Insights into the evolution of the Great Plains grassland ecosystem over the last 5 million years from paleotemperature and paleovegetation records

Author

Anne Fetrow, University of Puget SoundFollow

Abstract

Over the last 10 million years, the Great Plains transitioned to the modern C₄ grass dominated ecosystem. Well-preserved late Miocene to Holocene fossils and paleosols make the Meade Basin in southwest Kansas, USA a unique place to determine how paleoenvironmental conditions changed during C₄ grassland evolution. δ¹⁸O values of paleosol carbonates (δ¹⁸O_carb) in the Meade Basin decreased from the Miocene to Holocene while δ¹³C values increased; these trends were interpreted as an increase in temperature and/or in aridity coincident with an increase of C₄ grass biomass on the landscape. Estimating temperature from δ¹⁸O_carb is complicated, however, by the role of source water δ¹⁸O (δ¹⁸O_water) values in δ¹⁸O_carb values. Thus, we used carbonate clumped isotope (Δ₄₇) thermometry of paleosol carbonate nodules to develop independent paleotemperature estimates and estimated δ¹⁸O_water by combining temperature and δ¹⁸O_carb values.

Preliminary temperature estimates (5-1.8 Ma) in the Meade Basin range from 17°C to 24°C with no systematic change through time, when compared to the modern mean annual (14°C) and warm season (24°C) temperatures. In contrast, δ¹⁸O_water values increased through time. We preliminarily suggest that local/regional temperature change was not the primary factor that drove grassland ecosystem evolution in the Meade Basin, while increasing δ¹⁸O_water values suggest increased aridity may have been a bigger influence on C₄ biomass and faunal changes, although we cannot rule out atmospheric CO₂ (pCO₂)changes. Additionally, Δ₄₇ temperatures and δ¹⁸O_water values may reflect numerous factors besides air temperature and aridity changes, respectively, including depositional environment differences, soil type/depth, and source water changes. Further analyses and detailed organic biomarker records currently underway will help constrain the roles of paleoenvironmental factors in C₄ grassland expansion.

First Advisor

Kena Fox-Dobbs, University of Puget Sound

Second Advisor

Kathryn E. Snell, University of Colorado, Boulder

Degree Type

Thesis

Language

English

Rights

Default Rights Statement.

Degree Name

Bachelor of Science in Geology

Date of Award

Spring 5-17-2015

Department

Geology

Recommended Citation

Fetrow, Anne, "Insights into the evolution of the Great Plains grassland ecosystem over the last 5 million years from paleotemperature and paleovegetation records" (2015). Honors Program Theses. 13.
https://soundideas.pugetsound.edu/honors_program_theses/13