845 research outputs found
The evolution of Eocene planktonic foraminifera Dentoglobigerina
No full textDentoglobigerina is a diverse genus of planktonic foraminifera ranging from the Eocene to Recent. However, the ancestry of Dentoglobigerina has been controversial. A growing body of evidence indicates that the genus Dentoglobigerina was spinose in life and evolved from Eocene Subbotina, whilst others have suggested its origins stem from Acarinina. Here we explore whether Subbotina or Acarinina is the ancestor of Dentoglobigerina by examining 35 specimens, evaluating their morphology and their occurrences through the middle to late Eocene, from localities worldwide. We find that Dentoglobigerina evolved ∼4 million years earlier than previously documented, with the species Dentoglobigerina pseudovenezuelana and ‘Dentoglobigerina’ eotripartita recorded in middle Eocene, Zone E9. Morphological convergences between Dentoglobigerina and Subbotina were found with D. galavisi and D. pseudovenezuelana, and between Dentoglobigerina and Acarinina with ‘D.’ eotripartita. Spine holes were observed in D. galavisi and D. pseudovenezuelana, though not uniformly found in all forms. Our findings suggest that there are two distinct lineages: (1) Dentoglobigerina, encompassing the species D. pseudovenezuelana and D. galavisi as a descendant of Subbotina; and (2) ‘Dentoglobigerina’ (including ‘D.’ eotripartita) as a descendant of Acarinina. Our results contribute to a better understanding of Dentoglobigerina biostratigraphy, phylogeny and evolution, and have implications for taxonomy
Taxonomy, biostratigraphy, and phylogeny of Oligocene Subbotina
No full textThe taxonomy, biostratigraphy, and phylogeny of Oligocene Subbotina is discussed and reviewed. We include forms that have teeth extending into the umbilicus. A total of nine species are accepted as distinct, namely Subbotina angiporoides (Hornibrook), Subbotina corpulenta (Subbotina), Subbotina eocaena (Gümbel), Subbotina gortanii (Borsetti), Subbotina linaperta (Finlay), Subbotina minima (Jenkins), Subbotina projecta Olsson, Pearson and Wade n. sp., Subbotina tecta Pearson and Wade, and Subbotina utilisindex (Jenkins and Orr)
Review and revision of Cenozoic tropical planktonic foraminiferal biostratigraphy and calibration to the Geomagnetic Polarity and Astronomical Time Scale
No full textPlanktonic foraminifera are widely utilized for the biostratigraphy of Cretaceous and Cenozoic marine sediments and are a fundamental component of Cenozoic chronostratigraphy. The recent enhancements in deep sea drilling recovery, multiple coring and high resolution sampling both offshore and onshore, has improved the planktonic foraminiferal calibrations to magnetostratigraphy and/or modified species ranges. This accumulated new information has allowed many of the planktonic foraminiferal bioevents of the Cenozoic to be revised and a reassessment of the planktonic foraminiferal calibrations. We incorporate these developments and amendments into the existing biostratigraphic zonal scheme.In this paper we present an amended low-latitude (tropical and subtropical) Cenozoic planktonic foraminiferal zonation. We compile 187 revised calibrations of planktonic foraminiferal bioevents from multiple sources for the Cenozoic and have incorporated these recalibrations into a revised Cenozoic planktonic foraminiferal biochronology. We review and synthesize these calibrations to both the geomagnetic polarity time scale (GPTS) of the Cenozoic and astronomical time scale (ATS) of the Neogene and late Paleogene. On the whole, these recalibrations are consistent with previous work; however, in some cases, they have led to major adjustments to the duration of biochrons. Recalibrations of the early middle Eocene first appearance datums of Globigerinatheka kugleri, Hantkenina singanoae, Guembelitrioides nuttalli and Turborotalia frontosa have resulted in large changes in the durations of Biochrons E7, E8 and E9. We have introduced (upper Oligocene) Zone O7 utilizing the biostratigraphic utility of 'Paragloborotalia' pseudokugleri. For the Neogene Period, major revisions are applied to the fohsellid lineage of the middle Miocene and we have modified the criteria for recognition of Zones M7, M8 and M9, with additional adjustments regarding the Globigerinatella lineage to Zones M2 and M3. The revised and recalibrated datums provide a major advance in biochronologic resolution and a template for future progress to the Cenozoic time scale
