Intercalibration of Boreal and Tethyan timescales: the magneto-biostratigraphy of the Middle Triassic and the latest Early Triassic from Spitsbergen, Arctic Norway

An integrated bio-magnetostratigraphic study of the latest Early Triassic to the upper parts of the Middle Triassic, at Milne Edwardsfjellet in central Spitsbergen, Svalbard, allows a detailed correlation of Boreal and Tethyan biostratigraphies. The biostratigraphy consists of ammonoid and palynomorph zonations, supported by conodonts, through some 234 m of succession in two adjacent sections. The magnetostratigraphy consists of ten substantive normal–reverse polarity chrons defined by sampling at 150 stratigraphic levels. The magnetization is carried by magnetite and an unidentified magnetic sulphide, and is difficult to fully separate from a strong present-day like magnetization. The bio-magnetostratigraphy from the late Olenekian (Vendomdalen Member) is supplemented by data from nearby Vikinghøgda. The early and mid-Anisian has a high sedimentation rate, comprising over half the ca. 140-m thickness of the Botneheia Formation, whereas the late Anisian and lower Ladinian is condensed into about 20 m. The two latest Boreal Ladinian ammonoid zones are absent due to erosional truncation below the Tschermakfjellet Formation. Correlation to Tethyan bio-magnetostratigraphies shows the traditional base of the Boreal Anisian (base of G. taimyrensis Zone) precedes the base Anisian (using here definitions based on the Desli Caira section in Romania). The Boreal upper Anisian G. rotelliforme and F. nevadanus ammonoid zones correlate to most of the Tethyan Pelsonian and Illyrian substages. The base Ladinian defined in the Tethyan global boundary stratotype and point (GSSP) is closely equivalent to the traditional base of the Boreal Ladinian at the I. oleshkoi Zone. The latest Olenekian to early Anisian magnetic polarity timescale is refined using the Spitsbergen data

The Hambergfjellet Formation on Bjørnøya – sedimentary response to early Permian tectonics on the Stappen High

On Bjørnøya, the exhumed crest of the Stappen High, the lower Permian (Cisuralian) Hambergfjellet Formation represents the only exposed part of the Bjarmeland Group carbonate platform, which occurs widely elsewhere in the subsurface of the Barents Shelf. A complex stratigraphic architecture has earlier been noted for the Hambergfjellet Formation and thickness estimates range from c. 50 to more than 100 m. Moreover, the unit lacks a formal type section, which hampers accurate regional correlations and comparisons. In this stratigraphic study, we integrate new field observations and microfacies analysis with data from previous work to present a composite section which is proposed as the type section for the Hambergfjellet Formation. Four internal units are recognized. Units A and B (post ?late Asselian–?Sakmarian), which consist of mixed carbonate and siliciclastic rocks interpreted to be of shallow marine origin, are restricted to a series of fault-bounded basins defined by gently rotated basement fault blocks. Locally, units A and B onlap or truncate lowermost Permian strata and appear to transgressively fill in antecedent topography presumably created during Sakmarian uplift and erosion of the Stappen High. The distorted character of unit A suggests that slumping was an important process during the initial phase of infilling, amid or soon after transgression. Unit C (?Sakmarian–?early Artinskian) is a thick-bedded, sheet-like limestone unit which contains fauna elements consistent with deposition on a warm-water carbonate platform occasionally subject to subaerial exposure. Unit D (late Artinskian) is a brachiopod-dominated, fusulinid-bearing, bioclastic limestone unit deposited on a fully marine, transitional warm-temperate to cool-water carbonate platform which developed during a late Artinskian circum-Arctic transgression. The unit only occurs in the eastern part of the outcrop belt on southern Bjørnøya due to fault-controlled tilting and peneplanation prior to deposition of the Miseryfjellet Formation (Kungurian–Wordian) limestones. Distinct evidence, including breccia pipes, points to prolonged exposure and karstification of the Hambergfjellet Formation carbonate platform prior to transgression and submergence of the Stappen High in the middle to late Permian (Guadalupian). The presence of angular and highly diachronous unconformities at the base and top of the formation, a series of small grabens, internal dip variations, as well as a conspicuous north to north-eastward thinning manifest tectonism pre-dating the late Permian extensional event along the western Barents Shelf margin. As such, we shed a new light on the Permian tectonostratigraphic evolution of the Stappen High

Bivalve beds reveal rapid changes in ocean oxygenation in the Boreal Middle Triassic – a case study from Svalbard, Norway

