Tectonic evolution and extension at the Møre Margin – Offshore mid-Norway

Highlights • New and reprocessed seismic data improved structural mapping at the Møre Margin. • Time-structure and thickness maps of the Cretaceous units have been constructed. • Stratigraphy reconstruction of a transect reveals 188 km extension. • Average stretching factor is 2.2–3.6 depending on assumed initial crustal thickness. Abstract Lithospheric stretching is the key process in forming extensional sedimentary basins at passive rifted margins. This study explores the stretching factors, resulting extension, and structural evolution of the Møre segment on the Mid-Norwegian continental margin. Based on the interpretation of new and reprocessed high-quality seismic, we present updated structural maps of the Møre margin that show very thick post-rift sediments in the central Møre Basin and extensive sill intrusion into the Cretaceous sediments. A major shift in subsidence and deposition occurred during mid-Cretaceous. One transect across the Møre continental margin from the Slørebotn Subbasin to the continent-ocean boundary is reconstructed using the basin modelling software TecMod. We test different initial crustal configurations and rifting events and compare our structural reconstruction results to stretching factors derived both from crustal thinning and the classical backstripping/decompaction approach. Seismic interpretation in combination with structural reconstruction modelling does not support the lower crustal bodies as exhumed and serpentinised mantle. Our extension estimate along this transect is ~ 188 ± 28 km for initial crustal thickness varying between 30 and 40 km

Pre-breakup magmatism on the Vøring margin: Insight from new sub-basalt imaging and results from Ocean Drilling program hole 642E

Highlights • Sub-basalt imaging improvement on the Vøring Margin • Definition of a new seismic facies unit: the Lower Series Flows • Significant organic carbon content within the melting crustal segment • Apectodinium augustum marker for the PETM is reworked into the Lower Series Flows • The Lower Series Flows, early Eocene in age, predate the Vøring Margin breakup Abstract Improvements in sub-basalt imaging combined with petrological and geochemical observations from the Ocean Drilling Program (ODP) Hole 642E core provide new constraints on the initial breakup processes at the Vøring Margin. New and reprocessed high quality seismic data allow us to identify a new seismic facies unit which we define as the Lower Series Flows. This facies unit is seismically characterized by wavy to continuous subparallel reflections with an internal disrupted and hummocky shape. Drilled lithologies, which we correlate to this facies unit, have been interpreted as subaqueous flows extruding and intruding into wet sediments. Locally, the top boundary of this facies unit is defined as a negative in polarity reflection, and referred as the K-Reflection. This reflection can be correlated with the spatial extent of pyroclastic deposits, emplaced during transitional shallow marine to subaerial volcanic activities during the rift to drift transition. The drilled Lower Series Flows consist of peraluminous, cordierite bearing peperitic basaltic andesitic to dacitic flows interbedded with thick volcano-sedimentary deposits and intruded sills. The peraluminous geochemistry combined with available C (from calcite which fills vesicles and fractures), Sr, Nd, and Pb isotopes data point towards upper crustal rock-mantle magma interactions with a significant contribution of organic carbon rich pelagic sedimentary material during crustal anatexis. From biostratigraphic analyses, Apectodinium augustum was found in the The Lower Series Flows. This species is a marker for the Paleocene – Eocene Thermal Maximum (PETM). However, the absence of very low carbon isotope values (from bulk organic matter), that characterize the PETM, imply that A.augustum was reworked into the early Eocene sediments of this facies unit which predate the breakup time of the Vøring Margin. Finally, a plausible conceptual emplacement model for the Lower Series Flows facies unit is proposed. This model comprises several stages: (1) the emplacement of subaqueous peperitic basaltic andesitic flows intruding and/or extruding wet sediments; (2) a subaerial to shallow marine volcanism and extrusion of dacitic flows; (3) a proto-breakup phase with intense shallow marine to subaerial explosive volcanism responsible for pyroclastic flow deposits which can be correlated with the seismic K-Reflection and (4) the main breakup stage with intense transitional tholeiitic MORB-type volcanism and large subsidence concomitant with the buildup of the Seaward Dipping Reflector wedge

Cretaceous-Tertiary palaeo-bathymetry in the northern North Sea; integration of palaeo-water depth estimates obtained by structural restoration and micropalaeontological analysis

