault families: pre-Jurassic, Late Jurassic-earliest Cretaceous, Aptian-Albian, Albian-Cenomanian, three individual fault families within Late Cretaceous, and Paleocene. In addition, compressional deformation features are observed and related to volcanic build-up and doming of Cenozoic successions. Large parts of the study area are dominated by a prominent low-angle detachment fault complex informally named North Utrøst Ridge Fault Complex, and the study of the fault complex with the 3D seismic survey has brought forward new details into the composite Late Cretaceous-Paleocene rifting. A major component of the latter is low-angle detachment faulting that is also observed on the conjugate NE Greenland margin. This is a key evidence of conjugate, more ductile, mode of deformation at intermediate-to-deep crustal levels that consisted of lower- and upper-plate configurations and reflects a multiphase tectonic evolution. The study shows that the northern Lofoten-Vesterålen margin represents an essential area to study the tectono-stratigraphic evolution of the NE Atlantic margins.
Early Cretaceous evolution of the Tromsø Basin, SW Barents Sea, Norway
2021, Marine and Petroleum GeologyThis study presents an example of the extensional basin, namely Tromsø, which developed along the Southwestern Barents Sea (SWBS) transform margin. Three previous models have been proposed to explain the tectonic evolution and architecture of the basin, but there is no consensus on development of individual structures. In this study, we use 2D industry seismic reflection data, potential field and well data, as well as previously published information to understand the Early Cretaceous structural evolution of the Tromsø Basin in the context of the geodynamic processes in the SWBS. Mapping of the main seismic sequences and faults, time thickness map were integrated with modeled gravity anomalies along a composite 2D regional seismic section to facilitate the interpretation of crustal structures, which then were structurally restored. We propose a revised Early Cretaceous structural model for the Tromsø Basin, which involves oblique extension and formation of an intra-basinal transpressional transfer zone. This explains formation of the compressional faulting during overall extension in the SW Barents Sea. Basement heterogeneity most likely played an important role in localizing strain. The 2D sequential restoration of the composite regional seismic section yields an estimate of ca. 35 km of crustal extension in the SW Barents Sea margin, from the earliest Cretaceous until the present. Crustal thickness along the gravity modeled 2D regional section displayed a thinner crust below the Tromsø Basin as compared to the Sørvestnaget and Hammerfest basins favoring the interpretation of the Tromsø Basin as oblique rifting. This study illustrates the importance of detailed and regionally integrated analysis of rifted basins for reconstructing their evolution, as analysis of oblique rifted basins using two-dimensional plane strain can lead to erroneous assessment of faulting style and deformation.
Upper Cretaceous-Paleogene stratigraphy and development of the Mìmir High, Vøring Transform Margin, Norwegian Sea
2020, Marine and Petroleum GeologyTransform margins represent strike-slip type of plate boundaries that form during continental breakup and initial ocean opening. They are often characterized by margin-parallel highs with exposed pre- and syn-rift sequences. The Vøring Transform Margin, offshore mid-Norway, initiated in the earliest Eocene during the opening of the NE Atlantic. Here, 2D seismic reflection data reveal a transform margin high, the Mímir High. The western flank of this undrilled structure is a kilometer-high escarpment where seismic reflections of pre-breakup age are truncated at the seafloor. The aim of this study was to recover seabed rock samples from the outcropping or shallowly buried sedimentary sequences to provide a geological tie to the regional seismic framework, thereby constraining the basin history and tectono-stratigraphic development. Seabed samples were successfully collected from 14 gravity core and Selcore stations and 10 ROV (remotely operated vehicle) sites along a 750 m high sampling profile, recovering clay, shales, sandstones and glacial dropstones. Biostratigraphy results revealed that the ages of the sedimentary rocks follow the stratigraphic order predicted by the initial seismic interpretation, with Upper Cretaceous sediments at the base and lower Eocene sediments at the top. The integrated interpretation shows that the Mímir High area, including parts of the outer Vøring and Møre basins and the proto-Jan Mayen Microplate Complex, were characterized by the deposition of late Campanian to early Maastrichtian, near coastal and shale-dominated sequences with poor source rock qualities. The early Paleocene samples indicate deep marine conditions that abruptly ended by rapid uplift of the Mímir High in the earliest Eocene. Finally, a reworked Pliensbachian palynomorph assemblage in potential early Eocene strata indicate the presence of exposed Mesozoic sequences in the vicinity of the Mímir High. We argue that some of the lower Eocene sediments where deposited within a hypothetical drainage system sourced from Greenland (Traill Ø or Jameson Land) and/or from the Jan Mayen Ridge prior to continental separation, and not the result of recent ice-rafting.