Os isotope record of ODP Site 159-959

The known temporal relationship between the benthic foraminiferal d18O record and the marine Os isotope record is used to reinterpret the absolute chronology and paleoceanographic context of an episode of organic carbon burial on the West African margin Ocean Drilling Program (ODP) Site 959. Although organic-rich sediments require significant corrections for in situ decay of 187Re to 187Os, these results demonstrate the utility of the marine Os isotope record for chemostratigraphic correlation of organic-rich sediments that are devoid of age diagnostic microfossils with pelagic carbonate sequences. Revision of the ODP Site 959 chronology shifts the age assignment of an interval of biosiliceous, organic-rich sediment deposition from the Oligocene to the late Eocene and earliest Oligocene, likely culminating with the first major glaciation of the Oligocene (Oi1). We speculate that enhanced organic carbon burial over much of the West African margin may have contributed to drawdown of atmospheric carbon dioxide before and during the Oi1 event and suggest that Os isotope chemostratigraphy provides a valuable tool for further exploring this possibility.

Calculated sea surface temperatures of two sediment cores

The reconstruction of ocean history employs a large variety of methods with origins in the biological, chemical, and physical sciences, and uses modern statistical techniques for the interpretation of extensive and complex data sets. Various sediment properties deliver useful information for reconstructing environmental parameters. Those properties that have a close relationship to environmental parameters are called ''proxy variables'' (''proxies'' for short). Proxies are measurable descriptors for desired (but unobservable) variables. Surface water temperature is probably the most important parameter for describing the conditions of past oceans and is crucial for climate modelling. Proxies for temperature are: abundance of microfossils dwelling in surface waters, oxygen isotope composition of planktic foraminifers, the ratio of magnesium or strontium to calcium in calcareous shells or the ratio of certain organic molecules (e.g. alkenones produced by coccolithophorids). Surface water salinity, which is important in modelling of ocean circulation, is much more difficult to reconstruct. At present there is no established method for a direct determination of this parameter. Measurements associated with the paleochemistry of bottom waters to reconstruct bottom water age and flow are made on benthic foraminifers, ostracodes, and deep-sea corals. Important geochemical tracers are d13C and Cd/Ca ratios. When using benthic foraminifers, knowledge of the sediment depth habitat of species is crucial. Reconstructions of productivity patterns are of great interest because of important links to current patterns, mixing of water masses, wind, the global carbon cycle, and biogeography. Productivity is reflected in the flux of carbon into the sediment. There are a number of fluxes other than those of organic carbon that can be useful in assessing productivity fluctuations. Among others, carbonate and opal flux have been used, as well as particulate barite. Furthermore, microfossil assemblages contain clues to the intensity of production as some species occur preferentially in high-productivity regions while others avoid these. One marker for the fertility of sub-surface waters (that is, nutrient availability) is the carbon isotope ratio within that water (13C/12C, expressed as d13C). Carbon isotope ratios in today's ocean are negatively correlated with nitrate and phosphate contents. Another tracer of phosphate content in ocean waters is the Cd/Ca ratio. The correlation between this ratio and phosphate concentrations is quite well documented. A rather new development to obtain clues on ocean fertility (nitrate utilization) is the analysis of the 15N/14N ratio in organic matter. The fractionation dynamics are analogous to those of carbon isotopes. These various ratios are captured within the organisms growing within the tagged water. A number of reconstructions of the partial pressure of CO2 have been attempted using d13C differences between planktic and benthic foraminifers and d13C values of bulk organic material or individual organic components. To define the carbon system in sea water, two elements of the system have to be known in addition to temperature. These can be any combination of total CO2 , alkalinity, or pH. To reconstruct pH, the boron isotope composition of carbonates has been used. Ba patterns have been used to infer the distribution of alkalinity in past oceans. Information relating to atmospheric circulationand climate is transported to the ocean by wind or rivers, in the form of minerals or as plant andanimal remains. The most useful tracers in this respect are silt-sized particles and pollen.

