Clay mineralogy of the Cenozoic Pagodroma Group, East Antarctica

The Cenozoic Pagodroma Group in the northern Prince Charles Mountains, East Antarctica, is a glaciomarine succession of fjordal character, comprising four uplifted formations of different ages. The composition of the <2 µm fraction of sediments of the Pagodroma Group was analysed in order to help identify source areas, past weathering conditions and glacial regimes. Both clay and non-clay minerals have been quantified. The assemblage of the upper Oligocene to lower Miocene Mount Johnston Formation is characterised by the dominance of illite and intermediate concentrations of chlorite. Similar to that assemblage is the clay mineral suite of the middle Miocene Fisher Bench Formation, where illite and chlorite together account for 95% of the clay minerals. The middle to upper Miocene Battye Glacier Formation is the only formation with significant and persistent smectite concentrations, although illite is still dominant. The kaolinite concentration is also high and is even higher than that of chlorite. The clay fraction of the upper Pliocene to lower Pleistocene Bardin Bluffs Formation is characterised by maximum kaolinite concentrations and relatively low illite and chlorite concentrations. The bulk of the clay fraction in each formation can be explained by the physical weathering and erosion of a nearby source under glacial conditions. In the case of Mount Johnston Formation and Fisher Bench Formation this source may be situated in the metavolcanic and gneissic rocks of Fisher Massif. The sediments of the Bardin Bluffs Formation indicate a local source within the Amery Oasis, where Proterozoic granitoid rocks and gneisses, and Permo-Triassic fluvial rocks of the Amery Group are exposed. These results suggest a strong local imprint on the glacial sediments as northwards flowing ice eroded the bedrock in these areas. The origin of the clay fraction of the Battye Glacier Formation is a matter of debate. The smectite and kaolinite content most easily can be explained by erosion of sources largely hidden beneath the ice upstream. Less likely, these clay minerals reflect climatic conditions that were much warmer and wetter than today, facilitating chemical weathering.

Paleomagnetism of ODP Leg 115 sediments

Ocean Drilling Program Leg 115 was designed to study Neogene sedimentation history in the western Indian Ocean Basin as well as the Cenozoic evolution of the Reunion hotspot. We describe the paleomagnetic analysis of the sediments recovered on this leg, focusing on the sites that provided the most readily interpretable data: Sites 706, 709, 710, and 711. Sediments from Site 706 show no reversals but appear to give a reliable reversed polarity primary direction, judged on the basis of the demagnetization behavior of individual samples as well as from the results of a fold test formulated by comparing the two holes drilled at this site. Magnetic polarity stratigraphy in sediments from Site 709 can be deduced in two limited sections of Pliocene-Pleistocene and Oligocene-Miocene age. Sediments recovered at Site 710 (and, to a lesser extent, Site 711) render a relatively continuous magnetic polarity stratigraphy that spans most of the Neogene and adds significantly to the body of data available to address problems in Miocene geochronology. In addition to these magnetostratigraphic results, the paleomagnetism of these sediments can be used to determine paleolatitude. Using the most reliable inclination measurements from Sites 706, 710, and 711, we compared paleomagnetic estimates of paleolatitude with estimates derived from a hotspot-based absolute plate motion model. Our data, which covers the interval since 33 Ma, shows that paleolatitudes calculated with the geocentric axial dipole assumption are in general accord with the hotspot predictions. However, a correction for the long-term nondipole field brings the paleomagnetic results into even better agreement with plate motions that are based on the fixity of African hotspots.

