| 1. |
- Demangel, Isaline, et al.
(författare)
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Development of early calcareous nannoplankton in the late Triassic (Northern Calcareous Alps, Austria)
- 2020
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- Calcareous nannofossils are considered to be the most productive calcifying organisms, but the impact of their emergence on the chemistry of the ocean in the Late Triassic is not understood yet. Evolutionary details of this bio-event are missing due to the scarcity of well-preserved outcrops worldwide. The current study focuses on the calcareous nannofossil assemblage of the middle Norian to lower Rhaetian at Sommeraukogel and Steinbergkogel in the Northern Calcareous Alps (Austria). The sediments were deposited on a topographic high on a deeper shelf at a palaeolatitude around 20–30°N. The steps in the emergence of pelagic calcifiers are documented by a scanning electron microscope (SEM) study. The First Occurrence (FO) of coccolith, not identified at a species level, was recorded in the middle Norian (Alaunian 3). The oldest Crucirhabdus minutus and Archaeozygodiscus koessenensis were observed in the late Norian (Sevatian) and were followed by the FO of Crucirhabdus primulus in the early Rhaetian. These observations suggest a rather slow temporal evolution of the first coccolithophorids, with millions of years from the ancestor C. minutus to C. primulus, and in between the evolution of the new genus A. koessenensis. Diagenetic overprinting of the sedimentary succession has affected the preservation degree of the calcareous nannofossils but not the trend of their quantity in the studied samples, as proven by petrographic studies and trace element signatures of the calcareous sediments. This supports our quantitative estimates of the CaCO3 volume- and palaeo-fluxes due to the export productivity of the calcareous nannofossils, Prinsiosphaera triassica. Our results show the dominance and the increase in abundance of Prinsiosphaera triassica slightly above the Norian/Rhaetian boundary. However, calcareous nannofossils did not reach rock-forming abundances at this time and thus did not significantly influence the geochemical composition of the Western Tethys Ocean.
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| 2. |
- Demangel, Isaline, et al.
(författare)
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Fate of calcareous nannofossils during the Rhaetian (Late Triassic) : evidence from the Northern Calcareous Alps, Austria
- 2023
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Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 56:1
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Tidskriftsartikel (refereegranskat)abstract
- Calcareous nannofossils evolved in the global ocean from the Carnian (early Late Triassic) and have contributed to the accumulation of biogenic calcium carbonate in marine sediments since then. Bio-diversification and bio-productivity became more significant in the Rhaetian (Late Triassic), representing an important period to understand the dynamics of calcareous nannofossil evolution. The calcareous nannofossil content of the Zlambach Formation, Northern Calcareous Alps, Austria, was qualitatively and quantitatively investigated using both scanning electron and light microscopy. The nannolith, Prinsiosphaera triassica triassica, dominates the assemblage in most samples and increases slightly in abundance in the lower Rhaetian, followed by a small-scale short-term increase during the middle Rhaetian and reaches rock-forming abundance in the upper Rhaetian. A systematic size decrease is recorded from the lower Rhaetian onwards, possibly due to changes in the palaeo-environment. The abundance of P. triassica triassica is slightly affected by the occurrence of Eoconusphaera hallstattensis and strongly by E. zlambachensis. E. hallstattensis is constrained to a relatively short interval, from the upper Paracochloceras suessi Zone (lower Rhaetian) and disappeared during the lower Vandaites stuerzenbaumi Zone (middle Rhaetian), after the occurrence of a second Eoconusphaeraceae species: E. zlambachensis. The last occurrence of E. hallstattensis comes along with the subspecies Prinsiosphaera triassica crenulata showing characteristic parallel-oriented calcite lamellae. Those three species are suggested as good biostratigraphical markers for the Upper Triassic. The coccolithophorids are present in low abundance, increasing slightly in the middle Rhaetian. After the first record of coccoliths in the middle Norian (Alaunian), the oldest Crucirhabdus minutus and Archaeozygodiscus koessenensis were observed in the upper Norian (Sevatian) and the first occurrence of Crucirhabdus primulus was recorded in the lower Rhaetian. These observations suggest a rather slow temporal diversification of the first coccolithophorids.
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| 3. |
- Yu, He, et al.
(författare)
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Palaeogenomic analysis of black rat (Rattus rattus) reveals multiple European introductions associated with human economic history
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of the black rat (Rattus rattus) has been heavily influenced by its association with humans. The dispersal history of this non-native commensal rodent across Europe, however, remains poorly understood, and different introductions may have occurred during the Roman and medieval periods. Here, in order to reconstruct the population history of European black rats, we first generate a de novo genome assembly of the black rat. We then sequence 67 ancient and three modern black rat mitogenomes, and 36 ancient and three modern nuclear genomes from archaeological sites spanning the 1st-17th centuries CE in Europe and North Africa. Analyses of our newly reported sequences, together with published mitochondrial DNA sequences, confirm that black rats were introduced into the Mediterranean and Europe from Southwest Asia. Genomic analyses of the ancient rats reveal a population turnover in temperate Europe between the 6th and 10th centuries CE, coincident with an archaeologically attested decline in the black rat population. The near disappearance and re-emergence of black rats in Europe may have been the result of the breakdown of the Roman Empire, the First Plague Pandemic, and/or post-Roman climatic cooling. 'Archaeogenetic analysis of black rat remains reveals that this species was introduced into temperate Europe twice, in the Roman and medieval periods. This population turnover was likely associated with multiple historical and environmental factors.'
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