Composition of sediments, hydrothermal manifestations, interstitial waters, and aeolian material from the TAG Hydrothermal Field and Central Atlantic

The book is devoted to regularities of spatial distribution, mineralogy and geochemistry of hydrothermal and hydrothermal-sedimentary manifestations of the Mid-Atlantic Ridge rift zone.

Abundance of microzooplankton in surface waters of the East Atlantic and Mediterranean in August-September 1970

Abundance of microzooplankton was studied from August to October 1970 in a ship laboratory using the method of concentration of water samples by filtration and then counting living organisms under a microscope. The main groups (in order of decreasing abundance) were as follows: infusorians, nauplii, copepodids, radiolarians, appendicularians, and some others (rotifers, worm and mollusk larvae). Concentration of infusorians rarely exceeded 100 #/l, possibly an underestimate. Nauplii often numbered 20 to 30 #/l. Study of vertical distribution of microzooplankton showed that peak concentrations in the Mediterranean Sea were at depth of 20-30 m regardless of day time. There were 2 peaks in the Atlantic Ocean, one in the 10- to 20-m layer, the other in the 50- to 75-m layer.

Oligocene to middle Miocene radiolarians of Maud Rise, Weddell Sea

At Sites 689 and 690, drilled during ODP (Ocean Drilling Program) Leg 113 on the Maud Rise (southeast Weddell Sea), moderately to well preserved radiolarian assemblages were obtained from continuously recovered upper Oligocene and Neogene sequences. Based on radiolarian investigations, a biostratigraphic zonation for a time interval covering the late Oligocene to the middle Miocene is proposed. The radiolarian zonation comprises 10 zones. Five zones are new, and five zones previously defined by Chen (1975) were modified. The zones and the ranges of the nominate species are directly calibrated with a geomagnetic polarity record. This is the first attempt at a direct correlation of late Oligocene to middle Miocene radiolarian zones with the geomagnetic time scale. Six hiatuses were delineated in the studied upper Oligocene to middle Miocene sections. One major hiatus, spanning ca. 6 m.y., is between the upper Oligocene and the lower Miocene sequences. Another important hiatus separates the lower and middle Miocene sediments. As a base for the biostratigraphic investigations, a detailed taxonomic study of the recovered radiolarian taxa is achieved. Three new radiolarian species that occur in upper Oligocene and lower Miocene sediments are described (Cycladophora antiqua, Cyrtocapsella robusta, and Velicucullus altus).

Distribution of biological, anthropogenic, and volcanic constituents in the San Francisco Bay Coastal System

Although conventional sediment parameters (mean grain size, sorting, and skewness) and provenance have typically been used to infer sediment transport pathways, most freshwater, brackish, and marine environments are also characterized by abundant sediment constituents of biological, and possibly anthropogenic and volcanic, origin that can provide additional insight into local sedimentary processes. The biota will be spatially distributed according to its response to environmental parameters such as water temperature, salinity, dissolved oxygen, organic carbon content, grain size, and intensity of currents and tidal flow, whereas the presence of anthropogenic and volcanic constituents will reflect proximity to source areas and whether they are fluvially- or aerially-transported. Because each of these constituents have a unique environmental signature, they are a more precise proxy for that source area than the conventional sedimentary process indicators. This San Francisco Bay Coastal System study demonstrates that by applying a multi-proxy approach, the primary sites of sediment transport can be identified. Many of these sites are far from where the constituents originated, showing that sediment transport is widespread in the region. Although not often used, identifying and interpreting the distribution of naturally-occurring and allochthonous biologic, anthropogenic, and volcanic sediment constituents is a powerful tool to aid in the investigation of sediment transport pathways in other coastal systems.

Foraminifer, epifauna and infauna abundance of ODP Hole 183-1138A and core ELT54.007-PC, Kerguelen Plateau

Late Campanian and Maastrichtian benthic foraminifers are recorded from 12 samples from Ocean Drilling Program (ODP) Leg 183, Cores 183-1138A-52R through 63R (487.3-602.4 meters below seafloor), Kerguelen Plateau, Indian Ocean, and Danian benthics from one sample in the same section. The entire late Maastrichtian foraminifer fauna is noted from a dredge sample 220 km to the north. The structure of the fauna is compared with the Cenomanian-Turonian of the nearby Eltanin core E54-7. Faunas are reviewed in terms of planktonic percentage, composition, epifaunal/infaunal ratios, and dominance/diversity indices. The region was in the cool Austral Faunal Province through the Campanian-Maastrichtian and was probably warmer in the Cenomanian-Turonian. The ODP section is now 1600 meters below sea level and has subsided several hundred meters since deposition. Its fauna is dominated by epifaunal species suggesting little influence of upwelling. The dredge location has subsided little. Its fauna has a high infaunal content consistent with significant influence of upwelling near the plateau edge. The dominant benthic species remain constant through the ODP Cretaceous section, but subdominance changes, and the section is divided into three informal zones based on dominance/subdominance characteristics of the benthic fauna. Brief taxonomic comments are made on several species and some are figured.

