Ministromatolite modular framework reef, ~1.5 Ga, North China

A small lensoid mound, with cavernous framework formed by microbial carbonate, occurs in the ~1500-million-year-old (Myr) Wumishan Formation at Yesanpo, northern China. It consists of column and cones composed of innumerable conjoined ministromatolites, each ≤2 cm wide. The irregular, decimetric, framework cavities contain carbonate mud, pisoids, and marine cement. Geochemical signatures, together with traces of organic filaments in the ministromatolites, are consistent with slight oxygenation. The role of ministromatolites in creating this modular framework can broadly be compared with that of polyps in present-day scleractinian coral colonies. Cavernous habitats create extraordinary biodiversity in present-day tropical coral reefs. Yesanpo, currently the oldest known framework reef, predates earliest reported reef-dwelling animals by ~600 Myr. As oxygenation increased in the Late Proterozoic, microbial reef frameworks - similar in structure to Yesanpo - may have been occupied by cryptic biota. These habitats provide prime targets in the continued search for early marine animal life.

中国北部野三坡地区约15亿年（Myr）历史的雾迷山组中，产出一处由微生物碳酸盐岩（microbial carbonate）构成洞穴状格架的小型透镜状丘。该丘由无数相连的微型叠层石（ministromatolites）构成柱体与锥状体，单体宽度不超过2厘米。不规则的分米级格架空腔内充填有碳酸盐泥、豆粒（pisoids）与海相胶结物。地球化学特征与微型叠层石中发现的有机丝状体痕迹均指示存在轻度氧化作用。微型叠层石在构建该模块化格架中的作用，大致可类比现代石珊瑚（scleractinian coral）群落中珊瑚虫的造礁功能。洞穴状生境在现代热带珊瑚礁中造就了极高的生物多样性。野三坡这一目前已知最古老的格架礁，比已报道的最早礁栖动物早了约600 Myr。随着新元古代晚期（Late Proterozoic）氧化作用增强，结构与野三坡格架礁类似的微生物礁格架，可能已被隐蔽生物群所占据。此类生境为持续探寻早期海洋动物生命提供了关键研究目标。