Botneheia Formation Research Articles

Exceptional X-Ray contrast: Radiography imaging of a Middle Triassic mixosaurid from Svalbard.

The black shales of the Middle Triassic Botneheia Formation in Svalbard are known for their fossil richness with abundant ichthyosaur remains and beds of the bivalve Daonella. Vertebrate remains from the Muen Mountain on Edgeøya are shown to have exceptional X-ray contrast due to a combination of sulphide and sulphate permineralisation and pseudomorphing. Radiography imaging of a previously described specimen, PMO 219.250, revealed new and spectacular details such as more carpals, teeth, and skull sutures. Teeth and skull characters are taxonomically significant. supporting the referral of PMO 219.250 to Phalarodon and further suggesting an affinity to P. atavus. Three sulphur phases were identified, with the sulphide sphalerite (ZnS) being the highest temperature phase, followed by the sulphate baryte (BaSO4), and the sulphide pyrite (FeS2). Sulphate permineralisation is also seen in specimens from the Upper Jurassic on Svalbard. We suggest that sulphur-rich fluids have flowed and dissolved barium from the shales and deposited the sphalerite and baryte, and that this could be linked to the Cretaceous HALIP. The Jurassic specimens are only permineralised by baryte, while the Triassic specimens have also been permineralised, but mainly pseudomorphed by baryte with crystals of sphalerite. Lithology differences appear to have controlled the compaction of the Triassic specimens, while the Jurassic specimens have retained their three-dimensional shape due to the baryte emplacement relatively earlier in their depositional history. Although soft tissues are not preserved, the excellent X-ray contrast in the Middle Triassic specimens is reminiscent of pyritised fossil sites such as the Hunsrück Slate (Devonian), Beecher's Trilobite Bed (Ordovician), and the La Voulte-sur-Rhône marls (Jurassic).

North Barents Composite Tectono-Sedimentary Element

Abstract The North Barents Composite Tectono-Sedimentary Element could represent a prosperous petroleum province in the Arctic, with several large basins, platforms and highs identified. The sedimentary succession ranges from the Late Paleozoic and continues throughout most of the Mesozoic. Terrestrial sediments of the Billefjorden Group (Famennian–Visean) are likely to be present, and are overlain by evaporites and carbonates of the Gipsdalen Group (Serpukhovian–Late Artinskian). Most of the Triassic is dominated by deposits from a huge prograding deltaic system building out from the south, SE and east, becoming successively younger towards NW. The system was primarily sourced from the Urals but also partly from mainland Norway and, most probably, from Taimyr. The progradation started in the Late Permian and reached Svalbard in the Early Carnian. The entire delta system was flooded during the regional Early Norian transgression, resulting in the deposition of marine shales of the Flatsalen Formation (Svalbard) and the time-equivalent Akkar Member of the Fruholmen Formation (Barents Sea). The Cretaceous and the Paleogene are, respectively, comprehensively and completely eroded. During the Pliocene–Pleistocene, the entire Barents shelf was a site of repeated glaciations, resulting in extensive erosion. Hydrocarbon source rocks occur at several stratigraphic levels from the Carboniferous to the Jurassic, of which the most important is assumed to be the Lower–Middle Triassic Steinkobbe/Botneheia Formation. The Upper Jurassic Hekkingen Formation, where present, is likely to be immature across the whole area. Potential reservoir rocks are Permian carbonates and siliciclastic rocks of Carboniferous and Mesozoic age.

Linking facies variations, organic carbon richness and bulk bitumen content – A case study of the organic-rich Middle Triassic shales from eastern Svalbard

