Abstract
Palynostratigraphy and palynofacies analyses are applied to identify transgressive-regressive sequences and changes in paleoenvironment through the Middle Jurassic–Early Cretaceous succession of the Ramså Basin on Andøya. The conglomerate, the succeeding lacustrine-swamp deposits of the Hestberget and Kullgrøfta members (Ramså Formation) and the overlying terrestrial to marginal marine deposits of the lower Bonteigen Member (Ramså Formation), comprise the Bajocian T-R sequence. Bathonian–Oxfordian strata appear to be missing in the studied boreholes, and the second T-R cycle spans the Kimmeridgian to Berriasian open marine deposits of the upper Bonteigen Member and the Dragneset Formation (Breisanden, Taumhølet and Ratjønna members). The overlying Nybrua Formation comprises a condensed marine succession of Valanginian–Early Barremian calcareous sandstone and marl, followed by brownish-red siltstone. The upper T-R sequence (Skarstein Formation) consists of marine transgressive Barremian dark siltstones, silty shales and mudstones, followed by dark mudstone and shale. Marine palynomorphs recovered in these stacked marine slope turbidite sediments are of Late Barremian age, but possibly the youngest T-R cycle also includes Aptian deposits elsewhere in the basin.
Highlights
Studies on the Jurassic and Lower Cretaceous sedimentary rocks preserved in the Ramså Basin on Andøya were initiated more than 150 years ago by the pioneering works of Tellef Dahll on the coal resources in the late 1860s, and the subsequent paleontological and stratigraphic studies of Kierulf [1], Heer [2], Lundgren [3], Friis [4], Vogt [5] and Sokolov [6].Based on the fossils in material collected by Dahll, Kierulf [1] suggested the presence of Oxfordian rocks on Andøya, while Heer [2] identified fossils of Middle Jurassic age
Vogt divided the succession into an Early Jurassic unit, a Late Jurassic unit and an Early Cretaceous unit, based on the position of the coal beds, the sedimentary units identified in the boreholes, the records of fossils, and the observations on the structural geology
Palynostratigraphic and palynofacies analyses are applied for identification of transgressive-regressive sequences and changes in paleoenvironment through the Middle Jurassic–Early Cretaceous succession of the Ramså Basin on Andøya
Summary
Studies on the Jurassic and Lower Cretaceous sedimentary rocks preserved in the Ramså Basin on Andøya were initiated more than 150 years ago by the pioneering works of Tellef Dahll on the coal resources in the late 1860s, and the subsequent paleontological and stratigraphic studies of Kierulf [1], Heer [2], Lundgren [3], Friis [4], Vogt [5] and Sokolov [6]. According to Sturt et al [19] the basement has a thick weathered upper part overlain by a sandy carbonate rock, giving potassium/argon dates of inferred Paleozoic age This unit, named the Holen Formation, has not been confirmed by later studies, and it was not observed in the present studied boreholes in the Ramså Basin [17]. The overlying Kullgrøfta Member consists mainly of bituminous shale, and a few layers of siltstones and fine-grained sandstones. The upper part of the Ramså Formation is assigned to the Bonteigen Member which consists of medium- to coarse-grained sandstones, inter-bedded with siltstones and a few layers of shale and coal. The overlying Dragneset Formation consists of marine sandstones, siltstones and shales, with some of intervals of calcareous concretions and some glauconite-rich layers [18,20]. A few marine macrofossils are recovered, together with relatively common plant remains [18,20]
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