NW European Stratigraphic Lexica

MESOZOIC LITHOSTRATIGRAPHY

from: Dallmann. W.K. (ed.). Svalbard lithostratigraphic lexicon

  3.1 Stratigraphic development of Svalbard and the Barents Sea Shelf
  3.2 General subdivision
  3.3 Previous stratigraphic schemes
  3.4 Regional descriptions and major revisions
     3.4.1 Sassendalen Group
     3.4.2 Kapp Toscana Group
     3.4.3 Adventdalen Group
     3.4.4 Nygrunnen Group
     3.4.5 Intrusive rocks

3.1 Stratigraphic development of Svalbard and the Barents Sea Shelf

The chapter on Mesozoic stratigraphy of Svalbard also comprises the offshore deposits of the western Barents Sea Shelf, although offshore deposits are not included in the discussions of the Upper Palaeozoic and Cenozoic of Svalbard. The present knowledge of the essentially continuous stratigraphy and spatial relations of the Mesozoic succession of the entire Barents Sea Shelf supports the establishment of a common stratigraphic framework. The offshore units are included in the lexicon text and in the Correlation scheme (Fig. 3-05), but are not represented by maps and type sections. The reader is referred to the cited publications on the Barents Sea Shelf.

The Barents Sea Shelf, with Svalbard forming its exposed northwestern corner, was an area of clastic deposition during the entire Mesozoic. While carbonate sedimentation had prevailed from the late Carboniferous into the Permian, the late Permian had seen a transition to cherty/spiculitic mudstone deposition in basinal areas and interbedded bioclastic limestones and shales in platform settings. An extensive late Permian hiatus, seems to have developed everywhere. This hiatus was submarine in basinal areas, while marginal areas were exposed and locally not transgressed before the late Early Triassic. Major sedimentary basins were developed over the main Svalbard islands, the Bjørnøya Basin, Hammerfest Basin and Nordkapp Basin of the Western Barents Sea Shelf and the Central Barents Sea Depression west of Novaja Zemlja (Fig. 1-02). These basins were separated by shallow shelf or platform areas, surrounding land areas or local highs. An extensive seaway connected these basins – and other basins southward to the North Sea area – during most of the Mesozoic, and deltaic and coastal sediments prograded into the sea from different land areas, creating a complex pattern of sedimentary units. Erosion and redeposition of the clastic sediments was important during long periods.

During most of the Mesozoic, the main land and sedimentary provenance area for the successions deposited in Svalbard was situated to the west of Svalbard (eastern North Greenland), from where most sediment bodies built out into the easterly basin. An additional northern to northeastern source area became evident from the Late Triassic (Steel & Worsley 1984), and at Kong Karls Land also from north and east (Olaussen et al., in prep.). All Mesozoic sedimentary episodes led to sedimentation across all of Svalbard, possibly except northernmost areas, where the record is lacking, both due to the periodical absence of sedimentation and to later stripping off of sediments.

In the Barents Sea, a complete stratigraphic nomenclature is only established for the Hammerfest Basin, while in other areas only a few units are defined at present.

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3.2 General subdivision

Traditionally, three lithostratigraphic groups have been defined in the Mesozoic succession of Svalbard (Sassendalen, Kapp Toscana and Adventdalen groups: Buchan et al. 1965; Parker 1967) and five in the southwestern Barents Sea (Ingøydjupet, Realgrunnen, Teistengrunnen, Nordvestbanken and Nygrunnen groups: Worsley et al. 1988; Fig. 3-02). In the present proposal, those Barents Sea Shelf groups that have equivalents on land apply the group names defined on land. For the Triassic to Middle Jurassic of the Barents Sea Shelf, the previous subdivision is taken care of by converting previous groups into subgroups (Fig. 3-01). One group (Nygrunnen Group) was only deposited on the Barents Sea Shelf when Svalbard was uplifted at the end of the Mesozoic.