Mineralogical, sedimentological and paleontological analyses of ODP Hole 127-797B upper Quarternary sediments

Nearly continuous cores of Quaternary fine-grained sediments with distinct dark-light colored cycles were recovered from Sites 794, 795, and 797 in the basinal parts of the Japan Sea during Leg 127. A comparison of gray value (darkness) profiles supplemented by visual inspection of core photographs between sites indicated that most of the dark and light layers were correlatable between sites, and that two of the dark layers lie close to adjacent marker ash layers. These observations indicate that deposition of dark and light layers resulted from basin-wide synchronous events. In order to understand the origin of these dark-light cycles, petrographical, mineralogical, compositional, and paleontological studies were carried out on closely spaced samples from the upper Quaternary sediments recovered from Site 797. Age model was constructed based on comparison between variation in diatom abundance and the standard oxygen isotope curve of Imbrie et al. (1984), the latter was interpolated between the five age controlled levels established at Site 797. The two curves show similar patterns which enabled us to "tune" the sediment ages to the oxygen isotope stages. We have to use variation in diatom abundance as a substitute for oxygen isotope curve since oxygen isotopic data are not available at the studied sites. Bottom water oxygenation conditions were estimated based on two criteria: (1) the degree of lamina preservation and (2) the ratio of Corg to Stot. The surface water productivity was deduced from the Corg and biogenic silica content. Results suggest that the bottom water oxygenation level and the surface water productivity varied significantly in response to the glacial-interglacial cycles. Glacio-eustatic sea-level changes and subsequent changes in water circulation in the Japan Sea appear to have been responsible for these variations and consequent changes in sediment composition throughout the Quaternary.

Pollen distribution in marine sediment samples along the south-western African coast

The distribution of pollen in marine sediments is used to reconstruct pathways of terrigenous input to the oceans and provides a record of vegetation change on adjacent continents. The wind transport routes of aeolian pollen is comprehensively illustrated by clusters of trajectories. Isobaric, 4-day backward trajectories are calculated using the modelled wind-field of ECHAM3, and are clustered on a seasonal basis to estimate the main pathways of aeolian particles to sites of marine cores in the south-eastern Atlantic. Trajectories and clusters based on the modelled wind-field of the Last Glacial Maximum hardly differ from those of the present-day. Trajectory clusters show three regional, and two seasonal patterns, determining the pathways of aeolian pollen transport into the south-eastern Atlantic ocean. Mainly, transport out of the continent occurs during austral fall and winter, when easterly and south-easterly winds prevail. South of 25°S, winds blow mostly from the west and southwest, and aeolian terrestrial input is very low. Generally, a good latitudinal correspondence exists between the distribution patterns of pollen in marine surface sediments and the occurrence of the source plants on the adjacent continent. The northern Angola Basin receives pollen and spores from the Congolian and Zambezian forests mainly through river discharge. The Zambezian vegetation zone is the main source area for wind-blown pollen in sediments of the Angola Basin, while the semi-desert and desert areas are the main sources for pollen in sediments of the Walvis Basin and on the Walvis Ridge. A transect of six marine pollen records along the south-western African coast indicates considerable changes in the vegetation of southern Africa between glacial and interglacial periods. Important changes in the vegetation are the decline of forests in equatorial Africa and the north of southern Africa and a northward shift of winter rain vegetation along the western escarpment.