A fossil-rich interval in the organic-rich marine black mudstone of the Middle Triassic Botneheia Formation on eastern Svalbard was logged in high-resolution on an extremely well exposed section with emphasis on bivalve beds, taphonomic features, trace fossils and oxygenation proxies. The size distribution, fragmentation, articulation and orientation of three bivalve beds of the epifaunal flat clam Daonella were analysed. The logged section was studied for the recurrent occurrences of trace fossils and bivalve beds, and size distribution of framboidal pyrite. Daonella is most common in the shaly interval, while other taxa seem to outcompete Daonella in the siltier intervals. The comparison of fossil and sedimentological data with geochemical proxies for oxygenation revealed that the bivalve beds formed under dysoxic, conditions and due to low sedimentation rates and winnowing are not mass-mortality assemblages as previously suggested. The deposition on the sea floor was interrupted by anoxic intervals without benthic life. Recurrent beds containing the trace fossil Thalassinoides, however, show that oxygen levels fluctuated. The combination of water currents and oxygen fluctuations is a key to understanding why the black shales of the Botneheia Formation are so rich in benthic fossils

Stratigraphy and palaeosol profiles of the Upper Triassic Isfjorden Member, Svalbard

The Isfjorden Member forms the upper part of the De Geerdalen Formation in Svalbard and is well exposed throughout central and eastern Spitsbergen, including the island of Wilhelmøya. We examine palaeosol profiles identified in the Isfjorden Member and compare these to profiles seen in the remainder of the De Geerdalen Formation. In addition, we address the nuances of the Isfjorden Member, its practicality as a stratigraphic interval and attempt to constrain the unit’s presence, as well as the nature of its lower boundary throughout outcrops in Svalbard. The Isfjorden Member is easily recognised by its conspicuous beds of alternating red and green coloured palaeosols, occasional caliche profiles and bivalve coquina beds. These beds have commonly been used to identify the unit in outcrop and we explore their relevance to the formal stratigraphic definition. The lower boundary is typically difficult to identify, especially when using the original definition; however, we find that placing it at the top of the last major sandstone in the De Geerdalen Formation is a practical solution. The boundary is conformable throughout Spitsbergen with no obvious erosion or break in sedimentation observed.The abundance, thickness and maturity of palaeosols increases upwards through the De Geerdalen Formation. Mature palaeosol and occasional caliche horizons are found to dominate within the Isfjorden Member. Immature palaeosols are in general constrained to the strata below. The position of palaeosols in relation to sedimentary successions is typically restricted to floodplain and interdistributary bay deposits, or atop upper shoreface deposits. The transition from immature palaeosols with common histosols to mature palaeosols and caliche reflects the development of the delta plain from a dynamic paralic setting to a morestable proximal system.publishedVersio

Digitising Svalbard’s geology: the Festningen digital outcrop model

The renowned Festningen section in the outer part of Isfjorden, western Spitsbergen, offers a c. 7 km-long nearly continuous stratigraphic section of Lower Carboniferous to Cenozoic strata, spanning nearly 300 million years of geological history. Tectonic deformation associated with the Paleogene West-Spitsbergen-Fold-and-Thrust belt tilted the strata to near-vertical, allowing easy access to the section along the shoreline. The Festningen section is a regionally important stratigraphic reference profile, and thus a key locality for any geologist visiting Svalbard. The lithology variations, dinosaur footprints, and the many fossil groups, record more than 300 million years of continental drift, climate change, and sea level variations. In addition, the Festningen section is the only natural geoscientific monument protected by law (i.e. geotope) in Svalbard. In this contribution, we present a digital outcrop model (DOM) of the Festningen section processed from 3762 drone photographs. The resulting high-resolution model offers detail down to 7.01 mm, covers an area of 0.8 km2 and can be freely accessed via the Svalbox database. Through Svalbox, we also put the Festningen model in a regional geological context by comparing it to nearby offshore seismic, exploration boreholes penetrating the same stratigraphy and publications on the deep-time paleoclimate trends recorded at Festningen

The Svalbard Carboniferous to Cenozoic Composite Tectono-Stratigraphic Element

The Svalbard Composite Tectono-Stratigraphic Element is located on the north-western corner of the Barents Shelf and comprises a Carboniferous to Pleistocene sedimentary succession. Due to Cenozoic uplift the succession is subaerially exposed in the Svalbard archipelago. The oldest parts of the succession consist of Carboniferous to Permian mixed siliciclastic, carbonate and evaporite and spiculitic sediments that developed during multiple phases of extension. The majority of the Mesozoic succession is composed of siliciclastic deposits formed in sag basins and continental platforms. Episodes of Late Jurassic and Early Cretaceous contraction are evident in the eastern part of the archipelago and in nearby offshore areas. Differential uplift related to the opening of the Amerasian Basin and the Cretaceous emplacement of the High Arctic Large Igneous Province created a major hiatus spanning from most of the Late Cretaceous and early Danian throughout the Svalbard Composite Tectono-Stratigraphic Element. The West Spitsbergen Fold and Thrust Belt and the associated foreland basin in central Spitsbergen (Central Tertiary Basin) formed as a response to the Eurekan orogeny and the progressive northward opening of the North Atlantic during the Palaeogene. This event was followed by formation of yet another major hiatus spanning the Oligocene to Pliocene. Multiple reservoir and source rock units are exposed in Svalbard providing analogues to the offshore prolific offshore acreages in southwest Barents Sea and are important for de-risking of plays and prospects. However, the archipelago itself is regarded as high-risk acreage for petroleum exploration. This is due to Palaeogene contraction and late Neogene uplift of particularly the western and central parts. In the east there is an absence of mature source rocks, and the entire region is subjected to strict environmental protection