Diatom biostratigraphy, Argon ages and chronology of ODP Hole 183-1138A

A thick Neogene section was recovered in the upper ~300 m of Ocean Drilling Program Hole 1138A, drilled on the Central Kerguelen Plateau in the Indian sector of the Southern Ocean. Sediment lithologies consist primarily of mixed carbonate and biosiliceous clays and oozes, with several thin (1-3 cm) tephra horizons. The tephras are glass rich, well sorted, and dominantly trachytic to rhyolitic in composition. Volcaniclastic material in these horizons is interpreted to have originated from Heard Island, 180 km northwest of Site 1138, and was likely emplaced through both primary ash fall and turbiditic, submarine flows. A Neogene age-depth model for Hole 1138A is constructed primarily from 36 diatom biostratigraphic datums. Nannofossil and planktonic foraminifer biostratigraphy provides supporting age information. Additionally, four high-precision 40Ar-39Ar ages are derived from ash and tephra horizons, and these radiometric ages are in close agreement with the biostratigraphic ages. The integrated age-depth model reveals a reasonably complete lower Miocene to upper Pleistocene section in Hole 1138A, with the exception of a ~1-m.y. hiatus at the Miocene/Pliocene boundary. Another possible hiatus is also identified at the Oligocene/Miocene boundary. High Neogene sedimentation rates and the presence of both calcareous and siliceous microfossils, combined with datable tephra horizons, establish Site 1138 as a suitable target for future drilling legs with paleoceanographic objectives. This report also proposes two new diatom species, Fragilariopsis heardensis and Azpeitia harwoodii, from Pliocene strata of Hole 1138A.

Miocene to Quaternary paleoenvironments and uplift history on the mid Norwegian shelf

Based on benthic and planktic foraminifera, Bolboforma, oxygen isotope measurements and seismic data, major changes in Miocene, Pliocene and Pleistocene paleoenvironments on the mid Norwegian shelf are discussed and a possible scenario of the late Cenozoic uplift history is given. The dating of the Neogene sequence has been done using foraminifera and Bolboforma. Four main assemblage zones have been identified with nine distinct subzones. Most of the Miocene sequence is preserved. The lower Miocene sediments contain only siliceous microfossils. A period of high fertility and upwelling in the study area prevailed. The early Miocene-early mid Miocene (15 Ma?) change from a siliceous to a calcareous rich microfauna, dominated by Nonion barleeanum, can be related to increased surface-water circulation due to overflow across the Iceland-Faeroe ridge. During the Miocene the temperature decreased in the study area. Evidence of increased amounts of coarser sediments may suggest that an uplift of the mainland areas occurred during the mid-late Miocene. Lower Pliocene sediments contain a foraminiferal fauna that seems to occur in slightly colder conditions than the late Miocene fauna suggesting a further cooling. Possibly, Arctic waters entered the study area in the early Pliocene. A very marked change in lithology (from compacted claystone to unconsolidated diamicton), fauna (from deep dwelling to shallow dwelling species) and seismic signature (from flat lying reflectors to prograding clinoforms) occurs during the mid?-late Pliocene. A two step cooling trend is indicated by the microfauna of these prograding wedges. (1) The first wedge buildups might have been associated with an uplift of the mainland during the early late Pliocene (mid Pliocene, ca. 4 Ma). However, the age determination is somewhat uncertain and may very well be of late Pliocene age. (2) The second step of wedge buildup is associated with a glacial phase where the dominating microfauna exists of arctic species. Large continental ice sheets might have occurred at this time reaching coastal areas and that possibly many of the geomorphological features such as the strandflat were made during this episode. The Pleistocene epoch is represented by an increased percentage of boreal foraminifera intermingled with high arctic species which indicates that interglacial-glacial cycles prevailed and the dynamics of the glacier system changed.