Benthic foraminifera in Tertiary sediments of DSDP Leg 90 holes

Eocene through Pliocene benthic foraminifers were examined from seven sites located at middle and lower bathyal depths on the Lord Howe Rise in the Tasman Sea, from another site at lower bathyal depths in the Coral Sea, and from a site in the intermediate-depth, hemipelagic province of the Chatham Rise, east of southern New Zealand. Age-related, depth-related, and bioprovincial faunal variations are documented in this chapter. One new species, Rectuvigerina tasmana, is named. The paleoecologic indications of several key groups, including the miliolids, uvigerinids, nuttallitids, and cibicidids, are combined with sedimentologic and stable isotopic tracers to interpret paleoceanographic changes in the Tasman Sea. Because the total stratigraphic ranges of many bathyal benthic foraminifers are not yet known, most endpoints in the Tasman Sea are considered ecologically controlled events. The disappearances of Uvigerina rippensis and Cibicidoidesparki and the first appearances of U. pigmaea, Sphaeroidina bulloides, and Rotaliatina sulcigera at the Eocene/Oligocene boundary can be considered evolutionary events, as also can the first appearance of Cibicides wuellerstorfi in Zone NN5. Species which are restricted to the lower bathyal zone except during discrete pulses, most of which are related to the development of glacial conditions, include Melonis pompilioides, M. sphaeroides, Pullenia quinqueloba, Nuttallides umbonifera, and U. hispido-costata. Middle bathyal indigenes include U. spinulosa, U. gemmaeformis, Ehrenbergina marwicki, R. sulcigera, and all rectuvigerinids except Rectuvigerina spinea. Although the miliolids first occurred at lower bathyal depths, they were more common in the middle bathyal zone. Although the Neogene hispido-costate uvigerinids first developed at lower bathyal depths and at higher middle latitude sites, in the later Neogene this group migrated to shallower depths and became predominant also in the middle bathyal zone. Despite the relatively similar sedimentologic settings at the six middle bathyal Tasman sites, there was extensive intrageneric and intraspecific geographic variation. Mililiolids, strongly ornamented brizalinids, bolivinitids, Bulimina aculeata, Osangularia culter, and strongly porous morphotypes were more common at higher latitudes. Osangularia bengalensis, striate brizalinids such as Brizalina subaenariensis, Gaudryina solida, osangularids in general, and finely porous morphotypes were more common in the subtropics. There was strong covariance between faunas at lower middle latitude, lower bathyal Site 591, and higher middle latitude, middle bathyal Site 593. The following oceanographic history of the Tasman Sea is proposed; using the stable isotopic record as evidence for glacials and examining the ecologic correlations between (1) miliolids and carbonate saturation, (2) nuttallitids and undersaturated, cooled, or "new" water masses, (3) uvigerinids with high organic carbon in the sediment and high rates of sediment accumulation, and (4) cibicidids and terrestrial organic carbon. The glacial located near the Eocene/Oligocene boundary is characterized by the penetration of cooler, more corrosive waters at intermediate depths in high southern latitudes. This may have caused overturn, upwelling pulses, in other Tasman areas. The development of Neogenelike conditions began in the late Oligocene (Zone NP24/NP25) with the evolution of several common Neogene species. A large number of Paleogene benthics disappeared gradually through the course of the early Miocene, which was not well preserved at any Tasman site. Corrosive conditions shallowed into the middle bathyal zone in several pulses during the early Miocene. The development of glacial conditions in the middle Miocene was accompanied by major changes throughout the Tasman Sea. Sediment accumulation rates increased and high-productivity faunas and corrosive conditions developed at all but the lowest-latitude Site 588. This increase in productivity and accumulation rate is attributed to the eutrophication of Antarctic water masses feeding Tasman current systems, as well as to invigorated circulation in general. It overlaps with the beginning of the Pacific High-productivity Episode (10-5 Ma). During the latest Miocene glacial episode, corrosive conditions developed at lower bathyal depths, while cooler water and lower nutrient levels shallowed to middle bathyal depths. Lower input of terrestrial organic carbon may be related to the lower nutrient levels of this time and to the termination of the Pacific High-productivity Episode. The moderate glacial episode during the mid-Pliocene (Zone NN15/NN16, ~3.2 Ma) corresponds to a decline in sediment accumulation rates and a reorganization of faunas unlike that of all other times. New genera proliferate and indices for cool, noncorrosive conditions and high organic carbon expand throughout the middle bathyal zone coeval with the sedimentation rate decreases. By the latest Pliocene (about 2.5 Ma), however, during another glacial episode, faunal patterns typical of this and later glacials develop throughout the Tasman Sea. Benthic foraminiferal patterns suggest increased input of terrestrial organic matter to Tasman Sea sediments during this episode and during later glacials.

Cretaceous ostracodes from Wombat and Exmouth Plateau

The Cretaceous ostracodes species recognized on Leg 122 represent elements of South Gondwanan faunistic province. In Lower and middle Cretaceous cores, ostracodes species present were originally described from South Africa and in cores from Deep Sea Drilling Project Leg 36 (Falkland Plateau): Arculicythere tumida, Bythocypris? cf. nodosa, 'Bythocypris' cf. strogylae, Collosaboris? stanleyensis, Cytherella bensoni, Majungaella nematis, Robsoniella cf. falklandensis and Pirileberis aff. mkuzensis. In Upper Cretaceous levels, the Australian species Apateloschizocythere geniculata, Bairdia austracretacea, Cytherella cf. atypica, Cytherella cf. jonesi, Cytherelloidea cf. carnarvonensis, Cytherelloidea cf. colemani, Karsteneis aspericava, and Trachyleberis anteplana were found.