Taxonomy, biostratigraphy, and phylogeny of Oligocene Subbotina
No full textThe taxonomy, biostratigraphy, and phylogeny of Oligocene Subbotina is discussed and reviewed. We include forms that have teeth extending into the umbilicus. A total of nine species are accepted as distinct, namely Subbotina angiporoides (Hornibrook), Subbotina corpulenta (Subbotina), Subbotina eocaena (Gümbel), Subbotina gortanii (Borsetti), Subbotina linaperta (Finlay), Subbotina minima (Jenkins), Subbotina projecta Olsson, Pearson and Wade n. sp., Subbotina tecta Pearson and Wade, and Subbotina utilisindex (Jenkins and Orr)
Did Photosymbiont Bleaching Lead to the Demise of Planktic Foraminifer Morozovella at the Early Eocene Climatic Optimum?
No full textThe symbiont-bearing mixed-layer planktic foraminiferal genera Morozovella and Acarinina were among the most important calcifiers of early Paleogene tropical–subtropical oceans. A marked and permanent switch in the abundance of these genera is known to have occurred at low-latitude sites at the beginning of the Early Eocene Climatic Optimum(EECO), such that the relative abundance of Morozovella permanently and significantly decreased along with a progressive reduction in the number of species; concomitantly, the genus Acarinina almost doubled its abundance and diversified. Here we examine planktic foraminiferal assemblages and stable isotope compositions of their tests at Ocean Drilling Program Site 1051 (northwest Atlantic) to detail the timing of this biotic event, to document its details at the species level, and to test a potential cause: the loss of photosymbionts (bleaching). We also provide stable isotope measurements of bulk carbonate to refine the stratigraphy at Site 1051 and to determine when changes in Morozovella species composition and their test size occurred. We demonstrate that the switch in Morozovella and Acarinina abundance occurred rapidly and in coincidence with a negative carbon isotope excursion known as the J event (~53 Ma), which marks the start of the EECO.We provide evidence of photosymbiont loss after the J event from a size-restricted δ13C analysis. However, such inferred bleaching was transitory and also occurred in the acarininids. The geologically rapid switch in planktic foraminiferal genera during the early Eocene was a major evolutionary change within marine biota, but loss of photosymbionts was not the primary causal mechanism
Data report: Miocene planktonic foraminifers Dentoglobigerina and Globoquadrina from IODP Sites U1489 and U1490, Expedition 363
No full textInternational Ocean Discovery Program Expedition 363 Sites U1489 and U1490, located in the Western Pacific Warm Pool, con- tain diverse assemblages of planktonic foraminifers. We examined and imaged specimens of Miocene Dentoglobigerina and Globo- quadrina to determine the presence or absence of spine holes and pustules in their wall texture. A total of 15 specimens were observed across six species, including Dentoglobigerina baroemoenensis, Dentoglobigerina binaiensis, Dentoglobigerina globosa, Dentoglobi- gerina globularis, Dentoglobigerina tripartita, and Globoquadrina dehiscens. Here we present scanning electron microscope and z- stacking light microscope images in three views, including illustra- tions of their wall texture
Trilobatus Spezzaferri, Kucera, Pearson, Wade, Rappo, Poole, Morard & Stalder 2015
