Wed 22nd June 2022 @ 12:00 nn, 312.222 and online via Webex (meeting #: 2654 445 7342 and password: JYiaHrxg423)

Abstract:

In this study, continental paleoclimate from the early Cenozoic is reconstructed, when the Earth’s surface experienced a long-term warming trend punctuated by a series of short-lived global warming (hyperthermal) events that culminated in an extended interval of elevated CO2 and extreme warmth, the Early Eocene Climatic Optimum (EECO, 53.26 to 49.14 Ma). The hydrological cycle’s response to climate perturbations is thought to be highly variable, and can promote feedbacks that induce further warming or cooling, thus serving as critical lessons for future warm worlds. However, the response of the hydroclimate regime operating during the EECO is poorly constrained, especially for the mid-to-low latitudes and particularly from continental interior sites.

A multi-proxy approach was adopted, integrating geochemical, organic petrographic, and sedimentological perspectives from organic-rich sediments from the Green River Formation of the Uinta Basin, Utah and the Piceance Basin, Colorado, U.S.A., which were deposited in long-lived, large lakes at ~40ºN. We observed a wide range of organic matter types and distribution, with accumulation of organic matter at the lamination scale controlled by longer term sub-orbital cycles suggesting decadal periodicities in large organic-matter fluxes and associated carbon drawdown. Spatial and temporal variations in salinity conditions were the result of long-term tectonic controls driving the water balance between fresher and brine-rich inputs into the Uinta Basin, increasing ecological stress on biota living in the water column and leading to the cessation of conditions favouring prodigious organic accumulation in the Mahogany Zone, a regionally extensive marker unit. Lastly, hydrogen isotopes from organic molecules indicate that the hydrological cycle operates differently during gradual vs. transient warming events, and that a stable hydrological regime may have supported deep lake development and promoted organic matter preservation allowing for development of this quintessential oil-shale during the early Eocene. These organic-rich lake systems acted as an important negative feedback during the termination of the EECO, sequestering at least ~76 Gt of organic carbon over the ~400 kyr history of the Mahogany Zone.

Short bio:

Amy recently finished her PhD at the University of Southampton, UK, where she used geochemical and sedimentological tools to understand the depositional controls on organic-rich rocks from the Eocene Green River Formation. Prior to this, she focussed on fluvial and aeolian sedimentology for her master’s at Keele University which involved extensive fieldwork in Utah and Colorado, and mapped in Cantabria, N. Spain, where she won the William Smith Geological Society of London award for her 3rd year dissertation. A field geologist by heart, she has moved into multi-proxy approaches, bridging traditional sedimentological methods with biomarkers and stable isotopes, and looks forward to researching extreme fossilisation within concretions at the WA-OIGC under Prof. Kliti Grice.