The Sassendalen Group was defined on Spitsbergen by Buchan et al. (1965) and comprises shales, siltstones and sandstones of Early and Middle Triassic age. The group's coastal to deltaic sediments exposed on western Spitsbergen grade into organic-rich shelf mudstones eastwards in Svalbard and southwards into the Barents Sea Shelf, however, a thick marine to coastal clastic succession is deposited in the Hammerfest Basin (southwestern Barents Sea Shelf). Worsley et al. (1988) defined the "Ingøydjupet Group" in the Hammerfest Basin for the Induan to Anisian shales and claystones grading upwards into Ladinian and Carnian compositionally immature sandstones. In the present nomenclature, the name Ingøydjupet Subgroup is reserved for the finer-grained Induan - Anisian succession of the Barents Sea Shelf. The subgroup is correlated with and included in the Sassendalen Group. The Ladinian – Carnian sandstonerich succession is correlated with and included in the overlying Kapp Toscana Group.

The Kapp Toscana Group, originally defined by Buchan et al. (1965) as a formation, comprises sandstones and mudstones of late Middle Triassic to Middle Jurassic age. The group represents a significant change in sedimentary regime from the underlying groups, and a turn into similar shallow marine to deltaic depositional environments across the entire Barents Sea Shelf.

The Storfjorden Subgroup (new name) comprises the compositionally immature sandstones and mudstones of late Middle (Ladinian) and early Late Triassic age deposited in coastal to shallow marine environments. The subgroup comprises the lower part of the Kapp Toscana Group, including the upper, compositionally immature part of the "Ingøydjupet Group" on the southwestern Barents Sea Shelf as defined by Worsley et al. (1988).

Fig. 3-01: Group and subgroup subdivision of Mesozoic rocks

The Wilhelmøya Subgroup corresponds to the "Wilhelmøya Formation" (Worsley 1973; Bjærke & Dypvik 1977; Edwards et al. 1979) in the Svalbard area. The variedly condensed development in different areas of Svalbard led to the establishment of several formations within the succession and the change of the Wilhelmøya unit from formation to subgroup rank. The subgroup consists of texturally mature sandstones deposited on coastal plains and in deltaic through shallow marine environment; it shows an increasingly condensed development towards the west.

The Realgrunnen Subgroup was defined with group rank by Worsley et al. (1988) in the Hammerfest Basin. The recent understanding of the intermediate nature of the coeval deposits of Kong Karls Land, and data from numerous cored wells in the Barents Sea, correlate this succession with its condensed counterpart in Svalbard, the Wilhelmøya Subgroup and makes it appropriate to include the succession in the Kapp Toscana Group.

The Adventdalen Group was defined on Spitsbergen by Parker (1967) for the shales and minor sandstone successions of latest Middle Jurassic to Early Cretaceous age. The group is here laterally extended to include correlative sediments on Kong Karls Land and in the southwestern Barents Sea, previously referred to as the "Teistengrunnen" and "Nordvestbanken groups" (Worsley et al. 1988). Dark organic-rich shales of Late Jurassic age occur throughout the area. A hiatus of varying magnitude above these shales reflects a period of tectonic disturbance at the Jurassic - Cretaceous transition, well established in the Barents Sea. This is followed by calcareous sedimentation on platform areas and dark, but organic-lean, shales in the basins. In the north, in Svalbard, deltaic sedimentation gave rise to the deposition of prominent sandstone bodies.

The Janusfjellet Subgroup (Parker 1967) comprises the dark shale succession of latest Middle Jurassic to Hauterivian age in Svalbard.

The Nygrunnen Group (Worsley et al. 1988) is only documented in the southern part of the Barents Sea and comprises a basinal, shaley development, with condensed calcareous sandstones in platform setting. The group is of Late Cretaceous age.

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3.3 Previous stratigraphic schemes

Most authors who have elaborated previous stratigraphic schemes for Svalbard worked either on the Triassic to Middle Jurassic (Sassendalen and Kapp Toscana groups; Fig. 3-03), or the Middle Jurassic to Early Cretaceous (Adventdalen Group; Fig. 3-04). This was a natural consequence of the major sequence boundary between these two groups which also is reflected in the quite different lithologies below and above. Exceptions are Pčelina (1980, 1983), presenting results of the Russian research on the archipelago, and stratigraphers working on some of the eastern islands (Worsley 1973; Smith 1975; Smith et al. 1975, 1976).

