Late Cenozoic Micropaleontologic Events in the Equatorial Pacific Sediments

A microbiostratigraphical investigation of five deep-sea sediment cores from the equatorial Pacific was carried out by utilizing planktonic foraminifers, radiolarians and calcareous nannoplankton. Several micropaleontologic events characterized by the first occurrence of taxa were found to provide reliable datum planes for stratigraphic correlation of post-Miocene sediments. These datum planes are : The Buccinosphaera invaginata Datum, Collosphaera tuberosa Datum, Globoquadrina conglomerata Datum, Pulleniatina obliquil-oculata Datum, Gephyrocapsa oceanica Datum, Gephyrocapsa caribbeanica Datum, Anthocyrtidium angulare Datum and Globorotalia (G.) truncatulinoides Datum, in downward sequence. These datum planes are related to the biostratigraphic zonations based on various microfossils, and further to the previously determined paleomagnetic stratigraphy. One new radiolarian species, Amphiropalum praeypsilon, is described

Plasma chemistry of the chinstrap penguin Pygoscelis antarctica during fasting periods: A case of poor adaptation to food deprivation?

The chinstrap penguin (Pygoscelis antarctica) is the smallest penguin species to be used to study the physiology of fasting. We analysed body-mass change and plasma chemistry of five non-breeding chinstraps during an experimental fasting period in the breeding season. We also analysed the same parameters in six fasting birds under natural conditions (during an incubation shift, which lasts about 10 days). Both groups presented similar patterns of change, showing a rapid increase in urea and uric acid plasma concentrations. Urea surpassed 3 mmol/l after 5 fasting days, while uric acid reached 1 mmol/l after 9 days. Plasma glucose levels decreased after 11 days, whereas cholesterol also showed a clear reduction during fasting. These results as a whole suggest that chinstrap penguins reached phase III after a short period in comparison with other Pygoscelis species. Body size and ecological factors could explain these inter-specific differences.Peer Reviewe

Relative sea-level rise around East Antarctica during Oligocene glaciation

During the middle and late Eocene (∼48-34 Myr ago), the Earth's climate cooled and an ice sheet built up on Antarctica. The stepwise expansion of ice on Antarcticainduced crustal deformation and gravitational perturbations around the continent. Close to the ice sheet, sea level rosedespite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet. Here we identify the crustal response to ice-sheet growth by forcing a glacial-hydro isostatic adjustment model with an Antarctic ice-sheet model. We find that the shelf areas around East Antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed. The inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice-sheet margins. Consequently the coasts experienced a progressive relative sea-level rise. Our analysis of sediment cores from the vicinity of the Antarctic ice sheet are in agreement with the spatial patterns of relative sea-level change indicated by our simulations. Our results are consistent with the suggestion that near-field processes such as local sea-level change influence the equilibrium state obtained by an icesheet grounding line

Eocene cooling linked to early flow across the Tasmanian Gateway

The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52–50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO(2)). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began ∼49–50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2–4 °C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO(2) forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling

Evolution of structures and fabrics in the Barbados Accretionary Prism ; Insights from Leg 110 of the Ocean Drilling Program

The microstructures and crystal fabrics associated with the development of an amphibolite facies quartzo-feldspathic mylonitic shear zone (Torridon, NW Scotland) have been investigated using SEM electron channelling. Our results illustrate a variety of microstructures and fabrics which attest to a complex shear zone deformation history. Microstructural variation is particularly pronounced at low shear strains: significant intragranular deformation occurs via a domino-faulting style process, whilst mechanical incompatibilities between individual grains result in characteristic grain boundary deformation accommodation microstructures. A sudden reduction in grain size defines the transition to medium shear strains, but many of the boundaries inherited from the original and low shear strain regions can still be recognized and define distinctive bands oriented at low angles to the shear zone margin. Grains within these bands have somewhat steeper preferred dimensional orientations. These domains persist into the high shear strain mylonitic region, where they are oriented subparallel to the shear zone margin and consist of sub-20 μm grains. The microstructures suggest that the principal deformation mechanism was intracrystalline plasticity (with contributions from grain size reduction via dynamic recrystallization, grain boundary migration and grain boundary sliding). Crystal fabrics measured from the shear zone vary with position depending on the shear strain involved, and are consistent with the operation of several crystal slip systems (e.g. prism, basal, rhomb and acute rhomb planes) in a consistent direction (probably parallel to a and/or m). They also reveal the presence of Dauphine twinning and suggest that this may be a significant process in quartz deformation. A single crystal fabric evolution path linking the shear zone margin fabric with the mylonitic fabric was not observed. Rather, the mylonitic fabric reflects the instantaneous fabric which developed at a particular location for a particular shear strain and original parental grain orientation. The mature shear zone therefore consists of a series of deformed original grains stacked on top of each other in a manner which preserves original grain boundaries and intragranular features which develop during shear zone evolution. The stability of some microstructures to higher shear strains, the exploitation of others at lower shear strains, and a continuously evolving crystal fabric, mean that the strain gradient observed across many shear zones is unlikely to be equivalent to a time gradient

