Constraining the duration and magnitude of Late Ordovician to Early Silurian glaciation

制约晚奥陶纪到早志留世冰川的持续时间和规模Woodrow Fisher，Caltechnique-1053523摘要化石记录中最严重的大规模冰川运动之一发生在奥陶纪末期（4.88亿到4.44亿年前）。 虽然这一事件显然与全球变冷和冈瓦纳南部超大陆的冰川作用有关，但这种关系的确切性质被冰川作用时间、冈瓦纳冰盖的规模以及全球变冷对低纬度海洋温度的影响等基本不确定性所掩盖。 对于该项目，PI正在应用最近开发的碳酸盐？结块的？同位素古温度计保存完好的晚奥陶世和早志留世化石从安蒂科斯蒂岛，魁北克和美国中部大陆。 这种代用指标与传统的碳酸盐-水氧同位素古温度测定法相比具有一个主要的优点，即它不需要对海水的同位素组成进行假设。因此，它可以用来与传统的方法相结合，以帮助解决一个问题，从事古气候学家，地球化学家和古生物学家的半个世纪：什么是海水温度和全球冰量的相对贡献海洋碳酸盐的氧同位素组成的时间趋势？因此，这一替代物的应用有可能为古代气候变化提供更高分辨率的图像，使我们更好地了解过去的气候状态及其对全球生物群的影响。 拟议的工作有两个相关的目标：1）对一系列保存的碳酸盐相、分类群和沉积环境中的成块同位素系统学进行详细检查，以评估成岩作用的影响、潜在的生命效应，并强调化石保存古代气候信号的方式，2）利用这一知识，建立了晚奥陶世-早志留世高分辨率的温度和海水氧同位素组成时间序列。 这一方法将在温室气体（即二氧化碳）存量增加和大陆冰盖大量增加的时期提供关于气候动态的重要新信息。 这也将有助于阐明晚奥陶世-早志留世期间气候变化与灭绝模式之间的关系。

Constraining the Duration and Magnitude of Late Ordovician to Early Silurian GlaciationsWoodrow Fisher, CaltechEAR-1053523ABSTRACTOne of the most severe mass extinctions in the fossil record occurred near the end of the Ordovician Period (488 to 444 million years ago). Although this episode is clearly linked to global cooling and glaciation of the southern supercontinent of Gondwana, the precise nature of the relationship is obscured by fundamental uncertainties about the timing of glaciation, the magnitude of the Gondwanan ice sheet(s), and the impact of global cooling on low-latitude ocean temperatures. For this project PIs are applying the recently developed carbonate ?clumped? isotope paleothermometer to well-preserved Late Ordovician and Early Silurian fossils from Anticosti Island, Québec and the US midcontinent. This proxy offers a major advantage over conventional carbonate-water oxygen isotope paleothermometry in that it requires no assumptions about the isotopic composition of seawater. It can therefore be used, in combination with conventional approaches, to help resolve a problem that has engaged paleoclimatologists, geochemists, and paleontologists for half a century: what are the relative contributions of seawater temperature and global ice volume to temporal trends in the oxygen isotopic composition of marine carbonates? Application of this proxy thus has the potential to give a much more highly resolved picture of ancient climate changes, giving us a better understanding of past climate states and their effects on the global biota. The proposed work has two related objectives: 1) to conduct a detailed examination of clumped isotope systematics across a range of preserved carbonate phases, taxonomic groups, and depositional settings to evaluate the effects of diagenesis, potential vital effects, and highlight the ways in which fossils preserve signals of ancient climate, and 2) to use this knowledge to construct high-resolution time series of local temperature and seawater oxygen isotope composition through Late Ordovician and Early Silurian time. This approach will provide important new information on climate dynamics during an interval characterized by both a greater inventory of greenhouse gases (namely CO2) and substantial continental ice sheets. It will also help clarify the relationship between climate change and extinction patterns during the Late Ordovician-Early Silurian interval.