史晓颖++张世红++张传恒++冯庆来++杜远生

摘 要：华北中元古界发现大量生物成因凝块石，超微组构与有机矿物研究表明有机矿化是微生物岩形成的普遍过程。微生物岩受微生物类群与环境条件控制，能够提供早期海洋环境与微生物群落的特征及其相互作用信息。研究发现了中元古代太阳黑子周期性活动的地质记录，证明黑子活动对微生物活性和沉积具有重要影响；为揭示早期日—地—生物相互作用机理提供了重要信息，拓展了地球生物学研究的方向。在燕山盆地中元古代发现了两个重要的生物群更替事件，分别与海洋化学变化以及火山活动导致的营养盐输入相关。发现了多种真核生物化石，包括具刺疑源类、多细胞丝体、瓶状化石、梭型化石以及具复杂纹饰类型。表明这个时期真核生物已经出现明显的多样性分化，为进一步认识早期真核生物生物进化提供了重要参考。中元古代海洋DIC库经历了逐渐减小的演变；海洋硫酸盐浓度较低，氧化还原界面较浅。在浅水环境自养微生物控制了碳的代谢过程；而深水环境中，厌氧微生物代谢对海水化学组成有很大影响。氧化还原敏感元素研究表明中元代海水以Mo亏损的缺氧水体为主，但局部层段Mo等元素富集，反映海洋在1.64 Ga～1.56 Ga有重要变化，以硫化为主。在高于庄组底和上部分别获得锆石SHRIMP U-Pb年龄（1626±21）Ma、（1564±39）Ma，为中元古代年代地层学提供了重要约束。中元古代不同层段黑页岩的活性铁组分研究表明，多数贫铁氧化物，但含黄铁矿很少；FeHR/FeT和FeT/Al的比值平均值分别为0.28和0.57，表明多数层段形成于缺氧但非硫化环境，证明深海以广泛的铁化条件为主，但间夹有间歇性分布的硫化时段。华南晚埃迪卡拉纪-早寒武世的N、C同位素研究发现δ13Corg在浅水区和深水区存在显著差异，证明海洋仍具有缺氧分层的高梯度状态。N同位素在早寒武世早期有明显正异常，可能与缺乏固氮作用相关；随后趋于正常，氧化明显并伴生多细胞生物发育。硫化水体控制营养元素以及N、C、S循环，并影响生物演化。

关键词：元古代中期 微生物岩 微生物群 稳定同位素 氧化还原敏感元素 海洋化学条件 华北地台

"Geomicrobiological Processes in the Mesoproterozoic Ocean with Anomalous Sulfur Cycle" Anaual Report

Shi Xiaoying Zhang Shihong Zhang Chuanheng Feng Qinglai Du Yuansheng

（China University of Geosciences（Beijing））

Abstract：Abundant thrombolites were found in the Mesoproterozoic of the North China Platform. Ultra-fabrics and organo-minerals in the thrombolites suggest that organo-mineralization is a key process for the formation of microbialites， which was mainly controlled by microbe groups and the environment factors. We have also identified geological records of Sun spot activities in the Mesoproterozoic， and argued that the fluctuation of Solar energy input had exerted a great influence on the microbial activity and sedimentation. Two important biotic events were recognized in the Mesoproterozoic Yanshan Basin， which were likely related to the changes in ocean chemistry and enhanced nutrient influx. Many potential eukaryote fossils were found， including acanthomorphic aritarchs， multi-cellular algae filaments， vase-like， and ornamented fossils. This suggests a noticeable eukaryote diversification. The study shows that DIC reservoir of the Mesoproterozoic had reduced through time， with low sulfate concentration and shallow chemocline. In the shallow water environments， carbon was cycled mainly by autotrophics， while in deep waters， anaerobic microbes played important role in changing seawater chemical composition. Study of redox-sensitive elements reveals that the Mesoproterozoic ocean was dominated by Mo-depleted anoxic state. Mo-enrichment was identified in the sediments of 1.64 Ga～1.56 Ga， suggesting a change in ocean chemistry to euxinic. Fe speciation from several black shale intervals in the Mesoproterozoic reveals that most of them have low ferric oxides， with rare pyrites. The average values of FeHR/FeT and FeT/Al are 0.28 and 0.57 respectively， suggesting the intervals deposited in anoxic， bur not euxinic conditions， and confirming that the deep sea was predominantly ferruginous， with intermittently interspersed euxinic waterss during the time Study of N， C， and S isotopes revealed a significant gradient of δ13Corg in the Ediacaran to Lower Cambrian succession between shallow and deep water facies of South China， likely suggesting the ocean still markedly stratified， with a high redox gradient. N isotope anomaly was recognized in the lower most Cambrian，likely reflecting the absence of N2-fixation. with Multi-cellular metazoan occurrence accompanied with environment oxidation. We think that the euxinic state had controlled nutrient concentration and the N， C， and S cycles， which in turn had impacts on the biotic evolution.

Key Words：Mesoproterozoic； Microbiolite； Microbial assemblages； Stable isotopic compositions； Redox-sensitive elements； Ocean chemistry； North China platform

阅读全文链接（需实名注册）：http：//www.nstrs.cn/xiangxiBG.aspx？id=51654&flag=1