Sr/Ca ratios of Cenozoic benthic foraminifera

A Cenozoic multi-species record of benthic foraminiferal calcite Sr/Ca has been produced and is corrected for interspecific offsets (typically less than 0.3 mmol/mol) and for the linear relationship between decreasing benthic foraminiferal Sr/Ca and increasing water depth. The water depth correction, determined from Holocene, Late Glacial Maximum and Eocene paleowater-depth transects, is ~0.1 mmol/mol/km. The corrected Cenozoic benthic foraminiferal Sr/Ca record ranges from 1.2 to 2.0 mmol/mol, and has been interpreted in terms of long-term changes in seawater Sr/Ca, enabling issues related to higher-resolution variability in Sr/Ca to be ignored. We estimate that seawater Sr/Ca was ~1.5 times modern values in the late Cretaceous, but declined rapidly into the Paleogene. Following a minimum in the Eocene, seawater Sr/Ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late Miocene. By assuming scenarios for changing seawater calcium concentration, and using published carbonate accumulation rate data combined with suitable values for Sr partition coefficients into carbonates, the seawater Sr/Ca record is used to estimate global average river Sr fluxes. These fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity/tectonic outgassing to calculate changes in global average river 87Sr/86Sr through the Cenozoic. The absolute magnitude of Sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties. Nevertheless, our results suggest that river Sr flux increased from 35 Ma to the present day (roughly two-fold) accompanied by an overall increase in 87Sr/86Sr (by ~0 to 0.001). Between 75 and 35 Ma, river 87Sr/86Sr also increased (by ~0.001 to 0.002) but was accompanied by a decrease (two- to three-fold) in river Sr flux.

Benthic foraminifera extinctions in the Cenozoic record

In the late Pliocene-middle Pleistocene a group of 95 species of elongate, cylindrical, deep-sea (lower bathyal-abyssal) benthic foraminifera became extinct. This Extinction Group (Ext. Gp), belonging to three families (all the Stilostomellidae and Pleurostomellidae, some of the Nodosariidae), was a major component (20-70%) of deep-sea foraminiferal assemblages in the middle Cenozoic and subsequently declined in abundance and species richness before finally disappearing almost completely during the mid-Pleistocene Climatic Transition (MPT). So what caused these declines and extinction? In this study 127 Ext. Gp species are identified from eight Cenozoic bathyal and abyssal sequences in the North Atlantic and equatorial Pacific Oceans. Most species are long-ranging with 80% originating in the Eocene or earlier. The greatest abundance and diversity of the Ext. Gp was in the warm oceanic conditions of the middle Eocene-early Oligocene. The group was subjected to significant changes in the composition of the faunal dominants and slightly enhanced species turnover during and soon after the rapid Eocene-Oligocene cooling event. Declines in the relative abundance and flux of the Ext. Gp, together with enhanced species loss, occurred during middle-late Miocene cooling, particularly at abyssal sites. The overall number of Ext. Gp species present began declining earlier at mid abyssal depths (in middle Miocene) than at upper abyssal (in late Pliocene-early Pleistocene) and then lower bathyal depths (in MPT). By far the most significant Ext. Gp declines in abundance and species loss occurred during the more severe glacial stages of the late Pliocene-middle Pleistocene. Clearly, the decline and extinction of this group of deep-sea foraminifera was related to the function of their specialized apertures and the stepwise cooling of global climate and deep water. We infer that the apertural modifications may be related to the method of food collection or processing, and that the extinctions may have resulted from the decline or loss of their specific phytoplankton or prokaryote food source, that was more directly impacted than the foraminifera by the cooling temperatures.

Cenozoic clay mineralogy of DSDP Sites 93-604 and 93-605

Examination of the clay mineralogy of Cenozoic sediment samples from Deep Sea Drilling Project Sites 604 and 605 on the upper continental rise off New Jersey indicates that sediment deposition of two different clay mineral facies has occurred. These sites are marked by Paleogene deposition of illite with subordinate kaolinite and smectite covarying in inverse proportion, and by Neogene deposition dominated by illite with subordinate kaolinite and chlorite. Leg 93 results agree with the clay mineral facies proposed by Hathaway (1972), which defined a "Northern facies" consisting of illite and chlorite, with feldspar and hornblende, from erosion of rocks north of Cape Hatteras, and a "Southern facies" composed of smectite, kaolinite, and mixed-layer illite-smectites. Neogene and Quaternary sediments at Sites 604 and 605 contain the "Northern facies," and Paleogene sediments contain the "Southern facies" minerals. Feldspar is exclusively found in Neogene-Quaternary sediments, as is the majority of the amphibole found in these samples. Widespread Paleogene volcanic source materials are suggested by the presence of smectite throughout the early Paleocenemiddle Eocene sediments recovered at Site 605. The clay mineral stratigraphy at Leg 93 sites is comparable to the record at nearby DSDP sites on the lower continental rise and abyssal plain of the northwestern Atlantic (DSDP Sites 388, 105, and 106), and also with the sediments recovered by drilling on the Mazagan Plateau off northwestern Morocco (DSDP Sites 544-547) in the eastern North Atlantic.

