Ordovician-Silurian graptolite phylogeny, biodiversity history, chronostratigraphy, paleoenvironmental cycles, and oceanic anoxia

奥陶纪和志留纪(约5亿-4.2亿年前)是气候、海平面和生物多样性急剧变化的时代。地球历史上最大的物种灭绝事件之一发生在奥陶纪末期。在这些时期保存在海洋浮游生物中的最重要的一类动物是笔石族，这是一群几乎已经灭绝的半角类动物。它们丰富，地理分布广泛，演化迅速，这使它们成为识别地质时间短间隔和全球范围内这些间隔的对比的极佳化石。彻底了解这些生物及其在沉积地层中的分布，将使我们最大限度地利用它们来解决构造、沉积盆地历史和气候变化等领域的广泛地质问题。我的研究计划有几个主要目标：1)重建笔石的进化史；2)了解由于物种起源和灭绝速度的变化而导致的笔石生物多样性的变化历史，特别是通过以奥陶纪和志留纪为特征的气候和海洋变化周期；以及3)研究保存在岩层中的物理和化学记录，以更好地了解环境周期及其原因。对于最后一个目标，我特别感兴趣的是海洋中的缺氧史--海洋大片区域耗尽氧气的时代。我致力于利用地球化学和同位素信号检测海洋缺氧，并了解缺氧与气候、海洋环流和生物生产力变化的关系。我还将利用笔石及其在沉积地层中的产状来提高我们定义和细分地质时代的分辨率。通过提高我们对地质时间的分辨率，我们可以更清楚地了解进化和古环境过程的时间和速率。这项对气候变化、海洋环流和生物多样性之间长期联系的研究将提供见解，帮助我们更好地理解气候变化和生物多样性的现代世界。

The Ordovician and Silurian periods (ca. 500-420 million years ago) were times of dramatically changing climate, sea level, and biodiversity. One of the biggest mass extinction events in Earth History occurred near the end of the Ordovician Period. The most important group of animals preserved in the marine plankton during these time periods was the graptolites, a group of mostly extinct hemichordates. They were abundant, geographically widespread and evolved rapidly, which makes them excellent fossils for identifying short intervals of geologic time and correlation of those intervals around the globe. A thorough understanding of these organisms and their distribution in sedimentary strata maximizes our potential to use them to solve a wide range of geological problems in areas such as tectonics, sedimentary basin history, and climate change. My research program has several major objectives: 1) reconstruction of the evolutionary history of graptolites; 2) understanding the history of change of graptolite biodiversity as a result of changing rates of species origination and extinction, particularly through the cycles of climatic and oceanic changes that characterize the Ordovician and Silurian periods; and 3) studying the physical and chemical record preserved in rock strata to better understand the environmental cycles and their causes. For the last objective, I am particularly interested in the history of anoxia in the oceans - times when large areas of the ocean became depleted in oxygen. I am working on detection of oceanic anoxia using geochemical and isotopic signals, and understanding anoxia in terms of its relationship to changes in climate, ocean circulation and biological productivity. I will also use the graptolites and their occurrences in sedimentary strata to improve the resolution with which we can define and subdivide geological time. By improving our resolution of geological time, we can gain clearer insights into the timing and rates of evolutionary and paleoenvironmental processes. This research into the long-term links between climate change, ocean circulation and biodiversity will provide insights that will help us better understand the modern world of changing climate and biodiversity.