A palynological study across the Ordovician Kinnekulle bentonite, Sweden

University essay from Lunds universitet/Geologiska institutionen

Abstract: A palynological analysis across the Ordovician (Sandbian) Kinnekulle bentonites in south Central Sweden has been performed. The sedimentary successions were recovered from the Borenshult -1 drillcore in the Motala area, south central Sweden. The lithology is dominated by mudstones and two thick bentonite beds. Acritarchs dominate the palynological assemblage but a few chitinozoans and scolecodonts were encountered. The composition of acritarchs is stable throughout the core with the exception of the two consecutive top-most samples in which every morphological group diminishes and disappear except the sphaeromorph type. The acritarch abundance changes within the core, the earliest sample shows a steady state until it reaches the oldest bentonite layer. At this point the acritarch abundance decrease rapidly and then recovers. In the period between the bentonite layers a higher abundance is recorded. In the second layer, the signature seen in the first layer is repeated. An upswing in acritarch abundance yet again occur in the layers resting on the bentonite. In the top-most layers of the core, the acritarchs almost disappear. The scolecodonts and chitinozoans occur only in very low abundance throughout the core. The acritarchs were counted and divided into functional traits depending on their morphology based on the visual traits of the processes. The biomass density is lower in the bentonite layers compared to the non-volcanic parts. Directly on top of both the bentonite beds an increase of acritarch abundance can be observed. The acritarch assemblage indicates a lowering of the sea-level at the topmost the samples.

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