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

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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.