Sediment and pore fluid chemistry for IODP Sites 311-U1325 and 311-U1329

Analytical challenges in obtaining high quality measurements of rare earth elements (REEs) from small pore fluid volumes have limited the application of REEs as deep fluid geochemical tracers. Using a recently developed analytical technique, we analyzed REEs from pore fluids collected from Sites U1325 and U1329, drilled on the northern Cascadia margin during the Integrated Ocean Drilling Program (IODP) Expedition 311, to investigate the REE behavior during diagenesis and their utility as tracers of deep fluid migration. These sites were selected because they represent contrasting settings on an accretionary margin: a ponded basin at the toe of the margin, and the landward Tofino Basin near the shelf's edge. REE concentrations of pore fluid in the methanogenic zone at Sites U1325 and U1329 correlate positively with concentrations of dissolved organic carbon (DOC) and alkalinity. Fractionations across the REE series are driven by preferential complexation of the heavy REEs. Simultaneous enrichment of diagenetic indicators (DOC and alkalinity) and of REEs (in particular the heavy elements Ho to Lu), suggests that the heavy REEs are released during particulate organic carbon (POC) degradation and are subsequently chelated by DOC. REE concentrations are greater at Site U1325, a site where shorter residence times of POC in sulfate-bearing redox zones may enhance REE burial efficiency within sulfidic and methanogenic sediment zones where REE release ensues. Cross-plots of La concentrations versus Cl, Li and Sr delineate a distinct field for the deep fluids (z > 75 mbsf) at Site U1329, and indicate the presence of a fluid not observed at the other sites drilled on the Cascadia margin. Changes in REE patterns, the presence of a positive Eu anomaly, and other available geochemical data for this site suggest a complex hydrology and possible interaction with the igneous Crescent Terrane, located east of the drilled transect.

Grain size analyses of ODP Leg 178 sites

Sites 1095, 1096, and 1101 were drilled on the continental rise west of the Antarctic Peninsula (Fig. F1) to recover a continuous high-resolution record of Antarctic glaciation. Site 1095 is the subject of a short paper in this volume (Pudsey, 2001, doi:10.2973/odp.proc.sr.178.214.2001), whereas mass accumulation rates at the three sites are described by Wolf-Welling (2001, doi:10.2973/odp.proc.sr.178.223.2001) and ice-rafted debris at Site 1101 is discussed by Cowan (2001, doi:10.2973/odp.proc.sr.178.206.2001) This report documents grain-size data (sand and fine fraction) and the proportion of biogenic silica for the upper 300 m at Site 1095, the upper 250 m at Site 1096, and the whole 220 m at Site 1101.

Distribution of quaternary siliceous sponge spicules in sediments of ODP Leg 180 sites

Siliceous sponge spicules were found in Quaternary sediments recovered during drilling of Leg 180. The assemblage consists mainly of monaxon forms. Relative abundances of the various types are tabulated.

Age-depth correlations for Ontong Java Plateau sites

We used well logs, in some cases combined with shipboard physical properties measurements to make more complete profiles and to correlate between sites on the Ontong Java Plateau. By comparing sediment bulk density, velocity, and resistivity logs from adjacent holes at the same site, we showed that even subtle features of the well logs are reproducible and are caused by variations in sedimentation. With only minor amounts of biostratigraphic information, we could readily correlate these sedimentary features across the entire top of the Ontong Java Plateau, demonstrating that for most of the Neogene the top of the plateau is a single sedimentary province. We found it more difficult, but still possible, to correlate in detail sites from the top of the plateau to those drilled on the flanks. The pattern of sedimentation rate variation down the flank of the plateau cannot be interpreted as simply controlled by dissolution. Site 805, in particular, oscillates between accumulating sediment at roughly the same rate as cores on top of the Ontong Java Plateau, and accumulating sediment as slowly as Site 803, 200 m deeper in the water column. These oscillations do not match earlier reconstructions of central Pacific carbonate compensation depth variations.

Oligocene magnetostratigraphy for equatorial Pacific ODP Sites

An Oligocene magnetostratigraphy from ODP Sites 1218 and 1219 (Equatorial Pacific) has been obtained by measurements made on u-channel samples, augmented by about 221 discrete samples. U-channel samples were measured at 1 cm intervals and were stepwise demagnetized in alternating fields (AF) up to a maximum peak field of 80 mT. The magnetization directions were determined at 1 cm intervals by principal component analysis of demagnetization steps in the 20 to 60 mT peak field range. A similar treatment was carried out on the discrete samples, which confirmed the results obtained with u-channel measurements. Sites 1218 and 1219 were precisely correlated based on multisensor track, paleontological and shipboard magnetostratigraphic data; this correlation is substantiated by u-channel measurements. Although the magnetostratigraphy obtained from the u-channels is similar to the interpretation deduced from shipboard measurements based on blanket demagnetization at peak AF of 20 mT, the u-channel results are substantially more robust since many interpretative uncertainties are resolved by the stepwise demagnetization and higher stratigraphic resolution. The temporal resolution of u-channel-based magnetic stratigraphy in the Oligocene section of Sites 1218 and 1219 is better than 5 kyr, and it is therefore suitable for detection of brief polarity subchrons. However, in spite of the high resolution, we did not find any reversals corresponding to the numerous cryptochrons identified in this time span by Cande and Kent (1995, doi:10.1029/94JB03098).

