Microfossil occurrence in Pliocene-Quaternary sediments of the North Atlantic

Planktonic foraminiferal and nannoplankton stratigraphy of the Pliocene-Quatemary Sediments of the northern half of the Atlantic Ocean from the equator up to the Rockall Plateau and the Norwegian Sea, is considered. Lowlatitude zonations were used for the subdivision of the Pliocene and Quaternary Sediments of different climatic belts, and certain subglobal zonal units were recognized. Variations in the degree of resolution of the zonation in different latitudes were revealed; the resolution of zonal scales based on calcareous plankton diminishes northwards. Changes of taxonomic composition of the zonal foraminifer and nannoplankton assemblages within various latitudinal belts of the Atlantic were analyzed taking into consideration the influence of climatic factors and of local bionomic conditions. Correlation with the magnetostratigraphic time-scale permitted the establishment of the most reliable appearance and disappearance datums (datum planes) of planktonic foraminifer and nannoplankton species. Paleontologic plates demonstrate some guide forms of two groups of calcareous plankton, and a short description of the taxa is given in the text. Major stratigraphic problems of Pliocene and Quaternary marine deposits are discussed. The monograph can be used in different geological investigations by specialists in geology, paleontology, and oceanology.

Diversity of benthic foraminiferal faunas in Tertiary and Quaternary sediments of DSDP Hole 33-317_Site from the Manihiki Plateau, Pacific Ocean (Table 1)

A study is made of the benthic foraminifers (size fraction > 63 µm) recovered from 59 upper Eocene through Quaternary sediment samples at DSDP Site 317 (Leg 33), located at a depth of 2598 m in the central part of the Manihiki Plateau (South Pacific). The sediments cored are disturbed in only two samples. The stratigraphic assignements used are based on previous studies of planktic foraminifers and other microfossils. In total, 216 taxa are identified. A cluster analysis based on the 77 species which comprised 5% or more of the entire foraminiferal assemblage in at least one sample suggests the presence of 3 major biostratigraphic zones corresponding approximately to the following ages, zone A: middle Miocene-Quaternary; zones B-C: early Miocene-Oligocene; and zone D: Eocene. The most important faunal turnover occurred between the Eocene and the Oligocene; a less pronounced break took place between the early and the middle Miocene, and an additional minor turnover between the Oligocene and the early Miocene. Eighteen taxa are long-ranging, being recorded from the middle Eocene through the Pliocene-Quaternary. It is concluded that, in general, benthic foraminifers of the bathyal zone are poor worldwide stratigraphic guide fossils; the following taxa are conditionally considered as the most suitable in the Eocene-Quaternary sequence: Aragonia aragonensis, Quadrimorphina profunda, Nuttallides truempyi, Abyssamina poagi, Buliminella grata, Bulimina jarvisi, B. macilenta, Turrilina alsatica, Cibicides notocenicus, C. wuellerstorfi, Pyrgo murrhina. However, most of these species are relatively rare.

Dinoflagellate cysts abundance and events of ODP Hole 189-1168A sediments

Palynomorphs were studied in samples from Ocean Drilling Program (ODP) Leg 189, Hole 1168A (slope of the western margin of Tasmania; 2463 m water depth). Besides organic-walled dinoflagellate cysts (dinocysts), broad categories of other palynomorphs were quantified in terms of relative abundance. In this contribution, we provide an overview of the early late Eocene-Quaternary dinocyst distribution and illustrate main trends in palynomorph distribution. Dinocyst species throughout Hole 1168A are largely cosmopolitan with important contributions of typical low-latitude taxa and virtual absence of endemic Antarctic taxa. Dinocyst stratigraphic distribution broadly matches that known from the Northern Hemisphere and equatorial regions, although significant differences are noted. Selected potentially biochronostratigraphically useful events are summarized. The distribution of dinocysts in the middle-upper Miocene interval is rather patchy, probably due to prolonged exposure to oxygen. An important general aspect in the dinocyst assemblages is the near absence of Antarctic endemic species and the apparent influence of relatively warm waters throughout the succession at Site 1168. General palynomorph distribution indicates continued deepening from an initial shallow, even restricted, marine setting from late Eocene-Quaternary times. A curious massive influx of small skolochorate acritarchs is recorded throughout the late early-early middle Miocene; the significance of this signal is not yet understood. A general long-term oligotrophic nature of the surface waters influencing Site 1168 is suggested from the low abundance of (proto) peridinioid, presumably heterotrophic, species. The overall dinocyst distribution pattern corresponds to the long-term existence of a Leeuwin-like current influencing the region, including Site 1168, confirming results of earlier studies on other microfossil groups. The occasional influence of colder surface water conditions is, however, also apparent, notably during the late Pliocene-Quaternary, indicating the potential of high-resolution dinocyst analysis for future paleoceanographic studies.

