Northern Barents Shelf Research Articles

Sedimentary facies and mineral provenance of Upper Triassic sandstones offshore Kvitøya, Svalbard: implications for palaeogeographic interpretations in the northern Barents Shelf area

Upper Triassic (Carnian) sandstones of the De Geerdalen Formation cored south of the island of Kvitøya (80°N), north-easternmost Svalbard, are described in terms of sedimentary facies and petrography and compared regionally in the northern Barents Shelf. The succession off Kvitøya is characterized by its great thickness and is dominated by deltaic deposits with high sand content of lithic–feldspathic compositions. Comparison of sediment facies and sandstone compositions with adjacent areas suggest that the succession off Kvitøya is part of a larger delta system with its main sediment source from the east. The delta sedimentation was terminated by marine transgression in the earliest Norian. The sandstone compositions off Kvitøya differ from nearby locations by the higher content of cherty rock fragments and reworked volcanic debris in the Kvitøya sandstone, which is most distinct in the lower part of the succession. Provenance signatures are investigated by mineral–chemical analysis of detrital feldspars, rock fragments, garnet and Cr-spinel, characterizing a wide variety of igneous, metamorphic and sedimentary terranes, including palaeo-Urals and areas farther to east. Additional, more proximal sediment source areas may also have existed that could explain the increased sediment thickness and the mineralogical immature sandstone compositions of the Carnian sediments off Kvitøya.

Seal characterization and integrity in uplifted basins: Insights from the northern Barents Shelf

Seal integrity is a key property for petroleum exploration. This is even more the case in uplifted basins, as exemplified by the northern Barents Shelf. Uplift may lead to fracturing, decompaction, gas expansion and fluid flow. Therefore, it is critical to understand the mechanical behaviour of the Jurassic shale caprocks in the Greater Hoop area, where hydrocarbon accumulations are situated as little as 250 m below the seabed. In this contribution we study the Upper Jurassic Fuglen and Hekkingen formations. We analyse the mechanical properties of six wells in the study area in combination with leak-off tests and 3D seismic data to characterise the caprock variability over the area. Ductility appears to be largely a response to total organic content, with overall sealing properties appearing exceptionally good in southern parts but diminishing to the north in the study area due to increasing silt content and thinning of the more organic rich Hekkingen Formation.

Underpressure in the northern Barents shelf: Causes and implications for hydrocarbon exploration

The underexplored Barents shelf petroleum province is a globally unique example where naturally occurring underpressure is observed offshore and onshore. In the offshore parts of the northern Barents shelf, minor underpressure (up to 23 bar below hydrostatic pressure) is observed in the fault-bounded Mesozoic reservoirs of the Fingerdjupet subbasin. More severe (50 bar below hydrostatic pressure although irregular, occurrences of underpressure are encountered in the Triassic intervals of the neighboring Greater Hoop area. The abnormal pressures extend to the onshore archipelago of Svalbard, where pressures exceeding 60 bar below hydrostatic were encountered during drilling for a CO2 sequestration project. In Svalbard, reservoir pressures were constantly monitored over 3 yr, providing an insight into the reservoir behavior at unique time scales. The low-permeability (<2 md) reservoir in Svalbard is exposed some 15 km to the north of the drill site. Quantitative analysis with the apparent lack of a regional lateral seal suggests a geologically recent origin of underpressure. Evidence that the underpressure extends into the top seal provides further indication to the likely cause of underpressure. Similar to many global occurrences of underpressure in petroleum provinces, the Barents shelf has undergone severe uplift, most recently caused by deglaciation. Well data, outcrop observations, and isotope data combined with the area’s geological history indicate that glacial loading, unloading, and erosion, potentially with the aid of natural fractures, is the likely dominant underpressure-generating mechanism.

Nitrate supply and uptake in the Atlantic Arctic sea ice zone: seasonal cycle, mechanisms and drivers.