Abundance of zooplankton based on a long-term study at the Galata transect and covers the spring-summer periods from 1967 till 2005

The dataset is based on a long-term study (38 years) at the Galata transect and covers the spring-summer periods from 1967 till 2005. The whole dataset is composed of 360 data of total zooplankton biomass and abundance . Samples were collected in discrete layers 0-10m, 10-20m, 10-25m, 25-50m, 50-70m, 50-100m, 100-150. Mesozooplankton abundance: the collected material was analysed using the method of Domov (1959). Samples were brought to volume of 25-30 ml depending upon zooplankton density and mixed intensively until all organisms were distributed randomly in the sample volume. After that 5 ml of sample was taken and poured in the counting chamber for taxomomic identification and count. Large (> 1 mm body length) and not abundant species were calculated in whole sample. Counting and measuring of organisms were made in the Dimov chamber under the stereomicroscope to the lowest taxon possible. Taxonomic identification was done at the Institute of Fishery Resource by Prof. Asen Konsulov and Institute of Oceanology by Prof. Asen Konsulov, Lyudmila Kamburska and Kremena Stefanova using the relevant taxonomic literature (Mordukhay-Boltovskoy, F.D. (Ed.). 1968, 1969,1972). Taxon-specific mesozooplankton abundance: The collected material was analysed using the method of Domov (1959). Samples were brought to volume of 25-30 ml depending upon zooplankton density and mixed intensively until all organisms were distributed randomly in the sample volume. After that 5 ml of sample was taken and poured in the counting chamber for taxomomic identification and count. Copepods and Cladoceras were identified and enumerated; the other mesozooplankters were identified and enumerated at higher taxonomic level (commonly named as mesozooplankton groups). Large (> 1 mm body length) and not abundant species were calculated in whole sample. Counting and measuring of organisms were made in the Dimov chamber under the stereomicroscope to the lowest taxon possible. Taxonomic identification was done at the Institute of Fishery Resource by prof. Asen Konsulov and Institute of Oceanology by Prof. Asen Konsulov, Lyudmila Kamburska and Kremena Stefanova using the relevant taxonomic literature (Mordukhay-Boltovskoy, F.D. (Ed.). 1968, 1969,1972).

Cenozoic calcareous nannofossils from the Lesser Antilles Forearc Region

During Leg 110 of the Ocean Drilling Program, sediment was recovered from six sites in the vicinity of the Lesser Antilles Forearc. Hole 671B, drilled near the toe of the Barbados deformation front, was the first-ever penetration of the decollement between the underthrusting Atlantic Plate and the off scraped Barbados accretionary prism. Stratigraphic repetitions in sequence associated with tectonic movement along the decollement zone, first observed on DSDP Leg 78A, were further documented at four ODP Leg 110 sites. A significant biostratigraphic inversion is present at Site 671 at 128 mbsf in which upper Miocene sediments rest atop lower Pleistocene strata. Smaller repetitions in sequence are recorded at Sites 671, 673, 674, and 676. Leg 110 sediments range from middle Eocene to early Pleistocene in age. Pliocene/Pleistocene assemblages are generally well preserved; however, Miocene assemblages have undergone extensive dissolution at all Leg 110 sites. Paleogene sediments are sometimes recrystallized and the nannofossils contained within exhibit a range in preservation from poor to good.

The evolutionary history of size variation of planktic foraminiferal assemblages in the Cenozoic

The iterative evolutionary radiation of planktic foraminifers is a well-documented macroevolutionary process. Here we document the accompanying size changes in entire planktic foraminiferal assemblages for the past 70 My and their relationship to paleoenvironmental changes. After the size decrease at the Cretaceous/Paleogene (K/P) boundary, high latitude assemblages remained consistently small. Size evolution in low latitudes can be divided into three major phases: the first is characterized by dwarfs (65-42 Ma), the second shows moderate size fluctuations (42-14 Ma), and in the third phase, planktic foraminifers have grown to the unprecedented sizes observed today. Our analyses of size variability with paleoproxy records indicate that periods of size increase coincided with phases of global cooling (Eocene and Neogene). These periods were characterized by enhanced latitudinal and vertical temperature gradients in the oceans and high diversity (polytaxy). In the Paleocene and during the Oligocene, the observed (minor) size changes of the largely low-diversity (oligotaxic) assemblages seem to correlate with productivity changes. However, polytaxy per se was not responsible for larger test sizes.