Temporal and spatial variations in palaeo-water depth are crucial parameters in basin analysis since changes in palaeo-bathymetry detail the amount of sediment underfill during basin evolution. By carefully integrating seismic-stratigraphic observations with palaeo-water depth estimates from structural restoration and micropalaeontological data, changes in accommodation space throughout the Cretaceous-Tertiary post-rift interval are documented on a regional scale in the northern North Sea. Since it is not possible to determine the palaeo-water depth exactly, we have focussed on determining most likely water depth figures, and identifying the principal shallowing and deepening trends. The inferred trends from the investigated wells are generally in good agreement with each other on a regional scale, especially when the tectonic position within the basin is taken into account. The inferred general trends are: (1)general shallowing superimposed on several transgressive / regressive events during the Early Cretaceous; (2) deepening from the early Cenomanian to mid-Campanian; (3)shallowing from the mid-Campanian to latest Maastrichtian; (4) deepening in the Early to Late Paleocene; (5) shallowing from the Late Eocene to Late Miocene; (6) deepening from the Late Miocene to Early Pliocene; (7) shallowing during Pliocene time. The early Cenomanian to latest Maastrichtian and the late Eocene to Pliocene events correspond with changes in eustatic sea level, but the deepening / shallowing trends were probably amplified by tectono-thermal effects. The events in the Early Cretaceous, Early to Late Paleocene, and Late Miocene to Early Pliocene cannot be explained by the eustatic sea-level curve, and therefore need to be explained by purely tectono-thermal events

The influence of mechanically weak layers in controlling fault kinematics and graben configurations : Examples from analog experiments and the Norwegian continental margin

Fault systems in extensional basins commonly display geometries that vary with depth, reflecting depth- and lithology-dependent mechanical strength. Using an experimental approach, we investigate this relationship by deploying physical analog models with stratified sequences consisting of brittle–ductile (sand–silicone polymer) sequences subject to single and polyphase deformation. The experiments were used as analogs for a sandstone sequence interlayered by beds of evaporates or overpressured or unconsolidated mudstone in nature (the latter being representative of decollement horizons). Experiments (series 1 [S1]) using homogeneous and stratified quartz and feldspar sand produced asymmetric, composite single grabens with diverse fault frequencies and fault styles for the graben margin faults. For the mechanically stratified experiments with one decollement level (series 2), contrasting graben configurations were produced, in that the lowermost sequence was characterized by graben geometries of similar type to that of the S1 experiments, whereas the sequence above the decollement was characterized by large fault blocks, delineated by steepened or oversteepened faults. The experiments with two decollements (series 3) were displayed similarly but included graben geometries that widened upward, with each level being characterized by independent fault systems. The results can be used to explain strata-bound fault patterns and depth-dependent extension as seen in several places along the Norwegian continental margin and elsewhere

The influence of mechanically weak layers in controlling fault kinematics and graben configurations : Examples from analog experiments and the Norwegian continental margin

Fault systems in extensional basins commonly display geometries that vary with depth, reflecting depth- and lithology-dependent mechanical strength. Using an experimental approach, we investigate this relationship by deploying physical analog models with stratified sequences consisting of brittle–ductile (sand–silicone polymer) sequences subject to single and polyphase deformation. The experiments were used as analogs for a sandstone sequence interlayered by beds of evaporates or overpressured or unconsolidated mudstone in nature (the latter being representative of decollement horizons). Experiments (series 1 [S1]) using homogeneous and stratified quartz and feldspar sand produced asymmetric, composite single grabens with diverse fault frequencies and fault styles for the graben margin faults. For the mechanically stratified experiments with one decollement level (series 2), contrasting graben configurations were produced, in that the lowermost sequence was characterized by graben geometries of similar type to that of the S1 experiments, whereas the sequence above the decollement was characterized by large fault blocks, delineated by steepened or oversteepened faults. The experiments with two decollements (series 3) were displayed similarly but included graben geometries that widened upward, with each level being characterized by independent fault systems. The results can be used to explain strata-bound fault patterns and depth-dependent extension as seen in several places along the Norwegian continental margin and elsewhere

Permo-Carboniferous Salt Messing Up the Cenozoic Stratigraphy of the Sørvestnaget Basin, SW Barents Sea

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