Benthic foraminifera of the central Indian Ocean

Late Oligocene to late Pliocene vertical water-mass stratification along depth traverses in the northern Indian Ocean is depicted in this paper by benthic foraminifer index faunas. During most of this time, benthic faunas indicate well-oxygenated, bottom-water conditions at all depths except under the southern Indian upwelling and in the Pliocene in the southern Arabian Sea. Faunas suggest the initiation of lower oxygen conditions at intermediate depths in the northern Indian Ocean beginning in Oligocene Zone P21a. Lower oxygen conditions intensified during primary productivity pulses, possibly related to increased upwelling vigor, in the latest Oligocene and throughout most of the late middle through late Miocene. During times of elevated primary production, there may be more oxygen flux into sedimentary pore waters and the shallow infaunal habitat may become more oxygenated. One criterion for locating the source of "new" water masses is vertical homogeneity of benthic foraminifer indexes for well-oxygenated water masses from intermediate through abyssal depths. In the northern Mascarene Basin, this type of faunal homogeneity with depth corroborates the proposal that the northern Indian Ocean was an area of sinking well-oxygenated waters through most of the Miocene before Zone N17. Oxygenated, possibly "new" intermediate-water masses in the low- to middle-latitude Mascarene and Central Indian basins first developed in the late Oligocene. These well-oxygenated waters were probably more fertile than the Antarctic Intermediate Waters (AAIW) that cover intermediate depths in these areas today. Production of intermediate waters more similar to modern AAIW is indicated by the sparse benthic population of epifaunal rotaloid species in the northern Mascarene Basin during middle Miocene Zone N9 and from early through late Pliocene time. Deep-water characteristics are more difficult to interpret because of the extensive redeposition at the deeper sites. Redeposited intermediate, rather than shallow, water fossils and erosion from north to south in the Mascarene Basin are incompatible with the sluggish circulation from south to north through the western Indian Ocean basins today. Such erosion could result from the vigorous sinking of an intermediate-depth water mass of northern origin. Before late Oligocene Zone P22, benthic faunas indicate a twofold subdivision of the troposphere, with the boundary between upper and lower well-oxygenated water masses located from 2500-3000 mbsl. No characteristic bottom-water fauna developed before the end of late Oligocene Zone P22. Deep and abyssal benthic indexes suggest the development of water masses similar to those of the present day in the latest Miocene. Faunas containing deep-water benthic indexes, including the uvigerinids, suggestive of a water mass similar to modern Indian Deep Water (IDW), appeared during the late Miocene in the northern Mascarene and Central Indian basins. In the early Pliocene, this deep-water fauna was found only in the Central Indian Basin, whereas a fauna typical of modern Antarctic Bottom Water (AABW) spread through deep waters at 2800 mbsl in the Mascarene Basin. By late Pliocene Zone N21, however, deep-water faunas similar to their modern analogs were developed in both the eastern and western basins. Abyssal faunas, studied only in the Mascarene Basin, show more or less similarity to those under modern AABW. Bottom-water faunas containing Nuttallides umbonifera or Epistominella exiguua were first differentiated at the end of Zone P22, then appeared episodically during the early Miocene. These AABW-type faunas reappeared and migrated updepth into deep waters during the glacial episodes at the end of the Miocene and at the beginning of the Pliocene. By late Pliocene Zone N21, however, a bottom-water fauna similar to that under eastern Indian Bottom Water (IBW) developed in the Mascarene Basin. Modern bottom-water characteristics of the Mascarene Basin must have developed after ZoneN21.

Microfossil cyclicity in Late Albian sediments of Kirchrode I borehole

We studied the biological response to orbital forcing in marine Upper Albian sediments recovered from the 245 m-long Kirchrode I borehole in the Lower Saxony basin in northwestern Germany. Results from quantitative analysis of planktonic and benthic foraminifera, of calcareous nannofossils, and radiolaria were used for this study. Spectral analysis in the depth domain indicates for the high sedimentation rate part of the Upper Albian dominant periods with wavelengths of 10±13 m, 5±6 m, and 2±3 m, which we interpret to represent the biological response to orbital forcing in the Milankovitch frequency bands eccentricity, obliquity, and precession, respectively. In addition, a low amplitude 40±50 m cycle was found, which would represent the long-term eccentricity variation of roughly 400 ka. Microfossil cyclicity does not change significantly within the whole core indicating sedimentation rates of 11±12 cm/ka on an average, with variations between 3.5 and 13 ka. Microfossils show greater variability in their abundance changes than the physical and chemical parameters and also greater power in the higher-frequency bands (obliquity and precession). While most of the planktonic foraminifer species studied are dominated by variations in the obliquity, most benthic foraminifer species show an additional strong influence of precession. These differences in the cyclicity of the abundance changes are interpreted as reflecting a stronger influence of low latitude water in the deep waters of the Late Albian Lower Saxony basin than in the shallow waters. This basin was part of a wide, 'Boreal' epicontinental sea, which was connected to the Tethys to the south via the Polish strait and via the Paris basin, and which was connected with the North Atlantic and Arctic to the north. In analogy to results from analysis of data from the Late Neogene, strong effects of precession interpreted as being more characteristic for changes/influences triggered in the low latitudes and those of obliquity to be more characteristic for influences from the high latitudes. The presence of a relatively strong eccentricity cycle, not only in the compound parameters, but also in the abundance changes of single species during the Late Albian means that there must have been a non-linear response to orbital forcing and internal feedbacks.

