Lidya Tarhan, Ph.D.
Mailing address: P.O. Box 208109, New Haven CT 06520-8109
Street address: 210 Whitney Ave., New Haven CT 06511
Ph.D. (2013), Geological Sciences, University of California-Riverside
M.S. (2010), Geological Sciences, University of California-Riverside
B.A. (2008), Geology and English, Amherst College
My research interests center upon using the sedimentary record to develop a multidisciplinary understanding of ancient life during key intervals in Earth’s history. I investigate the interplay between animals and environments and the role of animals as ecosystem engineers—from the micron scale to landscape- and ocean-wide scales—in both ancient and modern settings. I am also interested in the processes of fossilization and the role preservational processes play in modifying the stratigraphic records of both ecosystems and environments. My research combines a traditional sedimentological and paleontological approach with a novel geochemical and experimental toolkit and is heavily field- as well as specimen- and laboratory-based.
Ediacaran Preservation, Paleoenvironments and Paleoecology
The Ediacara Biota, Earth’s earliest macroscopic, multicellular communities—which appeared in the fossil record just prior to the Cambrian Explosion—hold the key to reconstructing the evolution and radiation of complex life on this planet. Understanding the taphonomy (postmortem preservational processes) and diagenetic history of these deposits is an essential prerequisite to unraveling the habitat, phylogenetic relationships and paleoecology of early complex life and distinguishing genuine evolutionary signals from preservational artefacts. My recent work has focused on the mechanisms responsible for ‘Ediacara-style’ preservation (the paradoxical exceptional fossilization of soft-bodied organisms as three-dimensional casts and molds in sandstones). Using petrographic and geochemical (e.g., LA-ICP-MS, microprobe-based SEM-EDS and CL microscopy, SIMS Si and O isotope work), as well as paleontological data, I have been characterizing Ediacara-style fossilization and reconstructing the ecological, taphonomic and paragenetic history of these assemblages—particularly, the role played by precipitation of early diagenetic silica cements from oceans rich in dissolved silica prior to the evolution of silica-biomineralizers. I also use a sedimentological and geochemical (e.g., U isotopes) toolkit to investigate the environmental setting and habitat of the Ediacara Biota—a topic of ongoing controversy that is crucial to deciphering the radiation of metazoans.
Early Paleozoic Substrate Evolution and Mixed Layer Development
In order to resolve environmental-ecological feedbacks that accompanied the emergence of animal-dominated seafloor ecosystems, I use the sedimentary and trace fossil records to investigate the evolution of the infaunal (sediment-dwelling) niche. The radiation of mobile, sediment-mixing infauna is frequently invoked as the trigger for a myriad of geochemical, ecological and preservational phenomena associated with the Cambrian Explosion (such as oxygenation of the seafloor and deep ocean, the decline of microbialites and the closing of the exceptional Ediacara-style and Burgess Shale-type preservational windows). However, the evolution of the mixed layer—the zone of sediments chemically and physically homogenized by burrowing animals and which is mechanistically most responsible for the ecological, biogeochemical and preservational impact of bioturbation—is poorly constrained. My recent sedimentological, paleontological and geochemical modeling work indicates that the development of the sedimentary mixed layer was a protracted process. The implementation of efficient sediment-mixing behaviors lagged behind both the Cambrian Explosion and the Great Ordovician Biodiversification Event, and the delayed development of bioturbation directly impacted marine sulfate concentrations, and potentially oceanic and atmospheric oxygenation.
I also work on modern animal-sediment interactions, including quantifying bioturbation and its impact upon sediment geochemistry in both siliciclastic and carbonate settings, as well as characterizing modern marine microbialite-infauna interactions.