Chemical composition of interstitial waters from sediments of brine-bearing deeps of the Red Sea

Data on concentrations of the major ions (Cl, SO4, Alk, Na, K, Ca, Mg, NH4) in interstitial waters from sediments of three brine-bearing deeps of the Red Sea rift zone are reported. Interstitial waters of the Atlantis-II Deep have the highest salinity (310.1 g/l), of the Discovery Deep - slightly lower (298.8 g/l), and of the Suakin Deep - the lowest (159.9 g/l). Interstitial waters of all three deeps are characterized by low, compared with sea water, absolute and relative concentrations of Mg and SO4 ions and have extremely low alkaline reserve (0.15-0.64 meq/l). Concentrations of K, Ca and especially Na and Cl ions, as compared with sea water, are highly increased. Interstitial waters from the deeps in study have high, compared with sea water, concentrations of NH4 (12-62 mg/l).

Chemical composition of smectite-bearing basal metalliferous sediments from DSDP Leg 9

The mineralogy and P, Fe and Mn contents of basal metalliferous and nonmetalliferous sediments of two Deep Sea Drilling Project cores (Sites 77 and 80) were investigated. When compared with superjacent nonmetalliferous material, basal metalliferous sediments are significantly enriched in P, Fe and Mn. Among the phases present in the metalliferous sediment samples are a poorly-crystalline Fe-rich smectite and X-ray amorphous Fe oxyhydroxides. P is associated primarily with the oxyhydroxides. Adsorption of phosphate on smectite does not seem to play any role in the uptake of P by metalliferous sediments. An estimate of the removal of P by on- and off-ridge metallogenic deposition suggests that this process strongly affects the overall geochemical balance of phosphorus in the World Ocean.

Distribution of organic-rich sediments through the Phanerozoic

It is commonly assumed that rates of accumulation of organic-rich strata have varied through geologic time with some periods that were particularly favorable for accumulation of petroleum source rocks or coals. A rigorous analysis of the validity of such an assumption requires consideration of the basic fact that although sedimentary rocks have been lost through geologic time to erosion and metamorphism. Consequently, their present-day global abundance decreases with their geologic age. Measurements of the global abundance of coal-bearing strata suggest that conditions for coal accumulation were exceptionally favorable during the late Carboniferous. Strata of this age constitute 21% of the world's coal-bearing strata. Global rates of coal accumulation appear to have been relatively constant since the end of the Carboniferous, with the exception of the Triassic which contains only 1.75% of the world's coal-bearing strata. Estimation of the global amount of discovered oil by age of the source rock show that 58% of the world's oil has been sourced from Cretaceous or younger strata and 99% from Silurian or younger strata. Although most geologic periods were favourable for oil source-rock accumulation the mid-Permian to mid-Jurassic appears to have been particularly unfavourable accounting for less than 2% of the world's oil. Estimation of the global amount of discovered natural gas by age of the source rock show that 48% of the world's oil has been sourced from Cretaceous or younger strata and 99% from Silurian or younger strata. The Silurian and Late Carboniferous were particularly favourable for gas source-rock accumulation respectively accounting for 12.9% and 6.9% of the world's gas. By contrast, Permian and Triassic source rocks account for only 1.7% of the world's natural gas. Rather than invoking global climatic or oceanic events to explain the relative abundance of organic rich sediments through time, examination of the data suggests the more critical control is tectonic. The majority of coals are associated with foreland basins and the majority of oil-prone source rocks are associated with rifting. The relative abundance of these types of basin through time determines the abundance and location of coals and petroleum source rocks.

