Distribution of calcareous nannofossils in upper Cretaceous and Cenozoic sediments of the Kerguelen Plateau

ODP Leg 119 drilled 11 sites on the Kerguelen Plateau (southern Indian Ocean) and Prydz Bay (East Antarctica). Upper Pliocene through Quaternary sediments were recovered at Site 736 on the northern Kerguelen Plateau; calcareous nannofossils occurred in only a few samples. Over 700 m of middle Eocene through Quaternary sediments was cored at Site 737 on the northern Kerguelen Plateau, and calcareous nannofossils are abundant in the middle Eocene through the middle Miocene sediments. Nearly 500 m of sediments ranging from the lower Turanian to the Quaternary was recovered at Site 738 on the southern Kerguelen Plateau; calcareous nannofossils are abundant from the Miocene downward. Calcareous nannofossils are also abundant in the upper Eocene through Miocene section from Site 744 on the southern Kerguelen Plateau. Except for Core 119-746A-13H, the Neogene sequences drilled at deep-water Sites 745 and 746 off the southern Kerguelen Plateau are devoid of calcareous nannofossils. Occurrences of calcareous nannofossils were generally rare and sporadic at Sites 739 and 742 in Prydz Bay and suggest that the diamictite sequences recovered is as old as middle Eocene-early Oligocene age. Other sites drilled in Prydz Bay (Sites 740, 741, and 743) did not yield calcareous nannofossils. Species diversity of calcareous nannofossils was low (about a dozen) in the southern Indian Ocean in the Late Cretaceous. High-latitude nanno floral characteristics are apparent after the Cretaceous/Tertiary boundary extinctions. Cold climatic conditions limited Oligocene calcareous nannofossil assemblages to fewer than a dozen species, and extinctions of species generally were not compensated by originations of new species. Only a few species of calcareous nannofossils were found in the Miocene sequences, in which Coccolithuspelagicus and one or two species of Reticulofenestra exhibit extreme (0%-100%) fluctuations in assemblage dominance, and these fluctuations may reflect rapid fluctuations in the surface-water temperatures. Further deterioration of climate in the late Neogene essentially excluded calcareous nannoplankton from the Southern Ocean. Significantly warmer water conditions during part of the early-middle Pleistocene were inferred by a few lower-middle Pleistocene calcareous nannofossil species found on the Kerguelen Plateau. The calcareous nannofossil zonation of Roth (1978 doi:10.2973/dsdp.proc.44.134.1978) can be applied to the Upper Cretaceous section recovered at Site 738, and the zonation of Okada and Bukry (1980 doi:10.1016/0377-8398(80)90016-X) can be applied without much difficulty to the Paleocene to middle Eocene sequences from the Kerguelen Plateau. However, some conventional upper Paleogene markers are not useful for southern high latitudes, whereas a few nonconventional species events are useful for subdividing the upper Paleogene sequences. The latter species events include the first occurrence (FO) of Reticulofenestra reticulata, the FO and last occurrence (LO) of Reticulofenestra oamaruensis, the LO of Isthmolithus recurvus, and the LO of Chiasmolithus altus. As the Neogene sequences from the southern Indian Ocean contain only a few long-ranging, cold-water species, or are devoid of coccoliths, calcareous nannofossil zonations remain virtually unworkable for the Neogene in the high-latitude southern Indian Ocean as in other sectors of the Southern Ocean.

Heavy mineral composition of bottom sediments from the South China Sea

This paper presents results of investigations of unusual carbonate formations found in bottom sediments of the South China Sea shelf. These sediments were sampled from a deep fracture found by geophysical methods. According to gas-geochemical data there are high concentrations of methane, hydrogen and carbon dioxide in bottom waters of this area. The carbonate formations were defined as calcium siderite or siderodot by roentgenostructural, microprobe, atomic absorption, and thermal analyses, asawellas infrared spectroscopy. Formation of this mineral results from carbon dioxide and methane flows through bottom sediments.