Nutrient supply to the surface ocean is a key factor regulating primary production in the Arctic Ocean under current conditions and with ongoing warming and sea ice losses. Here we present seasonal nitrate concentration and hydrographic data from two oceanographic moorings on the northern Barents shelf between autumn 2017 and summer 2018. The eastern mooring was sea ice-covered to varying degrees during autumn, winter and spring, and was characterized by more Arctic-like oceanographic conditions, while the western mooring was ice-free year-round and showed a greater influence of Atlantic water masses. The seasonal cycle in nitrate dynamics was similar under ice-influenced and ice-free conditions, with biological nitrate uptake beginning near-synchronously in early May, but important differences between the moorings were observed. Nitrate supply to the surface ocean preceding and during the period of rapid drawdown was greater at the ice-free more Atlantic-like western mooring, and nitrate drawdown occurred more slowly over a longer period of time. This suggests that with ongoing sea ice losses and Atlantification, the expected shift from more Arctic-like ice-influenced conditions to more Atlantic-like ice-free conditions is likely to increase nutrient availability and the duration of seasonal drawdown in this Arctic shelf region. The extent to which this increased nutrient availability and longer drawdown periods will lead to increases in total nitrate uptake, and support the projected increases in primary production, will depend on changes in upper ocean stratification and their effect on light availability to phytoplankton as changes in climate and the physical environment proceed.This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Exploring the reservoir potential of Lower Cretaceous Clinoforms in the Fingerdjupet Subbasin, Norwegian Barents Sea

AbstractSandy clinothems are of interest as hydrocarbon reservoirs but there is no proven, economic, clinothem reservoir in the Norwegian Barents Sea. We used high‐resolution, 2D and 3D seismic, including proprietary data, to identify a previously untested, Barremian, clinoform wedge in the Fingerdjupet Subbasin (FSB). Data from recent well 7322/7‐1 plus seismic have been used to characterize this wedge and older Lower Cretaceous clinoforms in the FSB. In the latest Hauterivian – early Barremian, during post‐rift tectonic quiescence, shelf‐edge clinoforms (foreset height &gt; 150 m) prograded into an under‐filled basin. Increased sediment input was related to regional uplift of the hinterland (northern Barents Shelf). Early Barremian erosion in the north‐western FSB and mass wasting towards the SE were followed by deposition of delta‐scale (&lt;80 m high), high‐angle (c. 8°) clinoform sets seaward of older shelf‐edge clinoforms. This may be the local expression of a regional, early Barremian, regressive event. By the close of the Barremian, clinoforms had prograded, within a narrow, elongate basin, across the FSB and towards the uplifted Loppa High. A seismic wedge of high‐angle (10–12°), low‐relief, delta‐scale (25–80 m) clinoform sets occurs between shelf‐edge clinoforms to the NW and the uplifted area to the SE. Well 7322/7‐1, positioned on a direct hydrocarbon indicator, &lt;1 km NNW of the high‐angle, low‐relief, delta‐scale clinoforms, found upward coarsening siltstone‐cycles linked to relative sea‐level fluctuations on a marine shelf. Sand may have accumulated, offshore from the well, in high‐angle, low‐relief foresets of the delta‐scale clinothems (which are typical geometries elsewhere interpreted as ‘delta‐scale, sand‐prone subaqueous clinoforms’). Deposition was controlled by the paleosurface, storms and longshore currents on an otherwise mud‐dominated shelf. The study highlights challenges associated with exploration for sandstone reservoirs in seismic wedges on an outer shelf.

Magmatic and metamorphic events recorded within the Southwestern Basement Province of Svalbard

A recent increase in fieldwork activity within the Southwestern Basement Province (SBP) of Svalbard followed by detailed geochronological and petrological studies has allowed recognition of previously unknown magmatic and metamorphic events in the studied region. These discoveries of, e.g. true c. 950 Ma granitic magmatism, c. 640 Ma Torellian metamorphism, completely new localities of high-pressure rocks and a c. 360 Ma Ellesmerian, Barrovian-type metamorphic sequence emphasize the importance of further research in this part of the Svalbard Archipelago. Paleogene tectonic overprint of the SBP, manifested by the West Spitsbergen Fold and Thrust Belt, is an additional challenge for geologists working in this part of Svalbard’s crystalline basement, and must be taken into account in all interpretations of pre-Cenozoic structures. Several enigmatic issues concerning the evolution of the SBP remain unanswered. Hence, there is a need for continued research in this key area for understanding the geological evolution of the northern Barents Shelf and High Arctic in general.

Locations of nonstructural hydrocarbon traps on the shelf of the northern Barents Sea

This paper considers the results of summarized integrated geophysical investigations that were carried out from 2006 to 2012. The investigations included common depth point (CDP) seismic reflection survey, over water gravity survey, and differential hydromagnetic exploration with a total work scope of 30 000 linear kilometers. The deep structural tectonic plan, the structural and lithofacies features of the sedimentary cover section on the basic reflecting boundaries, and the features of the seismogeological complexes and seismic sections on a depth scale have been studied, and geological oil-and-gas zoning of the Northern Barents shelf has been made. Seventy-nine local anticlinal highs have been revealed, and the zones with potential nonstructural hydrocarbon traps have been determined. Due to the lack of huge anticlinal highs in the northern Barents Sea region, nonstructural traps are of interest in studying and replacing the mineral raw material base of Russia, as well as for arranging marine exploration.

