Benthic foraminifera stratigraphy of sediments from ODP Leg 199 sites

Benthic foraminifers from Ocean Drilling Program Leg 199 Holes 1215A, 1220B, and 1221C were examined across the Paleocene/Eocene boundary. Assemblages were studied in 240 samples. The benthic foraminiferal extinction event that correlates with the Paleocene/Eocene epoch boundary was recognized at these sites. Benthic assemblages before the event are characterized by high diversity, but those after the event are low in diversity. An assemblage of agglutinated foraminifers without carbonate cement was recognized at Sites 1220 and 1221. These assemblages were typically found after the event. The discovery of such agglutinated assemblages has never been reported before at this boundary.

Organic geochemistry of ODP Leg 135 sediment samples

The average total organic carbon (TOC) content obtained after Rock-Eval/TOC analysis of 156 sediment samples from the eight sites cored during Leg 135 is 0.05%. Hence, the TOC content of Leg 135 sediments is extremely low. The organic matter that is present in these samples is probably mostly reworked and oxidized material. Ten sediment samples were selected for extraction and analysis by gas chromatography and gas chromatography-mass spectrometry. Very low amounts of extractable hydrocarbons were obtained and some aspects of the biomarker distributions suggest that these hydrocarbons are not representative of the organic matter indigenous to the samples. A sample of an oil seep from Pili, Tongatapu was also analyzed. The seep is a biodegraded, mature oil that shows many characteristics in common with previously published analyses of oil seeps from Tongatapu. Biomarker evidence indicates that its source is a mature, marine carbonate of probable Late Cretaceous-Early Tertiary age. The source rock responsible for the Tongatapu oil seeps remains unknown.

Sporomorphs and dinoflagellate cysts of ODP Leg 113 holes

Palynological studies were carried out on Paleogene sections from Sites 693 and 696 of Ocean Drilling Project Leg 113 in the Weddell Sea region. Dinoflagellate cysts and sporomorphs were recovered at Site 696 (61°S, 42°W) indicating a middle Eocene to late Eocene/earliest Oligocene age for a glauconitic silt/sandstone. At Site 693 (70°S, 14°W) early Oligocene siliciclastic mud contains a low diversity palynoflora. In an upper Oligocene section (Site 693) only rare, reworked Mesozoic palynomorphs were encountered. Palynological data from Kerogen analyses, dinocysts, and sporomorphs are used to reconstruct the climatic change on the South Orkney microcontinent from the middle Eocene to the late Eocene/earliest Oligocene at Site 696 and the late early Oligocene/early late Oligocene time interval at Site 693 near the continental margin. The middle Eocene was a warm period in the Orkney region with good growing conditions for a warm temperate Nothofagus/conifer forest with an admixture of Proteaceae. Temperate surface water masses, which allowed the growth of a reasonably diverse dinocyst assemblage (ca. 15-20 species), persisted until the end of the Eocene at Site 696. Late early Oligocene sediments of Site 693 (Antarctic continental margin) contain only a low diversity dinocyst flora (two species). The major Cenozoic cooling event in the Weddell Sea region probably occurred at the Eocene/Oligocene boundary. A second dramatic climatic deterioration seems to have taken place during the late early/early late Oligocene, when dinocysts disappeared at the Dronning Maud Land margin area.

Diatom abundance in ODP Leg 178 holes

This paper documents the biostratigraphic distribution and abundance of diatoms from sites drilled during Ocean Drilling Program Leg 178, off the Pacific margin of the Antarctic Peninsula. Drift sediments cored on the continental rise at Sites 1095, 1096, and 1101 have good recovery and a well-defined paleomagnetic record. Well-preserved diatoms are present throughout the upper Miocene to middle Pliocene and in the upper Quaternary section of these sites. The stratigraphic occurrence of diatom species through these intervals defines numerous datum levels. Diatom events are given absolute age estimates through direct correlation to the established paleomagnetic stratigraphy of Sites 1095, 1096, and 1101. Leg 178 diatom biostratigraphic results enable the development of a regional stratigraphic framework for the Pacific sector of the Southern Ocean and record the interaction of open-ocean and shelf-margin diatom floras.