Diatom studies in surface and downcore sediments off southern Sumatra and Java

A wealth of sedimentary records aimed at reconstructing late Quaternary changes in productivity and temperature have been devoted to understanding linkages between the Indo-Pacific Warm Pool (IPWP) and other distant oceanic areas. Most of these reconstructions are based, however, on biogeochemical and sedimentological proxies, with comparatively less attention devoted to microfossils. A high-resolution (<1 ka) study of diatom concentrations and the community at site GeoB10038-4, recovered off southern Sumatra (ca. 6°S, 103°E), closely tracks the variations of diatom concentrations in the westernmost IPWP during the last glacial-interglacial cycle. The diatom record provides evidence that diatom paleoproductivity was highest during interglacials, primarily due to the input of lithogenics and nutrients following the rise in sea level after full glacials. In addition, the co-variation of total diatom concentration and Northern Hemisphere forcing for Marine Isotope Stage 5 suggests a direct response of diatom productivity and upwelling intensity to boreal summer insolation. Temporal shifts of the diverse diatom community at site GeoB10038-4 correspond well with the present-day seasonal monsoon pattern and the strengthening and weakening phases of upwelling along the southern coast of Sumatra. Resting spores of Chaetoceros, typical of nutrient-rich waters, were dominant during periods of highest diatom paleoproductivity and responded to the strengthening of the SE monsoon, while diatoms of oligotrophic to mesotrophic waters characterized intermonsoon periods. The close correspondence between the dominance of upwelling diatoms and the boreal summer insolation resembles the present-day dynamics of diatom production. The observed interglacial highs and glacial lows of diatom productivity at site GeoB10038-4 is a unique pattern in the late Quaternary tropics.

Planktonic foraminifer stratigraphy of late Pliocene sediments from ODP Hole 167-1021C

This report is an initial investigation of the planktonic foraminifers from the late Pliocene of Ocean Drilling Program Hole 1021C. Planktonic foraminifer assemblages show fair preservation in many samples. Assemblages are quantitatively dominated by Globigerina bulloides, dextral coiling Neogloboquadrina atlantica, and Globorotalia inflata and alternate between cool temperate and subarctic conditions.

Organic geochemistry of lower Cretaceous sediments at DSDP Hole 77-535

At Site 535, the four lithologic units of Cretaceous age are controlled by two types of sedimentologic facies: (1) the massive light-colored limestones or marly limestones in which the total organic carbon (TOC) content is low and the organic matter more or less oxidized and (2) laminated dark facies in which the TOC content is higher and associated with a well-preserved organic matter of Type II origin. Very little typical Type III organic matter occurs in the whole series from late Berriasian to Aptian and Cenomanian. Fluctuations from oxidizing to reducing environments of deposition are proposed to account for the variations in properties of the Type II organic matter between the different facies. Dark laminated layers are good but immature potential source rocks: petroleum potential is often higher than 2 kg HC/t of rock.

Chemical composition and accumulation rates of chemical elements in metalliferous sediments from axial zones of the East Pacific Rise and the Mid-Atlantic Ridge

In the monograph metalliferous sediments of the East Pacific Rise near 21°S are under consideration. Distribution trends of chemical, mineral and grain size compositions of metalliferous sediments accumulated near the axis of this ultrafast spreading segment of the EPR are shown. On the basis of lithological and geochemical investigations spatial and temporal variations of hydrothermal activity are estimated. Migration rates of hydrothermal fields along the spreading axis are calculated. The model of cyclic hydrothermal process is suggested as a result of tectono-magmatic development of the spreding centre.

Migration of C1 to C8 volatile organic compounds in sediments at DSDP Hole 75-530A

The distribution of C1 to C8 hydrocarbons in sediment samples from DSDP Leg 75, Hole 530A, indicates that significant amounts of methane and ethane have migrated from organic-rich to organic-lean shales in close proximity. Most compounds larger than ethane are not migrating out of black shales, where they occur in high concentrations. These results lead to a general model for assessing migration. In addition, three shale types are identified on the basis of organic carbon and pyrolysis products and patterns.

Pore water methane characteristics and sulphate reduction rates of ODP Leg 164 sediments

Anaerobic methane oxidation (AMO) was characterized in sediment cores from the Blake Ridge collected during Ocean Drilling Program (ODP) Leg 164. Three independent lines of evidence support the occurrence and scale of AMO at Sites 994 and 995. First, concentration depth profiles of methane from Hole 995B exhibit a region of upward concavity suggestive of methane consumption. Diagenetic modeling of the concentration profile indicates a 1.85-m-thick zone of AMO centered at 21.22 mbsf, with a peak rate of 12.4 nM/d. Second, subsurface maxima in tracer-based sulfate reduction rates from Holes 994B and 995B were observed at depths that coincide with the model-predicted AMO zone. The subsurface zone of sulfate reduction was 2 m thick and had a depth integrated rate that compared favorably to that of AMO (1.3 vs. 1.1 nmol/cm**2/d, respectively). These features suggest close coupling of AMO and sulfate reduction in the Blake Ridge sediments. Third, measured d13CH4 values are lightest at the point of peak model-predicted methane oxidation and become increasingly 13C-enriched with decreasing sediment depth, consistent with kinetic isotope fractionation during bacterially mediated methane oxidation. The isotopic data predict a somewhat (60 cm) shallower maximum depth of methane oxidation than do the model and sulfate reduction data.