Provenance of Triassic sandstones on the southwest Barents Shelf and the implication for sediment dispersal patterns in northwest Pangaea

Thick Triassic siliciclastic units form major reservoir targets for hydrocarbon exploration on the Barents Shelf; however, poor reservoir quality, possibly associated with variation in provenance, remains a key risk factor in the area. In this study, sandstone dispersal patterns on the southwest Barents Shelf are investigated through petrographic and heavy mineral analysis, garnet and rutile geochemistry and zircon U-Pb geochronology. The results show that until the Early Norian Maximum Flooding Surface, two contrasting sand types were present: (i) a Caledonian Sand Type, characterised by a high compositional maturity, a heavy mineral assemblage dominated by garnet and low chrome-spinel:zircon (CZi) values, predominantly metapelitic rutiles and mostly Proterozoic and Archaean detrital zircon ages, interpreted to be sourced from the Caledonides, and (ii) a Uralian Sand Type, characterised by a low compositional maturity, high CZi values, predominantly metamafic rutiles and Carboniferous zircon ages, sourced from the Uralian Orogeny. In addition, disparity in detrital zircon ages of the Uralian Sand Type with contiguous strata on the northern Barents Shelf reveals the presence of a Northern Uraloid Sand Type, interpreted to have been sourced from Taimyr and Severnaya Zemlya. As such, a coincidental system is inferred which delivered sand to the Northern Barents Shelf in the late Carnian/early Norian. Following the Early Norian Maximum Flooding Surface, a significant provenance change occurs. In response to Late Triassic/Early Jurassic hinterland rejuvenation, supply from the Uralian Orogen ceased and the northern Scandinavian (Caledonian) source became dominant, extending northwards out on to the southwest Barents Shelf. The data reveal a link between reservoir quality and sand type and illustrate how provenance played an important role in the development of clastic reservoirs within the Triassic of the Barents Shelf.

Trajectory analysis and inferences on geometric relationships of an Early Triassic prograding clinoform succession on the northern Barents Shelf

A sedimentary succession studied along three parallel seismic lines details a platform-edge progradation of 21–36 km in a northwesterly direction across the northwestern Barents Shelf. The intra-shelf clinoform succession is bounded at bottom and top by Base Olenekian and Early Ladinian seismic reflectors. The ca 800 m thick succession can be resolved into seven distinct clinothems. The system is characterized by an early sub-horizontal platform-edge trajectory with extensive progradation, limited relative sea level rise and restricted accommodation. Thereafter the system outlines a largely ascending trajectory, marking a major rise in relative sea level and creation of significant accommodation. The platform-edge appears to back-step along one line suggesting that relative sea level rise out-paced sediment influx and preserved a clinothem with a trajectory characterized by accretionary transgression. Thereafter the trajectory is overall ascending regressive, with some variation of the trajectory angle, culminating in a flat and finally descending trajectory with oblique clinoforms outlining extensive progradation and another period of limited accommodation. The clinoforms downlap onto a succession of basin-floor deposits which appear to comprise at least two separate periods of deposition, forming two separate units. The first five clinothems downlap onto the first basin-floor unit. The shift to downlap onto the second unit occurs around the second period of extensive platform-edge advance, suggesting limited accommodation promoted bypass of significant amounts of sediment to the basin floor.The Gardarbanken High has been considered an obstacle to Early Triassic sediment progradation in this part of the basin. This inference can be corroborated based on the seismic attributes, which show sediment infill and onlap near the High. The influence is also noticeable in the reduced slope relief near the High, indicating that the basin floor was topographically higher. However, other geometric attributes cannot provide any definitive measures of structural influence.The thickness of preserved topsets and the distance from the platform-edge to the toe pinch-out point of each clinothem is found to be inversely proportional. This relationship is most marked in the fully developed sigmoidal clinoforms, whereas the link appears weaker in the oblique clinoforms. A near-perfect correlation between clinothem average vertical thickness (the average sedimentary rock accumulation within the clinothem) and advance of the toe is found, with only a relatively close relationship between clinothem average vertical thickness and advance of the platform-edge. In the studied system it therefore appears the advance of the toe is governed solely by sediment influx while the advance of the platform-edge is also influenced by relative sea level.

Does evidence of faulting contradict a quiescent northern Barents Shelf during the Triassic?

