Drilling Program Research Articles

Eocene relative paleointensity of the geomagnetic field from Integrated Ocean Drilling Program Site U1403 and U1408 sediments in the northwest Atlantic

Published relative paleointensity (RPI) records older than ∼3Ma are extremely limited in time and space. To develop a more robust understanding of RPI variations, we have conducted rock magnetic and paleomagnetic measurements on Eocene marine sediments recovered at Integrated Ocean Drilling Program (IODP) Sites U1403 and U1408 in the northwest Atlantic. A series of rock magnetic measurements indicate that the main remanence carrier is single domain biogenic magnetite. Paleomagnetic measurements yielded RPI records for Chrons C18–C21 and C22n, which correlates to ∼38.4–49.6Ma. The record is compromised in a few short intervals by inhomogeneous rock magnetic properties. RPI minima always occur at chron boundaries and RPI fluctuates between highs and lows within each chron. This record is the first to show that these characteristics persist at least since the onset of Chron C22n at ∼49.3Ma. We conclude that these are intrinsic and fundamental features of the geomagnetic field regardless of the polarity reversal rate. We produce a stacked RPI curve for Chron 18, named PIS-C18, on the basis of the RPI records obtained in this study and those from IODP Sites U1331 and U1332 in the equatorial Pacific that are matched by visual inspection. The PIS-C18 RPI of the stack is generally high with no prominent lows during Chron C18n.2n, whereas it is not as high and has several prominent lows almost equivalent to the RPI minima at the chron boundaries during Chrons C18n.1n and C18r. A histogram of RPI during Chron 18 is slightly skewed to the right, and the ratio of the standard deviation to the mean paleointensity is 0.38. These characteristics are similar to a histogram of the RPI stack for the last 1.5 million years. We interpret this to imply that character of the geodynamo for 104–106 years timescales has been unchanged since the Eocene.

Tropical Radiolarian Biostratigraphy from the Early to Late Miocene at ODP Site 714 in the Tropical Indian Ocean

Detailed biostratigraphic study of a lower Neogene section with abundant, moderate to well preserved radiolarians from central Indian Ocean Drilling Program (ODP) Site 714 has resulted in the precise correlation of many radiolarian bioevents with calcareous nannofossil and planktonic foraminiferal biostratigraphy. The interval studied at Site 714 is divided into five radiolarian zones, RN6 to RN2. In this study, Zones RN5 (Dorcadospyris alata Interval Zone), RN4 (Calocycletta costata Interval Zone) and RN3 (Stichocorys wolffii Interval Zone) are divided into subzones based on the last occurrences of Calocycletta costata and Carpocanopsis cingulata, and the first occurrence of Liriospyris stauropora, respectively. Designation of these zones/subzones improved the biostratigraphic resolution (average of one subzone/zone per 1.2 million years). A new species, Pterocanium maldives, is described. Comparison of results from Site 714 with those of previous studies from the tropical Pacific Ocean enables identification of synchroneity and diachroneity of radiolarian datum events between the tropical Indian and Pacific Oceans. Of 64 radiolarian bioevents in the tropical Indian Ocean from the early to late Miocene, 22 were apparently synchronous or nearly synchronous. These radiolarian events provide useful biohorizons for stratigraphic correlation and age determination of lower Neogene sequences from the tropical Indian to Pacific Oceans. Patterns of synchroneity and diachroneity of first occurrences were different near the middle/late Miocene boundary. Below this transition, the first occurrences were synchronous from the tropical Indian and Pacific Oceans. Above this transition, they were earlier in the tropical Indian Ocean than in the tropical Pacific Ocean. Changes in these patterns might to have been influenced by the effective closure of the Indo–Pacific seaway. In contrast, the large majority of last occurrences showed synchroneity from the tropical Indian and Pacific Oceans during the early to late Miocene. This suggests that last occurrences during the early to late Miocene were affected by global climatic or oceanographic events.

