-
oa HYDROLOGICAL AND BIOGEOCHEMICAL CYCLING DURING RAPID WARMING EVENTS IN THE CONTINENTAL INTERIOR UNITED STATES
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 30th International Meeting on Organic Geochemistry (IMOG 2021), Sep 2021, Volume 2021, p.1 - 1
Abstract
The Green River Formation of the western US represents a ∼15 million-year record of unusually large, productive Eocene lakes. The development of a particularly organic-rich (up to 43% total organic content) Mahogany oil shale (49.3 to 48.7 Ma) occurred at a key climate transition and during the decline of the Early Eocene Climatic Optimum (EECO).
Hydrogen isotopic compositions (δ2H) of leaf wax (n-alkanes) and algal (phytane) lipids preserved in the Mahogany Zone are used to reconstruct precipitation and lake water δ2H, respectively. Algal lipid and leaf wax δ2H values exhibit a strong linear relationship (R2 = 0.8), suggesting that algae and higher plants are utilising the same hydrogen-bearing sources for biosynthesis (i.e. lake water δ2H).
δ2H in n-alkanes and phytane become increasingly depleted upward through the Mahogany Zone, indicating increased precipitation during the demise of the EECO. Similarly, biomarker trends differ from those expected during a lacustrine drying-up cycle, revealing a continental-interior hydrological response to cooling.
Results of algal lipid and leaf wax δ2H, with additional lipid and terrestrial biomarker profiles and petrographic data, allow hydrological change to be differentiated from broader ecosystem change during the EECO.