The organic-rich shales of the Middle Triassic Botneheia Formation in Svalbard and its correlative units offshore are considered important source rock intervals for oil and gas generation in the Norwegian Barents Shelf region. Detailed investigation of these intervals is essential to better understand the intra source rock variations and thus to improve exploration models. As source rocks are rarely cored during exploration campaigns, outcrop studies of analogue source rocks onshore Svalbard are of great importance for gaining a comprehensive understanding of the Triassic petroleum system offshore. This integrated sedimentological and geochemical study of the Botneheia Formation investigates the intricate relationship between mudstone facies, total sulfur, total organic/inorganic carbon, and the absolute and relative abundance of bulk bitumen content. Both the Muen Member (Anisian) and the overlying Blanknuten Member (mostly Ladinian) of the Botneheia Formation were densely sampled and analyzed from three outcrop localities on Edgeøya, eastern Svalbard. The results show that total sulfur, total organic carbon, bitumen richness, and relative and absolute aromatic hydrocarbon content increase from bioturbated, gray-colored shales in the lower to middle Muen Member upwards into non-bioturbated, phosphogenic black shales in the middle part of the Blanknuten Member. From here, organic carbon and bulk bitumen richness subsequently decrease upwards in concert with the occurrence of bioturbated, calcareous mudstones and impure limestones towards the top of the Blanknuten Member. Optical vitrinite reflectance variations do not suggest significant maturity variations with depth in the sample profiles, highlighting that the total organic carbon and bulk bitumen content are dominantly coupled with the developing source facies. These facies and chemostratigraphic trends mirror the implied marine vs. terrigenous organic matter sedimentation and benthic preservation potential, which were at a maximum in the middle Blanknuten Member. These processes appear to be closely related to the supply of nutritious upwelled waters that are further linked with an evolving pan-Arctic 2nd order Middle Triassic transgressive–regressive sequence. Facies and multivariate analyses of the geochemical data show that the lower to middle Muen Member are comparable to the pro-delta mudstones of the younger Tschermakfjellet Formation (Carnian), and that both units are clearly distinct from the increased source rock potential and richness in the upper part of the Muen Member and the entire Blanknuten Member. This provides evidence of genetically different paleo-depositional environments and source rock properties that are confined to the lower and upper parts of the Middle Triassic Botneheia Formation, and may have wide applications for Triassic source rock assessment in the offshore Norwegian Barents Sea.

Thermal maturity, hydrocarbon potential and kerogen type of some Triassic–Lower Cretaceous sediments from the SW Barents Sea and Svalbard

Rock-Eval and total organic carbon (TOC) analyses of 144 samples representing Triassic–Lower Cretaceous intervals from the SW Barents Sea (the Svalis Dome, the Nordkapp and Hammerfest basins, and the Bjarmeland Platform) and Svalbard demonstrate lateral variations in source rock properties. Good to excellent source rocks are present in the Lower–Middle Triassic Botneheia and Steinkobbe, and Upper Jurassic Hekkingen formations, 1 – 7 wt% and 6 – 19 wt% TOC, respectively. Hydrogen indices of 298 – 609 mg HC/g TOC in the Botneheia Formation from Svalbard, and 197 – 540 mg HC/g TOC in the Steinkobbe Formation of Svalis Dome suggest Type II (oil-prone) and Type II/III (oil/gas-prone) kerogens, respectively. The Kobbe Formation (Botneheia/Steinkobbe-equivalent) is organic-lean and generally gas-prone (Type III kerogen) on the Bjarmeland Platform and in the Nordkapp Basin, and is a good source rock with Type III/II kerogen in the Hammerfest Basin. In the investigated wells, the Hekkingen Formation is more oil-prone on the Bjarmeland Platform than in the Nordkapp Basin, while Lower Cretaceous samples have poor potential for oil. Upper Triassic samples show potential mainly for gas; however, coal/coaly-shale samples in well 7430/07-U-01 (Bjarmeland Platform) are oil/gas-prone. Most samples analysed are immature to early mature; thus, the variation in petroleum potential and kerogen type is a function of organic facies rather than maturity levels.

Ages of Norwegian oils and bitumen based on age-specific biomarkers

Norwegian oils are generally considered sourced primarily from the Kimmeridge Clay equivalent shales such as the Draupne, Mandal, Spekk and Hekkingen formations, with secondary contributions from the mid–lower Jurassic, and also from the Triassic in the Barents Sea (Botneheia Formation). Still, as most of our age inferences concerning source-oil correlation are based on facies-specific biomarkers, a number of proposed correlations have been questioned. Thus, source to oil correlations were frequently made on the basis of facies parameters, and rightfully so, but facies-specific signatures in oils will transgress age – and, in principle, not correlate with the phylogenetic evolution. This means that one could, in principle assign an oil to ‘the wrong’ age – when one is, in fact, linking it to a known source rock signature. A series of 40 oil samples and core extracts, which cover a wide range both stratigraphically and geographically, have been analysed. In this paper, we present for the first time a Norwegian oil-age map based on age-specific biomarkers among the nordiacholestanes and triaromatic steroids parameters, and delineate also where we find Cretaceous- and Palaeozoic-derived oils. The reasons for this distribution pattern, compared to that of Mesozoic oils on the Norwegian Continental Shelf (NCS), are discussed.