The use of phospholipid fatty acid analysis to measure impact of acid rock drainage on microbial communities in sediments

The impact of acid rock drainage (ARD) and eutrophication on microbial communities in stream sediments above and below an abandoned mine site in the Adelaide Hills, South Australia, was quantified by PLFA analysis. Multivariate analysis of water quality parameters, including anions, soluble heavy metals, pH, and conductivity, as well as total extractable metal concentrations in sediments, produced clustering of sample sites into three distinct groups. These groups corresponded with levels of nutrient enrichment and/or concentration of pollutants associated with ARD. Total PLFA concentration, which is indicative of microbial biomass, was reduced by >70% at sites along the stream between the mine site and as far as 18 km downstream. Further downstream, however, recovery of the microbial abundance was apparent, possibly reflecting dilution effect by downstream tributaries. Total PLFA was >40% higher at, and immediately below, the mine site (0-0.1 km), compared with sites further downstream (2.5-18 km), even after accounting for differences in specific surface area of different sediment samples. The increased microbial population in the proximity of the mine source may be associated with the presence of a thriving iron-oxidizing bacteria community as a consequence of optimal conditions for these organisms while the lower microbial population further downstream corresponded with greater sediments' metal concentrations. PCA of relative abundance revealed a number of PLFAs which were most influential in discriminating between ARD-polluted sites and the rest of the sites. These PLFA included the hydroxy fatty acids: 2OH12:0, 3OH12:0, 2OH16:0; the fungal marker: 18:2ω6; the sulfate-reducing bacteria marker 10Me16:1ω7; and the saturated fatty acids 12:0, 16:0, 18:0. Partial constrained ordination revealed that the environmental parameters with the greatest bearing on the PLFA profiles included pH, soluble aluminum, total extractable iron, and zinc. The study demonstrated the successful application of PLFA analysis to rapidly assess the toxicity of ARD-affected waters and sediments and to differentiate this response from the effects of other pollutants, such as increased nutrients and salinity.

Diverse and Novel nifH and nifH-Like Gene Sequences in the Deep-Sea Methane Seep Sediments of the Okhotsk Sea

Diverse nifH and nifH-like gene sequences were obtained from the deep-sea surface sediments of the methane hydrate-bearing Okhotsk Sea. Some sequences formed novel families of the NifH or NifH-like proteins, of currently unresolved bacterial or archaeal origin. Comparison with other marine environments indicates environmental specificity of some of the sequences, either unique to the methane seep sediments of the Okhotsk Sea or to the general deep-sea methane seep sedimentary environments.

Genetic model of the hydrate system in the fine grain sediments in the northern continental slope of South China Sea

Gas hydrate samples were obtained firstly in China by drilling on the northern margin of South China Sea (SCS). To understand the formation mechanism of this unique accumulation system, this paper discusses the factors controlling the formation of the system by accurate geophysical interpretation and geological analysis, based on the high precision 2-D and 3-D multichannel seismic data in the drilling area. There are three key factors controlling the accumulation of the gas hydrate system in fine grain sediment: (1) large volume of fluid bearing methane gas Joins the formation of gas hydrate. Active fluid flow in the northern South China Sea makes both thermal gas and/or biogenic gas migrate into shallow strata and form hydrate in the gas hydrate stability zone (GHSZ). The fluid flow includes mud diapir and gas chimney structure. They are commonly characterized by positive topographic relief, acoustic turbidity and push-down, and low reflection intensity on seismic profiles. The gas chimneys can reach to GHSZ, which favors the development of BSRs. It means that the active fluid flow has a close relationship with the formation and accumulation of gas hydrate. (2) The episodic process of fracture plays an important role in the generation of gas hydrate. It may provide the passage along which thermogenic or biogenic gas migrated into gas hydrate stability zone (GHSZ) upward. And it increases the pore space for the growth of hydrate crystal. (3) Submarine landslide induced the anomalous overpressure activity and development of fracture in the GHSZ. The formation model of high concentration gas hydrate in the drilling sea area was proposed on the basis of above analysis.

