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Late Eocene to Oligocene preservation history and biochronology of calcareous nannofossils from paleo-equatorial Pacific Ocean sediments
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
Chieti University, Italy.
2009 (English)In: Rivista italiana di paleontologia e stratigrafia, ISSN 0035-6883, E-ISSN 2039-4942, Vol. 1, 67-85 p.Article in journal (Refereed) Published
Abstract [en]

A continuous late Eocene through Oligocene carbonate sequence was recovered at Ocean Drilling Program (ODP) Site 1218 in the paleo-equatorial Pacific Ocean. The preservation history of selected calcareous nannofossil species across the Eocene/Oligocene (E/O) boundary is presented together with late Eocene and Oligocene calcareous nannofossil biochronology. The astronomically calibrated timescale of Pälike et al. (2006) is used here. Across the E/O boundary, placolith preservation is controlled by variation in carbonate content. Taxa less prone to dissolution are Reticulofenestra  umbilicus, Coccolithus  pelagicus, Ericsonia formosa and Dictyococites bisectus, while Cyclicargolithus floridanus is more susceptible to dissolution. A biochronologic framework has been established for the following taxa: the highest occurrences (HO) of Discoaster barbadiensis (34.773 Ma), D. saipanensis (34.435 Ma), E. formosa (32.919 Ma), R. umbilicus (32.021 Ma), Sphenolithus predistentus (26.928 Ma), S. distentus (26.812 Ma), and S. ciperoensis (24.432 Ma), and the lowest occurrences (LO) of S. distentus (29.997 Ma) and S. ciperoensis (27.142 Ma). The first consistent appearance of Triquetrorhabdulus carinatus occurs at 26.556 Ma, while the onset of the peak interval of T. carinatus was determined at 24.669 Ma. Biochronological comparisons are made with other sites from the Atlantic Ocean. A Triquetrorhabdulus morphotype, labeled as T. aff. carinatus, was recorded for the first time in the studied sediments, and precedes the LO of T. carinatus by ~ 0.7 Myr. Its stratigraphic range has a duration of about 3.3 Myr. T. aff. carinatus disappears concomitantly with the beginning of a sharp increase in abundance of T. carinatus.

Place, publisher, year, edition, pages
Italy: University of Milan , 2009. Vol. 1, 67-85 p.
Keyword [en]
calcareous nannofossils, preservation, biochronology, ODP Site 1218, paleo-equatorial Pacific Ocean, late Eocene, Oligocene, astronomical time scale
National Category
Geology
Research subject
Geology
Identifiers
URN: urn:nbn:se:su:diva-27584ISI: 000265232200005OAI: oai:DiVA.org:su-27584DiVA: diva2:216398
Available from: 2009-05-08 Created: 2009-05-08 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Late Eocene through Oligocene calcareous nannofossils from the paleo-equatorial Pacific Ocean – taxonomy, preservation history, biochronology and evolution
Open this publication in new window or tab >>Late Eocene through Oligocene calcareous nannofossils from the paleo-equatorial Pacific Ocean – taxonomy, preservation history, biochronology and evolution
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This study aims to unravel the ecological and evolutionary dynamics within the calcareous nannofossil communities at the Eocene/Oligocene (E/O) transition and during the Oligocene time when Cenozoic 'icehouse' conditions were established. The main question this study aims to answer is whether the changes in the nannofossil assemblages were controlled by intrinsic evolutionary trends or if the changes were controlled by environmental factors such as changes in temperature and nutrient availability in the surface water. These questions are addressed with detailed analyses of the taxonomy, biostratigraphy and fluctuations in abundance and diversity of calcareous nannofossil assemblages from a continuous latest Eocene through Oligocene sediment section from the ODP Site 1218 (8°53.38´N, 135°22.00´W), paleo-equatorial Pacific Ocean. An improved nannofossil taxonomy and biostratigraphy has been established. At the E/O transition, changes in the nannofossil preservation mimics changes in calcium carbonate content. A detailed investigation of late Eocene and Oligocene sediments yields age estimates for ten nannofossil bioevents. Morphometric studies of the Reticulofenestra umbilicus-R. hillae show that these cannot be subdivided into two different morphospecies. Based on different morphometry and stratigraphic ranges, the Oligocene Sphenolithus lineage appears to be the result of a combined anagenetic and cladogenetic evolution. A new nannolith species is described: Triquetrorhabdulus longus. High-resolution nannofossil data indicate changes in the composition, abundance and diversity of the mid-Oligocene assemblages. Intervals of high diversity index coincide with Oi-glaciation events. However, visual examination of the variations in abundance of nannofossil taxa do not appear to correlate with changes in either oxygen or carbon isotopes. This presumably indicates that a dynamic equilibrium did not exist between these Oligocene nannoplankton assemblages and changes in surface water temperature or productivity conditions.

 

Place, publisher, year, edition, pages
Stockholm: Department of Geology and Geochemistry, Stockholm University, 2009. 26 p.
Series
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 334
Keyword
marine sediments, calcareous nannofossils, late Eocene, Oligocene, biochronology, evolution, morphometry, taxonomy, ODP Leg 199 Site 1218, paleo-equatorial Pacific Ocean
National Category
Geology
Research subject
Marine Geoscience
Identifiers
urn:nbn:se:su:diva-27600 (URN)978-91-7155-890-9 (ISBN)
Public defence
2009-06-15, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
Doctoral Thesis in Marine Geoscience at Stockholm University, Sweden 2009Available from: 2009-05-25 Created: 2009-05-08 Last updated: 2009-05-26Bibliographically approved

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