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Late Eocene through Oligocene calcareous nannofossils from the paleo-equatorial Pacific Ocean – taxonomy, preservation history, biochronology and evolution
Stockholm University, Faculty of Science, Department of Geology and Geochemistry. (Marine Geosciences)
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 [en]
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: urn:nbn:se:su:diva-27600ISBN: 978-91-7155-890-9 (print)OAI: oai:DiVA.org:su-27600DiVA: diva2:216405
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
List of papers
1. Smear and spray preparation techniques put to the test (II): reproducibility and accuracy of calcareous nannofossil assemblage counts
Open this publication in new window or tab >>Smear and spray preparation techniques put to the test (II): reproducibility and accuracy of calcareous nannofossil assemblage counts
2007 (English)In: Journal of Nannoplankton Research, ISSN 1210-8049, Vol. 2, 92-100 p.Article in journal (Refereed) Published
Abstract [en]

In an earlier study (Henderiks and Törner, 2006, Marine Micropaleontology 58, 207-218), nannofossil proportion estimates between replicate smear slides showed substantially higher variance than those obtained from replicate sprayed slides. This study revisits this potentially disconcerting issue, detailing the internal accuracy and reproducibility of relative nannofossil species abundances obtained with the same two preparation techniques: the simple smear slide and the spray method. In addition, accuracy and reproducibility were tested for a semi-quantitative method, in which the number of specimens per mm2 is determined from smear slides.

To test the overall reproducibility of these two preparation methods, replicate slides were prepared and analyzed with each technique for a set of six samples selected from Oligocene deep-sea sediments from the Equatorial Pacific (ODP Leg 199). Both smear and spray replicates indicate a good reproducibility of proportion estimates within the same method, since no statistically significant differences between the replicate slides were observed. However, when comparing the smear with spray replicates, the data set reveals significantly different species proportion between slides, indicating that the two preparation techniques are not statistically comparable. It appears that the dominant taxon, Cyclicargolithus floridanus, is enriched in the smear slides, whereas the abundance of the subordinate taxa is about the same for either method. A comparative test of abundance counts between dense and thin areas on the same smear slide indicates nannofossil size sorting in the smearing technique, with proportionally more large specimens in the dense ripples. This study confirms an earlier observation that the smear method results in lower proportion estimates of larger nannofossil taxa in comparison to the spray method.

Place, publisher, year, edition, pages
UK: Cambridge University Press, 2007
Keyword
calcareous nannofossils, preparation techniques, light microscopy, accuracy, reproducibility, biostratigraphy
National Category
Geology
Research subject
Marine Geoscience
Identifiers
urn:nbn:se:su:diva-27589 (URN)
Available from: 2009-05-08 Created: 2009-05-08 Last updated: 2009-05-11Bibliographically approved
2. Late Eocene to Oligocene preservation history and biochronology of calcareous nannofossils from paleo-equatorial Pacific Ocean sediments
Open this publication in new window or tab >>Late Eocene to Oligocene preservation history and biochronology of calcareous nannofossils from paleo-equatorial Pacific Ocean sediments
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
Keyword
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:nbn:se:su:diva-27584 (URN)000265232200005 ()
Available from: 2009-05-08 Created: 2009-05-08 Last updated: 2017-12-13Bibliographically approved
3. The Oligocene nannolith Sphenolithus evolutionary lineage: morphometrical insights from the palaeo-equatorial Pacific Ocean
Open this publication in new window or tab >>The Oligocene nannolith Sphenolithus evolutionary lineage: morphometrical insights from the palaeo-equatorial Pacific Ocean
2010 (English)In: Journal of Micropalaeontology, ISSN 0262-821X, E-ISSN 2041-4978, no 29, 17-35 p.Article in journal (Refereed) Published
Abstract [en]

Changes in morphology within the biostratigraphically important Oligocene nannofossil lineage, Sphenolithus predistentus-distentus-ciperoensis, were investigated in carbonate sediments from the paleo-equatorial Pacific Ocean Site 1218 in order to determine the nature of this evolutionary lineage. Using differences in their morphology and stratigraphic ranges, the aim of this study was to determine whether this set of sphenolith species represents an anagenetic evolutionary lineage or a set of discrete species with overlapping geological ranges. 1000 specimens were analysed morphometrically and the basal ratio (the ratio between the proximal cycle height and basal width), was identified as a key parameter for study of this lineage. We conclude that S. distentus and S. predistentus are intergradational species forming an anagenetic lineage but that S. ciperoensis is a discrete species which evolved relatively abruptly in the Late Oligocene.

