山东东营凹陷古近纪沙河街组下部普遍发育膏盐岩系和颗石藻钙质页岩．研究认为膏盐岩系形成于早期的盐湖环境，而膏盐岩系之上的颗石藻钙质页岩形成于成度略低的成化湖泊环境．通过古今湖泊环境和生物类群等的分析对比，认为蓝细菌是古近纪沙河街组下部膏盐层系形成过程中的主要生产力代表，生产力水平为1500—2000g C m^-2a^-1．通过对钙质页岩中钙质超微化石的研究，发现颗石藻是钙质页岩形成时的主要生产力代表．根据钙质页岩的沉积速率、沉积纹层和纹层中颗石藻化石的计数统计，定量确定了颗石藻页岩形成时的古生产力水平为2250～3810g C m^-2a^-1，平均为3120gC m^-2a^-1．通过对地层中大量草莓状黄铁矿粒径的统计，发现膏盐岩系形成时的底层水体处于富硫化氢的缺氧状态，而钙质页岩形成时的底层水体为下贫氧状态．在此条件下，有机质均能有效保存．通过多参数的地球生物学模型的分析和计算，认为东营凹陷古近纪早期盐湖及成化湖泊中有机碳的保存效率约为10％～15％．
Abundant microconchid worm tubes were extracted from the microbialites deposit near the Permian-Triassic boundary at the Zuodeng Section, Baise area, Guangxi Zhuang Autonomous Re- gion, South China. These calcareous worm tubes were studied in both petrographic thin sections and isolated specimens using optical microscope and sensitive electronic microscope （SEM）, respectively. They are categorized into two morphological types： helically coiled and planispirally coiled tubes, which are assignable to Microconchus aberrans （Hohenstein, 1913） and M. utahesis （Zatofi et al., 2013）, respectively. The tube wall ultrastructnre is characterized by laminated micrites, which distinguish the studied microconchids from comparable microgastropods or spirorbid polychaete that usually has shell nltrastructnre of spar texture. The overwhelm majority of microconchids from the microbialite possess the planispirally coiled tubes. The lifestyle of extant, morphologically convergent spirorbids suggests that these planispirally coiled microconchids may have colonized in some local oxygenic oases probably produced by photosynthetic cyanobacteria in the oxygen-poor microbialite ecosystem in which they may have settled densely with high competition among various individuals and with other associated animals for oxygen consumption and food soucres. The deleterious environment condition of the mi- crobialite ecosystem immediately after the Permian-Triassic biocrisis is also indicated by various geochemical signals derived from the same section. Such a deleterious habitat may be inhospitable for most metazoans, but it has some local oxygenic oases that was favorable for opportunistic taxa to dwell.
Ocean anoxia has been widely implicated in the Permian-Triassic extinction. However, the duration and distribution of the ocean anoxia remains controversial. In this study, the detailed redox changes across the Permian-Triassic boundary （PTB） in the shallow platform interior at Great Bank of Guizhou （GBG） has been reconstructed based on the high-resolution microfossil composition and multiple paleo-redox proxies. The shallow platform is characterized by low sulfur （total sulfur （TS） and pyrite sulfur （Spy）） concentrations, low Spy/TOC ratios, and low DOP values before the mass extinction, representing oxic conditions well. Following the mass extinction, the shift of multiple geochemical proxies, including high Spy/TOC ratios and DOP values, indicates dysoxic-anoxic conditions in shallow ocean. Furthermore, we reconstruct the transition of the redox conditions of Nanpanjiang Basin： the intense volcanic eruptions, which release huge COz and SO2 before the mass extinction, provoke the temperature rising and the collapse of terrestrial ecosystem. As a result, the increased weathering influx causes the carbon iso- topic negative excursion and the expansion of the ocean oxygen minimum zone （OMZ）. When the OMZ expanded into the photic zone, the episodic H2S release events enhance the pyrite burial at Dajiang section. Thus, intense volcanic eruptions, temperature increase, and oceanic hypoxia together lead to the PTB extinction. Recent studies show high temperature might be the key mechanism of the PTB extinction. In addition, this study confirms that the microbialites were formed in the dysoxic- anoxic shallow water.
SONG HuYueTONG JinNanTIAN LiSONG HaiJunQIU HaiOuZHU YuanYuanThomas ALGEO
