| 1. |
- Backman, Jan, et al.
(författare)
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Biozonation and biochronology of Miocene through Pleistocene calcareous nannofossils from low and middle latitudes
- 2012
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Ingår i: Newsletters on stratigraphy. - Stuttgart : Schweizerbart. - 0078-0421. ; 45:3, s. 221-244
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Tidskriftsartikel (refereegranskat)abstract
- Calcareous nannofossils are widely used in Cenozoic marine biostratigraphy. At present, the two most widely used calcareous nannofossil biozonations were established approximately 40 years ago. These were derived from marine land sections and Deep Sea Drilling Project rotary cored sediments. Over nearly three decades, we have generated Miocene through Pleistocene calcareous nannofossil data from deep sea sediments in low and middle latitude regions. The sediments used here have been mostly recovered using the advanced piston coring technique, generating less core disturbance and complete recovery via multiple penetration of the sediment column at single sites. A consistent trait in our work on calcareous nannofossil biostratigraphy has been to use semi-quantiative methods in combination with short sample distances, close enough to capture the details of the abundance behaviour of individual calcareous nannofossil taxa. Such data represent the foundation of the new biozonation presented here, which still partly relies on the pioneering work presented by Er lend Martini and David Bukry about 40 years ago. A key aim here has been to employ a limited set of selected biohorizons for the purpose of establishing a relatively coarsely resolved and stable biozonation. We present 31 biozones using a new code system: CNM1-CNM20; Calcareous Nannofossil Miocene biozones 1 through 20. CNPL1-CNPL11; Calcareous Nannofossil Plio-Pleistocene biozones 1 through 11. As the new biozonation encompasses 23 million years, the average biozone resolution becomes 0.74 million years, ranging from 0.15 to 2.20 million years. A single biohorizon is used for the definition of each biozone boundary. Auxiliary markers are avoided, as well as subzones, in order to maintain stability to the new biozonation. Virtually every biozone holds one or several additional biohorizons. These, together with all biozone boundary markers, are assigned age estimates derived chiefly from astronomically tuned cyclostratigraphies.
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| 2. |
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| 3. |
- Pälike, Heiko, et al.
(författare)
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A Cenozoic record of the equatorial Pacific carbonate compensation depth
- 2012
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 488:7413, s. 609-614
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0-3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.
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| 4. |
- Stein, Ruediger, et al.
(författare)
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Cenozoic Arctic Ocean Climate History : Some Highlights from the Integrated Ocean Drilling Program Arctic Coring Expedition
- 2014. - 1
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Ingår i: Earth and Life Processes Discovered from Subseafloor Environments. - Amsterdam : Elsevier. - 9780444626172 ; , s. 259-293
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Bokkapitel (refereegranskat)abstract
- With the Arctic Coring Expedition (ACEX) (the first Mission Specific Platform expedition within the Integrated Ocean Drilling Program) Expedition 302 in 2004, a new era in Arctic research began. For the first time, a scientific drilling expedition in the permanently ice-covered Arctic Ocean was carried out, penetrating 428 m of Quaternary, Neogene, Paleogene, and Campanian sediment on the crest of Lomonosov Ridge close to the North Pole between 87 and 88°N. By studying the unique ACEX sequence, a large number of scientific discoveries that describe previously unknown Arctic paleoenvironments were obtained during the last decade. Key results include subtropical warm conditions during the Paleocene-Eocene Thermal Maximum and the early-mid Eocene, an episodic freshening of Arctic surface waters in the Eocene, black shales and euxinic conditions in the Eocene Arctic Ocean, and an early onset of Arctic sea ice (Northern Hemisphere glaciation) in the middle Eocene. While these results from ACEX were unprecedented, key questions related to the climate history of the Arctic Ocean on its course from Greenhouse to Icehouse conditions during early Cenozoic times remain unanswered, in part because of poor core recovery, and in part because of the possible presence of a major mid-Cenozoic hiatus within the ACEX record. Furthermore, the ACEX sites remain the one and only drill holes in the entire central Arctic Ocean to date. In order to decipher the paleoclimatic and tectonic history of this unique and sensitive but still not well-known region on Earth, future scientific Arctic drilling is certainly needed.
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