ON GOING COALBED METHANE (CBM) DEVELOPMENT IN THE SOUTH SUMATRA BASIN

Coalbed methane (CBM) is going to be an important facet of the nation’s energy mix. It is expected to contribute in importance energy back up for the future. CBM is natural gas, a clean-burning energy source that is reservoired in a coal seam. CBM is formed during the coal maturation process and may in a free or adsorbed state in coal seams in adjacent formations. CBM is dominantly methane but lesser concentrations of carbon dioxide and nitrogen, compare to conventional natural gas. However, in most cases, CBM is of sufficient quality for sale directly into natural gas transmission lines with a limited amount of moisture removal.CBM as natural gas has numerous benefits to include direct selling, well suited as city gas, electricity generation, boiler fuel, transportation fuel, and for many types of chemical industries feed. Beside CBM replaces coal to be greatly reduces the production of acid rain and other forms of air pollution, the development of CBM has benefitial for coal miners. It can contribute to improved mining safety as well as it can help reduce construction costs.CBM is probably one of the promising alternative fuel energy resources in Indonesia that its presence is actual and comparable with the existing coal resources in any potential basin. Unlike some well in developed countries where commercialization of methane production from coal seam has been developed, coals direct mined in Indonesia seem to be more attractive and preferable technique to supply the consumer demand of energy. This is because coal mines serve direct products, less complicated technology, low exploration risks, easy recovery, relatively low cost but quick yields and already have wide market. Consequently, people have overlooked the existence of consisting huge potential methane gas in coals.However, petroleum exploration data throughout Indonesia suggest that increasing coal rank occurs rapidly with depth in many basins and that gas kicks are almost common associated with some coal seams below 200 m depth. In addition, world CBM exploration now has shifted towards lower rank settings (i.e, vitrinite reflectance between 0.3% and 0.6% Ro). In Indonesia, thick coals generally are found at greater depth, higher in rank and therefore are expected to be more productive (Saghafi and Hadiyanto, 2000).LEMIGAS is currently conducting a drilling program to study the feasibility of CBM production in South Sumatra. The domain of the work is in the Muaraenim Formation (Upper – Middle Palembang). The coal sequences were deposited during Late Miocene. We believe that a big effort is extremely essential to establish the reserve and economic potential of CBM in South Sumatra to later extent to Indonesia.

Collapse and recovery of the marine biological carbon pump across the Cretaceous-Paleogene mass extinction

<p indent="0mm">The Cretaceous-Paleogene (K-Pg) mass extinction that ended the age of the dinosaurs occurred 66 million years ago, with competing hypotheses including the Deccan Traps volcanic eruption, climate change, and sea level change. However, it is the Chicxulub asteroid impact that has been widely accepted as the most plausible cause. Whatever the reason, the Earth’s ecological environment changed dramatically, leading to a mass extinction of both terrestrial and marine life. Primary producers lie at the base of the food chain and support higher trophic levels, so play an important role in the marine ecosystem. The predominant primary producers in the ocean, coccolithophores (phytoplankton with small CaCO₃ scales covering their cell surface), were among those most severely devastated by the K-Pg mass extinction. So, studying fossil coccolithophores across the K-Pg boundary can provide a better understanding of the destruction and post-event recovery processes of marine primary production (PP) and export production (EP), and the changes and controlling mechanisms of the marine biological carbon pump in the current global climate change. The four hypotheses previously proposed to interpret the post-event primary production, namely strangelove ocean (collapsed PP), living ocean (collapsed EP), resilient ocean (continued PP and EP), and heterogeneous ocean (geography-dependent responses of PP and EP), are illustrated and compared, and their pros and cons reviewed. A dataset is compiled from multiple locations in the global ocean basin including Deep Sea Drilling Program Site 465, Ocean Drilling Program Sites 690, 1210, and 1262, and the outcrop at El Kef (Tunisia), with each location having a high-precision cyclostratigraphic time control and an ocean surface-to-deep (bulk carbonate-benthic foraminifera) <italic>δ</italic>¹³C vertical gradient. This global dataset is analyzed to explore the changes in the efficiency of global marine biological carbon pump after the K-Pg boundary event. Three important patterns are observed: (1) Prior to the K-Pg event, the vertical <italic>δ</italic>¹³C gradient in all ocean basins falls between 0.8‰–1.5‰ and is consistent with that in the modern ocean, and this gradient seems to gradually increase from the shelf to the deep ocean possibly due to higher efficiency of the biological carbon pump in the open ocean commonly characterized by oligotrophy; (2) the global ocean vertical <italic>δ</italic>¹³C gradient collapses after the K-Pg event, suggesting drastic changes in primary and/or export production in the euphotic zone; (3) the vertical <italic>δ</italic>¹³C gradient collapse results from the abrupt negative shift of the surface ocean <italic>δ</italic>¹³C, and the magnitude of this negative shift gradually decreases from the continental shelf to the deep sea, which may be related to the selective extinction of shallow-water grazers, swimming organisms and plankton, as well as the limited buffering capacity of shelf environments. After the K-Pg event, the main primary producers change from larger coccolithophores to smaller picoplankton, and the more recalcitrant dissolved organic carbon is able to sink to the seafloor due to the operation of the microbial carbon pump in the photic zone, leading to sustained efficiency of the biological carbon pump. Although the picoplankton-dominated biological carbon pump is not as efficient as that by coccolithophores, it is still capable of removing enough nutrients and harmful substances from the photic zone via long-term operation, not only providing food for higher trophic level organisms, but improving the marine physicochemical environment that deteriorated after the K-Pg asteroid impact. This process paves the way for the restoration and development of the entire marine ecosystem. The switch of key marine primary producers and the controlling factors involved are critical scientific issues that deserve more focus in future studies of the deep-time marine carbon cycle. The regional or global variation patterns in the biological carbon pump after the K-Pg event reveal how different marine ecosystems operate under extreme environmental stress, and provide a reference for better understanding and predicting how they respond to the ongoing rapid global climate change.

