| 1. |
- Ferrow, Embaie, et al.
(författare)
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Multiproxy analysis of a new terrestrial and a marine Cretaceous-Paleogene (K-Pg) boundary site from New Zealand
- 2011
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 75:2, s. 657-672
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Tidskriftsartikel (refereegranskat)abstract
- An integrated study of palynology, Mossbauer spectroscopy, mineralogy and osmium isotopes has led to the detection of the first K-Pg boundary clay layer in a Southern Hemisphere terrestrial setting. The K-Pg boundary layer was independently identified at centimetre resolution by all the above mentioned methods at the marine K-Pg boundary site of mid-Waipara and the terrestrial site of Compressor Creek (Greymouth coal field), New Zealand. Mossbauer spectroscopy shows an anomaly of Fe-containing particles in both K-Pg boundary sections: jarosite at mid-Waipara and goethite at Compressor Creek. This anomaly coincides with a turnover in vegetation indicated by an interval dominated by fern spores and extinction of key pollen species in both sections. In addition to the terrestrial floristic changes, the mid-Waipara section reveals a turnover in the dinoflagellate assemblages and the appearance of global earliest Danian index species. Geochemical data reveal relatively small iridium enrichments in the boundary layers of 321 pg/g at mid-Waipara and 176 pg/g at Compressor Creek. Unradiogenic Os-187/Os-188 values of the boundary clay reveal the presence of a significant extraterrestrial component. We interpret the accumulation of Fe nano-phases at the boundary as originating from both the impactor and the crystalline basement target rock. The goethite and jarosite are interpreted as secondary phases formed by weathering and diagenesis. The primary phases were probably controlled by the initial composition of the vapor plume and condensation kinetics rather than condensation thermodynamics. This investigation indicates that identification of Fe in nano-phases by Mossbauer spectroscopy is an accurate and cost-effective method for identifying impact event horizons and it efficiently complements widely used biostratigraphic and geochemical methods. (C) 2010 Elsevier Ltd. All rights reserved.
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| 2. |
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| 3. |
- Pedersen, G. K., et al.
(författare)
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Molerområdets geologi – sedimenter, fossiler, askelag og glaicaltektonik
- 2011
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Ingår i: Geologisk Tidsskrift. - 1395-0150. ; :December 2011, s. 41-135
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Abstract in Danish I den vestlige del af Limfjorden findes en række kystklinter, hvor eocæne lag er blottet. Moler er en ca. 55-56 millioner år gammel diatomit, som indeholder lag af uforvitret vulkansk aske samt et stort antal velbevarede marine og terrestriske fossiler. Stolleklint Leret og Fur Formationen har et usædvanligt fossilselskab med mange repræsentanter for insekter, fisk, fugle og skildpadder men meget få kalkskallede, hvirvelløse dyr. De vulkanske askelag afspejler et stort antal gigantiske, eksplosive udbrud inden for en kort periode, hvor lavatilstrømningen var stor, samtidig med at udbruddene skete på lavt vand i den nydannede oceanbund. For ca. 25.000 år siden dannede fremrykkende iskapper folder og overskydninger i moler, askelag og glaciale sedimenter. Molerområdets geologi kan sammenfattes i følgende citat: ”…talrige tynde lag af sort vulkansk Aske...træde selv på lang Afstand tydelig frem i det hvide Moler …[Da de] ofte danner store Bugter og Folder, vil man forstaa, at de høje lyse Molerklinter i Solskin frembyde et malerisk og ejendommeligt Skue.” (N. V. Ussing i ’Danmarks Geologi’ 1904, s.143).
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| 4. |
- Schulte, Peter, et al.
(författare)
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Cretaceous Extinctions: Evidence Overlooked Response
- 2010
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 328:5981, s. 975-976
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Schulte, Peter, et al.
(författare)
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The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary
- 2010
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 327:5970, s. 1214-1218
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Tidskriftsartikel (refereegranskat)abstract
- The Cretaceous-Paleogene boundary similar to 65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.
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| 6. |
- Willumsen, Pi, et al.
(författare)
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A new early Paleocene dinoflagellate cyst species, Trithyrodinium partridgei: its biostratigraphic significance and palaeoecology
- 2010
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Ingår i: Alcheringa. - : Informa UK Limited. - 0311-5518. ; 34:4, s. 523-538
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Tidskriftsartikel (refereegranskat)abstract
- A palynological investigation of lower Paleocene (lower Teurian) marine sediments of the Abbotsford Formation, exposed in the Fairfield Quarry, Dunedin, New Zealand, reveals a well-preserved association of dinoflagellate cysts and miospores. Thirty-six dinoflagellate species representing 26 genera were recorded, including one new peridinioid dinoflagellate species, Trithyrodinium partridgei characterized by a three-layered wall and a distinct brown, foveolate mesophragm. Trithyrodinium partridgei has a narrow range and at Fairfield Quarry co-occurs with typical New Zealand late Danian to Selandian index species such as Glaphyrocysta perforata and Alterbidinium pentaradiatum; hence it may prove an additional useful stratigraphic marker. The terrestrial palynomorph assemblage from samples within the range of Trithyrodinium partridgei includes 36 spore-pollen species dominated by the podocarp pollen Phyllocladidites mawsonii. The presence of Nothofagidites waipawaensis and Tricolpites phillipsii confirms a Paleocene age for the assemblage. The abundance of terrestrial palynomorphs and the composition of the dinocyst assemblages suggest a marine nearshore depositional environment.