The Triassic to Middle Jurassic of Svalbard has historically often been referred to as the Triassic only, due to the fact that the Jurassic represents a very condensed succession in the best accessible (western and central) parts of Svalbard, often only a few metres thick. This changed with the recognition of the much thicker Jurassic sections on Wilhelmøya (Worsley 1973; Smith 1975), Hopen (Smith et al. 1975) and Kong Karls Land (Smith et al. 1976).

The "Triassic" stratigraphy was first summarised into a common scheme by Buchan et al. (1965) which was widely applied until the early 1980s. Several local adjustments were then made (Flood et al., 1971, and Lock et al. 1978, on Edgeøya and Barentsøya; Worsley & Mørk, 1978, in southern Spitsbergen), until Mørk et al. (1982) summarised the revised view into a new scheme, this time paying attention to the differential stratigraphic development on western and central/eastern Spitsbergen.

The "Jurassic-Cretaceous" stratigraphy was firstly summarised into a common scheme by Parker (1967). Minor adjustments or supplements for individual regions were made by Norwegian and British authors (Nagy 1970; Smith et al. 1976). A detailed subdivision of the Janusfjellet Subgroup in central and eastern Spitsbergen was presented by Dypvik et al. (1991).

More or less simultaneously with Mørk et al. (1982), a different stratigraphic nomenclature was developed by Pčelina (1980, 1983), also reflecting the regionally varying stratigraphic development, but showing a greater influence of chronostratigraphic thinking, i.e. a trend to summarise lithologies into formations (Russian: svity, lit. transl. "suites") according to their related stage.

A major effort was undertaken by the Stratigraphic Committee of Svalbard in the context of the present compilation to elaborate a synthesis of the Russian and Norwegian schemes, while maintaining as many names as possible shown on published maps without major redefinitions, and at the same time taking care of as many as possible priorities by first publication. This resulted, of course, in a number of compromises. Still, the revised scheme (Fig. 3-05) has preserved the traditional group subdivision and most formation names familiar from published maps. At the same time, it takes into account important stratigraphic units and correlations from the Russian scheme represented by Pčelina (1980, 1983), though this is not always reflected by the names themselves.

Historic priority is the main criterion for recognition and acceptance of lithological unit names, however, many terms have been poorly defined in the past or have first been mentioned in areas where they are poorly exposed or developed. Several units have been emended or redefined to adjust the stratigraphic framework to the meanwhile improved knowledge level, or to enable correlations between these areas and the Barents Sea Shelf. The present synthesis also tries to incorporate regional variations, often by redefining type sections (stratotypes), or by defining reference sections (hypostratotypes) in addition to the type sections, or by accepting locally or regionally developed subdivisions at member level.

Fig. 3-02. Revision of Mesozoic group/subgroup subdivision of the Barents Sea Shelf

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3.4 Regional descriptions and major revisions

3.4.1 Sassendalen Group
The Sassendalen Group is maintained as originally defined by Buchan et al. (1965) on central Spitsbergen. The major revision is the lateral extension of the group to include the Ingøydjupet Subgroup of the Barents Sea.

In Svalbard (except Bjørnøya) the subdivision of the group into three units has been applied in all previous stratigraphic work, although with different hierarchies and regional implications. The lower unit is characterised by shallow marine to coastal silt- and sandstones, the middle unit by upward coarsening shale-siltstone/sandstone sequences, and the upper unit by phosphatic, organic-rich shales and subordinate sandstones.

Buchan et al. (1965) defined three formations within this group, the Vardebukta Formation, "Sticky Keep Formation" and Botneheia Formation, of which the two upper units formed the "Kongressfjellet Subgroup". The latter was changed to formation rank by Flood et al. (1971), but this was only applied on the map sheet Adventdalen (Major & Nagy 1964,1972), and has been rejected by subsequent authors. This rejection may have been a consequence of the problems arising when defining the lower boundary of this unit.

