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Biotic and palaeoecological variations in the Permian-Triassic boundary microbialite (Xiejiacao, South China): Implication for a two-phase ecological crisis in microbialite ecosystems
Global and Planetary Change ( IF 3.9 ) Pub Date : 2021-10-16 , DOI: 10.1016/j.gloplacha.2021.103679
Chunmei Su 1 , Zhong-Qiang Chen 1 , Xue Wang 1 , Siqi Wu 1 , Zhen Guo 1
Affiliation  

The end-Permian mass extinction (EPME) severely impacted global biodiversity. Extinction selectivity of biotas behaved differently in various environmental settings, and biotic variations before, during, and after the EPME on the shallow platform remain unclear. This paper describes a new microbialite near the Permian-Triassic (P-Tr) boundary (PTB) from the Xiejiacao section, South China. The PTB microbialite comprises thrombolite and dendrolite fabrics and yields abundant columnar cyanobacteria and various microspheroids. Abundant metazoan fossils, including conodonts, foraminifers, ostracods, gastropods, ammonoids, brachiopods, and ophiuroids, are reported from the uppermost Permian bioclastic limestone, PTB microbialite (PTBM), and lowest Triassic strata in Xiejiacao. Stratigraphic occurrences of these taxa display a two-fold decline pattern of the end-Permian mass extinction, calibrating to the base and top of the PTB microbialite and corresponding to the first extinction phase (EP1) and second extinction phase (EP2) of the EPME, respectively. This two-fold extinction pattern is also reinforced by fossil fragment components of various clades through the P-Tr transition in Xiejiacao. Updated dataset of metazoan fossil records from 25 PTBM sections in South China is also compiled, and it shows the two-fold declines in biodiversity. The dominance role of foraminifers in the latest Permian faunas switched to ostracods in the PTB microbialite after EP1, and then to bivalves after EP2. Proportions of infaunal, stationary, and omnivore forms declined continuously across the EP1 and EP2, while pelagic, fast-moving, suspension-feeding, and predatory taxa underwent stepwise increases across these two extinctions. Proportions of epifaunal, slow-moving, and deposit-feeding taxa increased after EP1 but decreased after EP2. This might be associated with the extinction of brachiopods and, the immigration, and the proliferation of mollusks (bivalves, gastropods, and ammonoids). The metazoan fossil dataset of all PTBM sections across South China refutes the taphonomic window hypothesis and the refuge scenario, instead, supports that the post-extinction unique palaeoceanographic conditions in microbial ecosystems may have been beneficial to diversification of the PTBM faunas. The dataset of the stratigraphic distributions of all PTBM taxa in all palaeoenvironmental settings across South China shows that the drastic decline in biodiversity of the PTBM faunas during the cessation of microbialite was not due to facies control on fossil preservation, but closely related to the biotic extinction in EP2 of the EPME.



中文翻译:

二叠纪-三叠纪边界微生物岩(谢家草,华南)的生物和古生态变化:微生物岩生态系统两阶段生态危机的意义

二叠纪末大灭绝(EPME)严重影响了全球生物多样性。生物群的灭绝选择性在各种环境设置中表现不同,浅层平台上 EPME 之前、期间和之后的生物变化尚不清楚。本文描述了华南谢家槽剖面二叠纪-三叠纪 (P-Tr) 边界 (PTB) 附近的一种新微生物岩。PTB 微生物岩包括凝块石和树状晶织物,并产生丰富的柱状蓝藻和各种微球体。据报道,在谢家槽最上层的二叠纪生物碎屑灰岩、PTB微生物岩(PTBM)和最低的三叠纪地层中,发现了丰富的后生动物化石,包括牙形石类、有孔类动物、介形类动物、腹足类动物、菊石类、腕足类动物和蛇尾类动物。这些分类群的地层出现显示出二叠纪末大灭绝的双重下降模式,校准到 PTB 微生物岩的底部和顶部,对应于 EPME 的第一次灭绝阶段 (EP1) 和第二次灭绝阶段 (EP2) , 分别。通过谢家草的 P-Tr 转变,各种进化枝的化石碎片成分也加强了这种双重灭绝模式。还编译了来自华南 25 个 PTBM 剖面的后生动物化石记录的更新数据集,它显示了生物多样性的两倍下降。有孔虫在最新的二叠纪动物群中的主导作用在 EP1 之后转换为 PTB 微生物岩中的介形动物,然后在 EP2 之后转换为双壳类动物。在 EP1 和 EP2 中,底栖动物、静止动物和杂食动物的比例持续下降,而远洋的、快速移动的、在这两次灭绝中,悬浮进食和掠食性分类群逐步增加。EP1 后附生动物、缓慢移动和以沉积物为食的类群的比例增加,但在 EP2 后减少。这可能与腕足类动物的灭绝以及软体动物(双壳类、腹足类和菊类)的迁移和增殖有关。华南所有 PTBM 剖面的后生动物化石数据集驳斥了埋藏窗口假说和避难情景,相反,支持微生物生态系统中灭绝后独特的古海洋条件可能有利于 PTBM 动物群的多样化。

更新日期:2021-10-21
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