MIGRATED PETROLEUM IN OUTCROPPING MESOZOIC SEDIMENTARY ROCKS IN SPITSBERGEN: ORGANIC GEOCHEMICAL CHARACTERIZATION AND IMPLICATIONS FOR REGIONAL EXPLORATION

The presence of migrated petroleum in outcropping rocks on Spitsbergen (Svalbard archipelago) has been known for several decades but the petroleum has not been evaluated by modern geochemical methods. This paper presents detailed organic geochemical observations on bitumen in outcrop samples from central and eastern Spitsbergen. The samples comprise sandstones from the Lower Cretaceous Carolinefjellet Formation, the Upper Triassic – Middle Jurassic Wilhelmøya Subgroup and the Upper Triassic De Geerdalen Formation; a limestone from the De Geerdalen Formation; and carbonates from the Middle Jurassic – Lower Cretaceous Agardhfjellet Formation. In addition a palaeo‐seepage oil was sampled from a vug in the Middle Triassic Botneheia Formation. This data is integrated with the results of analyses of C1–C4 hydrocarbon fluid inclusions trapped in quartz and calcite cements in these samples.Organic geochemical data suggest that the petroleum present in the samples analysed can be divided into two compositional groups (Group I and Group II). Group I petroleums have distinctive biomarker characteristics including Pr/Ph ratios of about 1.3–1.5, high tricyclic terpanes relative to pentacyclic terpanes, and relatively high methyl‐dibenzothiophenes compared to methyl‐phenanthrenes. By contrast Group II petroleums have low tricyclic terpanes relative to pentacyclic terpanes and low methyl‐dibenzothiophenes compared to methyl‐phenanthrenes, and most Pr/Ph ratios range from 1.90 to 2.57. The petroleum in both groups was derived from marine shale source rocks deposited in proximal to open marine settings.Group I petroleums, present in the sandstones of the Wilhelmøya Subgroup and the De Geerdalen Formation and as a palaeo‐seepage oil in the vug in the Botneheia Formation, are likely to have been sourced from the Middle Triassic Botneheia Formation. Group II petroleums, found in the sandstone of the Carolinefjellet Formation, the limestone from the De Geerdalen Formation and in carbonates of the Agardhfjellet Formation, are inferred to have been generated from the Jurassic‐Cretaceous Agardhfjellet Formation.The analysis of biomarker and aromatic hydrocarbons in the petroleums indicate three relative maturation levels, equivalent to expulsion at vitrinite reflectances of about 0.7–0.8%Rc, 0.8–0.9%Rc and 1.0–1.6%Rc. On average, Triassic host rocks contain petroleum of higher maturity compared to the Jurassic and Cretaceous host rocks.The fluid inclusion data suggest that gaseous hydrocarbons from the sandstones of the Wilhelmøya Subgroup are thermogenic, and are of similar maturity to the petroleum in extracts from these sandstones, suggesting that the gas was generated together with oil in the oil window. By contrast the inclusion gases from carbonate rocks analysed have a mixed (thermogenic / biogenic) origin.The outcropping rocks in which these oils occur are analogous to offshore reservoirs on the Norwegian Continental Shelf. The study may therefore improve our understanding of the subsurface offshore petroleum systems in the Barents Sea and possibly also in other circum‐Arctic basins.

Magnetic properties of Triassic rocks of Svalbard Archipelago - preliminary results

