scholarly journals The distributions and geochemical implications of methylated 2-methyl-2-(4,8, 12-trimethyltridecyl)chromans in immature sediments

2021 ◽  
pp. 014459872110333
Author(s):  
Xin Wang ◽  
Meijun Li ◽  
Ronghui Fang ◽  
Hongfei Lai ◽  
Xiaolin Lu ◽  
...  
Keyword(s):  
South China Sea ◽  
Dynamic Stability ◽  
Marine Sediments ◽  
South China ◽  
Lacustrine Sediments ◽  
Molecular Simulations ◽  
Distribution Patterns ◽  
Mature Stage ◽  
Marine Environments ◽  
Hypersaline Environments

Methylated 2-methyl-2-(4,8,12-trimethyltridecyl)chromans are salinity-sensitive biomarkers that have been detected in immature – early mature petroleum and sediments. In this study, the occurrence and distribution patterns of 2-methyl-2-(4,8,12-trimethyltridecyl)chromans were investigated in a set of lacustrine sediments from Nördlinger Ries of southern Germany and marine sediments from the South China Sea. Among all of the 2-methyl-2-(4,8,12-trimethyltridecyl)chroman isomers detected, 8-Me-2-methyl-2-(4,8,12-trimethyltridecyl)chroman presented with high abundance in sediments deposited in hypersaline environments, while absent in samples from normal marine environments. In contrast, 5,7,8-triMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman was more enriched in sediments from marine environments. This study also showed that the ratio of 5,7,8-triMe-/5,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman can be applied as a potential salinity indicator on account of a positive correlation with other 2-methyl-2-(4,8,12-trimethyltridecyl)chroman salinity indicators. This ratio can be an alternative indicator of paleosalinity when 8-Me-2-methyl-2-(4,8,12-trimethyltridecyl)chroman is absent or present in quite low abundance. The content of 2-methyl-2-(4,8,12-trimethyltridecyl)chroman isomers may be affected by freshwater supply and lithology. Molecular simulations showed that 5,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman has a higher thermal dynamic stability than 7,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman. Thus, the ratio of 5,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman/7,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman may be a potential maturity parameter for sediments at a low thermal mature stage.

Decomposition conditions of methane hydrate in marine sediments from South China Sea

2016 ◽  
Vol 413 ◽  
pp. 110-115 ◽  
Author(s):  
Yu Zhang ◽  
Xiao-Sen Li ◽  
Yi Wang ◽  
Zhao-Yang Chen ◽  
Ke-Feng Yan
Keyword(s):  
South China Sea ◽  
Marine Sediments ◽  
South China ◽  
Methane Hydrate ◽  
China Sea

scholarly journals Strength Behaviors of Remolded Hydrate-Bearing Marine Sediments in Different Drilling Depths of the South China Sea

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 253 ◽  
Author(s):  
Yanghui Li ◽  
Tingting Luo ◽  
Xiang Sun ◽  
Weiguo Liu ◽  
Qingping Li ◽  
...  
Keyword(s):  
South China Sea ◽  
Marine Sediments ◽  
South China ◽  
The South China Sea ◽  
Triaxial Tests ◽  
Failure Strength ◽  
The South ◽  
Drilling Depth ◽  
China Sea ◽  
Hydrate Reservoirs

The mechanical behaviors of hydrate-bearing marine sediments (HBMS) drilled from the seafloor need to be understood in order to safely exploit natural gas from marine hydrate reservoirs. In this study, hydrates were prepared using ice powder and CH4 gas, and HBMS from the Shenhu area in the South China Sea were remolded using a mixed sample preparation method. A series of triaxial tests were conducted on the remolded HBMS to investigate the effects of soil particle gradation and the existence of hydrate on the mechanical properties of hydrate reservoirs. The results show that the stiffness and failure strength of HBMS decrease along with the decrease of mean particle size and soil aggregate morphology change at different drilling depths, and the reduction of failure strength is more than 20% when the drilling depth drops by 30 m. A better particle gradation of marine sediments may boost the stiffness and failure strength of HBMS. In addition, the existence of hydrate plays an important role in the strength behaviors of HBMS. The reduction of failure strength of HBMS with 30% initial hydrate saturation is more than 35% after complete hydrate dissociation.

scholarly journals Petrographical and Geochemical Signatures Linked to Fe/Mn Reduction in Subsurface Marine Sediments from the Hydrate-Bearing Area, Dongsha, the South China Sea

