Assessment on Redox Conditions and Organic Burial of Siliciferous Sediments at the Latest Permian Dalong Formation in Shangsi,Sichuan,South China

The redox sensitive elements, molybdenum （Mo） and uranium （U）, in marine sediments from the latest Permian Dalong （大隆） Formation at the Shangsi （上寺） Section, Northeast Sichnan （四川）, South China, were analyzed by inductively coupled plasma mass spectrometry （ICP-MS） to determine their response to a range of redox conditions, and to estimate the organic carbon burial rate. On the basis of the correlation between anthigenic Mo abundance and organic carbon content in modern oceans, the organic carbon burial rates were calculated for the rocks at Dalong Formation, ranging from 0.48-125.83 mmol/（m^2.d）, which shows a larger range than the mineralization rate of organic carbon at the continental margins （1.6-4.23 mmol/（m^2-d））. The Zr-normalized Mo and U abundances show large fluctuations in the entire section. The maxima of Zr-normalized Mo abundance and thus the maxima of the organic carbon burial rates were observed at the interval between the 155th and 156th beds （404-407 m above the base of Middle Permian）. A decrease （the minimum） in U/Mo ratios is present in this interval. It is speculated that the oxygen-limited conditions and ultimately anoxia or euxinia may develop within this depth interval. In contrast, an enhanced enrichment of Zr-normalized U abundance is found, in association with less enrichment in Zr-normalized Mo abundance in the interval from the 151st to 154th beds （395-404 m above the base of Middle Permian）, inferring the dominance of a suboxic/anoxic depositional condition （denitrifying condition）, or without free H2S. The presence of small quantities of dissolved oxygen may have caused the solubilization and loss of Mo from sediments. It is proposed that the multiple cycles of abrupt oxidation and reduction due to the upwelling at this interval lead to the enhanced accumulation of authigenic U, but less enrichment of Mo. A decrease in the contents of U, Mo, and TOC is found above the 157th bed （407 m above the base of Middle Permian）, in association with the enhanced U/Mo ratio, suggesting the overall oxic conditions at the end of the Dalong Formation.

Carbon Isotope Records Indicative of Paleoceanographical Events at the Latest Permian Dalong Formation at Shangsi,Northeast Sichuan,China

Paired organic and carbonate carbon isotope compositions of Late Permian Wujiaping （吴家坪） and Dalong （大隆） formations at Shangsi （上寺）, Northeast Sichuan （四川） were analyzed by MAT 251. An abrupt negative excursion in the two isotope records was observed in the middle part of Dalong Formation, in association with a drop in the carbon isotope difference of the two records and an increase of total organic carbon （TOC） content. The negative drop of the paired carbon isotope records is suggestive of the input of 12C-enriched CO2. The molecular ratios of pristane to phytane and dibenzothiophene to phenanthrene indicate the anoxic condition in this interval. The enhanced TOC content is indicative of the elevated preservation of organic matter due to the anoxic condition. These isotopic and organic geochemical data probably infer the occurrence of the upwelling in this interval. The additional contribution of volcanism activity observed in South China cannot be excluded to the input of 12C-enriched CO2 and the negative shifts in carbon isotope composition of bulk organic matter and carbonate.

Composition and distribution of NSO compounds in two different shales at the early maturity stage characterized by negative ion electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry

Gas chromatography/mass spectrometry （GC/MS） can only analyze volatile molecular compounds, and it has limitations when applied to determine the complex components of crude oils and hydrocarbon source rocks. Based on Fourier transform ion cyclotron resonance mass spectrometry （FT-ICR-MS） and GC/MS analyses, the molecular compositions of NSO compounds in extracts from the Permian Dalong Formation, Sichuan Basin and the Permian Lucaogou Formation, Junggar Basin in China were compared. Analyses of types of heteroatoms present （S~, $2, $3, OS, OS2, 02S, NS, and NOS compounds） suggest that marine shales from the Dalong Formation are mainly composed of carboxylic acids （02 com- pounds） with a high abundance of fatty acids, indicating a marine phytoplankton organic source. However, lacustrine shales from the Lucaogou Formation are dominated by pyrrolic compounds （N1 compounds） with abundant dibenzocar- bazole. It suggests that the organic source materials may be derived from lower aquatic organisms and lacustrine algae. Overall, FT-ICR-MS has potential for applications in analyses and determination of depositional environments and organic sources in petroleum geology.

Late Changhsingian (Latest Permian) Radiolarians from Chaohu,Anhui

This article reports a radiolarian fauna from the upper Dalong（大隆） Formation,Ping-dingshan（平顶山）,Chaohu（巢湖）,Anhui（安徽） Province,which includes 15 genera and 23 species.One new species,Copicyntra tongi Gui and Feng n.sp.,is described.Comparison of the fauna,lithology and biotic associations with those from Meishan（煤山） D and Dongpan（东攀） sections shows that the Dalong Formation in the Pingdingshan Section is deposited in a deep-water shelf basin,about 60-200 m in depth.On the basis of the biotic composition,diversity and morphology,the microfossil fauna from the Pingdingshan Section can be divided into three sedimentary assemblages and the extinction proc-esses of the assemblages are discussed.