Studies were carried out in three rock formations: the Vardebukta Formation (Early Triassic) and the Bravaisberget Formation (Middle Triassic) from Spitsbergen and the Botneheia Formation (Middle Triassic) from Edgeoya (Eastern Svalbard). Collected samples are diversified and represent various lithologies with different thermal and tectonic histories. Magnetic properties of the specimens were studied using rock-magnetic methods including: thermal demagnetization of saturated isothermal remanent magnetization (SIRM), hysteresis loops and analysis of magnetic susceptibility variations at high temperatures. Subsequently anisotropy of magnetic susceptibility (AMS) and analysis of the structure of natural remanent magnetization (NRM) using thermal and alternating field (AF) demagnetization were investigated. The obtained results show that magnetite represents the main magnetic mineral in all studied rocks, whereas pyrrothite, as a second magnetic information carrier, was noted in some of specimens only. The samples from Edgeoya possess the highest magnetic susceptibility (ca. 240∙10−6 SI) which tends to decrease in sites located further to the west and reaches the minimum value for samples from western Spitsbergen (ca. 30–40∙10−6 SI). AMS studies revealed that the Middle Triassic samples are characterized by inverse magnetic fabric and prolate AMS ellipsoids, whereas the Early Triassic specimens represent normal sedimentary fabric and oblate AMS ellipsoids. Inverse magnetic fabric can be carried by many minerals including: tourmaline, cordierite or goethite (Chadima et al., 2006). For investigated samples two models proposed by Rochette (1988) are highly probable: (1) presence of single-domain elongated magnetite grains or (2) presence of ferroan carbonates whose maximum susceptibility is parallel to the c-axis. Paleomagnetic results of the Botneheia Formation revealed only one characteristic NRM component characterized by steep inclination and maximal unblocking temperatures in range of 425–450°C. In turn, the Early Triassic rocks record several NRM components with partially overlapping unblocking temperatures. We have concluded that different magnetic properties observed in studied rocks might be related to various lithologies but also to distinct tectonic and thermal histories associated with complex tectonic evolution of the Barents Sea Shelf.

Organic matter–apatite–pyrite relationships in the Botneheia Formation (Middle Triassic) of eastern Svalbard: Relevance to the formation of petroleum source rocks in the NW Barents Sea shelf

The Middle Triassic Botneheia Formation of eastern Svalbard (Edgeøya and Barentsøya) comprises an organic carbon-rich, fine-grained clastic succession (∼100 m thick) that makes the best petroleum source rock horizon in the NW Barents Sea shelf. The succession records a transgressive–regressive interplay between the prodelta depositional system sourced in the southern Barents Sea shelf (black shale facies of the lower and middle parts of the Muen Member) and the open shelf phosphogenic system related to upwelling and nutrient supply from the Panthalassic Ocean (phosphogenic black shale facies of the upper part of the Muen Member and the Blanknuten Member). The relationships between organic matter, authigenic apatite, and pyrite in these facies allow to characterize the relative roles of redox conditions and oceanic productivity in the organic carbon preservation. The accumulation of terrestrial and autochthonous marine organic matter in the black shale facies occurred under dominating oxic conditions and increasing-upward productivity related to early transgressive phase and retrogradation of the prodelta system. The phosphogenic black shale facies deposited in an oxygen-minimum zone (OMZ) of the open shelf environment during the late transgressive to regressive phases under conditions of high biological productivity, suppressed sedimentation rates, and changing bottom redox. The phosphatic black shales occurring in the lower and upper parts of the phosphogenic succession reveal depositional conditions indicative of the shallower part of OMZ, including high input of autochthonous organic matter into sediment, oxic-to-dysoxic (episodically suboxic and/or anoxic) conditions, intense phosphogenesis, and recurrent reworking of the seabed. The massive phosphatic mudstone occurring in the middle of the phosphogenic succession reflects the development of euxinia in the deeper part of OMZ during high-stand of the sea. High input of autochthonous organic matter in this environment was coupled with mineral starvation and intermittent phosphogenesis. In mature sections in eastern Svalbard, the petroleum potential of the Botneheia Formation rises from moderate to good in the black shale facies, and from good to very good in the phosphogenic black shale facies, attaining maximum in the massive phosphatic mudstone.

Triassic ichthyopterygian assemblages of the Svalbard archipelago: a reassessment of taxonomy and distribution

Ichthyopterygians were amongst the most specialised lineages of secondarily aquatic amniotes; however, their origin and initial radiation remain obscure. The stratigraphically oldest and phylogenetically most basal taxa have been found in Early–Middle Triassic deposits throughout the northern hemisphere, but one of the earliest documented and arguably most important localities is the High Arctic Svalbard archipelago. Like many classic palaeontological sites, the Svalbard Triassic fossil-bearing horizons are plagued by inconsistent geological interpretations and taxonomic classifications. To resolve these conflicts, a comprehensive revision of the various ichthyopterygian assemblages was undertaken. The fossils were found to be distributed through three sequential rock units: the Olenekian Vikinghøgda Formation (six discernible taxa distributed over two distinct horizons), Anisian lower Botneheia Formation (two taxa) and the Ladinian–Carnian Blanknuten Member of the Botneheia Formation–Tschermakfjellet Formation (five taxa). Unfortunately, many of the specimens are non-diagnostic at species-level, although they do contribute a cohesive picture of marine faunal successions during the Early–earliest Late Triassic. Indeed, the Svalbard archipelago has produced one of the most diverse Early Triassic ichthyopterygian assemblages known worldwide, but is comparatively species poor throughout the early Middle Triassic, perhaps due to sampling biases.

