Clay mineralogy of carbonate-rich sediments of ODP Leg 101 sites

The insoluble residues of samples from ODP Sites 626 and 627 can be subdivided into four groups: (1) illite, 7 A minerals, quartz and feldspar; (2) smectite and zeolite (clinoptilolite); (3) palygorskite and in places sepiolite; and (4) glauconite and pyrite. Whereas group 1 is clearly terrigenous and group 4 authigenic, group 2 is most probably authigenic, as indicated by its abundance in samples with small insoluble residues and its appearance in SEM photographs. Group 3 is authigenic in Albian peritidal dolomite and possibly terrigenous in middle Miocene slumps and debris flows. Smectite crystallinity increases with age. This increase, however, is less pronounced in the Bahamian carbonate-rich samples than in the carbonate-poor silts south of Guatemala (DSDP Leg 84, Sites 569 and 570, the only comparable investigation) as far as can be judged from such a small number of samples.

Mineral, chemical and isotopic compositions of altered rocks at ODP Sites 193-1188 and 193-1189

During ODP Leg 193, 4 sites were drilled in the active PACMANUS hydrothermal field on the crest of the felsic Pual Ridge to examine the vertical and lateral variations in mineralization and alteration patterns. We present new data on clay mineral assemblages, clay and whole rock chemistry and clay mineral strontium and oxygen isotopic compositions of altered rocks from a site of diffuse low-temperature venting (Snowcap, Site 1188) and a site of high-temperature venting (Roman Ruins, Site 1189) in order to investigate the water-rock reactions and associated elemental exchanges. The volcanic succession at Snowcap has been hydrothermally altered, producing five alteration zones: (1) chlorite+/-illite-cristobalite-plagioclase alteration apparently overprinted locally by pyrophyllite bleaching at temperatures of 260-310°C; (2) chlorite+/-mixed-layer clay alteration at temperatures of 230°C; (3) chlorite and illite alteration; (4) illite and chlorite+/-illite mixed-layer alteration at temperatures of 250-260°C; and (5) illite+/-chlorite alteration at 290-300°C. Felsic rocks recovered from two holes (1189A and 1189B) at Roman Ruins, although very close together, show differing alteration features. Hole 1189A is characterized by a uniform chlorite-illite alteration formed at ~250°C, overprinted by quartz veining at 350°C. In contrast, four alteration zones occur in Hole 1189B: (1) illite+/-chlorite alteration formed at ~300°C; (2) chlorite+/-illite alteration at 235°C; (3) chlorite+/-illite and mixed layer clay alteration; and (4) chlorite+/-illite alteration at 220°C. Mass balance calculations indicate that the chloritization, illitization and bleaching (silica-pyrophyllite assemblages) alteration stages are accompanied by different chemical changes relative to a calculated pristine precursor lava. The element Cr appears to have a general enrichment in the altered samples from PACMANUS. The clay concentrate data show that Cr and Cu are predominantly present in the pyrophyllites. Illite shows a significant enrichment for Cs and Cu relative to the bulk altered samples. Considerations of mineral stability allow us to place some constraints on fluid chemistry. Hydrothermal fluid pH for the chloritization and illitization was neutral to slightly acidic and relatively acidic for the pyrophyllite alteration. In general the fluids, especially from Roman Ruins and at intermediate depths below Snowcap, show only a small proportion of seawater mixing (<10%). Fluids in shallow and deep parts of the Snowcap holes, in contrast, show stronger seawater influence.

(Table 1) Age determination of ODP Sites 124-769 and 124-768

The Sulu Sea is located in the 'warm pool' of the western Pacific Ocean, where mean annual temperatures are the highest of anywhere on Earth. Because this large heat source supplies the atmosphere with a significant portion of its water vapour and latent heat, understanding the climate history of the region is important for reconstructing global palaeoclimate and for predicting future climate change. Changes in the oxygen isotope composition of planktonic foraminifera from Sulu Sea sediments have previously been shown to reflect changes in the planetary ice volume at glacial-interglacial and millenial timeseales, and such records have been obtained for the late Pleistocene epoch and the last deglaciation (Linsley and Thunell, 1990, doi:10.1029/PA005i006p01025; Lindley and Dunbar, 1994, doi:10.1029/93PA03216; Kudrass et al., 1991, doi:10.1038/349406a0). Here I present results that extend the millenial time resolution record back to 150,000 years before present. On timescales of around 10,000 years, the Sulu Sea oxygen-isotope record matches changes in sea level deduced from coral terraces on the Huon peninsula (Chappell and Shackleton, doi:10.1038/324137a0). This is particularly the case during isotope stage 3 (an interglacial period 23,000 to 58,000 years ago) where the Sulu Sea oxygen-isotope record deviates from the SPECMAP deep-ocean oxygen-isotope record (Imbrie et al., 1984). Thus these results support the idea (Chappell and Shackleton, doi:10.1038/324137a0; Shackleton, 1987, doi:10.1016/0277-3791(87)90003-5) that there were higher sea levels and less continental ice during stage 3 than the SPECMAP record implies and that sea level during this interglacial was just 40-50 metres below present levels. The subsequent rate of increase in continental ice volume during the return to full glacial conditions was correspondingly faster than previously thought.

