238-3 Investigating the Paleoecology of Insects from Florissant, Colorado, Using Carbon Isotope Geochemistry

Abstract:

Florissant Colorado is home to one of the most unique fossil deposits in the world, one that preserves a rare assemblage of plants (leaves & tree stumps), insects, fish, mammals & aquatic diatoms. These fossils are preserved in lake sediments deposited 18 miles from the latest Eocene Guffey Volcanic Field, and their study can provide a window into the ecological relations of this ancient forest-lacustrine environment. For this project, over 50 plant fossils and 15 insect fossils were collected from paper shale deposits located in and outside Florissant Fossil Beds National Monument. Fossils were sampled with the goal of using their carbon isotope ratios (d13C) to make paleobiological and paleoecological interpretations. Primary observations include: i) an isotopic offset between angiosperm and gymnosperm plants, and ii) isotope ratios of Hymenoptera (ants) and Diptera (flies) that overlap with angiosperm plants. The former is consistent with offsets in d13C observed between angiosperm and gymnosperm plants in modern forests, while the latter suggests that ants & flies relied primarily on angiosperms as food sources, either directly or indirectly. This study is the first to include carbon isotope data from Florissant plants, and to the best of our knowledge it is the first study of any kind to include isotopic data from fossil insects. As such, it provides a baseline for future studies of Florissant’s ancient ecology and environment.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.