Diatom abundances in ODP Leg 114 holes

The practically continuous, paleomagnetically dated late Gauss-Brunhes sediment profiles of ODP Sites 699 and 701, south of the present Polar Front Zone (PFZ), and Site 704, north of the present PFZ, are used for a high-resolution study of abundance fluctuations of eight stratigraphic marker species in space and time. Ecological restrictions and preferences of the diatom species Hemidiscus karstenii, Actinocyclus ingens f. planus, Thalassiosira elliptipora, Thalassiosira kolbei, Thalassiosira vulnifica, Simonseniella barboi, Cosmiodiscus insignis, and Nitzschia weaveri are deduced. The ages of their first abundant appearance datums (FAAD), last-appearance datums (LAD), and last abundant appearance datums (LAAD) at the three sites are determined. The interpolated datum ages agree relatively well with those determined by other authors, if one interprets most of their LADs as LAADs. FAADs and LAADs produce more accurate datums than LADs. For the late Matuyama (younger than approximately 2.0 Ma), when PFZ fluctuations effected all three site sites, the datum ages determined agree within the methodically caused limits of accuracy for each datum. For the early Matuyama (older than approximately 2.0 Ma) the results can be interpreted as either that the ages of the FAAD of T. kolbei and LAAD of T. vulnifica datums determined at Sites 699 and 701 are more reliable or that these datums are diachronous between these two sites and Site 704. Such a diachroneity could be caused by different paleoceanographic conditions (stable subantarctic conditions over Site 704 and stable antarctic conditions over Sites 699 and 701). A few taxonomic changes were necessary. One new genus is defined (Simonseniella gen. nov.) and five new combinations are proposed: Simonseniella barboi (Brun) comb, nov., Simonseniella praebarboi (Schrader) comb, nov., Simonseniella curvirostris (Jousé) comb, nov., Thalassiosira elliptipora (Donahue) comb, nov., and Thalassiosira vulnifica (Gombos) comb. nov.

Chemical element concentrations in sediments from DSDP Holes 60-458 and 60-459

The development of laser ablation-inductively coupled plasma-mass spectrometry has revolutionized the analysis of tephras by providing (1) an efficient and precise method for determining abundances of a wide variety of trace elements at low concentrations in individual glass shards and (2) assessment of geochemical heterogeneities within individual ash horizons. This development is important for petrogenetic studies of intraoceanic arc systems, where tephras provide the most complete temporal record of magmatism. Results from the Izu-Bonin and Mariana arc systems indicate that despite close geographical proximity and similar tectonic evolution, they contrast strongly in terms of geochemical evolution since 35 Ma. Whereas the Mariana tephras have exceptional compositional diversity, ranging from low-K (Oligocene), to high-K (Miocene), and subsequently medium-K compositions (Pliocene-Quaternary), the Izu-Bonin arc has been dominated by low-K compositions throughout. The Mariana increases in K are paralleled by increases in abundances of incompatible trace elements and by increased values of diagnostic ratios (e.g., Nb/yb and Th/yb) regarded as monitors of potential mantle-source fertility. The relative uniformity of Nb/yb and Nb/Zr ratios in Izu-Bonin tephras indicates that cyclic processes of backarc basin development and mantle depletion do not necessarily induce large-scale temporal geochemical variations in the associated arc. Temporal variability within the Mariana arc, and its divergence from the Izu-Bonin arc ca. 13 Ma, can be traced to a major injection of subducted sediment in the Mariana system at this time.

Late Miocene to Holocene planktonic foraminifers from the subantarctic South Atlantic

Late Miocene to Holocene planktonic foraminifers from the subantarctic South Atlantic were investigated for their biostratigraphic and environmental significance. The calcareous planktonic microfauna are of low diversity and are very rare or absent at sites located below the CCD. The sediments recovered from Sites 703 and 704 on the Meteor Rise at about 47°S are useful for biostratigraphic and environmental studies. In the whole sequence 16 species or varieties of planktonic foraminifers were recognized. Two species occur in the uppermost Miocene. In the Pliocene the Globorotalia puncticulata population can be used to separate the early from the late Pliocene. The Pliocene/Quaternary boundary does not appear to be well distinguished in the foraminiferal assemblage. A faunal change noted at 2.5 Ma could correspond to the development of glaciation in the Northern Hemisphere and its Antarctic counterpart. At about 5.2 Ma the first increase in polar fauna near the Meteor Rise occurs. Two other cooling periods are indicated in these sequences at about 4 and 3 Ma. Moreover, the hydrologic environment became more productive at about 2.1 Ma and close to the Brunhes/Matuyama boundary.