Chapter 15 Triassic deltaic sequences in the northern Barents Sea

Abstract Seismic sequence interpretation, analysis of shallow boreholes and outcrop studies at Svalbard strongly indicate that the Triassic basin in the northern Barents Sea and eastern Svalbard was supplied by sediments from the south east by a large complex prograding delta system. The seismic facies interpretation suggests that the black Ladinian and Anisian shale (Botneheia Formation) is an integrated part of the prograding delta system and developed as the bottom sets of large pro-delta clinoforms. The clinoforms and their breaking points define a series of seismically detectable sequences at a shelf edge delta. Provenance areas are suggested to be Siberia, the Kola Peninsula and the Caledonides. Each sequence has a maximum thickness of 200–400 m and is interpreted to represent the water depth range in the basin. Seasonal flooding, stratified salinity and algal blooming are assumed to be important factors generating anoxic bottom conditions in a huge death zone in front of the prograding delta system. The folded and thrusted Triassic rocks in the western part of Svalbard are suggested to be part of an allochthonous nappe ejected from the Greenland region when Greenland moved northwards along the Hornsund Fault complex; their original position is suggested to be further south.

Intercalibration of Boreal and Tethyan time scales: the magnetobiostratigraphy of the Middle Triassic and the latest Early Triassic from Spitsbergen, Arctic Norway

An integrated biomagnetostratigraphic 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 10 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 biomagnetostratigraphy from the late Olenekian (Vendomdalen Member) is supplemented by data from nearby Vikinghøgda. The early and middle 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 as a result of erosional truncation below the Tschermakfjellet Formation. Correlation with Tethyan biomagnetostratigraphies shows the traditional base of the Boreal Anisian (base of the Grambergia taimyrensis Zone) precedes the base of the Anisian (using definitions based on the De? sli Caira section in Romania). The Boreal upper Anisian Gymnotoceras rotelliforme and Frechites nevadanus ammonoid zones correlate with 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 Intornites oleshkoi Zone. The latest Olenekian—early Anisian magnetic polarity time scale is refined using the Spitsbergen data.

Intercalibration of Boreal and Tethyan time scales: the magnetobiostratigraphy of the Middle Triassic and the latest Early Triassic from Spitsbergen, Arctic Norway

An integrated biomagnetostratigraphic 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 10 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 biomagnetostratigraphy from the late Olenekian (Vendomdalen Member) is supplemented by data from nearby Vikinghogda. The early and middle 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 as a result of erosional truncation below the Tschermakfjellet Formation. Correlation with Tethyan biomagnetostratigraphies shows the traditional base of the Boreal Anisian (base of the Grambergia taimyrensis Zone) precedes the base of the Anisian (using definitions based on the De? sli Caira section in Romania). The Boreal upper Anisian Gymnotoceras rotelliforme and Frechites nevadanus ammonoid zones correlate with 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 Intornites oleshkoi Zone. The latest Olenekian—early Anisian magnetic polarity time scale is refined using the Spitsbergen data.

Magneto-biostratigraphy of the Middle to Upper Triassic transition, central Spitsbergen, arctic Norway

Palaeomagnetic and biostratigraphic data were obtained for the latest Ladinian and most of the Carnian (Botneheia Formation to basal Kapp Toscana Group), from two sections in central Spitsbergen (Svalbard archipelago). Thermal and alternating field (AF) demagnetization reveals a magnetization of both normal and reversed polarities. The mean directions pass reversal and fold tests and are similar to other European Late Triassic palaeopoles. One of the sections displays 15° of vertical-axis, clockwise, tectonic rotation on a décollement in the underlying Botneheia Formation. The magnetostratigraphy is dominated by normal polarity in the uppermost Botneheia Formation and into the Tschermakfjellet and basal De Geerdalen formations. A substantial hiatus characterizes the Ladinian–Carnian boundary in central Spitsbergen, so reverse magnetozones, identified in Tethyan sections near this boundary, are absent. Magnetostratigraphic correlation, along with palynostratigraphic constraints, indicates that most of the De Geerdalen Formation is Lower Carnian. The magnetostratigraphy and palynology indicates that the Isfjorden Member (upper unit of the De Geerdalen Formation) is probably mid-Carnian in age. Change in the lithological architecture in the Isfjorden Member, compared with the underlying parts of the De Geerdalen Fm, suggests a hiatus near the base of the member, which may represent a mid-Carnian unconformity, not previously recognized on Spitsbergen.

