Miocene flood basalts in NW Spitsbergen: Emplacement environment and Arctic paleoclimate context

Large parts of the Arctic, including Svalbard, have experienced recurrent episodes of uplift and erosion over the last 15–20 million years, coinciding with localized magmatism and seafloor spreading. This has left sparse onshore stratigraphic records of the Miocene period, limiting our understanding of the tectono-sedimentary and paleo-landscape evolution across this vast region. The volcanic Seidfjellet Formation in northwestern Spitsbergen thus provides a rare e onshore Miocene record. To determine emplacement mechanisms, volcanic architecture, and the pre-volcanic paleoenvironment, we combined detailed field-based facies analysis with digital outcrop models, thin-section petrography, and palynology. We document 10–20 basaltic lava flows, totaling ∼400 m in cumulative thickness, now exposed at 600–1350 m elevation. The lava sequence rests on a gently undulating Devonian peneplane that locally is incised by several-hundred-meters-wide, up to 150-m-deep depressions interpreted as paleo-valleys. These valleys likely formed by stream rejuvenation associated with Miocene peneplane uplift. At valley bases we report previously unrecognized pockets of unconsolidated sediment, evidence of pre-volcanic sedimentation. Valley margins are locally draped by volcaniclastic deposits that contain in-situ charcoal-lined tree molds, indicating forested margins before eruption. The main valley fills are hyaloclastite deposits up to 150 m thick, arranged in steeply dipping forests that record southward progradation of a lava-fed delta after base-level rise and drowning of the valleys. Palynological data indicate a conifer-dominated wetland prior to lava emplacement, while the dinocyst assemblages appear partly reworked and are consistent with a Late Oligocene–Early Miocene signal but more likely reflect a Late Miocene age. This study provides the first systematic description of the Seidfjellet Formation volcanic facies and architecture, constrains its spatial extent, and, through its pre-volcanic sedimentary records, offers new paleoenvironmental reconstructions.