Popov, Leonid E.Álvaro, J.J.Holmer, Lars E.Bauert, HeikkiPour, Mansoureh GhobadiDronov, Andrei V.Lehnert, OliverHints, OlleMännik, PeepZhang, ZhifeiZhang, Zhiliang2023-06-172023-06-1720192045-232210.1038/s41598-019-43707-4https://hdl.handle.net/20.500.14352/13338The 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.engAtribución 3.0 Españajournal articlehttps://www.nature.com/articles/s41598-019-43707-4open access549.741:551.733.1Geología estratigráficaGeoquímicaMineralogía (Geología)2506.19 Estratigrafía2503 Geoquímica2506.11 Mineralogía