Spatial budgetary evaluation of organochlorine contaminants in the sediments of Cochin Estuary, India

This paper presents the first detailed investigation on the residual levels of organochlorine insecticide (OCI) concentrations in the Cochin estuarine sediment. It aims in elucidate their distribution and ecological impact on the aquatic system. Concentrations of persistent organochlorine compound (OC) were determined for 17 surface sediment samples which were collected from specific sites of Cochin Estuarine System (CES) over a period of November 2009 and November 2011. The contaminant levels in the CES were compared with other worldwide ecosystems. The sites bearing high concentration of organochlorine compounds are well associated with the complexities and low energy environment. Evaluation of ecotoxicological factors suggests that adverse biological effects are expected in certain areas of CES

A preliminary investigation of the release of oil from contaminated clays and other fine-grained sediments during consolidation

Fine-grained sediments on land, or in a freshwater or marine environment, may become contaminated with a wide range of pollutants including hydrocarbons. This paper is concerned with preliminary studies of the mobilization and transportation of hydrocarbons, during the process of consolidation, to adjacent sediments or water bodies. A modified Rowe Cell was used to measure the consolidation properties of prepared kaolinite and bentonite clay-water slurries, with and without the addition of oil, along with hydrocarbon-bearing drill-cuttings samples taken from the sea-bed adjacent to two North Sea oil-well platforms. The consolidation properties of the kaolinite and bentonite clay slurries were little altered by the addition of oil, which was present at concentrations of between 8073 and 59 572 mg kg(-1). During each consolidation stage, samples of the expelled pore-fluids were collected and analysed for oil content. These values were very low in comparison with the original oil concentration in the samples and changed little between each consolidation stage. Analysis of the slurry samples both before and after consolidation confirms that, proportionally, little oil is removed as a result of consolidation. The implication of these results is that, for the range of samples tested, the very high hydraulic gradients and particle rearrangements that occur during the process of consolidation are capable of releasing only proportionally small amounts of oil bound to the fine-grained clay and silt particles.

A preliminary investigation of the release of oil from contaminated clays and other fine-grained sediments during consolidation

Fine-grained sediments on land, or in a freshwater or marine environment, may become contaminated with a wide range of pollutants including hydrocarbons. This paper is concerned with preliminary studies of the mobilization and transportation of hydrocarbons, during the process of consolidation, to adjacent sediments or water bodies. A modified Rowe Cell was used to measure the consolidation properties of prepared kaolinite and bentonite clay-water slurries, with and without the addition of oil, along with hydrocarbon-bearing drill-cuttings samples taken from the sea-bed adjacent to two North Sea oil-well platforms. The consolidation properties of the kaolinite and bentonite clay slurries were little altered by the addition of oil, which was present at concentrations of between 8073 and 59 572 mg kg(-1). During each consolidation stage, samples of the expelled pore-fluids were collected and analysed for oil content. These values were very low in comparison with the original oil concentration in the samples and changed little between each consolidation stage. Analysis of the slurry samples both before and after consolidation confirms that, proportionally, little oil is removed as a result of consolidation. The implication of these results is that, for the range of samples tested, the very high hydraulic gradients and particle rearrangements that occur during the process of consolidation are capable of releasing only proportionally small amounts of oil bound to the fine-grained clay and silt particles.

Apatite as an indicator of fluid salinity: An experimental study of chlorine and fluorine partitioning in subducted sediments

In order to constrain the salinity of subduction zone fluids, piston-cylinder experiments have been conducted to investigate the partitioning behaviour of Cl and F in subducted sediments. These experiments were performed at H2O-undersaturated conditions with a synthetic pelite starting composition containing 800 ppm Cl, over a pressure and temperature range of 2.5–4.5 GPa and 630–900 °C. Repetitive experiments were conducted with 1900 ppm Cl + 1000 ppm F, and 2100 ppm Cl. Apatite represents the most Cl-abundant mineral phase, with Cl concentration varying in the range 0.1–2.82 wt%. Affinity for Cl decreases over the following sequence: aqueous fluid > apatite ⩾ melt > other hydrous minerals (phengite, biotite and amphibole). It was found that addition of F to the Cl-bearing starting composition significantly lowers the Cl partition coefficients between apatite and melt (DClAp–melt) and apatite and aqueous fluid (DClAp–aq). Cl–OH exchange coefficients between apatite and melt (KdCl–OHAp–melt) and apatite and aqueous fluid (KdCl–OHAp–aq) were subsequently calculated. KdCl–OHAp–melt was found to vary from 1 to 58, showing an increase with temperature and a decrease with pressure and displaying a regular decrease with increasing H2O content in melt. Mole fractions of Cl and OH in melt were calculated based on an ideal mixing model for H2O, OH, O, Cl and F. The Cl contents of other hydrous minerals (phengite, biotite and amphibole) fall between 200 and 800 ppm, with resultant Cl partition coefficients from 0.02 to 0.49, appearing independent of the bulk Cl and F content. Preliminary data from this study show that the partitioning behaviour of F is strongly in favour of apatite relative to melt and phengite, with DFAp–melt = 15–51. Apatites from representative eclogite facies metasediments were examined and found to have low Cl contents close to ∼100 ppm. Calculations using our experimentally determined KdCl–OHAp–aq of 0.004 at 2.5 GPa, 630 °C indicate a low salinity character (0.5–2 wt% NaCleq) for the fluid formed during dehydration of subducted oceanic sediment at ∼80 km depth.

