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

奥陶纪和志留纪时期（约。5亿至4.2亿年前）是气候、海平面和生物多样性急剧变化的时期。地球历史上最大的大灭绝事件之一发生在奥陶纪末期。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索动物。它们数量丰富，地理分布广泛，进化迅速，这使它们成为识别地质时间短间隔和地球仪相关间隔的绝佳化石。深入了解这些生物及其在沉积地层中的分布，可以最大限度地发挥我们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的潜力。我的研究计划有几个主要目标：1）重建笔石的进化历史; 2）了解笔石生物多样性的变化历史，作为物种起源和灭绝的变化率的结果，特别是通过奥陶纪和志留纪时期的气候和海洋变化的特点周期;（3）研究保存在岩层中的物理和化学记录，以更好地了解环境循环及其成因。对于最后一个目标，我特别感兴趣的是海洋缺氧的历史-海洋大面积缺氧的时代。我的工作是利用地球化学和同位素信号检测海洋缺氧，并了解缺氧与气候变化，海洋环流和生物生产力的关系。我还将利用笔石和它们在沉积地层中的出现来提高我们确定和细分地质时间的分辨率。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.