Degree

Doctor of Philosophy (PhD)

Department

Earth and Energy Sciences

Document Type

Dissertation

Abstract

Methane seeps are dynamic biogeochemical systems that influence carbon cycling, seafloor ecology, and gas hydrate stability along continental margins. Yet reconstructing past methane seepage remains challenging because most sedimentary proxies integrate over long timescales and cannot resolve the short-lived or spatially restricted methane pulses that characterize many seep environments. This dissertation evaluates the reliability, sensitivity, and limitations of benthic foraminiferal δ¹³C as a proxy for methane-rich porewater conditions across two contrasting seep systems: long-term seepage at Woolsey Mound in the northern Gulf of Mexico and short-term, spatially variable seepage along the Chilean Margin. Using Individual Foraminifera Analysis (IFA), scanning electron microscopy, assemblage ecology, and sediment geochemistry, this work investigates how species ecology, microhabitat structure, and seepage intensity shape the expression of methane-derived δ¹³C signals. At Woolsey Mound, IFA of Pyrgo spp. reveals highly variable and often extremely depleted δ¹³C values within single stratigraphic intervals, demonstrating a temporal decoupling between episodic methane release and the integrated signals preserved in bulk proxies. Along the Chilean Margin, foraminiferal assemblages and δ¹³C values vary systematically across different seepage styles, reflecting strong ecological and geochemical gradients. IFA captures fine-scale isotopic variability within each microhabitat, including a clear decoupling of δ¹³C and δ¹⁸O associated with AOM-derived DIC and hydrate-related oxygen isotope partitioning. Together, these findings demonstrate that benthic foraminiferal δ¹³C is a powerful but context-dependent proxy whose reliability is governed by species-specific ecology, microhabitat heterogeneity, and diagenetic conditions. IFA provides the temporal and ecological resolution necessary to detect short-lived methane pulses and refine paleo-seepage reconstructions.

Date

2-6-2026

DOI

https://proquest.com/docview/3347823082

First Committee Chair

Davide Oppo

Second Committee Chair

Brian Schubert

First Committee Member

Jennifer Hargrave

Second Committee Member

Kautubh Thirumalai

Third Committee Member

Michalis Charilaou

Fourth Committee Member

Tolga Karsili

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