Ordovician climate change, sea level history and bioevents: the Baltoscandic record
Final Report Abstract
The Siljan impact structure preserves unique Lower Palaeozoic sedimentary successions in its ring-like depression around the central uplift. The stratigraphy investigated in three core sections and visited outcrops provides surprisingly new informations about the development of this area that palaeogeographically was located near the western margin of Baltica. Based on these new data, several facies belts related to the Ordovician-Silurian foreland basin development can be recognized in the sedimentary record of this area, some 100 km away from the Caledonian front. The cores comprise strata ranging from the late Tremadocian to Wenlock in age and provide a huge dataset for studies in palaeoclimate, sea level, and changes in ecosystems. The discovery of multiple karst horizons and palaeocave formations in the Late Ordovician and Early Silurian strata of the Siljan area can be correlated to the sea level record in other parts of Baltica and on other palaeocontinents suggesting recurrent subaerial exposure of the Baltoscandian shelf during glacioeustatic sea level lowstands. The volcanic record (K-bentonites) can be correlated with ash layers in other parts of Baltoscandia, and serve as chronostratigraphic time-lines in a detailed stratigraphic framework including litho-, bio-, chemo- and sequence stratigraphic parameters. Within the upper part of the Silurian clastic succession in the western part of the ‘Siljan Ring’, we recognize the progradation of a delta system reflecting a regression in an overall subsiding basin, likely due to a global sea-level drop during the Sheinwoodian (early Wenlock) glaciation exposing the forebulge area to the west. Biogeochemical data of the siliciclastics suggest deposition in a range of lacustrine to brackish and marine environments. Biomarker data support deposition in a backbulge basin developed in the eastern part of the Caledonian foreland basin system forming during the collision between Laurentia and Baltica.
Publications
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(2013): Ordovician stratigraphy and sedimentary facies of the Stumsnäs 1 core from the southern Siljan Ring, central Sweden. GFF, 135 (2): 204-212
Lehnert, O., Meinhold, G., Arslan, A., Ebbestad, J.O.R. & Calner, M.
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(2014): Biomarker evidence for the origin of seep 1 oil and solid bitumen from the Late Devonian Siljan impact structure, Sweden. Organic Geochemistry, 68: 13-26
Ahmed, M., Lehnert, O., Fuentes, D., Meinhold, G.
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(2014): δ13C chemostratigraphy in Lower-Middle Ordovician succession of Öland (Sweden) and the global significance of the MDICE. In: Calner, M. et al. (eds.): Early Palaeozoic Global Change. GFF, 136 (1): 48-54
Calner, M., Lehnert, O., WU, R., Dahlqvist, P., & Joachimski, M. M.
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(2014): δ13C chemostratigraphy in the late Tremadocian through early Katian carbonate succession of the Siljan district (Central Sweden). In: Histon, K. & Zigaite, Z. (eds.): IGCP 591 Special Issue: Evolutionary Palaeoecology and Palaeobiogeography. Estonian Journal of Earth Sciences 63: 277-286
Lehnert, O., Meinhold, G., Wu, R., Calner, M & Joachimski, M. M.
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(2015): Analysis of borehole geophysical data from the Mora area of the Siljan Ring impact structure, central Sweden. Journal of Applied Geophysics 115: 183-196
Muhammad, H., Juhlin, C., Lehnert, O., Meinhold, G., Andersson, M., Garcia, M., Malehmir, A.
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(2015): Subaerial speleothems and deep karst in central Sweden linked to Hirnantian glaciations. Journal of the Geological Society
Kröger, B., Ebbestad, J. O, Lehnert, O., Ulvman, C. V. Korte, C., Frei, R. & Rasmussen, C. M. Ø.