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| 7. |
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| 8. |
- Willumsen, Pi
(författare)
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Maastrichtian to Paleocene dinocysts from the Clarence Valley, South Island, New Zealand
- 2011
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Ingår i: Alcheringa. - : Informa UK Limited. - 0311-5518. ; 35:2, s. 199-240
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Tidskriftsartikel (refereegranskat)abstract
- A palynological study of uppermost Maastrichtian to lower Paleocene marine strata from two stratigraphic sections in the Clarence Valley, Marlborough, New Zealand, revealed diverse organic-walled dinoflagellate cyst (dinocyst) assemblages. One hundred and twelve samples were investigated and 86 dinocyst species were identified, from the two sections studied: Branch and Mead streams. Nine new species are described herein: Cerodinium nielsii, Impagidinium agremon, I. cavea, I. crouchiae, I. hannahii, Lejeunecysta kammae, Pyxidinopsis epakros, P. everriculum and P. meadensis. Stratigraphic correlations are achieved using nine new index species and eight cyst acme intervals, named A to H, integrated with foraminiferal datums and the radiolarian zonation for the South Pacific. The first occurrence of Carpatella septata combined with a high relative abundance of Diconidinium martianum characterizes the interval directly below the Cretaceous-Paleogene (K-Pg) boundary or uppermost part of the Manumiella druggii Zone. Based on the results from both sections, the earliest Paleocene Trithyrodinium evittii Zone is subdivided into the following intervals: Senoniasphaera inornata, Carpatella cornuta, Cassidium fragile and Cerodinium striatum subzones. The following dinocyst species first appear at or near the top of the T. evittii Zone: Alterbidinium pentaradiatum, Glaphyrocysta perforata, Habibacysta sp. cf. H. tectata, Kallosphaeridium brevibarbatum, Lejeunecysta kammae, Pyxidinopsis sp. cf. P. waipawaensis, Spiniferella cornuta and Tectatodinium meandriforme. The boundary between the T. evittii and the overlying Palaeocystodinium golzowense Zone was recorded only in the Mead Stream section where it is dated to ca 64.0 Ma. A high relative abundance of Isabelidinium cingulatum succeeded by the first occurrence of Isabelidinium bakeri, Deflandrea foveolata and D. delineata characterizes the lower to middle part of the early Paleocene P. golzowense Zone. The last consistent occurrence of P. pyrophorum is recorded within the upper part of radiolarian Zone RP3 corresponding to the middle part of the early Paleocene calcareous nannoplankton Zone NP3 (Early Teurian) or ca 63.7 Ma. The K-Pg boundary is not characterized by a mass extinction of dinoflagellates in the New Zealand sections. Instead, there is a marked change in cyst associations directly above the boundary and several new species appear in the lowermost Paleocene. Several typical latest Maastrichtian taxa have their last occurrences within the lowermost Paleocene corresponding to an interval of ca 0.5-0.7 Myrs after the K-Pg boundary.
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| 9. |
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| 10. |
- Willumsen, Pi, et al.
(författare)
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Surface salinity and nutrient variations during the Littorina Stage in the Fårö Deep, Baltic Sea
- 2013
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 42:1, s. 210-223
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Tidskriftsartikel (refereegranskat)abstract
- Early to late Holocene sediments from core F80, Fårö Deep, Baltic Sea, are investigated for their palynomorph composition and dinoflagellate cyst record to map variations in sea-surface-water salinity and palaeoproductivity during the past 6000 years. The F80 palynomorph assemblages are subdivided into four Assemblage Zones (AZs) named A to D. The transition from the stratigraphically oldest AZ A to B reflects a marked increase in palaeoproductivity and a gradual increase in surface-water salinity over the ~1500 years between the Initial Littorina (former Mastogloia Sea Stage) and Littorina Sea Stage. A period with maximum sea-surface salinity is recorded within the overlying AZ C from 7200 to 5200 cal. a BP, where the process length of Operculodinium centrocarpum indicates that average salinities were probably the highest (~15–17 versus 7.5 psu today) since the last glaciation. The change from AZ C to D correlates with a shift from laminated to non-laminated sediments, and the dinoflagellate cyst assemblages suggest that the surface- and the deep-water environment altered from c. 5250 cal. a BP, with less productivity in the surface water and more oxygenated conditions in the deep water. Here we demonstrate that by mapping overall palynomorph composition, dinoflagellate cyst assemblages and variations in the process length of O. centrocarpum in relation to periods of laminated/non-laminated sedimentation have great potential to track past regional changes in surface salinity, primary productivity and deep-water oxygenation status. An understanding of past productivity changes is particularly important to better understand present-day environmental changes within the Baltic Sea region.
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