End-Permian (252 Mya) deforestation, wildfires and flooding-An ancient biotic crisis with lessons for the present
End-Permian (252 Mya) deforestation, wildfires and flooding-An ancient biotic crisis with lessons for the present
复制标题
DOI：
10.1016/j.epsl.2019.115875
复制
发表时间：
2020-01-01
影响因子：
5.3
通讯作者：
Nicoll, Robert S.
中科院分区：
文献类型：
--
作者：
Vajda, Vivi;McLoughlin, Stephen;Nicoll, Robert S.
当前的大规模砍伐森林对全球生态系统构成了威胁，并对水文和碳循环造成了重大和长期的变化。亚马逊和印度尼西亚的热带森林目前正在经历森林砍伐，造成了灾难性的生态后果，但在地球历史上曾多次发生过大范围的森林砍伐事件，这些事件为未来提供了经验教训。二叠纪末期大灭绝事件(EPE；类似于252 Ma)为现代森林砍伐和多样性丧失提供了一个全球性的、深层次的模拟。我们在澳大利亚悉尼盆地的Frazer海滩和Snapper Point地区进行了横跨二叠纪末期的地层的厘米分辨率孢粉学、沉积学、碳稳定同位素和古植物学调查。我们发现，典型的二叠纪温带、成煤、森林群落突然消失，随后积累了1米厚的泥岩，缺乏有机质，实际上代表着一个含有降解木片、木炭和真菌孢子的“死区”。这标志着南部高纬度陆地环境中植被死亡和灭绝的灾难性情景。湖泊系统，表现为横向广泛，但一般不到几米厚的层状粉砂岩，一般缺乏生物扰动，寄生藻囊和淡水原生生物组合，在植被死亡后不久形成。维管束植物恢复的最初痕迹发生在灭绝地平线上方1.6米处。基于与现代森林砍伐的类比，我们认为二叠纪-三叠纪过渡时期的全球真菌和疑难事件直接源于地下水位上升后盆地地区的洪水，这是对复杂植被突然从地貌中消失的反应。增量C-13(Org)值揭示了整个二叠纪末期向低同位素值的显著漂移，低至-千分之31(类似于千分之4的偏移)。当时的变化幅度记录了全球碳循环的变化，这些变化因当地微生物活动的增加而增强，可能还涉及蓝藻的繁殖。我们预计，被淹没的枯死森林提供的有机和矿物养分水平上升，盆地外地区风化和侵蚀加剧，加上当地火山灰的贡献，导致富营养化和盆地湖泊-泻湖环境盐度增加。我们认为，二叠纪末期全球近岸海洋环境中记录到的原生生物群落的变化在很大程度上是来自大陆的淡水藻类和营养物质涌入的结果。虽然这一事件与西伯利亚圈闭火山活动不谋而合，但我们注意到，当时沿着盘古会聚的潘塔拉桑边缘广泛发育了长英质-中级火山作用，可能也是导致二叠纪末期环境扰动的原因之一。(C)2019年提交人(S)。爱思唯尔出版公司(Elsevier B.V.)
Current large-scale deforestation poses a threat to ecosystems globally, and imposes substantial and prolonged changes on the hydrological and carbon cycles. The tropical forests of the Amazon and Indonesia are currently undergoing deforestation with catastrophic ecological consequences but widespread deforestation events have occurred several times in Earth's history and these provide lessons for the future. The end-Permian mass-extinction event (EPE; similar to 252 Ma) provides a global, deep-time analogue for modern deforestation and diversity loss. We undertook centimeter-resolution palynological, sedimentological, carbon stable-isotope and paleobotanical investigations of strata spanning the end-Permian event at the Frazer Beach and Snapper Point localities, in the Sydney Basin, Australia. We show that the typical Permian temperate, coal-forming, forest communities disappeared abruptly, followed by the accumulation of a 1-m-thick mudstone poor in organic matter that, in effect, represents a 'dead zone' hosting degraded wood fragments, charcoal and fungal spores. This signals a catastrophic scenario of vegetation die-off and extinction in southern high-latitude terrestrial settings. Lake systems, expressed by laterally extensive but generally less than a few-metres-thick laminated siltstones, generally lacking bioturbation, hosting assemblages of algal cysts and freshwater acritarchs, developed soon after the vegetation die-off. The first traces of vascular plant recovery occur similar to 1.6 m above the extinction horizon. Based on analogies with modern deforestation, we propose that the global fungal and acritarch events of the Permo-Triassic transition resulted directly from inundation of basinal areas following water-table rise as a response to the abrupt disappearance of complex vegetation from the landscape. The delta C-13(org) values reveal a significant excursion toward low isotopic values, down to -31 parts per thousand (a shift of similar to 4 parts per thousand), across the end-Permian event. The magnitude of the shift at that time records a combination of changes in the global carbon cycle that were enhanced by the local increase in microbial activity, possibly also involving cyanobacterial proliferation. We envisage that elevated levels of organic and mineral nutrients delivered from inundated dead forests, enhanced weathering and erosion of extra-basinal areas, together with local contributions of volcanic ash, led to eutrophication and increased salinity of basinal lacustrine-lagoonal environments. We propose that the change in acritarch communities recorded globally in nearshore marine settings across the end-Permian event is to a great extent a consequence of the influx of freshwater algae and nutrients from the continents. Although this event coincides with the Siberian trap volcanic activity, we note that felsic-intermediate volcanism was extensively developed along the convergent Panthalassan margin of Pangea at that time and might also have contributed to environmental perturbations at the close of the Permian. (C) 2019 The Author(s). Published by Elsevier B.V.