Keyword
Oligocene, Sphenolithus predistentus, S. distentus, S. ciperoensis, evolutionary lineage, morphometry, ODP Leg 199 Site 1218, Pacific Ocean
National Category
Geology
Research subject
Geology
Identifiers
urn:nbn:se:su:diva-27597 (URN)10.1144/jm.29.1.17 (DOI)000279030100003 ()
Available from: 2009-05-08 Created: 2009-05-08 Last updated: 2017-12-13Bibliographically approved
4. A new Oligocene Triquetrorhabdulus specie: Triquetrorhabdulus longus sp. nov.
Open this publication in new window or tab >>A new Oligocene Triquetrorhabdulus specie: Triquetrorhabdulus longus sp. nov.
2009 (English)Article in journal (Refereed) Submitted
Abstract [en]

While investigating the LO (Lowest Occurrence) of Triquetrorhabdulus carinatus at ODP Site 1218 in the paleo-equatorial Pacific, a form that resembles this species was observed and counted separately (Blaj et al., 2009). Based on differences in size, shape, and stratigraphic range compared with the typical Triquetrorhabdulus carinatus, we decided to describe this longer morphotype as a new and potentially biostratigraphically useful nannolith species, Triquetrorhabdulus longus sp. nov. 

Keyword
nannolith, Oligocene, Triquetrorhabdulus, Triquetrorhabdulus longus sp. nov., ODP Leg 199 Site 1218, paleo-equatorial Pacific Ocean
National Category
Geology
Research subject
Geology
Identifiers
urn:nbn:se:su:diva-27598 (URN)
Available from: 2009-05-08 Created: 2009-05-08 Last updated: 2009-05-11Bibliographically approved
5. Abundance and diversity changes among calcareous nannofossil assemblages across the early/late Oligocene boundary in the paleo-equatorial Pacific Ocean 
Open this publication in new window or tab >>Abundance and diversity changes among calcareous nannofossil assemblages across the early/late Oligocene boundary in the paleo-equatorial Pacific Ocean 
(English)Manuscript (Other (popular science, discussion, etc.))
Abstract [en]

Ocean Drilling Program (ODP) Leg 199 recovered a complete Oligocene sediment sequence at Site 1218 in the paleo-equatorial Pacific Ocean. This paper presents a high-resolution study of relative abundances and diversity fluctuations of calcareous nannofossil assemblages in an Oligocene interval showing high carbonate contents. The data generated are compared with stable isotope (C, O) and sediment flux data in order establish possible relationships to changes in sea surface temperature and productivity. The nannofossil assemblage is dominated by Cyclicargolithus floridanus, Sphenolithus moriformis and Coccolithus pelagicus, which show a combined mean abundance of 84 % throughout the investigated 3.6 Myr interval (30.0 - 26.4 Ma). All component taxa show fluctuations in abundance. Variations in abundance and Shannon diversity index have been used to subdivide the 3.6 Myr long study interval into four subintervals. Intervals of highest Shannon index diversity coincide with Oi-glaciation events. However, the variations in abundance of selected nannofossil taxa do not appear to correlate with changes in either oxygen isotopes or carbon isotopes. This presumably indicates that a dynamic equilibrium did not exist between these Oligocene calcareous nannoplankton assemblages and changes in surface water temperature or productivity conditions. Observed changes in the nannofossil assemblages thus could have probably been driven by other factors, like for example, the internal evolutionary dynamics within the coccolithophore communities.

 

Keyword
calcareous nannofossil, mid-Oligocene, Shannon diversity index, Site 1218, paleo-equatorial Pacific Ocean
National Category
Geology
Research subject
Geology
Identifiers
urn:nbn:se:su:diva-27599 (URN)
Available from: 2009-05-08 Created: 2009-05-08 Last updated: 2010-01-14Bibliographically approved

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Output format
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