Pleistocene palynostratigraphy and paleoceanography on the Yermak Plateau, Arctic Ocean: Preliminary results of a multi-proxy study

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The Holes 910A and 911A that were drilled during ODP Leg 151 on the Yermak Plateau (Myhre et al. 1995) are important sites to improve the Plio-/Pleistocene chronostratigraphy of the Eastern Arctic Ocean, and to reconstruct the paleoenvironmental history in the past 3 Ma. In particular, these sites may form stratigraphic reference sections for the planned drilling programs in the Central Arctic Ocean in the frame of IODP. A magnetostratigraphy and a stable isotope stratigraphy have been established previously that provide a chronostratigraphic framework to calibrate microfossil zonations.A multi-proxy study was started in summer 2003 to establish a dinoflagellate cyst stratigraphy which will be calibrated versus a refined stable oxygen isotope stratigraphy (Knies et al., this volume). Furthermore, the variability of sea-surface conditions and its interaction with the discharge of freshwater from Eurasia and the growth and decay of the northern Barents Sea ice sheets since the Pliocene will be reconstructed. Various micropaleontological, sedimentological and organic geochemical methods are applied on the same sample set to reveal the synchroneity/ asynchroneity of changes in the surface water regime and changes in the sediment supply and source areas. In the first year of the project, the studies focus on the Pleistocene sediments of Hole 910A that has an average sedimentation rate of 2 to 4 cm/k.y. (Flower 1997).A preliminary dinoflagellate cyst biostratigraphy is based on a first set of 80 out of ca. 220 samples from Hole 910A and the low-resolution study on Hole 911A by Matthiessen & Brenner (1996). Most samples of Hole 910A are productive but contain only few specimens of a small number of taxa. The presence of delicate spherical brown cysts indicates that preservation is generally good. Age-diagnostic species were not found in the Pleistocene and the ubiquitous species have long stratigraphic ranges (e.g. Rochon et al. 1999). The freshwater algae Pediastrum is present in a number of samples suggesting some freshwater supply from the Laptev and Kara seas during certain intervals.The coarse sand fraction (250 to 2000µm) and the number of gravel particles (>2mm/10g) that characterize supply by icebergs do not show much variability, except for a pronounced maximum in MIS 2 that is probably related to the last glacial maximum. Minor fluctuations of the gravel content might be related to Terminations and the onset of glaciations.Mineralogical and geochemical parameters show some variability in the late Pleistocene of Hole 910. Carbonate contents are principally low and range usually between 0 and 4%. The terrigenous minerals dolomite and siderite clearly dominate in most samples showing that only a rather small portion of bulk carbonate is of biological origin. Small fluctuations are obviously not related to glacial/interglacial cycles. Maximum values of 8 to 10% were measured in samples from MIS 2. Total organic carbon contents are predominately of terrestrial origin, and are obviously inversely correlated with carbonate contents.ReferencesFlower, B.P., 1997. Geology, 25, 147-150.Knies, Matthiessen, Vogt, Stein, this volume. Towards an improved Arctic Ocean chronostratigraphy.Matthiessen, J. & Brenner, W., 1996. Proc. ODP Sci.Res., 243-253.Myhre, A.M., Thiede, J., Firth, J.V. et al. 1995. Proc. ODP , Init. Repts, 151, 915p.

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Conference (Poster)
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Euroforum, ODP/IODP-Kolloquium, 17.-19. March, Bremen, Germany..
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Matthießen, J. , Knies, J. , Vogt, C. and Stein, R. (2004): Pleistocene palynostratigraphy and paleoceanography on the Yermak Plateau, Arctic Ocean: Preliminary results of a multi-proxy study , Euroforum, ODP/IODP-Kolloquium, 17.-19. March, Bremen, Germany. .

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