Marine oxygenation, lithistid sponges, and the early history of Paleozoic skeletal reefs
Marine oxygenation, lithistid sponges, and the early history of Paleozoic skeletal reefs
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DOI：
10.1016/j.earscirev.2018.04.003
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发表时间：
2018-06-01
影响因子：
12.1
通讯作者：
Riding, Robert
中科院分区：
文献类型：
--
作者：
Lee, Jeong-Hyun;Riding, Robert
微生物碳酸盐是早古生代生物礁的主要成分，直到中奥陶世出现珊瑚-层孔类-苔藓虫生物礁。在寒武纪早期，微生物礁由古细胞海绵增加，与寒武纪 15 Myr 类似，在其余与寒武纪类似 25 Myr 的情况下，由石石海绵增加，然后在第一个与奥陶纪 25 Myr 类似的石石海绵、calathiid 海绵和 pulchrilaminid 海绵增加。中晚寒武世微生物-石质海绵礁优势的影响因素仍不清楚。尽管氧气的增加似乎对寒武纪早期海洋动物生命的“爆发”做出了重大贡献，但随着海平面上升和二氧化碳增加，随后的一段较长时期以“温室”条件为主。寒武纪中晚期异常温暖，这些升高的温度预计会降低氧的溶解度，并促进广泛的热分层，导致海洋缺氧和缺氧。温室条件也会刺激碳酸盐平台的发展，局部进一步限制浅水循环。海洋含氧量低与寒武纪中晚期浮游植物、三叶虫和其他后生动物的间歇性灭绝有关。我们认为浅海环境中的缺氧-缺氧趋势也限制了许多后生动物造礁者。相比之下，在寒武纪中晚期，石质海绵能够承受低氧水平，使它们能够与主导全球珊瑚礁的微生物碳酸盐形成底栖联系。这些条件在奥陶纪得到改善，因为温度下降促进了海洋通风。 “寒武纪大爆发”和“奥陶纪大生物多样性事件”之间的低多样性珊瑚礁占据的时间间隔很长，反映出气温升高和海洋氧合减少，限制了浅海环境中后生动物的多样性。
Microbial carbonates were major components of early Paleozoic reefs until coral-stromatoporoid-bryozoan reefs appeared in the mid-Ordovician. Microbial reefs were augmented by archaeocyath sponges for similar to 15 Myr in the early Cambrian, by lithistid sponges for the remaining similar to 25 Myr of the Cambrian, and then by lithistid, calathiid and pulchrilaminid sponges for the first similar to 25 Myr of the Ordovician. The factors responsible for mid-late Cambrian microbial-lithistid sponge reef dominance remain unclear. Although oxygen increase appears to have significantly contributed to the early Cambrian 'Explosion' of marine animal life, it was followed by a prolonged period dominated by 'greenhouse' conditions, as sea-level rose and CO2 increased. The mid-late Cambrian was unusually warm, and these elevated temperatures can be expected to have lowered oxygen solubility, and to have promoted widespread thermal stratification resulting in marine dysoxia and hypoxia. Greenhouse conditions would also have stimulated carbonate platform development, locally further limiting shallow-water circulation. Low marine oxygenation has been linked to episodic extinctions of phytoplankton, trilobites and other metazoans during the mid-late Cambrian. We propose that this tendency to dysoxia-hypoxia in shallow marine environments also limited many metazoan reef-builders. In contrast, during the mid-late Cambrian, the ability of lithistid sponges to withstand low oxygen levels allowed them to create a benthic association with microbial carbonates that dominated global reefs. These conditions ameliorated during the Ordovician, as temperature decline promoted ocean ventilation. The prolonged time gap occupied by low diversity reefs between the 'Cambrian Explosion' and the 'Great Ordovician Biodiversification Event' reflects elevated temperatures and reduced marine oxygenation that limited metazoan diversification in shallow marine environments.