Late Miocene to Early Pliocene radiolarians from ODP Hole 178-1095B

Early Pliocene to middle late Miocene hemipelagic and distal turbidite sediments from Hole 1095B, near the Antarctic Peninsula, yield moderately abundant, moderately well preserved radiolarian faunas and other biosiliceous material (diatoms, silicoflagellates, and sponge spicules). Preservation characteristics, however, vary strongly even between closely related samples, and there are many intervals of poor preservation. In the 140- to 460-meters below seafloor interval studied, it was possible to identify the following standard Southern Ocean radiolarian zones: Upsilon, Tau, Amphymenium challengerae, Acrosphaera? labrata, Siphonosphaera vesuvius, and upper Acrosphaera australis (total age range ~4-10 Ma). Some normally common radiolarian groups, such as actinommids, are unusually rare in the studied material, and the relative ranges of several individual species, such as Acrosphaera labrata vs. A. australis, appear to be somewhat anomalous. These observations imply that the ranges of taxa in this section may be somewhat diachronous, due to either local ecologic factors and/or the highly variable preservation of the faunas. Thus, the ages of events reported are probably only approximate, although they are still useful for constraining the age of sediments in this section.

Petrology, geochemistry, and geodynamics at DSDP Hole 66-493

At Site 493, DSDP Leg 66, dioritic basement was reached below lower Miocene (NN1 Zone, 22-24 Ma) terrigenous sediments. Petrographical, mineralogical (including microprobe analyses), and chemical features of the dioritic rocks reveal their magmatic affinity with the calc-alkaline series. Furthermore, their radiometric age (35.3 m.y.) links the basement to the Sierra Madre Occidental in Mexico and to mid-Tertiary volcanic arcs in Central America. The presence of Oligocene diorite 50 km from the trench axis confirms the truncation of the south Mexico margin, which we explain as the result of a 650 to 800 km left-lateral displacement of Central America relative to North America. Truncation must have occurred in the late Miocene, after the diorite intrusion and prior to the present subduction.

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.

Pollen analysis of surface sediment off northwest Africa

Over 100 samples of recent surface sediments from the bottomn of the Atlantic Ocean offshore NW Africa between 34° and 6° N have been analysed palynologically. The objective of this study was to reveal the relation between source areas, transport systems, and resulting distribution patterns of pollen and spores in marine sediments off NW Africa, in order to lay a sound foundation for the interpretation of pollen records of marine cores from this area. The clear zonation of the NW-African vegetation (due to the distinct climatic gradient) is helpful in determining main source areas, and the presence of some major wind belts facilitates the registration of the average course of wind trajectories. The present circulation pattern is driven by the intertropical front (ITCZ) which shifts over the continent between c. 22° N (summer position) and c. 4° N (winter position) in the course of the year. Determination of the period of main pollen release and the average atmospheric circulation pattern effective at that time of the years is of prime importance. The distribution patterns in recent marine sediments of pollen of a series of genera and families appear to record climatological/ecological variables, such as the trajectory of the NE trade, January trades, African Easterly Jet (Saharan Air Layer), the northernmost and southernmost position of the intertropical convergence zone, and the extent and latitudinal situation of the NW-African vegetation belt. Pollen analysis of a series of dated deep-sea cores taken between c. 35° and the equator off NW African enable the construction of paleo-distribution maps for time slices of the past, forming a register of paleoclimatological/paleoecological information.

Sedimentary cycles on the Exmouth Plateau

Sedimentary cycles are observed in the nearly complete Lower Cretaceous to Eocene pelagic carbonates at Site 762 on the Exmouth Plateau off northwest Australia. The high-frequency cycles of variable clay and foraminifers in nannofossil chalk appear as color cycles repeating on a scale of centimeters to meters in thickness. Measured cycle thickness indicate that the dominant cycles appear to be related to the precession and obliquity periods. To evaluate the high-frequency variance observed on the gamma-ray curve, spectral analysis of the log was performed on two intervals: 260 to 365 mbsf in the Cenozoic, and 555 to 685 mbsf in the Mesozoic. Average Cenozoic sedimentation rates of 10.5 m/m.y. are high enough to show that variance is present in the full suite of eccentricity bands (413-123-95 k.y.). Spectral analysis of the Mesozoic section failed to produce dominant peaks that could be correlated to predicted orbital periods. The bioturbation observed in the cores in this interval may be responsible for diluting the signal and producing high-frequency noise, which is manifested in the spectra as low, broad amplitude peaks. Orbital forcing may be affecting sedimentation on the Exmouth Plateau by influencing cycles of increased carbonate production or dissolution. Alternatively, clay abundance cycles may be related to eolian deposition during cycles of increased aridity in western Australia. Four low-frequency events were also identified at Site 762 from the core and log data. The duration of these events is approximately 13 m.y., and the conformable boundaries of these sedimentary cycles correlate with observed nondepositional surfaces in other wells in western Australia. The causal mechanism for the onset of these events may be eustatic, but alternatively may be regional tectonism with associated circulation pattern changes.