Revised astronomically calibrated 40Ar/39Ar ages for the Fish Canyon Tuff sanidine – Closing the interlaboratory gap

The 40Ar/39Ar geochronology method is capable of high precision (<0.05%), but remains limited by relatively large uncertainties in 40K decay constants and the ages of natural reference mineral standards. The most widely used 40Ar/39Ar reference mineral is the well-known ca. 28 Ma Fish Canyon Tuff sanidine (FCTs). Several studies have attempted to calibrate FCTs against astronomically tuned tephra in Crete (Faneromeni A1 tephra) and Morocco (Messâdit Mes4 tuff) as well as deep-sea sedimentary sequences. Previously reported astronomically tuned ages range from 28.126 ± 0.019 to 28.21 ± 0.18 Ma (2σ), a range of ~0.3%, compared to precision levels of <0.05% achievable by new generation, multi-collector mass spectrometer systems. In this study, we revisit the astronomical calibration of FCTs. Relative to ages of 6.943 ± 0.005 Ma for A1 tuff sanidine (A1Ts) and 6.791 ± 0.010 Ma (2σ) for Mes4 tuff sanidine (Mes4Ts), we calculate revised astronomically tuned ages for Fish Canyon Tuff sanidine of 28.175 ± 0.012 Ma (±0.023 Ma, including the uncertainty in the age of A1Ts) and 28.176 ± 0.010 Ma (±0.042 Ma, including the uncertainty in the age of Mes4Ts), respectively (assuming negligible differential 39Ar recoil loss). This age is within uncertainty of most recent astronomical intercalibrations, permitting calculation of inter-laboratory mean ages of 28.176 ± 0.010 (±0.023) Ma and 28.179 ± 0.009 (±0.042) Ma, respectively. As the astronomical age of the A1 tuff is more precise than that of the Mes4 tuff, we recommend that the former value is adopted as the astronomical age for FCTs. This age is consistent with available U-Pb zircon age data, but remains distinctly older than recent astronomical ages of 28.10 and 28.150 Ma inferred from deep-sea Ocean Drilling Program sediments, indicating that further work is required to align the astronomical tuning of terrestrial versus deep-sea sediments. Based on previous R-values for the Alder Creek Rhyolite sanidine (ACRs) and Mount Dromedary biotite (MD-2b) reference minerals, co-irradiated with FCTs, we calculate revised astronomically calibrated ages of 1.18342 ± 0.00069 (±0.009) Ma for ACRs and 99.323 ± 0.077 (±0.33) Ma for MD-2b, the latter amended to 99.20 ± 0.01 (±0.38) Ma to account for relative recoil loss of 39ArK. To further enhance the accuracy of 40Ar/39Ar ages, our study also highlights the need to carefully control neutron fluence gradients and consider recoil effects.

Occurrence and origin of perylene in Paleogene sediments from the Tasmanian Gateway, Australia

Eocene to Lower Oligocene sediments were collected by Ocean Drilling Program Leg 189 at four sites in the Tasmanian Gateway, Australia, and geochemically characterised to investigate the occurrence and controlling factors of perylene. Perylene is enriched in samples from Site 1168, which is located closest to Tasmania, accounting for up to 53.4% of the total quantified aromatic hydrocarbons, with concentrations ranging from 15 ng/g dry weight sediment (dws) to 1700 ng/g dws. However, only trace amounts of perylene (<5 ng/g dws) are present in samples from the other three sites, except for two deep samples from Site 1171, which is furthest from Tasmania, with perylene concentrations of 15 ng/g dws and 95 ng/g dws. The concentrations of perylene increase with burial depth, suggesting its formation from diagenetic processes. Other molecular compositions, including land-plant-derived aromatic hydrocarbons, pyrogenic-related aromatic hydrocarbons and n-alkanes, indicate that the origin of perylene can be attributed to allochthonous organic material associated with terrigenous plants. Contributions from autochthonous organic matter and combustion cannot be validated. Detailed examination of the relationship between the concentrations of perylene and organic matter input and depositional conditions illustrate that both factors are important but not essential. The concentrations of perylene are positively correlated to pristane/phytane ratios, implying that perylene is probably formed under dysoxic rather than highly reducing conditions. Terrigenous-sourced organic matter was detected at all four sites, but perylene is only concentrated at the site closest to Tasmania. It is proposed that the preservation of the precursors of perylene is critical, as these are sensitive to destruction by oxidation. If the precursors of perylene are destroyed during transportation and early sedimentation, no perylene will be formed during diagenesis, no matter how strong the reducing conditions are.