Albaillellaridés (radiolaires) permiens d'un banc calcaire à Arrow Rocks dans la Waipapa Terrane (Nouvelle Zélande septentrionale)

Des radiolaires permiens bien conservés ont été trouvés dans un nodule calcaire à Arrow Rocks dans la région de Whangaroa de la Waipapa Terrane, Nouvelle Zélande. Cette faune contient huit espèces d\u27albaillellaridés, six espèces du genre Follicucullus et deux de Pseudoalbaillella, et est d\u27âge Permien moyen à début Permien supérieur. Dans la région de Whangaroa, des basaltes sont probablement aussi anciens que le Permien moyen, alors que les cherts sont principalement Permien supérieur. Bien que la faune à radiolaires à Arrow Rocks contiennent deux nouvelles espèces de Follicucullus, cette faune peut néanmoins être assimilée à une faune de basse latitude. Deux nouvelles espèces, Follicucullus sphaericus et Follicucullus whangaroaensis, sont décrites.Well-preserved Permian radiolarians are present in a limestone lens at Arrow Rocks in the Whangaroa Area within Waipapa Terrane, New Zealand. This fauna contains eight species of albaillellarians, six species of genus Follicucullus and two of Pseudoalbaillella, and is Late Middle to Early Late Permian in age. In the Whangaroa Area, basalts are probably as old as Middle Permian, while cherts are mostly Late Permian. Although the radiolarian fauna from Arrow Rocks contains two new species of Follicucullus, this fauna can nevertheless be assigned a low-latitude origin. Two new species, Follicucullus sphaericus and Follicucullus whangaroaensis, are described.</p

Statistical Analyses of Populations by Electronic Computer

This paper describes the method of computation and program of the electronic computer for statistical analyses of populations. The program includes an analysis for population structure by "Motomura\u27s Plane" and principal factor analysis for correlative analysis

Wall Microstructure of Globorotalia truncatulinoides (d\u27Orbigny)

Current studies on planktonic Foraminifera indicate that the external morphology of the test and the structure of the wall are of prime importance for taxonomy, ecology and studies on their evolution. Investigations on the spatial variation of the morphology and on the microstructure of the shell wall provides sound basis for the evaluation of the chronologic morphogenesis of the planktonic Foraminifera. In the present study the well known planktonic species, Globorotalia truncalulinoides (d\u27Orbigny), was analysed as to the geographic variation of its external morphology, and the wall structure was examined with the electron microscopes. Statistical analyses demonstrate that : 1) highly conical forms are seemingly concentrated in the lower latitudinal regions and the lower conical ones in the higher latitudes; 2) individuals with umbilical teeth and dextrally coiled shells dominate in the lower latitudes; the categories are independent of one another. Two methods of electron microscopy were employed for the study of the wall microstructure, namely, the transmitted type and the scanning type. A complete electron micrograph of a vertical section of the test was reconstructed, and a schematic diagram showing the fundamental wall structure constructed. The wall of G. truncatulinoides is basically divided into the lamellar layer and crust; these are different from each other in microstructure. The lamellar layer in each chamber is distinguished into the inner and outer lamellae by structure and texture. The inner lamella, limited in each chamber, consists of minute interlocking calcite grains and is lined by basal sublamella. The outer lamella is composed of interlocking columns and wedges perpendicular to the surface and finely bumpy in texture. The boundary between these lamellae is not defined by a sharp line or "canal" in contrast to those between the consecutive outer lamellae. Textural differentiation in the bilamellar layer is considered to be related to the contact with the protoplasmic mass. The crust composed of elongate, prismatic calcite units is a layer formed after the completion of the ultimate chamber. These calcite units exhibit a microstructure supposed to be cleavage. Pore concentration in the wall is usually 7 to 9 per 25×25μ square. Protuberances developed in and on the wall are classified into punctae and pustules on the basis of site of occurrence, structure, and external morphology. Keels, umbilical teeth, and inner margins of the umbilical walls are essentially identical in structure with the usual type of the wall, though each of them assumes a peculiar feature in some respects. The characteristic features of the keel are mostly due to the thickening of the basal suite of the lamellae formed by an inflection at the periphery