Compaction curves and sediment characteristics of ODP Leg 165 and Leg 130 sites

Compaction curves for 11 samples from the mixed sediments and calcareous chalk with clay from the Caribbean Sites 999 and 1001 are discussed with reference to compaction curves for calcareous ooze and chalk of the Ontong Java Plateau (Leg 130). The burial history is discussed from preconsolidation data and present burial conditions and suggests a removal of ~400 m of sediment at the hiatus 166 meters below seafloor (mbsf) at Site 1001. This interpretation predicts a previous burial to >500 mbsf for depth intervals containing microstylolites, which corresponds to observations at Sites 999 and 807 (Ontong Java Plateau). Thus, data from three sites from two widely separate regions indicate that microstylolites in carbonates form at minimum burial depths deeper than 500 m. No direct link between formation of microstylolites and cementation was found, suggesting that dissolution and precipitation are not necessarily related. Porosity rebound during core retrieval could not be detected for soft sediments, whereas a porosity rebound of ~2% was deduced for deeper, cemented intervals. Comparing the compaction curves, two distinct rates of porosity loss are noted: (1) samples dominated by clay (>45% insoluble residue) compact at a higher rate than samples dominated by fine-grained carbonate and (2) fine-grained carbonate supported samples (with <45% insoluble residue) compact at the same rate irrespective of the content of nonsupporting microfossils or pore-filling clay.

Pore water acetate and hydrogen, helium and methane gas concentrations in ODP Leg 204 sediments

Acetate and hydrogen concentrations in pore fluids were measured in samples taken at seven sites from southern Hydrate Ridge (SHR) offshore Oregon, USA. Acetate concentrations ranged from 3.17 to 2515 µM. The maximum acetate concentrations occurred at Site 1251, which was drilled on a slope basin to the east of SHR at depths just above the bottom-simulating reflector (BSR) that marks the boundary of gas hydrate stability. Acetate maxima and localized high acetate concentrations occurred at the BSR at all sites and frequently corresponded with areas of gas hydrate accumulation, suggesting an empirical relationship. Acetate concentrations were typically at a minimum near the seafloor and above the sulfate/methane interface, where sulfate-reducing bacteria may consume acetate. Hydrogen concentrations in pressure core samples ranged from 16.45 to 1036 parts per million by volume (ppmv). In some cases, hydrogen and acetate concentrations were elevated concurrently, suggesting a positive correlation. However, sampling of hydrogen was limited in comparison to acetate, so any relationships between the two analytes, if present, were difficult to discern.

Radiolarian biostratigraphy and chronology of radiolarian events of ODP Leg 199 sites and EW9709 sediment cores

A generally rich radiolarian fauna ranging in age from Quaternary to early Eocene (Zone RP7) was found at five of the eight sites drilled during Ocean Drilling Program (ODP) Leg 199. Of particular interest are the stratigraphically complete assemblages that range in age from middle Miocene (Zone RN5) to early Eocene (Zone RP7), composites of Sites 1218, 1219, and 1220. At the same sites, multisensor track (MST) data show consistent cycles in gamma ray attenuation density, color, and carbonate content that can be correlated on a submeter scale from the early Miocene to early Eocene. In addition, the magnetic reversal records from these three sites allow construction of an absolute timescale. A series of 305 radiolarian morphologic first and last occurrences and evolutionary transitions for radiolarians were determined and correlated directly with the accompanying MST and paleomagnetic data, resulting in a detailed and accurate dating of events. Since many of the bioevents are found at more than one site, it was also possible to test their reliability within the study area. Twelve new species are described: Calocycletta (Calocycletta) anekathen, Dorcadospyris anastasis, Dorcadospyris copelata, Dorcadospyris cyclacantha, Dorcadospyris ombros, Dorcadospyris scambos, Eucyrtidium mitodes, Theocyrtis careotuberosa, Theocyrtis perpumila, Theocyrtis perysinos, Theocyrtis setanios, and Thyrsocyrtis (Pentalacorys) orthotenes.

Curie temperatures and hysteresis properties of ODP Leg 183 sites, Kerguelen Plateau and Broken Ridge