Lithological description of subcropping Lower and Middle Triasic rocks from the Svalis Dome, Barents Sea

Eleven shallow cores display 315 m of the >700 m thick Lower and Middle Triasic successional of the Svalis Dome, a Salt diapir in the central south-western Barents Sea. The Svalis Dome was uplifted in the late Mesozoic. and Trisassic rocks suherop below Quaternary till around the Upper Palaeozoic core of the dome. Deposition of the Triassic succession took place in deep shelf to basinal environments below storm wave base. The succession is dated by macrofossils and palynomorphs and can be assigned to four formations. The basal beds of the shaly greenish grey Havert Formation (Griesbachian) occur above Permian bioclastic carbonate. The Klappmyss Formation (Smithian) in the lower part contains gravity flow sands deposited as submarine fans pussible triggered by tectonic movements along the adjacent ault zones overlian by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe overlain by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe Formation, and was deposited in a large bight by restricted water circulation. The Snadd Formation. on top, representes a marine shelf unit deposited in front of an emerging land area in the north-east. A minimum of six higher order transgressive-regressive sequences are recognized at the Svalis Dome and these are correlated with other Arctic areas

The environmental significance of the trace fossil Rhizocorallium jenense in the Lower Triassic of western Spitsbergen

The 500 m thick Lower Triassic succession of western comprises two shale-dominated formations, which both show upward-coarsening motifs. These reflect repeated coastal basin dominated by low energy fine-clastic sediments. The track fossils Rhizocorallium jenense and Skolithos are found in the coarser part of these units and variations in size and orientation of R. jenense give important palaeoenvironmental information. Rhizocorallium jenense occurs in storm-generated siltstones and stones, whose deposition interrupted prevailing intermediate energy levels. Size variations and trace fossil abundance suggest an optimal habitat in the shoreface zone, with poorer adaptation to both offshore and shallower environments. Age-equivalent marine sediments on north-eastern Greenland also contain local abundant occurrences Rhizocorallium. These Arctic occurrences contrast with the same trace fossil's distribution in the Jurassic of Britain and France, where it characterizes shallower and higher energy environments; such sequences on Spitsbergen show an ichnofauna dominated by Skolithos and bivalve escape shafts. Orientations shown by the R. jenense U-tubes show a generally, but not solely, unimodal distribution, with the curved distal entedusually oriented toward onshore. Presumed aperture lineations show strongly unimodal trends, probably related to longshore currents. Burrows in bed at the top of individual storm lobe units show more complex ably patterns probably reflecting both current and wave reworking following lobe abandonment. All finds suggest early colonization by the burrowing organisms. These were not followed by other burrowers, either because of the nutrient-poor nature of the sediment or because of high sedimentation rates

Ichnology of a marine regressive systems tract: the Middle Triassic of Svalbard

The Middle Triassic succession of Svalbard forms a pronounced second-order transgressive–regressive sequence. This is represented by deltaic sediments in western Spitsbergen, grading to deep restricted shelf deposits in central and eastern parts of the archipelago. Nine ichnogenera have been recognized, which form three local ichnofacies or trace fossil assemblages: a Thalassinoides assemblage that is dominant in low-energy shelf settings, a Taenidium– Rhizocorallium assemblage that occurs in intermediate-energy deltaic and shelf environments, and a Polykladichnus assemblage that dominates high-energy deltaic environments. These three trace fossil assemblages overlap, both as a result of fluctuations in energy level with time and because of differential preservation of the different tiers. The main control of the distribution of the assemblages is an upwards increase in energy regime during progradation of the deltaic sediments along western Spitsbergen, and a contemporaneous decrease in energy regime more distally. The succession has also experienced fluctuating oxygen levels during deposition, as evidenced by very high organic matter contents and mass mortality of juvenile bivalves. These anoxic periods have been interrupted by periods of bioturbation, with the development of extensive tiered ichnocoenoses. Phosphatization of Thalassinoides fills and subsequent modification of the phosphatic fill by compaction has brought about the formation of phosphate nodules. The typical Thalassinoides framework may be recognized on well-exposed bedding surfaces. The phosphate nodules also occur as conglomeratic lag deposits, commonly occurring at the base of siltstone beds, as a result of episodic heavy storms