Projects
Investigating the Messinian Salinity Crisis
Clara sailed on IODP Expedition 401 which drilled offshore Spain and Portugal to recover cores spanning the Messinian Salinity Crisis. She will be investigating the geochemistry of carbonate sediments and interstitial waters recovered during this cruise to learn more about the development of extreme saline conditions and their impact on outflow waters into the Atlantic.
Sulfur isotope records in carbonates
Sulfate incorporated into marine carbonate minerals provides our longest and most continuous record of the isotopic composition of past seawater sulfate. We seek to understand, assess, and improve the accuracy of this record by constraining how sulfur behaves during early marine diagenesis.
See publication: doi:10.1016/j.gca.2022.04.027
Chemosymbiosis in the fossil record
Lucinid bivalves host sulfur-oxidizing gill-endosymbionts which supply their hosts with nutritional organic compounds. Morphological evidence for this symbiotic relationship dates back to the Silurian Period. However, there is a lack of geochemical data to corroborate morphological evidence in fossil species. We used sulfur isotopic data in modern lucinid shells to develop a method for diagnosing chemosymbiosis in fossil Lucinidae.
See publication in Geology
Paleoproterozoic records of geochemical change
Ancient carbonates from Fennoscandia have the potential to provide insights into ocean chemistry, such as the evolution of marine carbon and sulfur isotope ratios, in the wake of the Great Oxidation Event. Understanding these archives will require some detailed geochemical detective work to piece together the primary global signals amidst the complicating effects of carbonate diagenesis and local variability.
Some preliminary results were presented recently at Goldschmidt and AGU.
Lingulid brachiopods
Brachiopods – especially lingulids, which make phosphatic shells – have the potential to help constrain the evolution of the Phanerozoic calcium cycle, which in turn has considerable implications for our understanding of the geologic carbon cycle. We will be exploring the potential of this geochemical archive using a suite of modern and fossil lingulid brachiopods – stay tuned.
Some preliminary results were presented recently at AGU.
HED meteorites
Collaborating with researchers at the Field Museum, we will help analyze the calcium isotopic composition of HED meteorites, assumed to be differentiation products of the asteroid 4-Vesta, to evaluate the petrogenetic relationships among them. We will also work with micrometeorites, which represent a majority of the extraterrestrial material that rains on the Earth.
Some preliminary results were presented by Maria Valdes at Goldschmidt.
Alkaline lake chemistry
Alkaline lake waters have been observed to experience distillation of calcium isotopes during lake drawdown events, but this behavior has not yet been observed in lake sediments, which have only captured a fraction of the hypothesized trend. To better understand this unusual geochemical system, we are using both natural and laboratory analogue systems. Stay tuned for results.
Boron isotopes in evaporites
Over the last couple of decades, the B isotope proxy has become one of the most useful constraints on Cenozoic climate and ocean acidification. Better estimates of seawater δ11B remain one of the most important steps needed to continue developing the B paleo-pH proxy beyond a few million years in the past. Halite fluid inclusions have been used successfully to reconstruct several aspects of seawater chemistry, making them a promising archive for reconstructing δ11B of ancient seawater. We will use experimentally precipitated halites and natural salt cores to investigate the behavior of B isotopes in halite evaporite formations to determine the phases that host B and contribute to the bulk B isotope ratios of halite fluid inclusions. Stay tuned for results!
Records of the Early Triassic
The patterns and causes of the delayed biotic recovery after the Permian–Triassic mass extinction are strongly debated, and possibly involve environmental, ecological, and preservational factors. We are working on Early Triassic rocks from NV, CA, and UT to understand what may be driving the extreme carbon isotope variability of this interval of time.
Environmental controls on glauconite formation
The authigenic mineral glauconite has the potential to be used as a marine paleoenvironmental indicator and provide insight into changing conditions in bottom waters and pore fluids over time. However, the environmental controls on glauconite formation are poorly constrained and often disputed. We will be conducting research in Mesoproterozoic and Cambrian glauconite-bearing units in the western U.S. to better understand the environmental conditions that drive variations in glauconite formation... and possibly what this may mean for reverse weathering. Stay tuned!
Older Projects
Ancient evaporites
Geochemical and mineralogical analysis of two-billion-year-old evaporites (the oldest massive salt deposit by over a billion years!) revealed an ancient ocean that was surprisingly rich in dissolved sulfate. This evidence changes our understanding of the evolution of Earth's surface after the Great Oxidation Event.
See publication: doi:10.1126/science.aar2687
One of our previous papers on evaporites inspired a sonnet! http://lablemminglounge.blogspot.com/2014/10/geosonnet-12.html
Ice age seawater from the Maldives
Based on their geochemical properties, pore fluids recovered from the Maldives archipelago appear to have characteristics preserved of seawater from the last glacial maximum (approximately 20 thousand years ago). These samples were collected during IODP Expedition 359 aboard the JOIDES Resolution.
See news article: https://news.uchicago.edu/story/scientists-discover-ancient-seawater-preserved-last-ice-age
See publication: doi:10.1016/j.gca.2019.04.030
Seafloor methane seeps
Authigenic carbonate nodules formed at methane seeps on the Norwegian shelf provide insights into the kinetics of carbonate precipitation. By analyzing some nodules and paired pore fluid profiles from the core sites, we found a surprisingly small calcium isotope fractionation associated with slow precipitation rates in this environment.
See publication: doi:10.1016/j.gca.2021.01.001