Contrasting intensity of aragonite dissolution and dolomite cementation in glacial versus interglacial intervals of a subtropical carbonate succession

AbstractAragonite and high‐Mg calcite are abundant in modern, neritic carbonate systems but almost absent in their fossil counterparts. Dissolution of these metastable mineral phases commonly leaves no visible trace in the sedimentary record, compromising the derivation of palaeoenvironmental information from the rock record. The upper 25 m of Integrated Ocean Drilling Program (IODP) Site U1460 on the outer ramp of the western Australian Shelf were investigated to study shallow burial (tens of metres) marine diagenesis in organic‐carbon poor sediments using microscopic, total organic carbon, biomarkers and mineralogical analysis in combination with porewater geochemistry. Aragonite dissolution is negligible at the seafloor but intensifies ca 5 m below, even though bulk porewaters are supersaturated for aragonite. This apparent contradiction likely results from dissolution in undersaturated microenvironments. Aragonite dissolution below 5 to 6 m is on average more intense in interglacial compared to glacial intervals. The presence of disseminated framboidal pyrite and porewater results indicate that minor sulphate reduction is active at IODP Site U1460. Sulphate reduction is probably limited by the low organic matter content (ca 0.2%). It is well‐known from the literature that incipient sulphate reduction can lead to a drop in pH and consequently to carbonate dissolution. It is therefore assumed that the slightly higher concentration of organic matter in the interglacial intervals allowed increased aragonite dissolution during sulphate reduction compared to glacial beds. Low amounts of dolomite cement (&lt;15%) start to form at the same depth (5 to 6 m) as aragonite dissolution intensifies. Dolomite formation and aragonite dissolution also show covariance on a metre‐scale below 5 to 6 m, indicating that a low carbonate saturation state might enhance dolomite formation. This mechanism provides an indirect link between dolomite formation, aragonite dissolution and orbital cycles. The outcome of this study, therefore, contributes to a better understanding of differential diagenesis in marine carbonates.

The impact of clay fraction on the strength and stress ratio ( K 0 ) in Gulf of Mexico mudrocks and quartz silt mixtures: implications for borehole stability and fracture gradient

Mudrock strength parameters are required to improve the prediction of fracture gradient during drilling in poorly consolidated formations. Understanding the influence that mineral composition and consolidation stress have on the mechanical properties of mudrocks aids safe well design. Small changes in the mudrock clay content are shown to have significant effects on two important engineering parameters: the lateral stress ratio at rest, K 0 , and the critical state effective friction angle, ϕ ′ cs . A laboratory-testing programme using quartz silt and a Gulf of Mexico clay mixture investigates the effects of mudrock clay content on K 0 and ϕ ′ cs at two stress levels: 1 and 10 MPa. Values of K 0 and ϕ ′ cs were obtained by subjecting composition-controlled clay–silt specimens to a drained uniaxial vertical strain ( K 0 consolidation) phase, followed by an undrained compression triaxial shear phase. Triaxial tests illustrate consistent and systematic increases in K 0 and decreases in ϕ ′ cs , with increases in clay content at both stress levels. Stress dependence is observed through increases in K 0 and decreases in ϕ ′ cs with increases in stress level. Stress-dependent behaviour is shown to be more pronounced in mudrocks of high clay content. A predictive model is presented for K 0 in normally consolidated mudrocks, as a function of clay content and effective stress. The model is used to calculate the fracture gradient (least horizontal stress) profile at the International Ocean Drilling Program (IODP) Expedition 308 Site 1324. The estimated fracture gradient illustrates the effects of clay content and consolidation stress on safe mud weight design. Thematic collection: This article is part of the Geopressure collection available at: https://www.lyellcollection.org/cc/geopressure

A Numerical Model for Determining Deep Methane Flux Linked to the Free Gas Zone: Application to the Ocean Drilling Program Site 995 and Implications for Regional Deep Methane Flux at the Blake Ridge

The lack of the quantification of deep dissolved methane flux prevents us from accurately understanding hydrate accumulation and distribution at a given geologic setting where vertically upward methane advection dominates the hydrate system. The upward deep methane flux was usually applied as an assumed value in many previous studies. Considering the deep methane flux changes the methane concentration in the pore water and further affects the phase transfer between the gas and aqueous phases depending on the in situ methane concentration, we link gas bubbles distribution to deep dissolved methane flux. Here, we constructed a numerical model to quantify the dissolved methane flux from depth based on the parameters related to gas bubble distribution, including the residual gas saturation in sediments and the free gas zone (FGZ) thickness. We then applied our model to ODP Site 995 at the Blake Ridge where methane was sourced from deep layers. Our model results predict an upward deep methane flux of 0.0231 mol/m2/a and the occurrence of another gas interval in deeper sediments, which are consistent with seismic data. We further explored the influence of upward methane flux on hydrate accumulation and found that the thin hydrate occurrence zone at nearby Site 994 likely resulted from a small deep methane flux. Combined with the previous conclusion of high deep methane flux at Site 997, we showed that along the Blake Ridge drilling transect the estimated deep methane fluxes decrease with increasing distance from the crest of the ridge. This approach for quantifying deep methane flux is complementary to the current hydrate accumulation model and provides new insights into the regional methane flux estimation at the Blake Ridge.