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 624 ◽  
Author(s):  
Xi Xiao ◽  
Qian-Zhi Zhou ◽  
Shao-Ying Fu ◽  
Qian-Yong Liang ◽  
Xiang-Po Xu ◽  
...  
Keyword(s):  
Organic Matter ◽  
South China Sea ◽  
Marine Sediments ◽  
South China ◽  
Inorganic Carbon ◽  
Solid Phase ◽  
The South China Sea ◽  
Anaerobic Oxidation Of Methane ◽  
The South ◽  
China Sea

Fe and Mn oxides and (oxy)-hydroxides are the most abundant solid-phase electron acceptors in marine sediments, and dissimilatory Fe/Mn reduction usually links with the anaerobic oxidation of methane (AOM) and organic matter oxidation (OMO) in sediments. In this study, we report the results from subsurface marine sediments in the Dongsha hydrate-bearing area in the South China Sea. The petrological and geochemical signatures show that the Fe/Mn reduction mediated by AOM and OMO might occur in sediments above the sulfate-methane transition zone. X-ray diffraction and scanning electron microscopy analyses of sediments indicate that Fe(III)/Mn(IV)-oxides and authigenic carbonate minerals coexisted in the Fe/Mn reduction zone. The lower δ13C values of dissolved inorganic carbon, coupled with an evident increase in total inorganic carbon contents and a decrease in Ca2+ and Mg2+ concentrations indicate the onset of AOM in this zone, and the greater variation of PO43− and NH4+ concentrations in pore water suggests the higher OMO rates in subsurface sediments. Geochemical and mineralogical analyses suggest that the previously buried Fe(III)/Mn(IV) oxides might be activated and lead to the onset of Fe/Mn reduction induced by AOM and OMO. These findings may extend our understanding of the biogeochemical processes involved in Fe/Mn reduction in continental shelves with abundant methane, organic matter, and terrigenous metal oxides.

Triaxial experiments on the mechanical properties of hydrate-bearing marine sediments of South China Sea

2016 ◽  
Vol 77 ◽  
pp. 507-514 ◽  
Author(s):  
Tingting Luo ◽  
Yongchen Song ◽  
Yiming Zhu ◽  
Weiguo Liu ◽  
Yu Liu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
South China Sea ◽  
Marine Sediments ◽  
South China ◽  
China Sea

scholarly journals Morphology, internal architectures and formation mechanisms of mega-pockmarks on the northwestern South China Sea margin

2021 ◽  
pp. 1-67
Author(s):  
Yintao Lu ◽  
Xiaoyong Xu ◽  
Xiwu Luan ◽  
Shu Jiang ◽  
Weimin Ran ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Seismic Data ◽  
Middle Miocene ◽  
Mature Stage ◽  
Formation Mechanisms ◽  
Three Dimension ◽  
Plan View ◽  
China Sea ◽  
Fluid Seepage

Pockmarks, as depression morphology related to fluid escape on the seafloor, are revealed by three-dimension (3D) seismic data on the northwestern South China Sea (SCS) margin. The pockmarks can be classified into two groups by their various shapes in plan-view, which are circular group and elongating group. These pockmarks in the study area could be defined as mega-pockmarks, as their maximum diameters can reach to 7.5 km. They commonly develop more than one crater, which are central crater and secondary crater. The seismic data illuminated their complicated internal architectures in the subsurface, as well as their evolution periods, such as initiation stage, mature stage and abandonment stage. According to the buried structures and their genesis mechanism, the mega-pockmarks could be classified into linear faults-associated pockmarks and volcano-associated pockmarks. The linear faults-associated pockmarks root on the top Middle Miocene, where the linear faults distribute. The linear faults on the top of fluid reservoir in Middle Miocene act as conduits for fluid seepage. The fluid seepage is driven by the break of balance between the hydrostatic and pore pressure. When the fluid seepage initiate, they will migrate along the linear faults, making the linear feature of pockmarks on the seafloor. Both thermogenic gas from deep intervals and biogenic gas in shallow intervals may be fluid source for the genesis of pockmarks. On the other hand, the volcanic activities control the genesis and evolution of volcano-associated pockmarks. The volcano-associated pockmarks root on the craters of volcanoes. The volcanoes underneath the pockmarks provide volcanic hydrothermal solutions, such as phreatomagmatic eruptions through the volcanic craters. The confined fluid seepages make the pockmarks on exhibiting more circular shape on the seafloor. Long-term, multi-episode fluid expulsions generate the complicated internal architecture that leads to multi-cratered mega-pockmarks on the northwestern margin of SCS.

Sign in / Sign up

Export Citation Format

Share Document