Planktonic foraminifera abundance in sediments of ODP Leg 170 sites

From October to December in 1996, Sites 1039 through 1043 were drilled on the lower continental slope and the bottom of the Middle American Trench. Planktonic foraminifers were obtained from 377 samples of the total 487 examined. The Pliocene- to Pleistocene-age sediments of Sites 1039 and 1043 are continuous from Zones N19 through N23. At Sites 1039 and 1040, middle Miocene sediments are also continuous, encompassing Zones N8 through N12. The sequences of the upper part of Sites 1040, 1041, 1042, and 1043 are décollements, tentatively assignable to Zone N19 for Sites 1040, 1041, and 1042 and to Zone N22 for Site 1043. The oldest sediments of these sites are assigned to Zone N7 (latest early Miocene), ~17 Ma in age.

Major and trace element composition of sepentine muds and metabasic rocks of ODP Leg 195 and Leg 125 sites

New geochemical data on serpentinite muds and metamorphic clasts recovered during Ocean Drilling Program Legs 195 (Holes 1200A-1200E) and 125 (Holes 778A and 779A) provide insights into the proportions of rock types of various sources that compose the serpentinite mudflows and the fluid-rock interactions that predominate in these muds. We interpret the metamorphic rock fragments as derivatives of mostly metamorphosed mafic rocks from the descending Pacific oceanic crust. Based on their mid-ocean-ridge basalt (MORB)-like Al2O3, TiO2, CaO, Si/Mg, and rare earth element (REE) systematics, these metamorphic rocks are classified as metabasalts/metagabbros and, therefore, ~30-km depths represent an active subduction zone setting. The serpentinite muds from Holes 1200A and 1200E have slightly lower REE when compared to Hole 1200D, but overall the REE abundance levels range between 0.1-1 x chondrite (CI) levels. The chondrite-normalized patterns have [La/Sm]N ~ 2.3 and [Sm/Yb]N ~ 2. With the exception of one sample, the analyzed metamorphic clasts show flat to slightly depleted light REE patterns with 1.0-15 x CI levels, resembling MORBs. Visually, ~6 vol% of the serpentinized muds are composed of 'exotic' materials (metamorphic clasts [schists]). Our mixing calculations confirm this result and show that the serpentinite muds are produced by additions of ~5% metamafic materials (with flat and up to 10 x CI REE levels) to serpentinized peridotite clast material (with very low REE abundances and U-shaped chondrite-normalized patterns). The preferential incorporation of B, Cs, Rb, Li, As, Sb, and Ba into the structure of H2O-bearing sheet silicates (different than serpentine) in the Leg 125 and Leg 195 metamorphic clasts (chlorite, amphibole, and micas) have little effect on the overall fluid-mobile element (FME) enrichments in the serpentinite muds (average B = ~13 ppm; average Cs = ~0.05 ppm; average As = ~1.25 ppm). The extent of FME enrichment in the serpentinized muds is similar to that described for the serpentinized peridotites, both recording interaction with fluids very rich in B, Cs, and As originating from the subducting Pacific slab.

Interstitial-water chemistry of ODP Leg 113 sites

Variations in the distribution of major elements and stable oxygen isotopes in ODP Leg 113 pore water are not related to lithology and thus appear to be controlled by minor constituents. Petrographic observations and geochemical considerations indicate that alteration of calc-alkalic volcanic material dispersed in the sediment is an important process. A diagenetic reaction is constructed that involves transformation of volcanic glass into smectite, zeolite (represented by phillipsite), chert, and iron sulfide. Mass balance calculations reveal that alteration of less than 10% (volume) of volcanogenic material may account for the observed depletion of magnesium, potassium, and 18O and enrichment of calcium. Alteration of this amount of volcanic glass produces less than 4% (volume) of smectite and zeolite. Hence, mass balance is obtained without having to invoke unreasonable large amounts of volcanic matter or interactions between seawater and basement.

