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- Álvaro, J. Javier, et al.
(författare)
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Submarine metalliferous carbonate mounds in the Cambrian of the Baltoscandian Basin induced by vent networks and water column stratification
- 2022
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Two massive precipitation events of polymetallic ore deposits, encrusted by a mixture of authigenic carbonates, are documented from the Cambrian of the semi-enclosed Baltoscandian Basin. δ34S (‒9.33 to ‒2.08‰) and δ33S (‒4.75 to ‒1.06‰) values from the basal sulphide breccias, sourced from contemporaneous Pb–Zn–Fe-bearing vein stockworks, reflect sulphide derived from both microbial and abiotic sulphate reduction. Submarine metalliferous deposits were triggered by non-buoyant hydrothermal plumes: plumes of buoyant fluid were trapped by water column stratification because their buoyancy with respect to the environment reversed, fluids became heavier than their surroundings and gravitational forces brought them to a halt, spreading out laterally from originating vents and resulting in the lateral dispersion of effluents and sulphide particle settling. Subsequently, polymetallic exhalites were sealed by carbonate crusts displaying three generations of ikaite-to-aragonite palisade crystals, now recrystallized to calcite and subsidiary vaterite. Th of fluid inclusions in early calcite crystals, ranging from 65 to 78 ºC, provide minimum entrapment temperatures for carbonate precipitation and early recrystallization. δ13Ccarb (‒1.1 to + 1.6‰) and δ18Ocarb (‒7.6 to ‒6.5‰) values are higher than those preserved in contemporaneous glendonite concretions (‒8.5 to ‒4.7‰ and ‒12.4 to ‒9.1‰, respectively) embedded in kerogenous shales, the latter related to thermal degradation of organic matter. Hydrothermal discharges graded from highly reduced, acidic, metalliferous, and hot (~ 150 ºC) to slightly alkaline, calcium-rich and warm (< 100 ºC), controlling the precipitation of authigenic carbonates.
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| 2. |
- Bauert, Heikki, et al.
(författare)
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New U-Pb zircon ages of the Sandbian (Upper Ordovician) "Big K-bentonite" in Baltoscandia (Estonia and Sweden) by LA-ICPMS
- 2014
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 136:1, s. 30-33
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Tidskriftsartikel (refereegranskat)abstract
- Oscillatory-zoned euhedral single zircons from the upper Sandbian (Upper Ordovician) Kinnekulle K-bentonite exposed in a hillock at Paaskula in Estonia and at the type locality on Mt Kinnekulle in Sweden were dated in a grain-by-grain manner by laser ablation-inductively coupled plasma mass spectrometer. The U-Pb (weighed mean) ages of the 25 grains from Mt Kinnekulle and 24 grains from Paaskula are 453.4 +/- 6.6 and 454.9 +/- 4.9Ma, respectively. This study provides the first ca. 454Ma (late Sandbian) age for the Ordovician K-bentonite in northern Estonia and confirmed its correlation with the type Kinnekulle bed across the Baltic Sea.
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| 3. |
- Butler, Aodhan, et al.
(författare)
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Recent palaeobiological and stratigraphical advances from the Cambrian of Estonia
- 2011
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Ingår i: The 2nd Wiman Meeting. - Uppsala. ; , s. 5-5
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Konferensbidrag (refereegranskat)abstract
- The unique Cambrian sediments of Estonia represent an important and understudied component of the Baltic system. Here we present an overview of recent field studies conducted by Uppsala University in association with colleagues from the Baltic Geotourism project, that have revealed a number of exciting discoveries in terms of Cambrian palaeontology and stratigraphy of Estonia. These include new purported stem lophotrochozoans with bizarre shell structure. Current efforts to describe and systematically appraise this material are outlined. The presence of unusual shell structure and whether this is the result of taphonomic alteration or indeed represents a novel shell structure type is examined. We propose herein affinities to the inarticulate stem-brachiopod Mickwitzia based upon the presence of an umbo and the overall gross morphology. Possible new records of Estoniadiscus discinoides (Schmidt 1888), an extremely rare enigmatic organism with postulated affinities to eldonioids or other stem-group lophophorates are also described from the type section at Kakumägi, within the Kakumägi member Member of the lower Cambrian Tiskre formationFormation. The discovery of Dictyonema Rhabdinopora sp. graptolites, which have until now demarcated the Cambrian-Ordovician boundary, in-situ approximately 3 m below the previous reported occurrence from the Pakri cape section of the Kallavere formation Formation is also significant. Our findings highlight the need for both a stratigraphical and palaeobiological reapprasal of these important sequences, and their correlative implications for the Swedish and broader Baltoscandian regions.
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| 4. |
- Popov, Leonid E, et al.
(författare)
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Glendonite occurrences in the Tremadocian of Baltica : first Early Palaeozoic evidence of massive ikaite precipitation at temperate latitude
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)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.
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