古杯是最早在全球范围内发挥造礁作用的后生动物, 首次出现在西伯利亚地台幸运阶底部, 直到寒武系第四阶基本灭绝。湖北宜昌第四阶的天河板组钙质微生物—古杯礁是华南目前已知含古杯生物礁的最高层位, 但是在全球范围内第四期的古杯礁报道非常少。本文首次报道了宜昌下茶庄剖面天河板组的钙质微生物—古杯礁, 为研究第四阶古杯类衰落阶段的古杯和微生物组成的礁群落古生态特征提供了新材料。该生物礁群落组成包括造礁生物原古杯Archaeocyathus yichangensis及多种钙质微生物, 包括Girvanella、Kordephyton、Botomaella、粗管状蓝细菌、Epiphyton及Renalcis, 附礁生物包括三叶虫、腕足动物、开腔骨及棘皮动物。总体来说, 造礁生物表现出古杯类物种单一而钙质微生物多样性较高的特征, 且钙质微生物Epiphyton及Renalcis与古杯的附生关系可能与现生海绵与其上的附生微生物关系类似。原古杯和钙质微生物是天河板组生物礁的主要组成部分, 生物礁造礁模式分析显示, 在原地生长的原古杯作为造礁者构成一级格架后, Girvanella附着于原古杯体壁生长从而稳定下覆的沉积物, 较小的Epiphyton和Renalcis个体附着于Girvanella包壳上继续生长, 也可以与格架中的席状或团块状Girvanella共生, 生长于原古杯间的空隙构成二级格架, 加固礁体; 在形成交错的网状格架之后, 由体积更小的Renalcis和Epiphyton个体填充空隙; 最后由细粒沉积物填充孔隙。华南地区天河板组含古杯生物礁横向对比表明不同古杯礁群落面貌的微小差异可能与水动力背景差异有关。此外, 寒武纪早期世界范围内钙质微生物—古杯礁演化的对比表明第四期钙质微生物—古杯礁群落中古杯的多样性明显降低, 而其中钙质微生物多样性较第三期有所增加, 此发现对揭示含古杯的生物礁群落的衰落有重要意义。

Archaeocyaths are the first metazoans to play a reef-building role on Earth. They first appeared in the early Fortunian on the Siberian Platform and survived until their extinction during the Cambrian Age 4. The calcimicrobe-archaeocyath reefs from the Tianheban Formation (Stage 4) in Yichang, Hubei Province, are the youngest known calcimicrobe-archaeocyath reefs in South China. However, there are rare reports of Age 4 calcimicrobe-archaeocyath reefs worldwide. In this paper, we report calcimicrobe-archaeocyath reefs from the Tianheban Formation at the Xiachazhuang section, Yichang. This discovery provides new materials for the study of palaeoecological characteristics of calcimicrobe-archaeocyath communities of the Cambrian Stage 4. The reefs include Archaeocyathus yichangensis and various calcimicrobes, including Girvanella, Kordephyton, Botomaella, thick tubular cyanobacteria, Epiphyton, and Renalcis. Other associated organisms include trilobites, brachiopods, chancelloriids, and echinoderms. The reef-building organisms show the characteristics of a single archaeocyath species and high diversity of calcimicrobes. The relationship between calcified microproblematica Epiphyton and Renalcis, and Archaeocyathus may be similar to that between modern marine sponges and their associated microorganisms. Archaeocyathus and calcimicrobes are the main components of the reefs from the Tianheban Formation. Analysis of the reef-building modes shows that Archaeocyathus grow in situ and form the first-order framework, acting as bafflers. Then Girvanella cover the surfaces of Archaeocyathus to stabilize the underlying sediments. The smaller Epiphyton and Renalcis form small rigid frameworks. They can also co-grow with sheet or cluster Girvanella, and in the space among Archaeocyathus to form a secondary framework to strengthen the reefs. After forming a staggered reticular framework, the interstitial space is filled by smaller Renalcis and Epiphyton. Lastly, the cavities re filled with fine cements. The correlation of calcimicrobe-archaeocyath reefs of the Tianheban Formation from South China suggests that the community appearances of calcimicrobe-archaeocyath are slightly different, which may be related to the differences in hydrodynamic background. In addition, comparison of calcimicrobe-archaeocyath evolution from the early Cambrian shows that the diversity of archaeocyaths decreased significantly in the calcimicrobe-archaeocyath reef communities from Age 4, and the diversity of calcareous organisms increased compared with that from Age 3. These evolutionary trends are significant in revealing the decline of calcimicrobe-archaeocyath reefs.

国家自然科学基金(42072127, 41930319, 41972143, 42272006)和国家重点研发计划(2023YFF0803600)联合资助