Mineralogy, geochemistry and selected chemical formulas of sediments from ODP Holes 161-986B and 161-977A

Upper Miocene to Pleistocene hemipelagites and resedimented facies recovered at Holes 976B and 977A (Leg 161) in the Alboran Basin consist mainly of biogenic and detrital components, with a minor contribution of neoformed mineral phases. Diagenetic processes have not obliterated the primary deposition signal, and therefore detrital components (quartz, feldspar, detrital dolomite, rock fragments, and clays) provide information about source rocks and provenances. No major bulk or clay mineralogy differences were recognized between resedimented and hemipelagic facies; in fact, similar mineral assemblages in both types of facies suggest common source rocks. However, mineral abundance fluctuations can be related to climate variations and tectonic factors, as the main controls of sediment fill of this basin. A marked increase in smectites in Messinian sediments suggests an extensive development of soils during that time, probably favored by the alternation of wet and dry climate episodes and the relative aridification of the Mediterranean borderlands. A notable increase in detrital components suggests a sea-level fall and/or tectonic uplift during the late Pliocene. The significant increase in detrital dolomite in the uppermost Pliocene deposits suggests the uplift of dolomite-rich rocks as source areas. Mineral components in Pleistocene sediments indicate increasing tectonic stability, and clay-mineral fluctuations during the Pleistocene can be related not only to tectonic events, but also to alternating cooling and warming periods.

3He/4He and 4He/20Ne ratios in pore water and gas in Pacific deep-sea sediments

We have measured the 3He/3He and 3He/20 Ne ratios of thirty-nine pore water and gas samples in deep-sea sediments collected at twelve sites on the Pacific Ocean bottom during the cruises of Deep Sea Drilling Project Legs 87, 89, 90 and 92. The 3He/4He and 4He/20Ne ratios vary from 0.000000215 to 0.00000165 and from 0.29 to 20, respectively. He in the sample is composed of four components: (1) atmospheric He dissolved in seawater; (2) atmospheric He with mantle-derived He in Pacific bottom water; (3) in situ radiogenic He in the sediment; and (4) crustal He in the basement rock. Assuming that the 20Ne contents are constant with the value of seawater, the depth variations in the 4He/20Ne ratios at five Sites, 583D, 594, 597A, 598A and 504B, may provide useful information on 4He flux at the ocean bottom. The estimated 4He fluxes vary from 2000 to 40000 atoms cm**-2 s**-1 and are one to three orders of magnitude less than those calculated from the excess He in deep ocean water. An overall similarity between the geographical distribution of the 3He/4He ratios and heat flow data is found in the study area, between the East Pacific Rise across the Pacific Ocean and the Japanese Islands. The tendency is well explained by a conventional sea-floor spreading model.

Calcareous nannofossils in sediments of the southeast Pacific

This study provides the first detailed documentation of calcareous nannofossil assemblages in Eocene subantarctic Eltanin piston cores recovered from the southeast Pacific Ocean. These Eltanin cores are important because they have been reported to contain ice-rafted quartz. The present study confirms early and middle Eocene ages for the cores and dates them more precisely using calcareous nannofossils. Semiquantitative study of the nannoflora indicates that they are of a warmer water character than those from the higher latitudes (such as Falkland Plateau, Maud Rise, and Kerguelen Plateau). This study concludes that it is unlikely for the ice-rafted quartz in the Eocene sections to be downcore contaminants from the overlying Neogene sediment and suggests that the grains are probably the result of Eocene ice-rafting from Antarctica when the Drake Passage was closed and water circulation patterns were different from those of today.

Lead and strontium isotopic composition of some metalliferous and pelagic sediments and basalts at DSDP Leg 70 Holes