Desiccation of phyllosilicate-bearing samples as analog for desiccation cracks on Mars: Experimental setup and initial results

The surface of Mars is host to many regions displaying polygonal crack patterns that have been identified as potential desiccation cracks. These regions are mostly within Noachian-aged terrains and are closely associated with phyllosilicate occurrences and smectites in particular. We have built a laboratory setup that allows us to carry out desiccation experiments on Mars-analog materials in an effort to constrain the physical and chemical properties of sediments that display polygonal cracks. The setup is complemented by a pre-existing simulation chamber that enables the investigation of the spectral and photometric properties of analog materials in Mars-like conditions. The initial experiments that have been carried out show that (1) crack patterns are visible in smectite-bearing materials in varying concentrations down to similar to 10% smectite by weight, (2) chlorides, and potentially other salts, delay the onset of cracking and may even block it from occurring entirely, and (3) the polygonal patterns, while being indicative of the presence of phyllosilicates, cannot be used to differentiate between various phyllosilicate-bearing deposits. However, their size-scale and morphology yields important information regarding their thickness and the hydrological conditions at the time of formation. Furthermore, the complementary spectral measurements for some of the analog samples shows that crack patterns may develop in materials with such low concentrations of smectites that would not be expected to be identified using remote-sensing instruments. This may explain the presence of polygonal patterns on Mars in sediments that lack spectral confirmation of phyllosilicates. (C) 2015 Elsevier Ltd. All rights reserved.

Stable isotope and geochemical record of sediments from the Bering Sea

here is controversy over the role of marine methane hydrates in atmospheric methane concentrations and climate change during the last glacial period. In this study of two sediment cores from the southeast Bering Sea (700 m and 1467 m water depth), we identify multiple episodes during the last glacial period of intense methane flux reaching the seafloor. Within the uncertainty of the radiocarbon age model, the episodes are contemporaneous in the two cores and have similar timing and duration as Dansgaard-Oeschger events. The episodes are marked by horizons of sediment containing 13C-depleted authigenic carbonate minerals; 13C-depleted archaeal and bacterial lipids, which resemble those found in ANME-1 type anaerobic methane oxidizing microbial consortia; and changes in the abundance and species distribution of benthic foraminifera. The similar timing and isotopic composition of the authigenic carbonates in the two cores is consistent with a region-wide increase in the upward flux of methane bearing fluids. This study is the first observation outside Santa Barbara Basin of pervasive, repeated methane flux in glacial sediments. However, contrary to the "Clathrate Gun Hypothesis" (Kennett et al., 2003), these coring sites are too deep for methane hydrate destabilization to be the cause, implying that a much larger part of the ocean's sedimentary methane may participate in climate or carbon cycle feedback at millennial timescales. We speculate that pulses of methane in these opal-rich sediments could be caused by the sudden release of overpressure in pore fluids that builds up gradually with silica diagenesis. The release could be triggered by seismic shaking on the Aleutian subduction zone caused by hydrostatic pressure increase associated with sea level rise at the start of interstadials.