Strontium and neodymium concentrations and isotope compositions in fossil fish teeth and pore waters at ODP Sites 130-807 and 125-786

We analyzed Nd and Sr isotopic compositions of Neogene fossil fish teeth from two sites in the Pacific in order to determine the effect of cleaning protocols and burial diagenesis on the preservation of seawater isotopic values. Sr is incorporated into the teeth at the time of growth; thus Sr isotopes are potentially valuable for chemostratigraphy. Nd isotopes are potential conservative tracers of paleocirculation; however, Nd is incorporated post-mortem, and may record diagenetic pore waters rather than seawater. We evaluated samples from two sites (Site 807A, Ontong Java Plateau and Site 786A, Izu-Bonin Arc) that were exposed to similar bottom waters, but have distinct lithologies and pore water chemistries. The Sr isotopic values of the fish teeth appear to accurately reflect contemporaneous seawater at both sites. The excellent correlation between the Nd isotopic values of teeth from the two sites suggests that the Nd is incorporated while the teeth are in chemical equilibrium with seawater, and that the signal is preserved over geologic timescales and subsequent burial. These data also corroborate paleoseawater Nd isotopic compositions derived from Pacific ferromanganese crusts that were recovered from similar water depths (Ling et al., 1997; doi:10.1016/S0012-821X(96)00224-5). This corroboration strongly suggests that both materials preserve seawater Nd isotope values. Variations in Pacific deepwater e-Nd values are consistent with predictions for the shoaling of the Isthmus of Panama and the subsequent initiation of nonradiogenic North Atlantic Deep Water that entered the Pacific via the Antarctic Circumpolar Current.

Tomographic measurements of O. umbonatus and N. truempyi during the PETM and ETM-2 at ODP Sites 208-1262 and 208-1263

Predicting the impact of ongoing anthropogenic CO2 emissions on calcifying marine organisms is complex, owing to the synergy between direct changes (acidification) and indirect changes through climate change (e.g., warming, changes in ocean circulation, and deoxygenation). Laboratory experiments, particularly on longer-lived organisms, tend to be too short to reveal the potential of organisms to acclimatize, adapt, or evolve and usually do not incorporate multiple stressors. We studied two examples of rapid carbon release in the geological record, Eocene Thermal Maximum 2 (~53.2 Ma) and the Paleocene Eocene Thermal Maximum (PETM, ~55.5 Ma), the best analogs over the last 65 Ma for future ocean acidification related to high atmospheric CO2 levels. We use benthic foraminifers, which suffered severe extinction during the PETM, as a model group. Using synchrotron radiation X-ray tomographic microscopy, we reconstruct the calcification response of survivor species and find, contrary to expectations, that calcification significantly increased during the PETM. In contrast, there was no significant response to the smaller Eocene Thermal Maximum 2, which was associated with a minor change in diversity only. These observations suggest that there is a response threshold for extinction and calcification response, while highlighting the utility of the geological record in helping constrain the sensitivity of biotic response to environmental change.

Age and petrographic characterization of volcanic ash from ODP Leg 198 and Leg 126 sites

In this study of volcanic ash retrieved from Shatsky Rise during Ocean Drilling Program Leg 198, the texture and composition of the volcanic components (glass and crystals) were used to fingerprint ash layers for detailed correlation. Correlations among ash layers in holes drilled at the same site as well as between sites, including sites on different parts (highs) of the rise, were tested. Although high-to-high correlations failed, intrahigh correlations were more successful. Our data suggest a significantly different source for some pyroclastic debris, especially at Site 1208, possibly associated with pumice rafts carried northward from the Izu-Bonin arc by the Kuroshio Current. Other ashes are consistent with rhyolitic to dacitic air fall ash from Asian arc volcanoes. We were not able to texturally distinguish between air fall ash and pumice-raft fallout but suspect that the latter is associated with higher percentages of vesiculated ash components, as we demonstrate occur in more proximal Izu-Bonin pyroclastic deposits.

Calcium carbonate content and concentration of phosphorus components in sediments of ODP Leg 171B sites

Quantifying phosphorus (P) concentrations in marine sediments is necessary for constraining the oceanic record of phosphorus burial and helps to constrain P sedimentary geochemistry. To understand P geochemistry in the sediments, we must determine the geochemical forms of P as well as the transformations occurring between these P components with depth and age. Although several records now exist of P geochemistry in the western and eastern equatorial Pacific (Filippelli and Delaney, 1995, doi:10.2973/odp.proc.sr.138.144.1995; 1996, doi:10.1016/0016-7037(96)00042-7), the western equatorial Atlantic (Delaney and Anderson, 1997, doi:10.2973/odp.proc.sr.154.124.1997), the California Current (Delaney and Anderson, in press), and the Benguela Current (Anderson et al., 2001, doi:10.1029/2000GB001270), most of these are Neogene records. Relatively little data exist from sediments of the Paleogene or Cretaceous, time periods when carbon isotope records indicate major carbon shifts and when the nature of P geochemistry has not been well constrained. Samples from several sites at various water depths, oceanographic regions, and ages are needed to understand how P geochemistry and burial in sediments reflect ocean history. We determined P geochemistry and reactive P concentrations in Atlantic sediments of Eocene to Cretaceous age. These are the first records of P geochemistry with good age control from this period. Blake Nose sites are ideal for investigating P geochemistry, as the sediments are shallowly buried at a range of water depths and sedimentation rates. We determined P concentrations and geochemistry, along with calcium carbonate contents, in mid-Cretaceous to upper Eocene sediments drilled on Blake Nose (Ocean Drilling Program Leg 171B) in a depth transect of four sites (Sites 1052, 1051, 1050, and 1049; water depths: 1345, 1983, 2300, and 2656 m, respectively).