Borehole Seismic Observations From the Chicxulub Impact Drilling: Implications for Seismic Reflectivity and Impact Damage

AbstractWe conducted a vertical seismic profile (VSP) in the borehole of International Ocean Discovery Program/International Continental Scientific Drilling Program Expedition 364 Site M0077 to better understand the nature of the seismic reflectivity and the in situ seismic properties associated with the Chicxulub impact structure peak ring. Extraction of the up‐going wavefield from the VSP shows that a strong seismic reflection event imaged in seismic reflection data results from discontinuities in the elastic impedanceZ(the product of density and wave speed) at the top and bottom of a zone of hydrothermally altered melt‐bearing polymict breccia (suevite) that are characterized by anomalously lowZ. Below this strong carbonate/suevite reflection event, the upgoing seismic wavefield is chaotic, indicating high levels of scattering from the suevites and underlying melt rocks and shocked granitoids of the peak ring, in contrast to the clear coherent reflections throughout the overlying Cenozoic sediments. We extract shear wave speeds, which, together with those provided from the complementary sonic log and densities from core scanning, allowed determination ofVP/VSand Poisson's ratiov. These values are anomalously high relative to comparable terrestrial lithologies. We also calculate a variety of damage parameters for the disrupted peak ring granitoids. These values may assist in linking seismic observations to shock levels that are necessary to calibrate current impact models and may also be useful in assessing levels of fracturing within major fault zones.

The Late Miocene‐Early Pliocene Biogenic Bloom in the Eastern Equatorial Pacific: New Insights From Integrated Ocean Drilling Program Site U1335

AbstractThe late Miocene‐early Pliocene “biogenic bloom” (BB) manifests as greatly enhanced biogenic sedimentation in sites along the Equator that has been linked to cooler sea surface temperature (SST) in the eastern equatorial Pacific (EEP). However, the full extent and geometry of the BB in the EEP is less known. To improve on this, we have generated new carbonate content (CaCO3%) and bulk carbonate stable isotope (δ13C and δ18O) records spanning the last 7 Ma at IODP Site U1335, located ca. 5° north of the Equator and to the west of the EEP. Site U1335 δ13C and δ18O records display high‐frequency variations coupled to changes in sediment composition and physical properties comparable to patterns seen at on‐Equator sites further east. During the late Miocene and the early Pliocene bulk δ18O is higher at Site U1335 compared to two off‐Equator sites further east, suggesting cooler SSTs generated by stronger equatorial upwelling reaching northwest of the modern core‐equatorial upwelling belt. Enhanced upwelling at Site U1335 is supported by relatively higher sedimentation rates prior to 4.6 Ma, symptomatic of higher biological production during the BB. These observations suggest that during the BB the equatorial upwelling circulation was more focused and less parallel to the Equator compared to present day.

Sensitivity of the West Antarctic Ice Sheet to +2 °C (SWAIS 2C)

Abstract. The West Antarctic Ice Sheet (WAIS) presently holds enough ice to raise global sea level by 4.3 m if completely melted. The unknown response of the WAIS to future warming remains a significant challenge for numerical models in quantifying predictions of future sea level rise. Sea level rise is one of the clearest planet-wide signals of human-induced climate change. The Sensitivity of the West Antarctic Ice Sheet to a Warming of 2 ∘C (SWAIS 2C) Project aims to understand past and current drivers and thresholds of WAIS dynamics to improve projections of the rate and size of ice sheet changes under a range of elevated greenhouse gas levels in the atmosphere as well as the associated average global temperature scenarios to and beyond the +2 ∘C target of the Paris Climate Agreement. Despite efforts through previous land and ship-based drilling on and along the Antarctic margin, unequivocal evidence of major WAIS retreat or collapse and its causes has remained elusive. To evaluate and plan for the interdisciplinary scientific opportunities and engineering challenges that an International Continental Drilling Program (ICDP) project along the Siple coast near the grounding zone of the WAIS could offer (Fig. 1), researchers, engineers, and logistics providers representing 10 countries held a virtual workshop in October 2020. This international partnership comprised of geologists, glaciologists, oceanographers, geophysicists, microbiologists, climate and ice sheet modelers, and engineers outlined specific research objectives and logistical challenges associated with the recovery of Neogene and Quaternary geological records from the West Antarctic interior adjacent to the Kamb Ice Stream and at Crary Ice Rise. New geophysical surveys at these locations have identified drilling targets in which new drilling technologies will allow for the recovery of up to 200 m of sediments beneath the ice sheet. Sub-ice-shelf records have so far proven difficult to obtain but are critical to better constrain marine ice sheet sensitivity to past and future increases in global mean surface temperature up to 2 ∘C above pre-industrial levels. Thus, the scientific and technological advances developed through this program will enable us to test whether WAIS collapsed during past intervals of warmth and determine its sensitivity to a +2 ∘C global warming threshold (UNFCCC, 2015).

