Due to its history, development of its hydrologic regime, recharge-discharge mechanisms, geologic formations and development of its hydrodynamic pattern, the groundwater resources of the Morsott–El Aouinet basin show a very wide range of chemistries. In this paper, the groundwater hydrochemistries are studied through well sampling from study area. Hydrochemical and members are identified and the sources of water salinization are defined. It was found that the evaporites within the Triassic rocks are the main contributors to the salinization of groundwater. The ionic speciation and mineral dissolution/precipitation was calculated by WATEQF package software. The increase in salinity is related to the dissolution and/or precipitation processes during the water-rock interaction and to the cationic exchange reactions between groundwater and clay minerals. The isotopic analysis of some groundwater samples shows a similarity with the meteoric waters, which reflects their short residence time and a lowest evaporation phenomenon of infiltrated groundwater.
Thermochemical reduction of MgSO4 by natural gas was carried out in the presence of water. Chemical and carbon isotopic variations were characterized with microcoulometry, gas chromatography, FT-IR, XRD and GC-C-IRMS. It was found that natural gas reacted with MgSO4 to produce H2S, CO2, MgO and solid bitumen as the main products of thermochemical sulfate reduction (TSR). Gas dryness, gas souring index and the extent of reaction parameter positively correlated with temperature. The extent of acidulation and oxidation of natural gas were intensified as TSR proceeded. TSR has induced an evident carbon isotope fractionation in natural gas. Based on the experimental results, the reaction mechanism was tentatively investigated. It was found that the catalytic role of a metallic ion in the TSR process may be controlled by at least three factors: the charges and the radius of a metallic ion and the number of Lewis acid centers scatted on the surface of the sulfates. The last factor is largely determined by the amount of water in a TSR system. A small amount of water and metallic ions with more charges and short radius may effectively initiate the TSR.
Geochemical characteristics of hydrothermal fluids in the Iheya North hydrothermal field, mid-Okinawa Trough, was investigated. Twelve-years observation reveals temporal variation of vent fluid chemistry potentially controlled by temporally varying pattern of the phase-separation and -segregation, while the constant Element/Cl ratios among the periods and chimneys indicate the stable chemical composition of the source hydrothermal fluid prior to undergoing phase-separation. The high K contents in the estimated source fluid are typical in the arc-backarc hydrothermal systems due to the hydrothermal reaction with the K-enriched felsic rocks. The high I, B and NH4 contents and alkalinity are derived from decomposition of the sedimentary organic matters. Compositional and isotopic properties of gas species, CH4, H2, CO2, and C2H6, strongly suggest a dominance of biogenic CH4 associated with the sedimentary organic matter. Based on the carbon mass balance calculation and the multidisciplinary investigations of the Iheya North hydrothermal system since the discovery, we hypothesized that the microbial methanogenesis occurs not only within the Central Valley where hydrothermal vents exist, but also in the spatially abundant and widespread basin-filling sediments surrounding the Iheya North Knoll, and that the microbially produced CH4 is recharged together with the source fluid into the deep hydrothermal reaction zone. This “Microbial Methanogenesis at Recharge area in hydrothermal circulation” (MMR) model would be an implication for the generation and incorporation of hydrothermal fluid CH4 in the deep-sea hydrothermal systems but also for those of cold seep CH4 and for the presently uncertain hydrothermal fluid paths in the subseafloor environments. In the near future, the IODP drilling will be conducted in the Iheya North hydrothermal system, and give an excellent opportunity to testify our MMR model.
A pair of series straight long-chain 2- and 1-alkyl naphthalenes (aNs) with alkyl chain carbon number up to 30 was detected in late Cretaceous sedimentary source rocks of the onshore Songliao Basin, NE China. Their sedimentary profile was shown to correlate positively with the relative abundances of several higher plant biomarkers including iP-iHMN and phenanthrene and weakly inversely with the relative abundance of alkylbenzenes. In contrast, the aNs distribution shows no relationship with hydrocarbon maturity indicators. The TOC, δ13C profile and other molecular features (e.g., CPI, OEP, Pr/Ph, Ga/C31H) were consistent with transgressive/regressive water cycles of the palaeo-lake of Songliao Basin. Decreasing Pr/Ph values in the upper horizon indicative of increasingly anoxic conditions. The distinctive occurrence and distribution of the long-chain aN compounds on the profile of the SK-1 borehole may imply some unique source inputs under particular lacustrine environmental conditions.