The type section of the Vikingh�gda Formation: a new Lower Triassic unit in central and eastern Svalbard

The Vikinghogda Formation (250 m) is defined with a stratotype in Deltadalen-Vikinghogda in central Spitsbergen. The Vikinghogda Formation replaces the Vardebukta and Sticky Keep Formations of Buchan et al. (1965) and the lower part of the Barentsoya Formation of Lock et al. (1978) as extended geographically by Mork, Knarud et al. (1982) in central Spitsbergen, Barentsoya and Edgeoya. The formation consists of three member: the Deltadalen Member (composed of mudstones with sandstones and siltstones), the Lusitaniadalen Member (dominated by mudstones with thin siltstone beds and some limestone concretions) and the Vendomdalen Member (composed of dark shales with dolomite interbeds and nodules). The Lusitaniadalen and Vendomdalen members replace the former Sticky Keep Formation/ Member in the siirne areu. The Vikinghoda Formation can be followed through central and eastern Spitsbergen to Barentoya and Edgeoya and includes all sediments between the chert-rich Kapp Starostin Formation (Permian) and the organic-rich shales of the Botneheia Formation (Middle Triassic). The subdivision into three members is also reflected in the organic carbon content and palynofacies. Upwards, each succeeding member becomes more distal, organic-rich and oil-prone than the one below. The Vikinghoda Formation is well-dated by six ammonoid zones, although the transitional beds between the Deltadalen and Lusitaniadalen members lack age diagnostic macrofossils. Corresponding palynozonation and magnetustratigraphy have also been determined. The overall stratigraphical development correlates well with other key Triassic areas in the Arctic, although intervals in the late Dienerian and early Smithian may be condensed or missing.

The type section of the Vikinghøgda Formation: a new Lower Triassic unit in central and eastern Svalbard

The Vikinghøgda Formation (250 m) is defined with a stratotype in Deltadalen-Vikinghøgda in central Spitsbergen. The Vikinghøgda Formation replaces the Vardebukta and Sticky Keep Formations of Buchan et al. (1965) and the lower part of the Barentsøya Formation of Lock et al. (1978) as extended geographically by Mørk, Knarud et al. (1982) in central Spitsbergen, Barentsøya and Edgeøya. The formation consists of three member: the Deltadalen Member (composed of mudstones with sandstones and siltstones), the Lusitaniadalen Member (dominated by mudstones with thin siltstone beds and some limestone concretions) and the Vendomdalen Member (composed of dark shales with dolomite interbeds and nodules). The Lusitaniadalen and Vendomdalen members replace the former Sticky Keep Formation/ Member in the siirne areu. The Vikinghøda Formation can be followed through central and eastern Spitsbergen to Barentøya and Edgeøya and includes all sediments between the chert-rich Kapp Starostin Formation (Permian) and the organic-rich shales of the Botneheia Formation (Middle Triassic). The subdivision into three members is also reflected in the organic carbon content and palynofacies. Upwards, each succeeding member becomes more distal, organic-rich and oil-prone than the one below. The Vikinghøda Formation is well-dated by six ammonoid zones, although the transitional beds between the Deltadalen and Lusitaniadalen members lack age diagnostic macrofossils. Corresponding palynozonation and magnetustratigraphy have also been determined. The overall stratigraphical development correlates well with other key Triassic areas in the Arctic, although intervals in the late Dienerian and early Smithian may be condensed or missing.

The Triassic ammonite Aristoptychites kolymensis (Kiparisova) from Botneheia, Spitsbergen

Arisroplychifes kolymensis (Kiparisova) is investigated and described in detail from collections made at Botneheia, Spitsbergen, where it occurs at the top of the Botneheia Formation (Daonella Shale). It is a rather small species and the stratigraphically highest representative of the genus in Spitsbergen. Its suture line is remarkable by its possession of the additional U,-lobes between the internal lobe and the first umbilical lobe. A lobe of this kind has so far been described only once, with Arcesfes (Proarcesres) bicarinatuc by Schindewolf (1968), which suggests affinities between Ptychitidae and Arcestidae.