Age-depth relation and red colour reflectance of ODP Leg 177 sites

The Antarctic Polar Front is an important biogeochemical divider in the Southern Ocean. Laminated diatom mat deposits record episodes of massive flux of the diatom Thalassiothrix antarctica beneath the Antarctic Polar Front and provide a marker for tracking the migration of the Front through time. Ocean Drilling Program Sites 1091, 1093 and 1094 are the only deep piston cored record hitherto sampled from the sediments of the circumpolar biogenic opal belt. Mapping of diatom mat deposits between these sites indicates a glacial-interglacial front migration of up to 6 degrees of latitude in the early/mid Pleistocene. The mid-Pleistocene transition marks a stepwise minimum 7° northward migration of the locus of the Polar Front sustained for about 450 kyr until an abrupt southward return to a locus similar to its modern position and further south than any mid-Pleistocene locus. This interval from a "900 ka event" that saw major cooling of the oceans and a d13C minimum through to the 424 ka Mid-Brunhes Event at Termination V is also seemingly characterised by 1) sustained decreased carbonate in the sub-tropical south Atlantic, 2) reduced strength of Antarctic deep meridional circulation, 3) lower interglacial temperatures and lower interglacial atmospheric CO2 levels (by some 30 per mil) than those of the last 400 kyr, evidencing less complete deglaciation. This evidence is consistent with a prolonged period lasting 450 kyr of only partial ventilation of the deep ocean during interglacials and suggests that the mechanisms highlighted by recent hypotheses linking mid-latitude atmospheric conditions to the extent of deep ocean ventilation and carbon sequestration over glacial-interglacial cycles are likely in operation during the longer time scale characteristic of the mid-Pleistocene transition. The cooling that initiated the "900 ka event" may have been driven by minima in insolation amplitude related to eccentricity modulation of precession that also affected low latitude climates as marked by threshold changes in the African monsoon system. The major thresholds in earth system behaviour through the mid-Pleistocene transition were likely governed by an interplay of the 100 kyr and 400 kyr eccentricity modulation of precession.

Petrography and geochemistry of lithic clasts in sediments obtained from ODP Leg 180 sites

This report includes the petrographic description and reviews the distribution of lithic clasts in sediments drilled during Leg 180 in the Woodlark Basin (southwest Pacific). The lithic clasts include (1) metamorphic rocks; (2) granites; (3) serpentinites, gabbros, dolerites, and basalts likely derived from the Papuan ophiolite belt; (4) rare alkaline volcanites reworked in middle Miocene sediments; (5) medium- to high-K calc-alkaline island arc volcanites, in part as reworked clasts, and explosive products deposited by fallout or reworked by turbiditic currents; and (6) rare sedimentary fragments. At the footwall sites the clast assemblage evidences the association of dolerites and evolved gabbroic rocks; the serpentinite likely pertaining to the same ophiolitic complex are likely derived from onland outcrops and transported by means of turbidity currents. On the whole, extensional tectonics active at least since the middle Pliocene can be inferred. The calc-alkaline volcanism is in continuity with the arc-related products from the Papua Peninsula and D'Entrecasteaux Islands and with the latest volcanics of the Miocene Trobrian arc. However, the medium- to high-K and shoshonitic products do not display a significant temporal evolution within the stratigraphic setting. Lava clasts, volcanogenic grains, and glass shards are associated with turbidity currents, whereas in the Pliocene of northern margin the increasing frequency of tephra (glass shards and vesicular silicic fragments) suggests more explosive activity and increasing contribution to the sediments from aerial fallout materials. Evidence of localized alkalic volcanism of presumable early to middle Miocene age is a new finding. It could represent a rift phase earlier than or coeval to the first opening of the Woodlark Basin or, less probably, could derive from depositional trajectories diverted from an adjacent basin.

Geochemistry and mineralogy of interstitial waters and clays in sediments of ODP Leg 180 sites

Oxygen and strontium isotopes and Rb and Ba were determined in interstitial water (IW) collected from Sites 1109, 1115, and 1118 drilled on the Woodlark Rise during Ocean Drilling Program Leg 180. The trace element and mineralogical composition of the clay fraction of sediments isolated from the squeeze cakes corresponding to IW samples from Site 1109 was also determined.