摘要:除某些蓝细菌之外，绝大多数白云岩中很难出现底栖后生动物化石。位于塔里木板块北部新疆阿克苏地区肖尔布拉克剖面的寒武系第二统吾松格尔组岩性以白云岩为主夹少量灰岩，属广阔浅潮汐带大面积强蒸发高盐度云坪环境而不利于底栖和游泳的后生动物群生存。本文首次报导该层位中一个低分异度的遗迹类群，它们均产出于薄层泥晶灰岩，鉴定遗迹属包括：Chondrites，Helminthopsis，Skolithos，Stelloglyphu，Taenidium，Thalassinoides，其形态均为小型简单的动物潜穴，属于古生代浅海地层中的常见分子；薄层灰岩中还见少量三叶虫和密集产出软舌螺。吾松格尔组白云岩沉积期海水高盐度环境在很大程度上不但抑制实体化石保存的底栖型和游泳型后生动物，也同样抑制没有实体化石保存的后生动物型遗迹造主栖居，遗迹化石的造主和带壳后生动物只能在正常盐度和动荡环境的薄层灰岩沉积期短暂迁移到此。本实例从环境角度诠释生物进化的制约机制，云坪不是后生动物的理想生态条件，这在寒武纪早期生命大爆发过程中就已经显现出来。
关键词: 遗迹/
吾松格尔组/
寒武系/
塔里木板块/
中国西北
Abstract:It is a common sense that most of benthic metazoan fauna, except some cyanomicrobes, unlikely survive in dolomitic flats. The Cambrian （Stage 2） Wusonger Formation is dolostone-dominated with less limestone beds at the Xiaoerbulak section, Aksu of northern Tarim block in Xinjiang, NW China. Dolostones were largely formed in a wide shallow and strong evaporate tidal belt where was unfavorable for inhabitation of metazoan fauna including both benthic and nektonic communities. A low diverse ichnofauna is reported here for the first time, of which the taxa are all yielded from thin-bedded micritic limestones and identified as Chondrites, Helminthopsis, Skolithos, Stelloglyphu, Taenidium, Thalassinoides with descending order in abundance. Their morphological features are small burrows with simple structures and commonly occurred from shallow marine settings in Paleozoic time. Sparse trilobites and hyolithes shelly concentrations are also specially yielded from thin-bedded limestones. Therefore, palaeosalinity condition played an essential role in constraining of metazoan fauna. Both trace-makers without mineralization bodies and shelly fauna could migrated herein instantly once resurgences of normal salinity and turbulence environments coinciding to the deposition of thin-bedded limestones. The present case illustrates an evolutionary pattern that dolomitic flat hasn??t been idealized setting for metazoan fauna thriving since their Early Cambrian Explosion of the Phanerozoic.
Key words:?Ichnofossils/
Wusonger Formation/
Cambrian/
Tarim block/
NW China
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