豫西荥阳陆相二叠纪-三叠纪之交的微生物成因构造(MISS)及其地质意义

Characteristic and Geological Significance of Microbially Induced Sedimentary Structures(MISS) in Terrestrial P-T Boundary in Xingyang,Western He'nan Province

微生物成因构造(MISS)是微生物活动及其生物地质作用的沉积记录,为人们认识早期地球生物以及微生物活动提供了依据。微生物成因构造在前寒武纪以及显生宙地质危机期海相地层中分布较广,而在陆相地层中则报道较少。在豫西荥阳地区二叠纪—三叠纪之交的陆相地层孙家沟组和刘家沟组中,发现了较为丰富的三大类微生物成因构造(生长构造、破坏构造和腐烂构造),可详分为瘤状突起、变余波痕、隆脊构造、似正弦状脱水裂痕、纺锤状脱水裂痕、树枝状脱水裂痕、多边形脱水裂痕、曲形脱水裂痕、砂火山构造、微生物席砂片和似雨痕构造11个小类。微观分析显示:脊处纵切面显示U型、石英颗粒和黏土矿物条带定向排列、捕捉的云母颗粒不连续和近平行等特征,这些均表明其为微生物成因。研究区发育丰富的微生物成因构造,是二叠纪末灾变事件导致研究区陆地生态系统迅速退化,微生物大量繁殖而形成的,代表着以微生物群落为基础、后生生物少、钙质结核等特殊沉积发育的灾后陆地生态系统。通过对陆相微生物成因构造的研究,有助于人们全面了解二叠纪—三叠纪之交全球灾变事件在陆相环境中的具体表现,为认识微生物席在全球的空间分布提供新资料。

Microbially Induced Sedimentary Structures （MISS） are primary sedimentary structures that arise syndepositionally from microbial community activity. Especially valuable are MISS for the analysis of early Archean （and extraterrestrial） deposits. However, most reports of MISS have focused on the Precambrian and Phanerozoie mass extinction marine sediments, and only a few and terrestrial MISS have been studied. The MISS presented in this paper, which mainly consists of mat growth feature, mat destruction feature and mat decay feature, are welt preserved in terrestrial clastic rocks around the P-T boundary in Xiyang area, western Henan. Large U ridges, ori- ented sand quartz, mica grains and thin clayey laminae arranged parallel to bedding plane are the main features vis- ible under the microscope. Several lines of evidence indicate that the Xingyang MISS are of biogenic origin. Abun- dant MISS in Xingyang may indicate the degradation of terrestrial ecosystems and proliferation of microbial mats im- mediately after the severe Permian-Triassic mass extinction. Study aiming at MISS helps to analyze their space dis- tribution in the globe and to probe into links between microbial proliferation and environmental stresses following the end-Permian mass extinction in terrestrial ecosystems.