No full text<p> Genus <i>Trilobatus</i> Spezzaferri, Kucera, Pearson, Wade, Rappo, Poole, Morard, & Stalder, 2015</p> <p> <b>Type species.</b> <i>Globigerina triloba</i> Reuss, 1850.</p> <p> <b>Diagnosis.</b> Type of wall: normal perforate, spinose, coarsely cancellate ‘ <i>sacculifer</i> -type’ wall texture, though commonly obscured by a heterogeneous secondary, ‘gametogenic’ calcite. Test morphology: test low trochospiral, three to four usually globose, near-spherical chambers in the final whorl, generally high chamber expansion rate; sutures distinct, depressed, slightly straight to curved on both sides; umbilicus typically narrow; primary aperture usually extraumbilical-umbilical, generally a low arch, numerous apertures on spiral side, one per chamber, placed at the sutures of the preceding chamber and third-previous chamber (see Spezzaferri <i>et al</i>. 2015 for further detail).</p> <p> <b>Remarks.</b> <i>Trilobatus</i> is discerned from its ancestor <i>Globoturborotalita</i> Hofker, 1976 by possessing one or more supplementary apertures on the spiral side. <i>Globigerinoides</i> Cushman, 1927 also possesses supplementary apertures but differs from <i>Trilobatus</i> as the latter possesses a strictly <i>sacculifer</i> - type wall texture, whereas the former exhibits a <i>ruber-</i> or <i>ruber</i> / <i>sacculifer</i> - type wall texture (see Hemleben & Olsson 2006 for wall texture classification). Morphospecies of <i>Globigerinoides</i> also show a tendency towards higher arched primary apertures, whilst those of <i>Trilobatus</i> generally have low-arched, often slit-like primary apertures. <i>Globigerinoidesella</i> differs in having digitate protuberances on the final chamber(s) and usually exhibits a larger test size compared to <i>Trilobatus</i>. See also Spezzaferri <i>et al</i>. (2015, table 2) for comparison of morphological characters.</p> <p> <i>Trilobatus</i> was erected to encompass the ‘ <i>sacculifer</i> lineage’ (<i>sensu</i> Spezzaferri <i>et al</i>. 2015), and distinguish it from the ‘ <i>ruber</i> lineage’, which were both formerly part of <i>Globigerinoides</i> Cushman, 1927. Spezzaferri <i>et al</i>. (2015) demonstrated that the two lineages developed independently and thus placed the two groups in separate genera to avoid polyphyly (see Introduction for further detail).</p> <p> <b>Range.</b> Latest Oligocene to Recent.</p>Published as part of <i>Poole, Christopher R. & Wade, Bridget S., 2019, Systematic taxonomy of the Trilobatus sacculifer plexus and descendant Globigerinoidesella fistulosa (planktonic foraminifera), pp. 1989-2030 in Journal of Systematic Palaeontology 17 (23)</i> on page 1999, DOI: 10.1080/14772019.2019.1578831, <a href="http://zenodo.org/record/10883327">http://zenodo.org/record/10883327</a>
Planktic foraminiferal response to early Eocene carbon cycle perturbations in the southeast Atlantic Ocean (ODP Site 1263)
No full textAt low latitude locations in the northern hemisphere, striking changes in the relative abundances and diversity of the two dominant planktic foraminifera genera, Morozovella and Acarinina, are known to have occurred close to the Early Eocene Climatic Optimum (EECO; ~ 49–53 Ma). Lower Eocene carbonate-rich sediments at Ocean Drilling Program (ODP) Site 1263 were deposited on a bathymetric high (Walvis Ridge) at ~ 40° S, and afford an opportunity to examine such planktic foraminiferal assemblage changes in a temperate southern hemisphere setting. We present here quantified counts of early Eocene planktic foraminiferal assemblages from Hole 1263B, along with bulk sediment stable isotope analyses and proxy measurements for carbonate dissolution. The bulk sediment δ13C record at Site 1263 resembles similar records generated elsewhere, such that known and inferred hyperthermal events can be readily identified. Although some carbonate dissolution has occurred, the well-preserved planktic foraminiferal assemblages mostly represent primary changes in environmental conditions. Our results document the permanent decrease in Morozovella abundance and increase in Acarinina abundance at the beginning of the EECO, although this switch occurred ~ 165 kyr after that at low-latitude northern hemisphere locations. This suggests that unfavourable environmental conditions for morozovellids at the start of the EECO, such as sustained passage of a temperature threshold or other changes in surface waters, occurred at lower latitudes first. The remarkable turnover from Morozovella to Acarinina was widely geographically widespread, although the causal mechanism remains elusive. In addition, at Site 1263, we document the virtual disappearance within the EECO of the biserial chiloguembelinids, commonly considered as inhabiting intermediate water depths, and a reduction in abundance of the thermocline-dwelling subbotinids. We interpret these changes as signals of subsurface water properties, perhaps warming, and the associated contraction of ecological niches