(Table T1) Porosity and permeability of samples from ODP Leg 180 sites

Woodlark Basin, an area of continental extension, is an ideal location to study the evolution of permeability and the development of overpressures within an active rift basin. In this investigation, we measured sediment permeabilities of cores from Woodlark Basin and used numerical modeling to determine if pore fluid overpressures are likely at the base of the rift basin. Constant-rate flow tests were conducted on cores from Site 1108, located in the rift basin, and Sites 1115 and 1118, located on the northern margin of the basin. Results of the laboratory tests indicated permeabilities that range from 1.5 x 10**-18 to 1 x 10**-16 m**2. Results of the numerical modeling of Site 1108 suggest that overpressures due to sedimentation are unlikely.

Stable isotope ratios of interstitial fluids from ODP Leg 110 sites

Delta18O values of pore waters from the northern Barbados accretionary prism range from -0.3 to -3.6? and reflect pervasive reaction of volcanic ash to form smectite within the sedimentary sequence and continued low temperature alteration of basalt in the underlying ocean crust with the overprint of diffusive exchange between water in the sediment pores and the open ocean. Delta D values of pore waters in sediments sampled seaward of the deformation front drop from +5? at the sediment surface to -6? at the deepest levels sampled. These changes may also be related to alteration processes but remain largely enigmatic. Sediment deformation caused by impingement of the Caribbean plate on the Atlantic plate has instigated migration of chemically and isotopically distinct fluid along faults and coarse-grained sedimentary beds; delta18O values of pore waters are also locally affected by thrust stacking which increases diffusive pathlengths and possibly modifies diagenetic reaction rates in Pleistocene sediments. Migrating fluids are distinguished by anomalous delta18O values that are as much as 1? higher than those of surrounding fluids. Uncertainties in hydrogen isotope fractionation resulting from processes occurring under these conditions hinder identification of the hydrogen isotope composition of expelled fluid. Stable isotope analyses of pore waters help constrain the fluid migration history of the accretionary prism by limiting the source of fluids, the paths along which fluid flows, and the timing of faulting and subsequent fluid flow.

(Table T1) Physical properties of minicores from ODP Leg 193 sites, PACMANUS field

Permeability of the ocean crust is one of the most crucial parameters for constraining submarine fluid flow systems. Active hydrothermal fields are dynamic areas where fluid flow strongly affects the geochemistry and biology of the surrounding environment. There have been few permeability measurements in these regions, especially in felsic-hosted hydrothermal systems. We present a data set of 38 permeability and porosity measurements from the PACMANUS hydrothermal field, an actively venting, felsic hydrothermal field in the eastern Manus Basin. Permeability was measured using a complex transient method on 2.54-cm minicores. Permeability varies greatly between the samples, spanning over five orders of magnitude. Permeability decreases with both depth and decreasing porosity. When the alteration intensity of individual samples is considered, relationships between depth and porosity and permeability become more clearly defined. For incompletely altered samples (defined as >5% fresh rock), permeability and porosity are constant with depth. For completely altered samples (defined as <5% fresh rock), permeability and porosity decrease with depth. On average, the permeability values from the PACMANUS hydrothermal field are greater than those in other submarine environments using similar core-scale laboratory measurements; the average permeability, 4.5 x 10-16 m**2, is two to four orders of magnitude greater than in other areas. Although the core-scale permeability is higher than in other seafloor environments, it is still too low to obtain the fluid velocities observed in the PACMANUS hydrothermal field based on simplified analytical calculations. It is likely that core-scale permeability measurements are not representative of bulk rock permeability of the hydrothermal system overall, and that the latter is predominantly fracture controlled.