Continuous He, 222Rn concentrations and gamma dose rate were simultaneously monitored for pre-seismic signatures at two thermal springs in India that are separated at a distance of approximately 1612 km. The recordings of six month monitoring period (September 15, 2007–March 15, 2008) are presented here. In this paper, we make a cross correlation study of the simultaneously recorded multi-component gas-geochemical data from the two thermal springs. In the monitoring period a number of prominent fluctuations beyond the regular diurnal variations in the gas composition were recorded. We attempt to find out the linkage between the recorded distinct variations with local and remote seismic activities. Anomalous fluctuations in the spring gases were observed during the period December 24–27, 2007 at both the thermal springs and these anomalies may be correlated to the distant (~1000 km) China earthquake of magnitude M = 6.3 that occurred on January 09, 2008. Based on the obtained sequence of data points a time series analysis to relate earthquake magnitude, epicentral distance and precursor time through statistical methods and empirical equations related to the zone of influence is made. Concurrent monitoring of multi-component gas-geochemical anomalies recorded at a number of distant sites appears to be a potential tool to deal with the commonly debated question of earthquake precursors.
One extremely young volcano (0.05–1 Ma) and other young volcanoes (1.8, 4.2, 6.0, and 8.5 Ma) composed of strongly alkaline magma were recently discovered on the abyssal plain of the Early Cretaceous (135 Ma) Pacific Plate. These volcanoes were dubbed “petit-spots”. The petit-spot volcanic province represents more than 8 Myr of activity over a large area (~600 km along the direction of plate motion), but with a relatively small volume of magma production, thus indicating a small supply of heat inconsistent with a hotspot. The low-flux petit-spot volcanoes may be related to the occurrence of a tensional field of lithosphere caused by plate flexure, with the ascending melt derived from a mantle source susceptible to partial melting. Rock samples from the young volcanoes are highly vesicular (up to 60%) despite high hydrostatic pressures at 6000 m water depth, indicating volatile-rich magmas. The depleted heavy rare earth elements and high radiometric isotopic ratios of noble gases indicate the magma was derived from upper mantle. Nevertheless, the low 143Nd/144Nd, high 87Sr/86Sr, low 206Pb/204Pb, and low 207Pb/204Pb ratios are similar to enriched or fertile compositions such as oceanic island basalts. These apparently conflicting data are explained by the extremely small degree of partial melting of recycled materials in the degassing mantle of the asthenosphere, probably with carbonate in the source. The petit-spot volcanoes, therefore, provide a unique window into the nature of the oceanic plate and underlying asthenosphere prior to subduction.
We have devised a new supplementary activator for lead isotope measurements performed using thermal ionization mass spectrometry (TIMS). The activator consisted of a mixture of 250 ppm Ge and 500 ppm Re and was used with normal colloidal silica. This new substance shows excellent performance in terms of enhancing the ion beam intensity. The supplementary activator yielded 3.5–4.5 × 10–11 A 208Pb for 10 ng Pb, 1.5–2.5 × 10–11 A for 5 ng Pb, and ~1.5 × 10–11 A for 2.5 ng Pb samples, indicating that the new activator was superior to those currently in use. This improvement should be applicable to samples with low Pb content, for example, in environmental tracer studies and Pb–Pb chronology studies.
The sea-to-air flux of C2H5I (iodoethane) in the Indian Ocean and the Southern Ocean was estimated from the Henry’s law constant (KH) and the measured partial pressures of C2H5I in surface seawater and air. The values of KH, defined as the ratio of molar concentration (mol l–1) to partial pressure (atm), for ten volatile organic compounds (VOCs) (CFCl3 (CFC-11), C5H8 (isoprene), C2H2F4 (HFC-134a), CHF2Cl (HCFC-22), CH3I, CH2Br2, C2H5I, CH2Cl2, CH2ClI, and CHBr3) were measured with an equilibrator and a purge-and-trap system in combination with gas chromatography-mass spectrometry. Ours is the first report of the KH values for C2H5I and C5H8 as functions of temperature. The KH values for the other VOCs were in good agreement with previously reported values. We calculated the sea-to-air flux of C2H5I using the newly determined KH. Large sea-to-air fluxes (average, 0.04 nmol m–2h–1) were widespread in the Southern Ocean. We suggest that high biological productivity led to a high rate of C2H5I production in the subpolar water, and that the strong winds that frequently blow over the Southern Ocean resulted in the large sea-to-air flux.