Abstract Tore Klausen comments on the far-field stress hypothesis for the NW Triassic Barents Sea. A. Braathen, I. Anell, P-T. Osmundsen and S. Olaussen publish their response.

Evidence of faulting contradicts a quiescent northern Barents Shelf during the Triassic

It has generally been considered that the Triassic was a tectonically quiescent period on the northern Barents Shelf. Located on the distal Uralide foreland, sedimentation was dominated by the advance of prograding deltaic systems. The Triassic succession exposed on Edgeøya (east Svalbard) displays two interacting types of growth fault: listric faults that sole out in the Triassic pro-delta/marine shales; and steeper, more planar, normal faults with a deeper-seated origin. In the nearby offshore realm, 2D seismic data suggest a previously undocumented phase of minor extensional movements during the Triassic that renewed activity on deep-rooted faults initiated during the Palaeozoic. The faults strike approximately east–west, onshore and offshore, with most fault throws down to the south. The seismic data in the Upper Triassic sequence also show smallscale offsets, curved reflectors, and a generally more chaotic signature suggestive of syn-sedimentary disruption. The coeval timing and orientation suggest a link between the reactivation of faults that reach the basement and the development of shallow growth faults. Triassic fault activity has previously been documented in the south. Its occurrence in the north, too, suggests a regional, crustal-scale driving force. We speculate that Uralide foreland deformation preferentially reactivated older east–west basement-seated fault zones.

Evolution of the Triassic shelf in the northern Barents Sea region

The interpretation of an unpublished data set of shallow stratigraphic cores and deep, seismic profiles from the northern Barents Shelf has provided new information about the Middle and Late Triassic development of the Barents Shelf and Svalbard. At that time, sediment sources along the eastern and south-eastern margins of the Barents Sea controlled the infilling of a previously deeper shelf area, gradually converting it into a paralic platform. Compared with the eastern source, sediment volumes from other areas were small. In our data, there are no indications of a provenance area north of Svalbard. Progradation from the ESE resulted in diachronous lithostratigraphic boundaries. The organic-rich shales of the Botneheia and Steinkobbe formations were deposited in the remaining deeper shelf areas in the western and north-western Barents Sea shelf, from the Olenekian to the latest Ladinian, by which time the progradation from the ESE had reached eastern Svalbard. In mid-Carnian times, the area of paralic deposits extended from the eastern Barents Sea into the Svalbard Archipelago.

Quantification of the Pliocene-Pleistocene erosion of the Barents Sea from present-day bathymetry

We present an attempt to quantify the Tertiary and Quaternary erosion on the Barents Shelf in a two step model. The first step is a tectonically related uplift in the order of 500–2000 m of the NW Barents Shelf in the Early Tertiary with subsequent erosion in the Eocene-Miocene period and transport of 950,000 km 3 of erosional products to the sedimentary basins on the southern and eastern Barents shelf and to the continental margins to west and north. The second step involves a regional glacial erosion in Pliocene-Pleistocene times with removal of 1,280,000 km 3 of sediments that today are located in wedges along the western and northern Barents Shelf margins. With the present-day topography and bathymetry, the preglacial relief is reconstructed and used to calculate the glacial erosion by isostatic modelling. The results indicate that the total erosion increases from 500–700 m in the Southern Barents Sea, to an excess of 2000 m in a zone from Spitsbergen to Franz Josephs Land. Planimetering of this erosional map gives a total of 1,200,000 km 3 of eroded material, which agrees with the estimated 1,280,000 km 3 of material in the sedimentary wedges along the western and northern Barents Shelf Margin.

The first oceanographic section across the Nansen Basin in the Arctic Ocean

The first quasi-synoptic oceanographic section across a major deep basin of the Arctic Ocean reveals three different regimes: a narrow boundary current system along the northern Barents Shelf slope, a wide interior basin regime and a northern boundary curret regime with several distinct cores along the Nansen-Gakkel Ridge at 86°N. The southern boundary current cores are marked by high oxygen concentrations, high salinities and low temperatures that indicate sources on the shelf and in Fram Strait. The northern boundary current regime contains water mass signatures that are thought to come from the Amundsen Basin as well as from Fram Strait. The Nansen Basin interior is only slowly ventilated from the boundary currents and shelves, the deep water having an age of several decades. At 83°N characteristics change abruptly from those representative of the southern half of the section to those typical for the northern half and deep Arctic basins. Waters of the southern half of the basin, which have a strong melt-water component in their surface layers, largely originate directly in Fram Strait River runoff from the Siberian rivers and sea ice from the Laptev Sea contributes to the northern part of our section.