Geochemistry and sedimentology of the Upper Ordovician–lower Silurian black shale in the northern margin of the Upper Yangtze Platform, South China: implications for depositional controls on organic-matter accumulation

Organic-rich black shales from the Upper Yangtze Platform from the Upper Ordovician and lower Silurian are considered excellent source rocks and unconventional reservoirs of hydrocarbons in South China. This research combined geochemical analyses and detailed sedimentological observations to investigate the depositional controls on organic-matter abundance in the prolific black mudstone of the Wufeng Formation and Long-1 Member of the lower Silurian Longmaxi. Six primary lithofacies deposited at variable marine water depths and under different water column chemistries were identified from a ∼50 m-long profile based on microscopic observations of sediment texture and structure, and analyses of total organic carbon (TOC) content, major and trace-element abundances, and pyrite framboid size. Our results showed that TOC content is strongly correlated with terrigenous SiO2 content and the non-detrital components of V, U and Mo, suggesting that the accumulation of organic matter in the studied shale was controlled by terrigenous clast fluxes and anoxic water conditions. However, the weak covariance relationship between TOC content and productivity proxies, including P/Ti and Ba/Al, demonstrates that the accumulation of organic matter was not controlled by primary productivity. The three high-productivity lithofacies of the Wufeng Formation and Long-1 Member have low Co*Mn values, indicating active marine upwelling during sedimentary periods. The northern margin of the Upper Yangtze Platform was an open basin system influenced by the Kwangsian Orogeny and global sea-level changes, but oxygen-depleted bottom waters in the basin favoured the accumulation and preservation of sedimentary organic matter, resulting in the formation of organic-rich black shales.</p

Synthesis and Characterization of <i>trans</i>-[Os(en)₂py(H)]²⁺ and Related Studies

trans-[Os(en)2pyH](Otf)2, 2, is recovered from an acidic solution of trans-[Os(en)2py(H2)](OTf)2, 1, which has been subjected to one electron oxidation. The structures of both 1 and 2 have been determined by single crystal X-ray analysis. In cyclic voltammetry, 2 shows a one electron oxidation wave at 0.95 V and a one electron reduction wave at −1.2 V, neither accompanied by a signal for the reverse process. Reduction of 2 by Zn/Hg in methanol solution leads to quantitative formation of [Os(en)2(py)H2)]2+, predominantly in the trans-form. In aqueous solution, species 2 reacts rapidly with N-methylacridium ion, [MAH]+, by hydride transfer. One electron chemical oxidation of 2 to the corresponding Os(IV) is slower than that of 1 to 2 owing to the increase in coordination number when Os(IV) is produced. Treatment of 1, or the cis-form, 1‘, in DMSO by sodium t-butoxide produces mainly the corresponding isomers of the monohydrides of OsII, that derived from 1‘ is deep red in color while the trans-monohydride is colorless. Both react with [MAH]+ to form [MAH]2, and both disappear rapidly in acetone or acetonitrile, presumably by reducing the solvents. Reaction of trans-[Os(NH3)4(H2)H2O](BPh4)2, 4, in acetone-d6 as solvent with either CH3CHO or styrene leads to hydrogenation of the substrate. Reactions which compete with trans-[Os(en)2(η2-H2)(CF3SO)3]CF3SO3 release of substrate from the trans-complex before isomerization to the cis-form, required for hydrogenation to occur, result in the trans-derivative of the added solute. When H2CCHCH2SCH3 is the substrate, binding takes place at sulfur. Complete conversion to the cis-substrate isomer is observed, without hydrogenation occurring even though contact between dihydrogen and the double bond is possible

Structure and properties of a quasi-one-dimensional compound BaTiS₃ under pressure

We report the studies of structure and properties of a quasi-one-dimensional (quasi-1D) compound BaTiS3 under pressure. The poly-crystalline samples are synthesized by solid-state reaction method and single-crystalline samples are produced by chemical vapor transport method. The XRD measurement under ambient pressure confirms the hexagonal structure, which consists of face-sharing octahedral TiS6 chains along c-axis and displays a quasi-1D feature. When applying pressure, the synchrotron X-ray diffraction experiments show that the sample undergoes a phase transition from hexagonal phase to orthorhombic phase at around 10 GPa due to the zig–zag deformation of TiS6 chains, while the quasi-1D structure is reserved. At ambient pressure, BaTiS3 exhibits an insulating behavior with a band gap about 0.273 eV. When applying pressure, the sample undergoes a crossover from insulator to metal due to the enhancement of inter-chain electron hopping.</p