Reconstructing late-pleistocene climatic and glacial history of central North America using loess-derived land snail stable isotopes and detrital zircon provenance

Dendy, Sarah

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https://hdl.handle.net/2142/121470 Copy

Description

Title

Reconstructing late-pleistocene climatic and glacial history of central North America using loess-derived land snail stable isotopes and detrital zircon provenance

Author(s)

Dendy, Sarah

Issue Date

2023-07-12

Director of Research (if dissertation) or Advisor (if thesis)

Conroy, Jessica L

Doctoral Committee Chair(s)

Conroy, Jessica L

Committee Member(s)

• Guenthner, William R
• Grimley, David A
• Anders, Alison M

Department of Study

Earth Sci & Environmental Chng

Discipline

Geology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Quaternary
• geochronology, detrital zircon provenance
• stable isotope
• isoscape
• loess
• land snail

Abstract

Earth systems models are vital for projecting climate change and informing policy decisions, but they require comprehensive forcing and benchmarking of data to produce accurate predictions. Sea level models, for example, need information on both the last glacial and penultimate glacial ice sheet thickness and extent to accurately reflect isostatic adjustment. Likewise, climate models must be rigorously benchmarked with instrumental and proxy climate observations. Geochronologic data and terrestrial paleoclimatic data dating to and preceding the last glacial maximum (LGM) in North America are relatively rare, limiting the ability of climate and sea level models to simulate the full range of earth system variability in past glacial periods. A solution to data scarcity in the North American midcontinent lies beneath our feet in the form of windblown silt (loess), which preserves information about past ice sheet extent via changes in glaciogenic sediment provenance, as well as past changes in climate via fossil land snails. Here, I present two loess-derived datasets from along the length of the Mississippi River Valley, utilizing detrital zircon (DZ) and aragonitic land snail fossils to provide information about past sediment provenance, ice sheet extent, loess chronology, and climate variability in central North America. Loess-derived DZ geochronology provides a comprehensive record of a zircon crystal's journey from formation in a magmatic province to aeolian deposition, making it a valuable tool for characterizing mixed assemblies of glacial lobe sources. By analyzing LGM-aged till, I examined the DZ age distributions of five glacial lobes that contributed sediment to thick LGM loess in bluffs along the Illinois and Mississippi River valleys. The resulting spatial and temporal differences in loess DZ age distributions correspond with known diversions in fluvial transport influenced by glaciation. Furthermore, the disparities between Illinois Episode and Wisconsin Episode loess DZ age distributions indicate the persistent presence of the Quebec-Labrador Ice Dome throughout the Illinois Episode. To further investigate DZ provenance, I added potential non-glacial sources to the same down-stream loess sites. I then used a statistical mixing model to approximate the relative contributions from glacial and non-glacial sources. Incorporating glacial and fluvial sources better resolves DZ U-Pb provenance in midcontinental USA loess deposits. Comparison of mixing model results from Wisconsin Episode, Illinois Episode, and pre-Illinois Episode loess deposits again confirms the persistence of the Quebec-Labrador Ice Dome through multiple glacial cycles. Mixing models for Illinois Episode and pre-Illinois Episode loess in downstream locations, along the present Mississippi River Valley, suggest ancestral Missouri and Arkansas River sediment input. The stable oxygen isotopic composition of aragonitic land snail fossils provide valuable records of past climate variability, including precipitation, temperature, δ18O of precipitation (δ18Op), and atmospheric circulation. In this study, I investigate an assemblage of LGM-age land snail fossils sampled from near the southern margin of the LGM Laurentide Ice Sheet, extending southward towards the Gulf of Mexico. The fossil dataset is mainly composed of Succineidae fossils and is supplemented by corrected Stenotrema and Vertigo fossil shells to create a composite dataset. A flux balance model and a mean July temperature estimated via Mutual Climatic Range were used to calculate δ18Op. The result is a steeper north-south gradient in warm season δ18Op along the length of the Mississippi River Valley during the LGM relative to present day, which I hypothesize is due to a steepened warm season temperature gradient driving increased rainout and isotopic distillation.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Sarah Dendy

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