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- Agnini, Claudia, et al.
(författare)
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Proposal for the Global Boundary Stratotype Section and Point (GSSP) for the Priabonian Stage (Eocene) at the Alano section (Italy)
- 2021
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Ingår i: Episodes. - : International Union of Geological Sciences. - 0705-3797 .- 2586-1298. ; 44:2, s. 151-173
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Tidskriftsartikel (refereegranskat)abstract
- The base of the Priabonian Stage is one of two stage boundaries in the Paleogene that remains to be formalized. The Alano section (NE Italy) was elected by consensus as a suitable candidate for the base of the Priabonian during the Priabonian Working Group meeting held in Alano di Piave in June 2012. Further detailed research on the section is now followed by a formal proposal, which identifies the base of a prominent crystal tuff layer, the Tiziano bed, at meter 63.57 of the Alano section, as a suitable candidate for the Priabonian Stage. The choice of the Tiziano bed is appropriate from the historical point of view and several bio-magnetostratigraphic events are available to approximate this chronostratigraphic boundary and guarantee a high degree of correlatability over wide geographic areas. Events which approximate the base of the Priabonian Stage in the Alano section are the successive extinction of large acarininids and Morozovelloides (planktonic foraminifera), the Base of common and continuous Cribrocentrum erbae and the Top of Chiasmolithus grandis (nannofossils), as well as the Base of Subchron C17n.2n and the Base of Chron C17n (magnetostratigraphy). Cyclostratigraphic analysis of the Bartonian-Priabonian transition of the Alano section as well as radioisotopic data of the Tiziano tuff layer provide an absolute age (37.710 - 37.762 Ma, respectively) of this bed and, consequently, of the base of the Priabonian Stage.
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| 2. |
- Agnini, Claudia, et al.
(författare)
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Stable isotope and calcareous nannofossil assemblage record of the late Paleocene and early Eocene (Cicogna section)
- 2016
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 12:4, s. 883-909
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Tidskriftsartikel (refereegranskat)abstract
- We present records of stable carbon and oxygen isotopes, CaCO3 content, and changes in calcareous nannofossil assemblages across an 81 m thick section of upper Paleocene lower Eocene marine sedimentary rocks now exposed along the Cicogna Stream in northeast Italy. The studied stratigraphic section represents sediment accumulation in a bathyal hemipelagic setting from approximately 57.5 to 52.2 Ma, a multi-million-year time interval characterized by perturbations in the global carbon cycle and changes in calcareous nannofossil assemblages. The bulk carbonate delta C-13 profile for the Cicogna section, once placed on a common timescale, resembles that at several other locations across the world, and includes both a long-term drop in delta C-13 and multiple short-term carbon isotope excursions (CIEs). This precise correlation of widely separated delta C-13 records in marine sequences results from temporal changes in the carbon composition of the exogenic carbon cycle. However, diagenesis has likely modified the delta C-13 record at Cicogna, an interpretation supported by variations in bulk carbonate 8180, which do not conform to expectations for a primary signal. The record of CaCO3 content reflects a combination of carbonate dilution and dissolution, as also inferred at other sites. Our detailed documentation and statistical analysis of calcareous nannofossil assemblages show major differences before, during and after the Paleocene Eocene Thermal Maximum. Other CIEs in our lower Paleogene section do not exhibit such a distinctive change; instead, these events are sometimes characterized by variations restricted to a limited number of taxa and transient shifts in the relative abundance of primary assemblage components. Both long-lasting and short-lived modifications to calcareous nannofossil assemblages preferentially affected nannoliths or holococcoliths such as Discoaster,, Fasciculithus, Rhomboaster/Tribrachiatus, Sphenolithus and Zygrhablithus, which underwent distinct variations in abundance as well as permanent evolutionary changes in terms of appearances and disappearances. By contrast, placoliths such as Coccolithus and Tow eius, which represent the main component of the assemblages, were characterized by a gradual decline in abundance over time. Comparisons of detailed nannofossil assemblage records at the Cicogna section and at ODP Site 1262 support the idea that variations in the relative and absolute abundances, even some minor changes, were globally synchronous. An obvious link is through climate forcing and carbon cycling, although the linkages between variations in calcareous nannoplankton, changes in delta C-13 records and oceanography will need additional work.
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| 3. |
- 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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| 6. |
- 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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| 7. |
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| 8. |
- Pälike, Heiko
(författare)
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The PACIFIC EQUATORIAL AGE TRANSECT (“PEAT”): New insights into the Cenozoic link between climate and calcium carbonate compensation
- 2009
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Ingår i: <em>Eos, Trans. American Geophysysical Union,</em> 90(52)(Suppl.):PP43C-06.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Integrated Ocean Drilling Program (IODP) Expeditions 320 and 321,“Pacific Equatorial Age Transect” (Sites U1331-U1338), were designedto recover a continuous Cenozoic record of the palaeoequatorialPacific by coring above the palaeoposition of the equator atsuccessive crustal ages on the Pacific plate. These sediments recordthe evolution of the palaeoequatorial climate system throughout theCenozoic. As we have gained more information about the past movementof plates, and when in Earth’s history “critical” climate events tookplace, it became possible to drill an age-transect (“flow-line”) alongthe position of the paleoequator in the Pacific, targeting importanttime slices where the sedimentary archive allows us the reconstructionof past climatic and tectonic conditions. The Pacific Equatorial AgeTransect (PEAT) cored eight sites from the sediment surface tobasement, with basalt aged between 53 to 18 Ma, covering the timeperiod following maximum Cenozoic warmth, through initial majorglaciations, to today. The PEAT program allows the reconstruction ofextreme changes of the calcium carbonate compensation depth acrossmajor geological boundaries during the last 53 m.y. A very shallow CCDduring most of the Paleogene makes it difficult to obtain wellpreserved carbonate sediments during these stratigraphic intervals,but we recovered a unique sedimentary biogenic sediment archive fortime periods just after the Paleocene-Eocene boundary event, theEocene cooling, the Eocene/Oligocene transition, the “one cold pole”Oligocene, the Oligocene-Miocene transition, and the middle Miocenecooling. Together with older ODP and DSDP drilling in the equatorialPacific, we can also delineate the position of the palaeoequator andvariations in sediment thickness from approximately 150°W to 110°Wlongitude. We will present a preliminary reconstruction of the Pacificcarbonate compensation depth (CCD) throughout the time intervalrecovered.
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| 9. |
- 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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