In recent years, metalliferous sediments have been discovered overlying newly generated oceanic crust in the East Pacific, North Atlantic, Indian Ocean, Red Sea, Gulf of Aden, and elsewhere (e.g., Boström, 1973; Lalou et al., 1977; Bischoff, 1969; Boström and Fisher, 1971; Cann et al., 1977, respectively). Such material has also been recovered by drilling from sediments lying upon older oceanic crust (Boström et al., 1972, 1976; Horowitz and Cronan, 1976). Hydrothermal circulation of seawater at a spreading ridge results in the leaching of Fe, Mn, and possibly other elements from the basaltic volcanic layer and their transport and discharge into ocean bottom waters, whereupon fine-grained Fe-Mn-rich precipitates form and settle into the ambient sediment (cf. Corliss, 1971; Dasch et al., 1971; Spooner and Fyfe, 1973; Bischoff and Dickson, 1975; Heath and Dymond, 1977; Corliss et al., 1979, Edmond et al., 1979). Mn-rich crusts have also been recovered from active ridges and are inferred to have formed in the vicinity of hydrothermal discharge areas (Scott et al., 1974; Moore and Vogt, 1976; Corliss et al., 1978; Hoffert et al., 1978). The source of the trace elements in the metalliferous deposits is generally not clear. They may be derived from seawater by adsorption onto the precipitates or crusts, or from hydrothermal solutions which have leached them from the basalts. Pb, however, can be used as a geochemical tracer because of the known isotopic compositional differences between oceanic basalts and seawater. Isotopic investigations of Pb in ferruginous sediments from the East Pacific have shown that it has been derived partly or mostly from a basaltic source (Bender et al., 1971; Dasch et al., 1971; Dymond et al., 1973). In the present study, Pb isotopic analyses have been made of a suite of metalliferous sediments (nontronite, Mn-oxide crust, Mn-Fe-oxide mud), pelagic sediments, and basalts from the Galapagos mounds area. The main purposes of the Pb study were to determine the source or sources of Pb in the metalliferous sediments, and whether or not stratigraphic variations exist in the isòtopic composition of Pb in the sediments.

Phosphorus partition and acumulation rates in sediments of ODP Legs 130 and 138

Understanding phosphorus (P) geochemistry and burial in oceanic sediments is important because of the role of P for modulating oceanic productivity on long timescales. We investigated P geochemistry in seven equatorial Pacific sites over the last 53 Ma, using a sequential extraction technique to elucidate sedimentary P composition and P diagenesis within the sediments. The dominant P-bearing component in these sediments is authigenic P (61-86% of total P), followed in order of relative dominance by iron-bound P (7-17%), organic P (3-12%), adsorbed P (2-9%), and detrital P (0-1%). Clear temporal trends in P component composition exist. Organic P decreases rapidly in younger sediments in the eastern Pacific (the only sites with high sample resolution in the younger intervals), from a mean concentration of 2.3 µmol P/g sediment in the 0-1 Ma interval to 0.4 µmol/g in the 5- 6 Ma interval. Over this same time interval, decreases are also observed for iron-bound P (from 2.1 to 1.1 µmol P/g) and adsorbed P (from 1.5 to 0.7 µmol P/g). These decreases are in contrast to increases in authigenic P (from 6.0-9.6 µmol P/g) and no significant changes in detrital P (0.1 µmol P/g) and total P (12 µmol P/g). These temporal trends in P geochemistry suggest that (1) organic matter, the principal shuttle of P to the seafloor, is regenerated in sediments and releases associated P to interstitial waters, (2) P associated with iron-rich oxyhydroxides is released to interstitial waters upon microbial iron reduction, (3) the decrease in adsorbed P with age and depth probably indicates a similar decrease in interstitial water P concentrations, and (4) carbonate fluorapatite (CFA), or another authigenic P-bearing phase, precipitates due to the release of P from organic matter and iron oxyhydroxides and becomes an increasingly significant P sink with age and depth. The reorganization of P between various sedimentary pools, and its eventual incorporation in CFA, has been recognized in a variety of continental margin environments, but this is the first time these processes have been revealed in deep-sea sediments. Phosphorus accumulation rate data from this study and others indicates that the global pre-anthropogenic input rate of P to the ocean (20x10**10 mol P/yr) is about a factor of four times higher than previously thought, supporting recent suggestions that the residence time of P in the oceans may be as short as 10000-20000 years.

Geochemistry of ODP Sites 128-798 and 128-799 sediments

Nineteen trace elements, including seven rare earth elements (REE's), and 10 major and minor elements in 76 sediment samples from Sites 798 (Oki Ridge) and 799 (Yamato Trough) were determined by means of instrumental neutron activation analysis and X-ray fluorescence spectrometry. Most REE patterns (chondrite-normalized) of the sediments from both sites were nearly identical to the patterns of terrigenous materials. The cerium anomaly (slightly positive) frequently appeared in REE patterns of the sediments (200-750 mbsf) from Site 799. Cerium may be selectively incorporated into the sediments with hydrogenous manganese precipitation. However, the degree of the anomaly was not well correlated with manganese content, suggesting that cerium may behave as a trivalent REE (like the other REE's) during diagenesis while manganese is transported in the sediment column accompanied by reduction to a lower oxidation state. The Th/Sc ratio of the sediments from Sites 798 and 799 tended to decrease with penetration depth. Such a depth profile may indicate a decrease in basic volcanism activities from the Pliocene (Site 798) and Miocene (Site 799). The La/Yb ratio and degree of europium anomaly also varied with depth, which may imply that two or more components with different REE patterns were supplied throughout sedimentation at sites in the Japan Sea.