Ship-board determination of whole-rock (ultra-)trace element concentrations by laser ablation-inductively coupled plasma mass spectrometry analysis of pressed powder pellets aboard the D/V &amp;lt;i&amp;gt;Chikyu&amp;lt;/i&amp;gt;

Abstract. The Oman Drilling Project (OmanDP), performed under the International Continental Scientific Drilling Program (ICDP), is an international scientific research project that undertook drilling at a range of sites in the Semail ophiolite (Oman) to collect core samples spanning the stratigraphy of the ophiolite, from the upper oceanic crust down to the basal thrust. The cores were logged to International Ocean Discovery Program (IODP) standards aboard the D/V Chikyu. During ChikyuOman2018 Leg 3 (July–August 2018), participants described cores from the crust–mantle transition (CM) sites. The main rock types recovered at these sites were gabbros, dunites and harzburgites, rocks typically forming the base of the oceanic crust and the shallow mantle beneath present-day spreading centres. In addition to the core description, selected samples were analysed by X-ray fluorescence spectrometry (XRF) for their chemical compositions, including major, minor and some trace elements. To complement these standard procedures, we developed new approaches to measure ultra-trace element concentrations using a procedure adapted from previous works to prepare fine-grained pressed powder pellets coupled with laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis using instrumentation aboard the D/V Chikyu. First, three (ultra)mafic reference materials were investigated to test and validate our procedure (BHVO-2, BIR-1a and JP-1), and then the procedure was applied to a selection of gabbro and dunite samples from the CM cores to explore the limitations of the method in its current stage of development. The obtained results are in good agreement with preferred values for the reference materials and with subsequent solution replicate analyses of the same samples performed in shore-based laboratories following Leg 3 for the CM samples. We describe this procedure for the determination of 37 minor and (ultra-)trace elements (transition elements and Ga, Li and Large-Ion Lithophile Elements (LILE), Rare Earth Elements (REE), High-Field-Strength Elements (HFSE), U, Th, and Pb) in mafic and ultramafic rocks. The presented method has the major advantage that it allows the determination at sea of the (ultra-)trace element concentrations in a “dry”, safe way, without using acid reagents. Our new approach could be extended for other elements of interest and/or be improved to be adapted to other rock materials during future ocean drilling operations aboard the D/V Chikyu and other platforms.

Isotopic filtering reveals high sensitivity of planktic calcifiers to Paleocene–Eocene thermal maximum warming and acidification

Ocean warming and acidification driven by anthropogenic carbon emissions pose an existential threat to marine calcifying communities. A similar perturbation to global carbon cycling and ocean chemistry occurred ∼56 Ma during the Paleocene-Eocene thermal maximum (PETM), but microfossil records of the marine biotic response are distorted by sediment mixing. Here, we use the carbon isotope excursion marking the PETM to distinguish planktic foraminifer shells calcified during the PETM from those calcified prior to the event and then isotopically filter anachronous specimens from the PETM microfossil assemblages. We find that nearly one-half of foraminifer shells in a deep-sea PETM record from the central Pacific (Ocean Drilling Program Site 865) are reworked contaminants. Contrary to previous interpretations, corrected assemblages reveal a transient but significant decrease in tropical planktic foraminifer diversity at this open-ocean site during the PETM. The decrease in local diversity was caused by extirpation of shallow- and deep-dwelling taxa as they underwent extratropical migrations in response to heat stress, with one prominent lineage showing signs of impaired calcification possibly due to ocean acidification. An absence of subbotinids in the corrected assemblages suggests that ocean deoxygenation may have rendered thermocline depths uninhabitable for some deeper-dwelling taxa. Latitudinal range shifts provided a rapid-response survival mechanism for tropical planktic foraminifers during the PETM, but the rapidity of ocean warming and acidification projected for the coming centuries will likely strain the adaptability of these resilient calcifiers.