From the 1970s onward, separate subdivisions were introduced for central/eastern and western Svalbard, due to the different facies development in both areas. The two developments are thought to have a transition at depth below the younger fill of the Central Cenozoic Basin, with a proximal, coarse-grained facies to the west, and a more distal, shaledominated facies to the east.

The suggested member subdivision of the Sassendalen Group's formations in Svalbard (Fig. 3-05) is a synthesis of the units of Buchan et al. (1965), Birkenmajer (1977), Mørk et al. (1982) and Pčelina (1983), some of them with a revised rank. A few members, from all of these authors, may be subjected to further refinements after more thorough fieldwork. These units are provisionally maintained with an informal status (Fig. 3-05).

Central and eastern areas:
Lock et al. (1978) included all shales of Early and Middle Triassic age on the islands Barentsøya and Edgeøya in the "Barentsøya Formation", with the organic-rich dark shales (previously named Botneheia Formation) distinguished as the "Oil Shales Member". For central and eastern Spitsbergen, Mørk et al. (1982) kept the terminology of Lock et al. (1978), but retained the three previously defined formations of Buchan et al. (1965) at member level. Pčelina (1983) also retained a tripartite subdivision of the Lower and Middle Triassic, and introduced the new name "Wichebukta Formation" for the upper Lower Triassic (Olenekian) of eastern Svalbard, while restricting the Botneheia Formation to the organic-rich shale lithologies in central and eastern Spitsbergen, Barentsøya and Edgeøya.

As indicated above, there were difficulties in recognising the boundary between the two lower subunits of the group (Deltadalen and "Sticky Keep" members) in central Spitsbergen. This may be due to the circumstance that there is another similar, distinct lithological boundary within the "Sticky Keep Member". Even the best available regional survey, Major & Nagy's (1964) map sheet Adventdalen has – in many places – mixed up the base of the "Sticky Keep Member" (base of "Kongressfjellet Formation") with the other boundary (Mørk et al. 1999).

The two lower units, consequently, are here assigned to only one formation, the Vikinghøgda Formation, with its type section at Vikinghøgda (Mørk et al. 1999), a mountain separated from the neighbouring mountain Sticky Keep by the valley Deltadalen, i.e. in the traditional type area for several of the units (Buchan et al. 1965; Mørk et al. 1982). To avoid redefinitions and to facilitate boundary recognitions in the field, a threefold subdivision of the Vikinghøgda Formation is proposed. These three units are the Deltadalen Member (unchanged definition), Lusitaniadalen Member and Vendomdalen Member, the latter two replacing the "Sticky Keep Member". All member names are now from tributary valleys of the major valley Sassendalen in the type area.

Western Spitsbergen:
Along western Spitsbergen, the threefold subdivision of Buchan et al. (1965) is retained, with the Vardebukta Formation (Induan; Buchan et al. 1965) at its base, followed by the Tvillingodden Formation (Olenekian) and the Bravaisberget Formation (Anisian and Ladinian) (Mørk et al. 1982). This subdivision is also followed by Pčelina (1983) although she used a different name for the middle unit ("Pitnerodden Formation").

Bjørnøya and Barents Sea:
The coeval units of the southwestern Barents Sea, the Havert, Klappmyss and Kobbe formations (Worsley et al. 1988) are summarised in the Ingøydjupet Subgroup. It is defined in the Hammerfest Basin and contains shales and sandstones of Early and partially Middle Triassic age (Ingøydjupet "Group" of Worsley et al. 1988). With the southward extension of the Kapp Toscana Group into the Barents Sea and the incorporation of the Snadd Formation into the latter, the Ingøydjupet Subgroup is restricted to the southwestern Barents Sea.

The Steinkobbe Formation (Mørk & Elvebakk 1999), overlying rocks of the Ingøydjupet Subgroup on the Loppa High, shows more similarities with its time-equivalents in Svalbard.

The Sassendalen Group also includes the coeval deposits on Bjørnøya, the Urd Formation Krasil'ščikov & Livšic 1974; Mørk et al. 1982).