Distribution of B, Cl and Their Isotopes in Pore Waters Separated from Gas Hydrate Potential Areas, Offshore Southwestern Taiwan

Section: Introductionmentioning

confidence: 57%

Methane Venting in Gas Hydrate Potential Area Offshore of SW Taiwan: Evidence of Gas Analysis of Water Column Samples

Yang¹,

Chuang²,

Lin³

et al. 2006

“…Geological and geochemical characteristics of the cored sediments have been investigated, they include: grain sizes, mineral components and physical properties of the sediments and clay mineral distribution (Jiang et al 2006), SO 4 2-, Cl -, organic carbon and sulfide distribution in the sediments , salinity and CH 4 concentration in the bottom water and CH 4 and carbon isotopic composition of the pore-space gases of cored sediments Yang et al 2006), B and Cl isotopes in the pore waters (Chao and You 2006), and magnetic properties of magnetic minerals in the sediments (Horng and Chen 2006). Methanederived authigenic carbonate with highly depleted carbon isotope values (-54 to -43%) have been found both on and offshore of SW Taiwan .…”

Section: Cgs Gas Hydrate Investigation Programmentioning

confidence: 99%

Distribution and Characters of Gas Hydrate Offshore of Southwestern Taiwan

Liu¹,

Schnürle²,

Wang³

et al. 2006

149

108

ABSTRACT1 Institute of Oceanography, National Taiwan University, Taipei, Taiwan, ROC 2 Central Geologic Survey, Taipei, Taiwan, ROC 3 Exploration Department, Chinese Petroleum Company, Miaoli, Taiwan, ROC * Corresponding author address: Prof. Char-Shine Liu, Institute of Oceanography, National Taiwan University, Taipei, Taiwan, ROC; E-mail: csliu@ntu.edu.tw Bottom simulating reflector (BSR) is a key indicator for the presence of gas hydrate beneath the sea floor. Widely distributed BSRs have been observed in the area offshore of southwestern Taiwan where the active accretionary complex meets with the passive China continental margin. In order to better understand the distribution and characters of the gas hydrate in the region, closely spaced (1.86-km line spacing) multichannel seismic reflection surveys have been conducted in recent years under the support of the Central Geological Survey, ROC. Over 10000 km of multichannel seismic reflection profiles have been collected that cover an area of about 10000 km 2 offshore of southwestern Taiwan. BSRs can be identified along 50% of the seismic profiles that we collected. A newly compiled BSR distribution map suggests that gas hydrates are distributed both in the passive margin of the China continental slope as well as in the submarine Taiwan accretionary wedge, from water depths of 500 to over 3000 m. Gas hydrates are most concentrated underneath anticlinal ridges in the accretionary wedge, and underneath the slope ridges of the passive continental margin that were formed due to sedimentary processes. Active fluid activities are evident from various features observed on seismic reflection and chirp sonar profiles, such as mud volcanoes, gas plumes and gas charged shallow sedimentary layers. Fluid migration model has been established from a set of pseudo 3D seismic reflection data. The predicted locations of high fluid Terr. Atmos. Ocean. Sci., Vol. 17, No. 4, December 2006 616 flux correlate well with those interpreted from geochemical analyses that show very high methane concentrations and very shallow sulfate-methane interfaces (SMI). This demonstrates the importance of structural control over gas hydrate emplacement. From the observed gas hydrate distribution and characters, the area offshore of southwestern Taiwan provides an ideal place to study and compare the formation and migration of gas hydrates under different tectonic settings.

“…The potential of methane as a major future source of energy and as a mechanism in altering global climate have been the focus of intense scientific research (e.g., Kvenvolden 1988;MacDonald 1990). A number of geophysical and geochemical data indicates that gas hydrate may exist in the southwestern Taiwan continental margin sediments (Chi et al 1998;Liu et al 2003;Chao and You 2006;Chiu et al 2006;Chuang et al 2006;Horng and Chen 2006;Huang et al 2006;Jiang et al 2006;Liu et al 2006;Oung et al 2006;Shyu et al 2006;Yang et al 2006). Geophysical studies (Liu et al 2004a;Chiu et al 2006;Liu et al 2006) of the Taiwan gas hydrate program showed that a strong Bottom Simulating Reflector (BSR) covered a large area of the southwestern Taiwan continental margin, indicating abundant gas hydrate exists in the sediments of the active continental margin near Taiwan.…”

Section: Introductionmentioning

confidence: 99%

Methane Migration and Its Influence on Sulfate Reduction in the Good Weather Ridge Region, South China Sea Continental Margin Sediments

Lin¹,

Hsieh²,

Lim³

et al. 2006

ABSTRACT1 Institute of Oceanography, National Taiwan University, Taipei, Taiwan, ROC 2 Department of Geosciences, National Taiwan University, Taipei, Taiwan, ROC 3 Central Geological Survey, MOEA, Taipei, Taiwan, ROC * Corresponding author address: Prof. Saulwood Lin, Institute of Oceanography, National Taiwan University, Taipei, Taiwan, ROC; E-mail: swlin@ntu.edu.tw Bacteria sulfate reduction is a major pathway for organic carbon oxidation in marine sediments. Upward diffusion of methane from gas hydrate deep in the sedimentary strata might be another important source of carbon for sulfate reducing bacteria and subsequently induce higher rates of sulfate reduction in sediments. Since abundant gas may migrate upward to the surface as a result of tectonic activity occurring in the accretionary wedge, this study investigates the effect of methane migration on the sulfate reduction process in continental margin sediments offshore southwestern Taiwan. Piston and gravity core samples were taken in order to evaluate vertical and spatial variations of sulfate and methane. Pore water sulfate, sulfide, methane, sediment pyrite, and organic carbon were extracted and analyzed.Rapid sulfate reduction, high pyrite contents in sediments and higher concentrations of dissolved sulfide and methane were found in the study area with relatively low organic carbon concentrations. Up to 300 µmole g -1 of pyrite, 10 mM dissolved sulfide and 9 mM methane were found in the study region. Sulfate depletion was as shallow as ~1 m beneath the sediment/water interface. At similar water depths, however, low methane and pyrite were found in some areas with almost no sulfate reduction.Terr. Atmos. Ocean. Sci., Vol. 17, No. 4, December 2006 884 Sulfate flux in the study region is among the highest reported. Large spatial variations were a result of high methane flux, probably originating from gas hydrate deeper in sediments. Co-existence of rapid sulfate reduction and high methane concentrations in sediments indicated that methane is controlling sulfate reduction in the region. Downward diffusion of sulfate is linearly correlated with upward methane flux in the Good Weather Ridge region. Methane becomes an important source of carbon for the sulfate reducer and subsequently controlling sulfate reduction and pyrite formation.