The in-situ NMR evidence of gas hydrate forming in micro-pores in the Shenhu area, South China Sea

Nuclear magnetic resonance (NMR) measurement could provide information during the formation and dissociation of gas hydrate on the pore structure properties which are of great important to understand the gas production behavior. In this study, the in–situ NMR and other well logging data achieved during the natural gas hydrate drilling program were used to study the pore size and hydrate formation properties in the Shenhu area, South China Sea by comparing transverse magnetic relaxation time (T2) distributions between the gas hydrate zone and the upper water–saturated zone whose properties represent the virgin status. Compared with those of the upper water–saturated layer, increasing resistivity, higher–than–baseline shear modulus, less–than–density–porosity NMR porosity, shortening T2 peak time, reducing amplitude and covered area of T2 distributions and decreasing water–filling pore size denote the association of hydrate. Based on eight bin porosities distribution derived from user-defined time intervals of the T2 distribution for researching the hydrate formation characteristic in different pore size, macro–pores (T2 ≥ 10 ms, rc≥ 0.9 μm), meso–pores (3 ms ≤ T2 < 10 ms, 0.27 μm ≤rc<0.9μm) and micro–pores (T2 < 3 ms, rc< 0.27 μm) were divided. It was found that the meso–pores are the dominant pore size in the Shenhu area, but hydrate form more easily in the macro–pores. Just as the previous experience, gas hydrate forms primarily in macro–pores and meso–pores resulting in an increase of micro–pores. In addition, another mode was achieved that gas hydrate forms in the three types of pore spaces leading to a decrease of micro–pores. Both forming modes can develop reservoirs with high hydrate saturation that can exceed 30%.

Atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; estimates for the Miocene to Pleistocene based on foraminiferal &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;11&amp;lt;/sup&amp;gt;B at Ocean Drilling Program Sites 806 and 807 in the Western Equatorial Pacific

Abstract. Constraints on the evolution of atmospheric CO2 levels throughout Earth's history are foundational to our understanding of past variations in climate. Despite considerable effort, records vary in their temporal and spatial coverage and estimates of past CO2 levels do not always converge, and therefore new records and proxies are valuable. Here we reconstruct atmospheric CO2 values across major climate transitions over the past 16 million years using the boron isotopic composition (δ11B) of planktic foraminifera from 89 samples obtained from two sites in the West Pacific Warm Pool, Ocean Drilling Program (ODP) Sites 806 and 807, measured using high-precision multi-collector inductively coupled plasma mass spectrometry. We compare our results to published data from ODP Site 872, also in the Western Equatorial Pacific, that goes back to 22 million years ago. These sites are in a region that today is near equilibrium with the atmosphere and are thought to have been in equilibrium with the atmosphere for the interval studied. We show that δ11B data from this region are consistent with other boron-based studies. The data show evidence for elevated pCO2 during the Middle Miocene and Early to Middle Pliocene, and reductions in pCO2 of ∼200 ppm during the Middle Miocene Climate Transition, ∼250 ppm during Pliocene Glacial Intensification and ∼50 ppm during the Mid-Pleistocene Climate Transition. During the Mid-Pleistocene Transition there is a minimum pCO2 at marine isotopic stage (MIS) 30. Our results are consistent with a coupling between pCO2, temperature and ice sheet expansion from the Miocene to the late Quaternary.

Geochemical constraints on mantle source nature and recycling of subducted sediments in the Sulu Sea

The Sulu Sea is a marginal spreading basin in the triple junction of Euro-Asia/Indian/Pacific plates. The genesis of seafloor basalts is crucial for understanding the nature and evolution history of the underlying mantle in this region. Nevertheless, the mantle source of the Sulu Sea remains unclear due to limited geochemical data. In this study, we report a complete set of whole-rock major and trace elements and Sr-Nd-Pb-Hf isotopes for the volcanic rocks at Ocean Drilling Program Site U768 in the Southeast Sulu Sea. These volcanic rock samples are characterized by transitional trace element compositions between mid-ocean ridge basalts (MORBs) and island arc basalts (IABs). A subduction modified depleted mantle source is indicated by their higher Th/Yb ratios than the MORB-OIB array and trace element patterns. We propose that the pelagic sediments contributed to the mantle source of the Southeast Sulu Sea based on the plots of 206Pb/204Pb vs. Ce/Pb and Th/Nb. Based on the decoupled Hf–Nd isotopes and the variation of Pb isotopes for Site U768 volcanic rocks, we suggest that subducted pelagic sediments contributed to the origin of the Indian-type mantle of the Southeast Sulu Sea.

