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The Callovian to Kimmeridgian deposits from Janusfjellet section of Spitsbergen (Agardhfjellet Fm) consists mainly of shales with variable organic carbon content. Five foraminiferal morphogroups (A to E) have been established according to shell features.
MG A: tubular and unilocular shells with inferred epifaunal suspensivorous habit (e.g. Rhizammina).
MG B: globular, pseudospheric and unilocular shells including epifaunal passive depositivorous forms (e.g. Thuramminoides).
MG C: elongated, subcylindrical, multilocular shells, with infaunal life-habit being detritivorous bacterial scavengers forming three subgroups:
Subgroup C1: uniserial forms, living in shallow to deep infaunal habitats (e.g. Reophax).
Subgroup C2: planispiral or streptospiral initial stage and uniserial final stage, living as shallow infauna (e.g. Ammobaculites).
Subgroup C3: biserial, triserial or elongated trochospiral forms, with shallow to deep infaunal strategies (e.g. Verneuilina).
MG D: spiral multilocular shells, living as epifaunal detritivores with two subgroups:
Subgroup D1: globular and plano-convex shape and trochospiral coiling (e.g. Trochammina).
Subgroup D2: rounded, planispiral forms (e.g. Cribrostomoides).
MG E: flattened shells with two chambers with spiral or irregular coiling, living as epifaunal and phytal herbivorous and detritivorous (e.g. Ammodiscus).
The paleoenvironmental evolution is interpreted from the stratigraphic distribution of the morphogroups and sedimentological features.
The first part of the section is a fining-upward succession with sandstones, siltstones and shales (Oppdalen Mb.). The upward trends are characterised by increasing organic carbon content and proportion of epifaunal foraminifera, while diversity and deep infaunal foraminifera (C2 and C3), decrease; this is congruent with upward decreasing oxygenation. This interval represents a major regional transgressive event. The fining-upward trend finishes in black paper shales containing high amounts of organic matter (Lardyfjellet Mb.). Morphogroups B and D1 increase and D2 diminishes. The foraminiferal assemblage shows low diversity values and is dominated by epifauna. These features suggest dysaerobic to anaerobic conditions. Absence of oxygen in infaunal microhabitats explains the dominance of epifauna. These shales have been interpreted in relation to a maximum flooding interval and a stagnant water column.
The second part of the studied section consists of sandstones and silty shales (Oppdalsta and Slottmøya Mbs.), with an upwards decreasing organic carbon content. At the base, the member is characterised by low values of epifauna (D1) and high values of shallow infauna (D2). Further up the organic carbon content and the proportion of epifauna increase. The trend in lithofacies and foraminifera in Oppdalsta and Slottmøya Mbs suggests an initial upward increasing oxygenation interpreted in a regressive phase, while the top of this interval is interpreted in a transgressive context.
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