Analysis of elements at DSDP Holes 70-506 and 70-509B

Sediments in the area of the Galapagos hydrothermal mounds are divided into two major categories. The first group, pelagic sediments, are nannofossil oozes with varying amounts of siliceous microfossils. The second group are hydrothermal sediments consisting of manganese-oxide crust fragments and green nontronitic clay granules. Hydrothermal sediments occur only in the upper half to two-thirds of the cores and are interbedded and mixed with pelagic sediments. Petrologic evidence indicates that hydrothermal nontronite forms as both a primary precipitate and as a replacement mineral of pre-existing pelagic sediment and hydrothermal manganese-oxide crust fragments. In addition, physical evidence supports chemical equations indicating that the pelagic sediments are being dissolved by hydrothermal solutions. The formation of hydrothermal nontronite is not merely confined to the surface of mounds, but also occurs at depth within their immediate area; hydrothermal nontronite is very likely forming today. Geologically speaking, the mounds and their hydrothermal sediments form almost instantaneously. The Galapagos mounds area is a unique one in the ocean basins, where pelagic sediments can be diagenetically transformed, dissolved, and replaced, possibly within a matter of years.

Calcareous nannofossil abundance and datums of ODP Hole 194-1193A sediments, Marion Plateau, Australia

During Leg 194, a series of eight sites was drilled through Oligocene-Holocene mixed carbonate and siliciclastic sediments on the Marion Plateau, northeast Australia. The major objective was to constrain the magnitude and timing of sea level changes in the Miocene. Site 1193, located on the Marion Plateau in 348 m of water ~80 km from the south central Great Barrier Reef margin, is probably the most important site for constraining the major middle to late Miocene sea level drop and reconstructing the evolution history of the Marion Plateau during the Miocene (Isern, Anselmetti, Blum, et al., 2002, doi:10.2973/odp.proc.ir.194.2002). However, there is no biostratigraphic or other chronological data for the critical interval between 36 and 211 meters below seafloor (mbsf) (virtually the entire late and middle Miocene) due to poor core recovery and a virtual absence of planktonic microfossils in the core catcher samples examined aboard the ship (Isern, Anselmetti, Blum, et al., 2002, doi:10.2973/odp.proc.ir.194.2002). The main purpose of this report is to refine the shipboard nannofossil biostratigraphy through examination of new samples and more detailed examination of those samples reported on board the ship. This results in a refinement for most of the nannofossil datums and provides some useful age information to fill the critical data gap for the middle Miocene. Previous Neogene nannofossil biostratigraphic studies of the Marion Plateau and Queensland Plateau include Gartner et al. (1993, doi:10.2973/odp.proc.sr.133.213.1993) and Wei and Gartner (1993, doi:10.2973/odp.proc.sr.133.216.1993).

Range charts of stratigraphically important radiolarian species in sediments of ODP Leg 165 sites

The Paleogene sequences from three sites in the Caribbean were examined for radiolarians. In general, samples are highly lithified, requiring lengthy and repetitive cleaning procedures, and the assemblages are usually fragmented and/or partially dissolved. Both abundances and preservation of the assemblages vary considerably from site to site and within a single site; even within a single sample more than one degree of preservation was observed. It was possible, however, to construct at least partial stratigraphies for each of the three sites. Because the abundance of radiolarians is high even in extremely poorly preserved assemblages, we conclude that the differences in biogenic silica preservation are the result of postdepositional processes and not productivity. In both Sites 999 and 1001, near the Paleocene/Eocene boundary (Bekoma bidartensis Zone [RP7]), there is a short interval in which the abundance and preservation state of the radiolarians improves relative to overlying and underlying assemblages. In each case the intervals corresponds to the level, identified by calcareous microfossils, as representing changes in paleoceanographic conditions associated with the late Paleocene thermal maximum.

