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Glendonite occurrences in the Tremadocian of Baltica: first Early Palaeozoic evidence of massive ikaite precipitation at temperate latitudes

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Popov, Leonid E. and Álvaro, J.J. and Holmer, Lars E. and Bauert, Heikki and Pour, Mansoureh Ghobadi and Dronov, Andrei V. and Lehnert, Oliver and Hints, Olle and Männik, Peep and Zhang, Zhifei and Zhang, Zhiliang (2019) Glendonite occurrences in the Tremadocian of Baltica: first Early Palaeozoic evidence of massive ikaite precipitation at temperate latitudes. Scientific Reports, 9 . ISSN 2045-2322

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Official URL: https://www.nature.com/articles/s41598-019-43707-4



Abstract

The Tremadocian (Early Ordovician) is currently considered a time span of greenhouse conditions with tropical water surface temperature estimates, interpolated from oxygen isotopes, approaching 40 °C. In the mid-latitude Baltoscandian Basin, conodonts displaying low δ18O values, which suggest high temperatures (>40 °C) in the water column, are in contrast with the discovery of contemporaneous glendonite clusters, a pseudomorph of ikaite (CaCO3·6H2O) traditionally considered as indicator of near-freezing bottom-water conditions. The massive precipitation of this temperature sensitive mineral is associated with transgressive conditions and high organic productivity. As a result, the lower Tremadocian sediments of Baltoscandia apparently contain both “greenhouse” pelagic signals and near-freezing substrate indicators. This paradox points to other primary controlling mechanisms for ikaite precipitation in kerogenous substrates, such as carbonate alkalinity, pH and Mg/Ca ratios, as recently constrained by laboratory experiments. Preservation of “hot” conodonts embedded in kerogenous shales rich in δ18O-depleted glendonites suggests both the onset of sharp thermal stratification patterns in a semi-closed basin and the assumed influence of isotopically depleted freshwater yielded by fluvial systems.


Item Type:Article
Subjects:Sciences > Geology > Stratigraphic geology
Sciences > Geology > Geochemistry
Sciences > Geology > Mineralogy
ID Code:55501
Deposited On:29 May 2019 18:16
Last Modified:29 May 2019 18:16

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