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

奥陶纪和志留纪时期（约5 - 4.2亿年前）是气候、海平面和生物多样性急剧变化的时期。地球历史上最大的一次物种大灭绝发生在奥陶纪末期。在这些时期，海洋浮游生物中保存下来的最重要的动物群是笔石，这是一群几乎灭绝的半足动物。它们数量丰富，地理分布广泛，进化迅速，这使它们成为识别短地质时间间隔和全球范围内这些间隔的相关性的绝佳化石。对这些生物及其在沉积地层中的分布有了透彻的了解，我们就能最大限度地利用它们来解决构造学、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)了解笔石生物多样性的变化历史是由于物种起源和灭绝的速率变化，特别是通过奥陶系和志留系特征的气候和海洋变化周期；3)研究地层中保存的物理和化学记录，以更好地了解环境循环及其原因。对于最后一个目标，我对海洋缺氧的历史特别感兴趣——当海洋的大片地区氧气耗尽的时候。我的工作是利用地球化学和同位素信号检测海洋缺氧，了解缺氧与气候、海洋环流和生物生产力变化的关系。我还将使用笔石及其在沉积地层中的出现来提高分辨率，以便我们可以定义和细分地质时间。通过提高我们对地质年代的分辨率，我们可以更清楚地了解进化和古环境过程的时间和速度。这项对气候变化、海洋环流和生物多样性之间的长期联系的研究将提供见解，帮助我们更好地了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.