Luo Genming

Guadalupian (Middle Permian) Conodont Faunas at Shangsi Section,Northeast Sichuan Province

ABSTRACT This study recovered the Guadalupian conodont faunas from Shangsi Section in Northeast Sichuan. Four genera and nine species were identified, and three conodont zones were recognized and established; they include Jinogondolella nankingensis Zone, J. aserrata Zone, and J. postserrata Zone. The Roadian and Wordian boundary is set in the interval 5 m from the top of Bed 86 by the first appearance of the conodont J. aserrata . The Wordian and Capitanian boundary is set in the interval 2.3 m from the top of the Bed 95 by the first appearance of J. postserrata . Most of the specimens demonstrated low color alteration index (CAI) as 1.5–3, indicating that most part of the Maokou Formation may have the suitable thermal conditions for the formation of oil source rocks.

Molecular Records of Primary Producers and Sedimentary Environmental Conditions of Late Permian Rocks in Northeast Sichuan, China

ABSTRACT A series of biomarkers were identified in the aliphatic and aromatic fractions of the extracts from Late Permian Dalong and Wujiaping formations in Shangsi Section, Northeast Sichuan, South China, on the basis of the analysis of gas chromatography-mass spectrometry (GC-MC). The dominance of lower-molecular-weight n -alkanes throughout the profile suggests the dominant contribution of algae and bacteria to the organics preserved in the marine section. Wujiaping Formation is characterized by the elevated contribution from algae as well as other photoautotrophs such as photosynthetic bacteria as shown by the molecular ratios of hopanes to steranes or tricyclic terpanes as well as the ratio of pristane (Pr) and phytane (Ph) to C 17 and C 18 n -alkanes. This is in accord with the data from the microscopic measurement on the calcareous algae. In contrast, Dalong Formation is featured by enhanced contribution from bacteria and probably terrestrial organics indicated by the enhanced C 24 tetracyclic terpanes relative to tricyclic terpanes. The two formations also show a distinct discrimination in sedimentary environmental conditions including redox condition and salinity. The anoxic condition was only found in the middle of the Dalong Formation as shown by the ratios of Pr/Ph and dibenzothiophene to phenanthrene, consistent with the reported data of Mo and U. An enhanced salinity indicated by the homohopane index is observed at the shallow Wujiaping Formation. On the basis of the composition of primary productivity and the redox condition, Dalong Formation is proposed, herein, to be potential hydrocarbon source rocks in the study site. It is notable that the topmost end-Permian is characterized by a large perturbance in both the redox condition and salinity, with oxic conditions being frequently interrupted by short-term anoxia, likely showing a causal relationship with the episodic biotic crisis across the Permian—Triassic boundary.

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

ABSTRACT Paired organic and carbonate carbon isotope compositions of Late Permian Wujiaping and Dalong formations at Shangsi, Northeast Sichuan 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.

Microbial influences on paleoenvironmental changes during the Permian-Triassic boundary crisis

The biosphere interacts and co-evolves with natural environments. Much is known about the biosphere’s response to ancient environmental perturbations, but less about the biosphere’s influences on environmental change through earth history. Here, we discuss the roles of microbes in environmental changes during the critical Permian-Triassic (P-Tr) transition and present a perspective on future geomicrobiological investigations. Lipid biomarkers, stable isotopic compositions of carbon, nitrogen and sulfur, and mineralogical investigations have shown that a series of microbial functional groups might have flourished during the P-Tr transition, including those capable of sulfate reduction, anaerobic H2S oxidation, methanogenesis, aerobic CH4 oxidation, denitrification, and nitrogen fixation. These microbes may have served to both enhance and degrade the habitability of the Earth-surface environment during this crisis. The integrated microbial roles have enabled the Earth’s exosphere to be a self-regulating system.

Molecular Evidence for Primary Producers and Paleo-environmental Conditions in Mesoproterozoic in the Xuanlong Depression in North China

ABSTRACT The molecular organic compounds have been identified by gas chromatography (GC) and GC-mass spectrometry (GC-MS) from Mesoproterozoic rocks in the Xuanlong depression in North China. The main saturated compounds are n -alkanes, monomethylalkanes, n -alkylcyclohexanes, acyclic isoprenoids, and hopanes. The dominant lower-molecular-weight n -alkanes are indicative of the main contribution of microorganisms, in particular, the chemosynthetic bacteria. The presence of abundant monomethylalkanes (mid- and end-branched) and the long chained (>C 20 ) acyclic isoprenoids indicates the existence of abundant bacteria and/or archaea in ancient oceans. The low abundance of pristane and phytane is suggestive of the relatively low abundance of photosynthetic autotrophs in comparison with chemosynthetic bacteria in the Mesoproterozoic oceans in North China. The sedimentary environmental condition is suboxic/anoxic, as indicated by the low value of the Pr/Ph ratio as well as the presence of abundant sulfur-bearing organic compounds, consistent with the other geochemical data in North China and elsewhere in the world. Both the composition of the primary producers and the sedimentary environmental conditions are favorable for the formation of hydrocarbon source rocks.