title: The nature of Ordovician limestone-marl alternations in the Oslo-Asker District (Norway): witnesses of primary glacio-eustasy or diagenetic rhythms?
abstract: Ordovician limestone-marl alternations in the Oslo-Asker District have been interpreted as signaling glacio-eustatic lowstands, which would support a prolonged "Early Palaeozoic Icehouse". However, these rhythmites could alternatively reflect differential diagenesis, without sedimentary trigger. Here, we test both hypotheses through one Darriwilian and three Katian sections. Our methodology consists of a bed-by-bed analysis of palynological (chitinozoan) and geochemical (XRF) data, to evaluate whether the limestone/marl couplets reflect an original cyclic signal. The results reveal similar palynomorph assemblages in limestones and marls. Exceptions, which could be interpreted as reflecting palaeoclimatological fluctuations, exist at the species level: Ancyrochitina bornholmensis seems to be more abundant in the marl samples from the lower Frognerkilen Formation on Nakkholmen Island. However, these rare cases where chitinozoans differ between limestone/marl facies are deemed insufficient for the identification of original cyclicity. The geochemical data show a near-perfect correlation between insoluble elements in the limestone and the marls, which indicates a similar composition of the potential precursor sediment, also in the Frognerkilen Formation. This is consistent with the palynological data. Although an original cyclic pattern could still be recorded by other, uninvestigated parameters, our palaeontological and geochemical data combined do not support the presence of such a signal.
authors.affiliation: UMR 8198 du CNRS: Evo-Eco-Paleo, Université de Lille - Sciences et Technologies, Avenue Paul Langevin, SN5, 59655 Villeneuve d'Ascq, France.
authors.forename: Chloé E A
authors.initials: CE
authors.lastname: Amberg
authors.affiliation: Department of Geology (WE13), Ghent University, Krijgslaan 281-S8, B-9000 Ghent, Belgium.
authors.forename: Tim
authors.initials: T
authors.lastname: Collart
authors.affiliation: Department of Geology (WE13), Ghent University, Krijgslaan 281-S8, B-9000 Ghent, Belgium.|Nicholas School of Environment, Duke University, Environment Hall, 9 Circuit drive, Box 90328, Durham, NC 277708, USA.
authors.forename: Wout
authors.initials: W
authors.lastname: Salenbien
authors.affiliation: FG Paläoumwelt, GeoZentrum Nordbayern, Friedrich-Alexander University of Erlangen-Nuremberg, Loewenichstr. 28, D-91054 Erlangen, Germany.|Paleoenvironmental Dynamics Group Institute of Earth Sciences, University of Heidelberg, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Egger
authors.affiliation: FG Paläoumwelt, GeoZentrum Nordbayern, Friedrich-Alexander University of Erlangen-Nuremberg, Loewenichstr. 28, D-91054 Erlangen, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Munnecke
authors.affiliation: Natural History Museum of Denmark (Geological Museum), University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark.
authors.forename: Arne T
authors.initials: AT
authors.lastname: Nielsen
authors.affiliation: UMR 8198 du CNRS: Evo-Eco-Paleo, Université de Lille - Sciences et Technologies, Avenue Paul Langevin, SN5, 59655 Villeneuve d'Ascq, France.
authors.forename: Claude
authors.initials: C
authors.lastname: Monnet
authors.affiliation: Natural History Museum, University of Oslo, Sars gate 1, 0318 Oslo, Norway.
authors.forename: Øyvind
authors.initials: Ø
authors.lastname: Hammer
authors.affiliation: UMR 8198 du CNRS: Evo-Eco-Paleo, Université de Lille - Sciences et Technologies, Avenue Paul Langevin, SN5, 59655 Villeneuve d'Ascq, France.|Department of Geology (WE13), Ghent University, Krijgslaan 281-S8, B-9000 Ghent, Belgium.
authors.forename: Thijs R A
authors.initials: TR
authors.lastname: Vandenbroucke