Hopen revisited: integrated palynology and provenance data from legacy wells indicate a potential Carnian Pluvial Episode signal on the Barents Shelf

Hopen, a narrow island in the southeast Svalbard archipelago, is one of the key Upper Triassic reference localities of the Norwegian Barents Shelf. Its importance lies not only in its well-exposed outcrop succession, but also in the presence of two legacy exploration wells, Hopen-1 and Hopen-2, drilled by Norsk Fina in 1971–73. These remain the only deep wells between Edgeøya, c. 100 km to the northwest, and exploration wells more than 300 km to the south, yet the subsurface dataset they provide has been comparatively underutilised. Here we present new integrated biostratigraphic, sedimentological, provenance and geochronological results from these wells, archived in the Harland Collection of the Sedgwick Museum (University of Cambridge). Together, these provide the first comprehensive framework spanning the complete penetrated Triassic succession and the underlying Permian and Carboniferous units.

Integration of extensive QEMSCAN and petrographic analysis of drill cuttings allows the Triassic succession in Hopen-1 and Hopen-2 to be tied confidently to the standard lithostratigraphic scheme for Svalbard, from the Svenskøya, Flatsalen, De Geerdalen and Tschermakfjellet formations of the Kapp Toscana Group into the underlying Botneheia and Vikinghøgda formations of the Sassendalen Group. Palynological analysis of cuttings and core provides the principal age control and basis for palaeoecological interpretation.

Recognised palynozones include the Quadraeculina anellaeformis (Svenskøya Formation; Norian), Classopollis torosus (Flatsalen Formation; Norian), Protodiploxypinus spp. (uppermost De Geerdalen Formation, Hopen Member; upper Carnian), Leschikisporis aduncus (middle–upper De Geerdalen Formation; upper Carnian), and Podosporites vigraniae zones (lower–middle De Geerdalen Formation; lower Carnian), previously described from Upper Triassic outcrops on Hopen and well material elsewhere on the Barents Shelf. The Tschermakfjellet, Botneheia and Vikinghøgda formations yield degraded, largely non-diagnostic Middle to Lower Triassic assemblages; this interval is also characterised by markedly darker palynomorphs (TAI c. 3–3+) and vitrinite reflectance values indicating a shift from late mature to postmature conditions, possibly linked to a steep geothermal gradient. The age constraints indicate a relatively condensed Lower and Middle Triassic, overlain by a greatly expanded Carnian succession, which in turn is capped by a condensed Norian. Beneath the Triassic in Hopen-2, the Tempelfjorden Group yields assemblages corresponding to the Scutasporites sp. cf. unicus–Lunatisporites sp. Zone (Guadalupian–Lopingian), the Gipsdalen Group is barren, and the lowermost part of the well (?Billefjorden Group) contains Famennian–Viséan assemblages.

The resultant chronostratigraphic framework provides the basis for interpreting changes in sediment provenance. Within the De Geerdalen Formation, three sandstone types are recognised in the lower, middle and upper parts of the unit, respectively. Detrital zircon and apatite U–Pb ages record a shift from mixed local/Uralian input to dominantly Uralian derivation from the southeast through the early Carnian (Julian), and finally to a younger, volcanically influenced easterly source in the late Carnian (Tuvalian). Crucially, this provenance change coincides with both maximum progradation of the De Geerdalen Formation deltaic system and an acme of the hygrophytic fern spore Leschikisporis aduncus. We interpret the coupling of palynological, stratigraphic and provenance signals as a potential expression of the Carnian Pluvial Episode. More broadly, the study demonstrates how integrated re-analysis of legacy well material can connect classical outcrop localities to the subsurface, while generating new biostratigraphic and palaeoenvironmental insights of direct relevance to regional correlation and basin evolution.