Bottom water redox dynamics during the Early Cretaceous Weissert Event in ODP Hole 692B (Weddell Sea, Antarctica) reconstructed from the benthic foraminiferal assemblages

Benthic foraminifera at Ocean Drilling Program (ODP) Hole 692B were studied to understand variations in oxygen and organic-matter fluxes in bottom waters during the Early Cretaceous. The upper Berriasian to lower Barremian black shales, characterized by high concentrations of total organic carbon (TOC) ranging between 1.3 and 18%, were deposited in an outer neritic-upper bathyal environment (~200–500 m) according to benthic foraminifera assemblages. A new high-resolution record of benthic foraminiferal assemblages of high-latitude, dominated by infaunal taxa ( Citharina , Eoguttulina , Laevidentalina , Lagena , Lenticulina , Marginulina , N odosaria, Planularia , Saracenaria , and Vaginulinopsis ), is described in depleted‑oxygen and high organic‑carbon flux conditions. Extremely dysoxic conditions are recorded at the onset of the carbon isotope excursion (CIE) marking the Weissert Event (late Valanginian), followed by a period of anoxic conditions in bottom waters. A repopulation event of benthic foraminifera, linked to an increase in oxygen concentrations, coincided with the global cooling episode that characterized the late part of the Weissert Event. Subsequently, there were short periods in the late Valanginian and the late early Hauterivian when the bottom waters experienced increased oxygen concentrations. Possibly, bottom currents related to the influx of Southern Ocean waters favored short-term pulses of ventilation under constant increased organic‑carbon flux during the late Valanginian and late Hauterivian. • New Lower Cretaceous micropaleontological data from the southern high latitudes • Benthic foraminifera indicate an outer neritic-upper bathyal setting. • Alternated anoxic and dysoxic conditions during the Weissert Event in bottom-waters • Benthic foraminiferal repopulation through the Weissert Event • ODP 692B was influenced by the interplay of short-term pulses of ventilation.

Hydromechanical Effects of Micro‐Organisms on Fine‐Grained Sediments During Early Burial

AbstractMicro‐organisms are known to change fluid flow and permeability processes in subsurface environments, but this has only been demonstrated for coarse‐grained sediments and fractures. For fine‐grained sediments (mudstones), little is known about the effects of micro‐organisms on hydromechanical properties. Here, we investigated the influence of micro‐organisms on the porosity, permeability, and compressibility of fine‐grained sediments. We performed resedimentation experiments with and without micro‐organisms added to two reconstituted, fine‐grained sediment samples. These sediments were collected from the Ursa and Brazos‐Trinity Basins in the Gulf of Mexico during Integrated Ocean Drilling Program Expedition 308. Micro‐organisms caused a systematic, yet small increase in compression index for both sediments. Changes to permeability caused by micro‐organisms, while relatively minor, were greater for the Ursa sediment than the Brazos‐Trinity sediment. Additionally, the effect of micro‐organisms on permeability is greater at higher porosities and lower vertical effective stresses. Differences in permeability behavior between the two sediments are likely due to differences in sediment properties and nutrients for microbial growth. We therefore suggest that the effectiveness of micro‐organisms at altering fluid flow in fine‐grained sediments is dependent on burial depth (porosity as a function of vertical effective stress) and the grain size, pore and pore throat size, and specific surface area of a sediment. Characterizing the effects of micro‐organisms on the hydromechanical properties of fine‐grained sediments can further our understanding of the controls on pore pressure near the sediment–water interface in marine environments and aid in bioclogging practices around contaminated sites in terrestrial environments.

First evidence for Neoproterozoic rocks offshore South-East Greenland

AbstractMeta-sedimentary rocks recovered beneath Palaeogene basalts near the base of Ocean Drilling Program (ODP) Leg 152-917A offshore South-East Greenland were thought to be of Late Cretaceous age. This interpretation, however, has several inconsistencies as it requires a tectono-metamorphic event during the Cretaceous not recognized in the North Atlantic region, and the presence of a wide Mesozoic sedimentary basin that extended from SE-Greenland to the Rockall Plateau, for which there is currently no evidence. Here, we report a Neoproterozoic U/Pb apatite age of 905 ± 21 Ma and a younger 40Ar/39Ar isochron whole-rock age of 820 ± 40 Ma for an altered tuff layer that occurs in the upper part of the meta-volcaniclastic sequence recovered from hole 917A. The 40Ar/39Ar step-heating ages on biotite and whole-rock mini-cores from deeper in hole 917A yielded Palaeoproterozic dates that cluster around 1950 to 1850 Ma, pointing toward a Palaeoproterozoic source. The U/Pb apatite date is interpreted as the eruption age of the tuff layer, whereas the younger whole-rock 40Ar/39Ar age is consistent with low-temperature greenschist alteration of volcanic glass and secondary mineral growth during sedimentary burial in an extensional regime. The c. 905 Ma age for the tuff provides the first evidence for Neoproterozoic rocks offshore South-East Greenland and suggests a correlation between this sequence and the Torridon Group in the Hebridean Foreland of the Scottish Caledonides. The calc-alkaline nature of the volcaniclastic rocks and the age of the tuff layer point toward a source area with arc-magmatism related to the Renlandian event of the Valhalla Orogeny.