Composition of bottom sediments from the Central Basin of the Indian Ocean

A study of petrographic and mineral compositions of 26 sediment cores from the western part of the Central Basin of the Indian Ocean has identified biogenic, terrigenous, volcanogenic, and authigenic sediment types formed in certain facies conditions. On the basis of bio- and paleomagnetic stratigraphy data from the cores sedimentation rates of different sediment types have been calculated. Modern and Pliocene-Pleistocene positions of the main facies boundaries (the critical depth of carbonate accumulation, the geochemical boundary between hemi- and miopelagic zones, the frontal boundaries of the equatorial belt of biogenic silica accumulation) have been determined. It has been shown that the sedimentary process during Pliocene-Quaternary had cycle variations characterized by successive changes of different sedimentation types - hemipelagic, miopelagic, and biogenic.

Biosiliceous sedimentation at ODP Site 128-798

Upper Pliocene through Holocene sediments recovered at Site 798 in the Japan Sea (Oki Ridge) exhibit rhythmic variation in weight percent biogenic opal at intervals of ~5 m and periods equivalent to the 41-k.y. obliquity cycle. Variance at 17 and 100 k.y. is observed prior to 1.3 Ma. These cycles are also clearly defined by log data and correspond to clusters of decimeter-scale dark-colored sediment units alternating with clusters of light-colored units. Opal content varies between 3% and 22% between 0 and 1.3 Ma and from 3% to 43% between 1.3 and 2.6 Ma. Long-term opal accumulation rates average 1.8 g/cm**2/k.y. in the late Pliocene/early Pleistocene and decrease by about 60% at ~1.3 Ma. Rough calculations suggest that opal accumulation rates increased and terrigenous flux decreased during the Holocene relative to the last glacial period. Our age control is not yet sufficient to allow a similar analysis of the 41-k.y. cyclicity in opal content throughout the Pleistocene. Stable isotope results from planktonic foraminifers confirm previous suggestions of a strong surface-water freshening event during isotope stage 2; however, this episode appears to be unique during the Pleistocene. Benthic foraminifers are depleted in 18O during parts of glacial stages 2 and 6 relative to adjacent interglacials, suggesting unusual warming and/or freshening of deep waters. Collectively, the stable isotope and %opal data are consistent with continuing isolation of the Japan Sea during the Quaternary with important transitions occurring at 1.3, 0.7 to 1.0, and 0.2 to 0.3 Ma. Complex relationships among the stable isotope results, %opal data, and sediment characteristics such as color and organic and inorganic carbon content preclude development of a simple model to explain cyclical sedimentation. Opal maxima occur within both light and dark intervals and the processes that control surface-water productivity are at times decoupled from the factors that regulate deep-water dysaerobia. We suggest that water column overturn is controlled largely by regional atmospheric circulation that must also have an as yet poorly understood effect on surface-water fertility.

(Table 1) Sound velocity, wet-bulk density, and acoustic impedance of some indurated sediment from DSDP Leg 64 Holes

The Pliocene-Quaternary sediments that we drilled at eight sites in the Gulf of California consist of silty clays to clayey silts, diatomaceous oozes, and mixtures of both types. In this chapter I have summarized various measurements of their physical properties, relating this information to burial depth and effective overburden pressure. Rapid deposition and frequent intercalations of mud turbidites may cause underconsolidation in some cases; overconsolidation probably can be excluded. General lithification begins at depths between 200 and 300 meters sub-bottom, at porosities between 55 and 60% (for silty clays) and as high as 70% (for diatomaceous ooze). Diatom-rich sediments have low strength and very high porosities (70-90%) and can maintain this state to a depth of nearly 400 meters (where the overburden pressure = 1.4 MPa). The field compressibility curves of all sites are compared to data published earlier. Where sediments are affected by basaltic sills, these curves clearly show the effects of additional loading and thermal stress (diagenesis near the contacts). Strength measurements on well-preserved hydraulic piston cores yielded results similar to those obtained on selected samples from standard drilling. Volumetric shrinkage dropped to low values at 100 to 400 meters burial depth (0.3 to 2.0 MPa overburden pressure). Porosity after shrinkage depends on the composition of sediments.