Carbonate preservation reconstructed from ODP Sites 154-927 and 154-929 at Ceará Rise

Enhanced Atlantic overturning during the Pliocene was first proposed almost 10 yrs ago. Evidence for this Pliocene super conveyor scenario has been collected using a number of proxies (e.g., benthic d13C, Nd isotopic composition of manganese crusts). The present study contributes to the existing evidences by using carbonate dissolution and current vigour history of early Pliocene sediments from the Ceará Rise (ODP Sites 927 and 929). In order to reveal carbonate dissolution history, a number of commonly used and newly established proxies were applied, i.e., sand and carbonate contents, foraminifer fragmentation index, Bulloides Dissolution Index and carbonate silt grain-size distributions. Terrigenous silt grain-size distributions were used to unravel variations in relative current strength and sediment input to the two sites. Overall good carbonate preservation at the shallow Site 927 (3314 m water depth) shows that this level was bathed in North Atlantic Deep Water throughout the early Pliocene. The contrastingly poor carbonate preservation record of the deeper Site 929 (4358 m water depth, at present exposed to Antarctic Bottom Water) is frequently interrupted by phases of good carbonate preservation. These results indicate that the depth of the calcite lysocline was mainly tied to present level (ab. 4200 m water depth), and sometimes even dropped to water depths greater than 4360 m due to even more enhanced circulation. Surprisingly the expansion of NADW is not clearly reflected by an increase in current speed as shown by continuously fine terrigenous grain size.

Calcareous nannofossils in ODP Sites 135-840 and 135-841

Ocean Drilling Program Leg 135 drilled at two sites on the Tonga Ridge. Calcareous nannofossils recovered at Site 840 on the Tonga Ridge date the sedimentary sequence as late Pleistocene or Holocene (CN15) through late Miocene (CN9) in age. A hiatus occurs in the mid Pliocene. Site 841 in the Tonga Trench yielded a sedimentary sequence with nannofossils from middle Pleistocene Subzone CN14b through the middle or late Eocene Subzones CP14a-CP15b overlying a rhyolitic volcanic basement. Part of the Eocene interval contains the shallow-water nannofossil taxa Braarudosphaera, Micrantholithus, and Pemma. A major unconformity separates lower Oligocene Zone CP 16 from lower middle Miocene Zone CN4 strata.

Eolian and silica deposition of ODP sites in the central North Pacific

Sediments recovered at Ocean Drilling Program Sites 885/886 (central North Pacific Ocean at 44°41'N, 168°14'W and 44°41'N, 168°16'W, respectively) record eolian deposition during the Cenozoic and late Mesozoic. We constructed a record of eolian MAR, which is a proxy for aridity/humidity of the climate in the continental source area. Eolian fluxes are low during the Late Cretaceous through Eocene, reflecting humid conditions in the source area. During the Oligocene, more arid climates prevailed at the source area, as indicated by increased eolian accumulation. The "Diatom Dump", an interval of enhanced silica deposition mainly apparent in the northwest Pacific, is reflected in the record at Sites 885/886 by two- to fivefold higher opal fluxes compared with younger and older sediments. Increased eolian deposition starting at 3.5 Ma and culminating at 2-2.6 Ma are coincident with the onset of Northern Hemisphere glaciation. Sites 885/886 lie 10° north of sites examined previously for the history of eolian deposition in the central North Pacific and therefore allow enhanced understanding of the latitudinal variation of the wind system.

Total organic carbon, delta13C, biomarker, gas compilations and hopanoids analysis from IODP Sites 307-U1317 and 307-U1318

During the Integrated Ocean Drilling Program (IODP) Expedition 307 for the first time a cold-water coral carbonate mound was drilled down through its base into the underlying sediments. In the current study, sample material from within and below Challenger Mound, located in the Belgica carbonate mound province in the Porcupine Basin offshore Ireland, was investigated for its distribution of microbial communities and gas composition using biogeochemical and geochemical approaches to elucidate the question on the initiation of carbonate mounds. Past and living microbial populations are lower in the mound section compared to the underlying sediments or sediments of an upslope reference site. A reason for this might be a reduced substrate feedstock, reflected by low total organic carbon (TOC) contents, in the once coral dominated mound sequence. In contrast, in the reference site a lithostratigraphic sequence with comparatively high TOC contents shows higher abundances of both past and present microbial communities, indicating favourable living conditions from time of sedimentation until today. Composition and isotopic values of gases below the mound base seem to point to a mixed gas of biogenic and thermogenic origin with a higher proportion of biogenic gas. Oil-derived hydrocarbons were not detected at the mound site. This suggests that at least in the investigated part of the mound base the upward flow of fossil hydrocarbons, being one hypothesis for the initiation of the formation of carbonate mounds, seems to be only of minor significance.