Oil and gas discoveries within Proterozoic-Cambrian strata and the majority of shale gas production occurs in relatively stable tectonic regions and characterised by moderate thermal maturity (Ro°<°2.5%). The Sinian–Silurian gas resource located in China's Sichuan Basin is a definitely different example of a concurrent conventional and unconventional gas system within a tectonically complicated basin and sourced from overly-mature organic shales (Ro°>°2.5%). The system comprises two components, namely a conventional Sinian–Cambrian dolomite-hosted gas resource and an unconventional Cambrian-Silurian shale gas deposit, both represent trillion cubic meter accumulations. The migration-accumulation type Sinian–Cambrian gas system, is a result of numerous processes, including (1) paleo-high trapping within a relatively stable tectonic setting, (2) appropriate source materials located in a paleo-rift trough, (3) large-scale dolomite grainstone reservoirs located near the paleo-high, (4) adequate gas produced from in-situ crude oil cracking, and, (5) gypsum-salt and shale cap rock preservation. The self-contained source-reservoir Cambrian–Silurian shale gas system, is localized by deepwater organic-rich shelf facies, characterized by high silicon and calcium contents. The recent discovery of these two massive gas fields in old and over-matured sedimentary strata, has effectively extended the upper maturity limit of Ro over 3.0%, which may indicate the efficacy of broadening current natural gas exploration areas, thus potentially increasing global natural gas resources significantly. Furthermore, the discovery may spark interest in natural gas exploration in widely distributed old strata, thus encouraging co-development of conventional and unconventional petroleum accumulations.
A sample of Er3+-doped 80GeS2-10In2S3-10CsI(mol%)chalcohalide glass was fabricated by the melt-quench method. Absorption spectra and upconversion emission spectra of the glass were investigated,and upconversion mechanisms of Er3+in the glass were analyzed. The intensity parameters Ωt(t=2,4,6),the oscillator strengths,the spontaneous transition probabilities and fluorescence branching ratios were calculated by the theory of Judd-Ofelt. Under 980 nm diode laser excitation,Intense green emissions centered at 527 nm and 548 nm,corresponding to the transitions of H11/2→4I15/2 and 4S3/2→4I15/2,respectively,were observed for the first time in this glass. The upconversion emission intensity varies with the power of infared excitation intensity. A plot of logI vs logP yields two fitted lines with slope 1.90 and 2.06,respectively,which indicates a two-photon process for the green emission. The results suggest the In-based chalcohalide glass containing Er3+ ions is expected to find applications in visible lasers,high density optical storage and three-dimensional color displays.
Carbon-isotope stratigraphy launched since the early technological development of carbon-isotope measurement in 1950s, however, the emergence and advance of terrestrial carbon-isotope stratigraphy took quite a long way. At early stage the exploration of carbon-isotope stratigraphy based on the marine biological shell carbonates was verified by repeatable carbon-isotope stratigraphic data, laboratory chemical experiments and the later laboratory foraminiferal culture experiments. The breakthrough for testifying the fundamentals of terrestrial carbon-isotope stratigraphy lies on the synchronous fluctuations between the carbon-isotope stratigraphic curves derived from marine biological shell carbonates and those derived from terrestrial C3 plants. The character that carbon-isotope stratigraphic curves can be globally synchronously correlated over the marine and terrestrial/atmospheric reservoir mainly excludes the potential biasing factors, such as diagenetic bias, carbon-isotope variations in intra/inter individual plant in same species or between species, ecological changes, changes in aridity, changes in source input and representative sampling. Therefore, the fundamentals of terrestrial carbon-isotope stratigraphy based on C3 plant successfully established. The terrestrial carbon-isotope stratigraphy can be used for global stratigraphic correlation, reconstructing the evolution of atmospheric CO2 and can further verify the published global carbon-cycle models. The terrestrial carbon-isotope stratigraphy based on the compound specific biomarkers and single-grained pollen may be a promising perspective in future.
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