In this manuscript, we present rock magnetic results of samples recovered during Leg 183. The Leg 183 cores were recovered from six drill sites and display variable rock magnetic properties. The differences in the rock magnetic properties are a function of mineralogy and alteration. Cretaceous subaerial basalt samples with titanomagnetite exhibit a strong Verwey transition in the vicinity of 110 K and have frequency-dependent susceptibility curves that resemble those of synthetic (titano) magnetites. These results are in good agreement with the thermomagnetic characteristics where titanomagnetites with Curie temperatures of ~580°C were identified. The hysteresis ratios suggest that the bulk magnetic grain size is in the psuedo-single-domain boundary. These subaerial basalts experienced high-temperature oxidation and maintained reliable paleomagnetic records. In contrast, the 34-Ma submarine pillow basalts do not show the Verwey transition during the low-temperature experiments. Thermomagnetic analysis shows that the remanent magnetization in this group is mainly carried by a thermally unstable mineral titanomaghemite. The frequency-dependent relationships are opposite of those from the first group and show little sign of titanomagnetite characteristics. Rocks from the third group are oxidized titanomagnetites and have multiple magnetic phases. They have irreversible thermaomagnetic curves and hysteresis ratios clustering toward the multidomain region (with higher Hcr/Hc ratios). The combined investigation suggests that variations in magnetic properties correlate with changes in lithology, which results in differences in the abundance and size of magnetic minerals. The rock magnetic data on Leg 183 samples clearly indicate that titanomagnetite is the dominant mineral and the primary remanence carrier in subaerial basalt. The generally good magnetic stability and other properties exhibited by titanomagnetite-bearing rocks support the inference that the ChRM isolated from the Cretaceous sites were acquired during the Cretaceous Normal Superchron. The stable inclinations identified from these samples are therefore useful for future tectonic studies.

Isotopic composition of interstitial waters from ODP Leg 174A sites

An investigation of the isotopic composition of the interstitial waters was conducted at Sites 1071, 1072, and 1073 on the New Jersey continental shelf and slope during Ocean Drilling Program Leg 174A. Sites 1071 and 1072 are closely spaced drill holes on the continental shelf located ~130 km from the shoreline in 88 and 98 m of water, respectively. Site 1073 is located on the continental slope in 640 m water and penetrated a total of 664 m of sediment of which ~520 m is Quaternary age. A total of 125 oxygen and hydrogen isotopic analyses of pore fluids are presented from all three sites. Twelve strontium isotopic ratios are reported from Site 1071.

Stable foraminifer isotope composition and age of ODP Sites 184-1147 and 184-1148, South China Sea

Sites 1147 (18°50.11'N, 116°33.28'E; water depth = 3246 m) and 1148 (18°50.17'N, 116°33.94'E; water depth = 3294 m) are located on the lowermost continental slope off southern China near the continent/ocean crust boundary of the South China Sea Basin. Site 1147 is located upslope ~0.45 nmi west of Site 1148. Three advanced piston corer holes at Site 1147 and two extended core barrel holes at Site 1148 were cored and combined into a composite (spliced) stratigraphic section, which provided a relatively continuous profile for the lower Oligocene to Holocene (Wang, Prell, Blum, et al., 2000, doi:10.2973/odp.proc.ir.184.2000; Jian, et al., 2001, doi:10.1007/BF02907088) for studying stratigraphy and paleoceanography. A total of 1047 planktonic foraminifers stable isotope measurements were performed on 975 samples covering the upper 409.58 meters composite depth (mcd) at ~42-cm intervals (Tables T1, T2), and a total of 1864 benthic foraminifers measurements were performed on 1650 samples in the upper 837.11 mcd at ~51-cm intervals (Tables T3, T4). We significantly improved the time resolution of the benthic stable isotope record in the upper 476.68 mcd by reducing the average sample spacing to ~29 cm. This translates into an average sampling resolution of ~16 k.y. for the Miocene sequence and ~8 k.y. for the Pliocene-Holocene interval, assuming a change in sedimentation rates from ~1.8 to ~3.5 cm/k.y., as suggested by shipboard stratigraphy. These data sets provide the basis for upcoming studies to establish an oxygen isotope stratigraphy and examine the Neogene evolution of deep and surface water signatures (temperature, salinity, and nutrients) in the South China Sea.