Atmospheric carbon dioxide through the Eocene–Oligocene climate transition
No full textGeological and geochemical evidence1, 2, 3 indicates that the Antarctic ice sheet formed during the Eocene–Oligocene transition4, 33.5–34.0 million years ago. Modelling studies5, 6 suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels () fell below a critical threshold of 750 p.p.m.v., but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear. Here we use the boron isotope pH proxy7, 8 on exceptionally well-preserved carbonate microfossils from a recently discovered geological section in Tanzania9, 10 to estimate before, during and after the climate transition. Our data suggest that a reduction in occurred before the main phase of ice growth, followed by a sharp recovery to pre-transition values and then a more gradual decline. During maximum ice-sheet growth, was between 450 and 1,500 p.p.m.v., with a central estimate of 760 p.p.m.v. The ice cap survived the period of recovery, although possibly with some reduction in its volume, implying (as models predict11) a nonlinear response to climate forcing during melting. Overall, our results confirm the central role of declining in the development of the Antarctic ice sheet (in broad agreement with carbon cycle modelling12) and help to constrain mechanisms and feedbacks associated with the Earth's biggest climate switch of the past 65 Myr
Revisiting carbonate chemistry controls on planktic foraminifera Mg / Ca: implications for sea surface temperature and hydrology shifts over the Paleocene–Eocene Thermal Maximum and Eocene–Oligocene transition
No full textMuch of our knowledge of past ocean temperatures comes from the foraminifera Mg / Ca palaeothermometer. Several nonthermal controls on foraminifera Mg incorporation have been identified, of which vital effects, salinity, and secular variation in seawater Mg / Ca are the most commonly considered. Ocean carbonate chemistry is also known to influence Mg / Ca, yet this is rarely examined as a source of uncertainty, either because (1) precise pH and [CO32−] reconstructions are sparse or (2) it is not clear from existing culture studies how a correction should be applied. We present new culture data of the relationship between carbonate chemistry and Mg / Ca for the surface-dwelling planktic species Globigerinoides ruber and compare our results to data compiled from existing studies. We find a coherent relationship between Mg / Ca and the carbonate system and argue that pH rather than [CO32−] is likely to be the dominant control. Applying these new calibrations to data sets for the Paleocene–Eocene Thermal Maximum (PETM) and Eocene–Oligocene transition (EOT) enables us to produce a more accurate picture of surface hydrology change for the former and a reassessment of the amount of subtropical precursor cooling for the latter. We show that pH-adjusted Mg / Ca and δ18O data sets for the PETM are within error of no salinity change and that the amount of precursor cooling over the EOT has been previously underestimated by ∼ 2 °C based on Mg / Ca. Finally, we present new laser-ablation data of EOT-age Turborotalia ampliapertura from St. Stephens Quarry (Alabama), for which a solution inductively coupled plasma mass spectrometry (ICPMS) Mg / Ca record is available (Wade et al., 2012). We show that the two data sets are in excellent agreement, demonstrating that fossil solution and laser-ablation data may be directly comparable. Together with an advancing understanding of the effect of Mg / Casw, the coherent picture of the relationship between Mg / Ca and pH that we outline here represents a step towards producing accurate and quantitative palaeotemperatures using this proxy
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