The widespread glaciomarine record of the Hirnantian (end-Ordovician) glaciation is confined to peri-Gondwanan terranes in Variscan Europe and, hence, is of little use for assessing the equatorward range of icebergs that calved from the North Gondwana ice sheet into the Rheic Ocean. New sedimentological investigations aided by laser ablation–inductively coupled plasma–mass spectrometry detrital zircon dating of Hirnantian diamictites from the East European craton in Poland demonstrate that the iceberg pathways extended to subtropical Baltica. The diamictites occur in a series of north-thinning (0.4–9.6 m) pods that are traceable for a 700 km subcrop length within the marly portion of a carbonate-shelf ramp. Dropstone-bearing textures, soft-sediment deformation style, and thickness trend point to deposition from floating and grounded icebergs driven northward by along-shelf circulation. Density plots of detrital zircon U-Pb ages from the diamictites reveal a North Gondwana provenance suggestive of iceberg-calving sites located on the North African margin. This implies a minimum 3500 km drifting distance for icebergs that reached the western shelf of Baltica. Our discovery provides a new constraint for modeling Late Ordovician climate and ocean-circulation patterns.
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Research Article|February 06, 2019
Hirnantian icebergs in the subtropical shelf of Baltica: Evidence from sedimentology and detrital zircon provenance
S.J. Porębski
S.J. Porębski
1Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology, Mickiewicza 30, 30-059 Kraków, Poland
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R. Anczkiewicz
R. Anczkiewicz
2Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Kraków, Senacka 1, 31-002 Kraków, Poland
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M. Paszkowski
M. Paszkowski
2Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Kraków, Senacka 1, 31-002 Kraków, Poland
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S. Skompski
S. Skompski
3Faculty of Geology, University of Warsaw, Żwirki i Wigury 93, 02-089 Warszawa, Poland
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A. Kędzior
A. Kędzior
2Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Kraków, Senacka 1, 31-002 Kraków, Poland
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S. Mazur
S. Mazur
2Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Kraków, Senacka 1, 31-002 Kraków, Poland
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J. Szczepański
J. Szczepański
4Institute of Geological Sciences, University of Wrocław, M. Borna 9, 50-205 Wrocław, Poland
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A. Buniak
A. Buniak
5Orlen Upstream, Bielańska 12, 00-085 Warszawa, Poland
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Z. Mikołajewski
Z. Mikołajewski
6Polish Oil and Gas Company, Staszica 9, 64-920 Piła, Poland
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Geology (2019)
Article history
received:
29 Jun 2018
rev-recd:
31 Dec 2018
accepted:
05 Jan 2019
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S.J. Porębski, R. Anczkiewicz, M. Paszkowski, S. Skompski, A. Kędzior, S. Mazur, J. Szczepański, A. Buniak, Z. Mikołajewski; Hirnantian icebergs in the subtropical shelf of Baltica: Evidence from sedimentology and detrital zircon provenance. Geology doi: https://doi.org/10.1130/G45777.1
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