Age models of ODP Site 184-1143

Here we present an improved astronomical timescale since 5 Ma as recorded in the ODP Site 1143 in the southern South China Sea, using a recently published Asian summer monsoon record (hematite to goethite content ratio, Hm/Gt) and a parallel benthic d18O record. Correlation of the benthic d18O record to the stack of 57 globally distributed benthic d18O records (LR04 stack) and the Hm/Gt curve to the 65°N summer insolation curve is a particularly useful approach to obtain refined timescales. Hence, it constitutes the basis for our effort. Our proposed modifications result in a more accurate and robust chronology than the existing astronomical timescale for the ODP Site 1143. This updated timescale further enables a detailed study of the orbital variability of low-latitude Asian summer monsoon throughout the Plio-Pleistocene. Comparison of the Hm/Gt record with the d18O record from the same core reveals that the oscillations of low-latitude Asian summer monsoon over orbital scales differed considerably from the glacial-interglacial climate cycles. The popular view that summer monsoon intensifies during interglacial stages and weakens during glacial stages appears to be too simplistic for low-latitude Asia. In low-latitude Asia, some strong summer monsoon intervals appear to have also occurred during glacial stages in addition to their increased occurrence during interglacial stages. Vice versa, some notably weak summer monsoon intervals have also occurred during interglacial stages next to their anticipated occurrence during glacial stages. The well-known mid-Pleistocene transition (MPT) is only identified in the benthic d18O record but not in the Hm/Gt record from the same core. This suggests that the MPT may be a feature of high- and middle-latitude climates, possibly determined by high-latitude ice sheet dynamics. For low-latitude monsoonal climate, its orbital-scale variations respond more directly to insolation and are little influenced by high-latitude processes, thus the MPT is likely not recorded. In addition, the Hm/Gt record suggests that low-latitude Asian summer monsoon intensity has a long-term decreasing trend since 2.8 Ma with increased oscillation amplitude. This long-term variability is presumably linked to the Northern Hemisphere glaciation since then.

Dissolved inorganic carbon isotopes in pore waters of ODP Leg 204 sediments

Isotopic characterization of carbon in the dissolved inorganic carbon (DIC) pool is fundamental for a wide array of scientific studies directly related to gas hydrate research. In order to generate integrated and internally consistent data of d13C of DIC in pore waters from Hydrate Ridge, we used the modern continuous flow technology of a GasBench II automated sampler interfaced to a gas source stable isotope mass spectrometer for the rapid determination (~80 samples/day) of d13C DIC in small-volume water samples. The overall precision of this technique is conservatively estimated to be better than ±0.15 per mil (1 sigma), which is similar to the precision of methods in current use. Here we present the data generated from Ocean Drilling Program Leg 204 pore water samples.

Rare earth element data for sediments from ODP Leg 127

The relative effects of paleoceanographic and paleogeographic variations, sediment lithology, and diagenetic processes on the recorded rare earth element (REE) chemistry of Japan Sea sediments are evaluated by investigating REE total abundances and relative fractionations in 59 samples from Ocean Drilling Program Leg 127. REE total abundances (Sum REE) in the Japan Sea are strongly dependent upon the paleoceanographic position of a given site with respect to terrigenous and biogenic sources. REE concentrations at Site 794 (Yamato Basin) overall correspond well to aluminosilicate chemical indices and are strongly diluted by SiO2 within the late Miocene-Pliocene diatomaceous sequence. Eu/Eu* values at Site 794 reach a maximum through the diatomaceous interval as well, most likely suggesting an association of Eu/Eu* with the siliceous component, or reflecting slight incorporation of a detrital feldspar phase. Sum REE at Site 795 (Japan Basin) also is affiliated strongly with aluminosilicate phases, yet is diluted only slightly by siliceous input. At Site 797 (Yamato Basin), REE is not as clearly associated with the aluminosilicate fraction, is correlated moderately to siliceous input, and may be sporadically influenced by detrital heavy minerals originating from the nearby rifted continental fragment composing the Yamato Rise. The biogenic influence is largest at Site 794, moderately developed at Site 797, and of only minor importance at Site 795, reflecting basinal contrasts in productivity such that the Yamato Basin records greater biogenic input than the Japan Basin, while the most productive waters overlie the easternmost sequence of Site 794. Ce/Ce* profiles at all three sites increase monotonically with depth, and record progressive diagenetic LREE fractionation. The observed Ce/Ce* record does not respond to changes in oxygenation state of the overlying water, and Ce/Ce* correlates slightly better with depth than with age. The downhole increase in Ce/Ce* at Site 794 and Site 797 is a passive response to diagenetic transfer of LREE (except Ce) from sediment to interstitial water. At Site 795, the overall lack of correlation between Ce/Ce* and La_n/Yb_n suggests that other processes are occurring which mask the diagenetic behavior of all LREEs. First-order calculations of the Ce budget in Japan Sea waters and sediment indicate that ~20% of the excess Ce adsorbed by settling particles is recycled within the water column, and that an additional ~38% is recycled at or near the seafloor (data from Masuzawa and Koyama, 1989). Thus, because the remaining excess Ce is only ~10% of the total Ce, there is not a large source of Ce to the deeply buried sediment, further suggesting that the downhole increase in Ce/Ce* is a passive response to diagenetic behavior of the other LREEs. The REE chemistry of Japan Sea sediment therefore predicts successive downhole addition of LREEs to deeply-buried interstitial waters.