Physical properties, grain size distribution and clay mineralogy of ODP Leg 117 sites

The fabric of sediments recovered at sites drilled on the Indus Fan, Owen Ridge, and Oman margin during Ocean Drilling Program Leg 117 was examined by scanning electron microscopy to document changes that accompany sediment burial. Two sediment types were studied: (1) biogenic sediments consisting of a variety of marly nannofossil and nannofossil oozes and chalks and (2) terrigenous sediments consisting of fine-grained turbidites deposited in association with the Indus Fan. Biogenic sediments were examined with samples from the seafloor to depths of 306 m below seafloor (mbsf) on the Owen Ridge (Site 722) and 368 mbsf on the Oman margin (Sites 723 and 728). Over these depth ranges the biogenic sediments are characterized by a random arrangement of microfossils and display little chemical diagenetic alteration. The microfossils are dispersed within a fine-grained matrix that is predominantly microcrystalline carbonate particles on the Owen Ridge and clay and organic matter on the Oman margin. Sediments with abundant siliceous microfossils display distinct, open fabrics with high porosity. Porosity reduction resulting from gravitational compaction appears to be the primary process affecting fabric change in the biogenic sediment sections. Fabric of illite-rich clayey silts and silty claystones from the Indus Fan (Site 720) and Owen Ridge (Sites 722 and 731) was examined for a composite section extending from 45 to 985 mbsf. In this section fabric of the fine-grained turbidites changes from one with small flocculated clay domains, random particle arrangement, and high porosity to a fabric with larger domains, strong preferred particle orientation roughly parallel to bedding, and lower porosity. These changes are accomplished by a growth in domain size, primarily through increasing face-to-face contacts, and by particle reorientation which is characterized by a sharp increase in alignment with bedding between 200 and 400 mbsf. Despite extensive particle reorientation, flocculated clay fabric persists in the deepest samples examined, particularly adjacent to silt grains, and the sediments lack fissility. Fabric changes over the 45-985 mbsf interval occur in response to gravitational compaction. Porosity reduction and development of preferred particle orientation in the Indus Fan and Owen Ridge sections occur at greater depths than outlined in previous fabric models for terrigenous sediments as a consequence of a greater abundance of silt and a greater abundance of illite and chlorite clays.

Miocene foraminiferal, bolboformid, dinoflagellate and diatom age calibrations for the northeastern North Atlantic

This study presents a new Miocene biostratigraphic synthesis for the high-latitude northeastern North Atlantic region. Via correlations to the bio-magnetostratigraphy and oxygen isotope records of Ocean Drilling Program and Deep Sea Drilling Project Sites, the ages of shallower North Sea deposits have been better constrained. The result has been an improved precision and documentation of the age designations of the existing North Sea foraminiferal zonal boundaries of King (1989) and Gradstein and Bäckström (1996). All calibrations have been updated to the Astronomically Tuned Neogene Time Scale (ATNTS) of Lourens et al. (2004). This improved Miocene biozonation has been achieved through: the updating of age calibrations for key microfossil bioevents, identification of new events, and integration of new biostratigraphic data from a foraminiferal analysis of commercial wells in the North Sea and Norwegian Sea. The new zonation has been successfully applied to two commercial wells and an onshore research borehole. At these high latitudes, where standard zonal markers are often absent, integration of microfossil groups significantly improves temporal resolution. The new zonation comprises 11 Nordic Miocene (NM) Zones with an average duration of 1 to 2 million years. This multi-group combination of a total of 92 bioevents (70 foraminifers and bolboformids; 16 dinoflagellate cysts and acritarchs; 6 marine diatoms) facilitates zonal identification throughout the Nordic Atlantic region. With the highest proportion of events being of calcareous walled microfossils, this zonation is primarily suited to micropaleontologists. A correlation of this Miocene biostratigraphy with a re-calibrated oxygen isotope record for DSDP Site 608 suggests a strong correlation between Miocene planktonic microfossil turnover rates and the inferred paleoclimatic trends. Benthic foraminifera zonal boundaries appear to often coincide with Miocene global sequence boundaries. The biostratigraphic record is punctuated by four main stratigraphic hiati which show variation in their geographic and temporal extent. These are related to the following regional unconformities: basal Neogene, Lower/Middle Miocene ("mid-Miocene unconformity"), basal Upper Miocene and basal Messinian unconformities. Further coring of Neogene sections in the North Sea and Norwegian Sea may better constrain their extent and their effect on the biostratigraphic record.