| 1. |
- Blaj, Teodora, 1979-
(författare)
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Late Eocene through Oligocene calcareous nannofossils from the paleo-equatorial Pacific Ocean – taxonomy, preservation history, biochronology and evolution
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Blaj, Teodora, 1979-, et al.
(författare)
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Late Eocene to Oligocene preservation history and biochronology of calcareous nannofossils from paleo-equatorial Pacific Ocean sediments
- 2009
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Ingår i: Rivista italiana di paleontologia e stratigrafia. - Italy : University of Milan. - 0035-6883 .- 2039-4942. ; 1, s. 67-85
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Blaj, Teodora, 1979-, et al.
(författare)
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Smear and spray preparation techniques put to the test (II): reproducibility and accuracy of calcareous nannofossil assemblage counts
- 2007
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Ingår i: Journal of Nannoplankton Research. - UK : Cambridge University Press. - 1210-8049. ; 2, s. 92-100
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Blaj, Teodora, 1979-, et al.
(författare)
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The Oligocene nannolith Sphenolithus evolutionary lineage : morphometrical insights from the palaeo-equatorial Pacific Ocean
- 2010
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Ingår i: Journal of Micropalaeontology. - : Copernicus GmbH. - 0262-821X .- 2041-4978. ; :29, s. 17-35
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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