新元古代极端冰期事件中生物避难所的环境条件

Environmental conditions for refuges surviving from severe Neoproterozoic glaciations

新元古代成冰纪(南华纪)(720~635 Ma)以全球性冰期事件而闻名。这次冰期事件对早期生命演化产生了显著影响,被认为是生命演化的“过滤器”和“瓶颈”。冰期前后生物对比表明生物演化并未中断,暗示冰期过程中存在生物避难所。扬子板块北缘神农架地区成冰系南沱组中发现了罕见的宏体藻类生物记录——宋洛生物群。为了探究成冰纪全球性冰期背景下,古环境与生物幸存之间的关系,本文对扬子北缘宋洛剖面和青林口剖面南沱组内含化石页岩层和不含化石泥岩层开展了元素地球化学对比研究。结果显示,不含化石泥岩层沉积于半咸水氧化环境,而含“宋洛生物群”化石的页岩层沉积于冰消期末期,当时海洋为正常盐度、次氧化状态,该地区具有相对温暖的气候条件。这可能为“宋洛生物群”在极端冰期下幸存并保存为化石提供了有利条件。该研究也表明新元古代极端冰期事件中的确存在适合复杂生命生存的避难所。

The Neoproterozoic Glaciation(Nanhua)period(720~635 Ma)is globally recognized for its significant glaciation events,which had a profound impact on the early evolution of life.It is widely understood as a critical phase,acting as both a“filter”and a“bottleneck”in the evolutionary process.However,when comparing biological evolution before and after this glacial period,it becomes evident that the process was not completely disrupted.This indicates the existence of biological refuges that provided protection for life during the glaciation period.In the Shennongjia area,situated on the northern margin of the Yangtze Block in South China,an exceptional macroscopic algal biota known as the Songluo biota has been discovered within the Nantuo Formation.To investigate the relationship between paleoenvironment and biological survival against the backdrop of global glaciation,this study conducts a comparative analysis of element geochemistry between fossil shale intercalations and non-fossil mudstone intercalations from the Nantuo Formation at the Songluo section and Qinglinkou section on the northern margin of the Yangtze Block.The results of this study demonstrate that the Songluo biota thrived at the end of the deglaciation period,characterized by normal ocean salinity and suboxic conditions,along with a warm and humid climate in the region.These favorable environmental circumstances likely facilitated the endurance and preservation of fossils for the“Songluo biota”amidst the extreme glaciations.Furthermore,this study provides evidence of the presence of sanctuaries suitable for complex life during the Neoproterozoic extreme glaciation.