Date of Award

5-11-2025

Date Published

June 2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth & Environmental Sciences

Advisor(s)

Zunli Lu

Keywords

body size;coral;Devonian;laser-ablation-inductively-coupled-mass-spectroscopy;microfossils

Subject Categories

Earth Sciences | Geochemistry | Physical Sciences and Mathematics

Abstract

Paleoclimatology provides context for understanding the timescales and animal responses to environmental change under modern climate change scenarios. The key drivers of climate variability are identified using proxies for environmental conditions. Biological archives are especially useful for linking changing conditions to ecosystem responses. This dissertation establishes the foundation for utilizing dacryoconarid microfossils as biostratigraphic indicators of environmental change in the Paleozoic. It also presents a protocol for measuring iodine-to-calcium (I/Ca) ratios—an established proxy for localized hypoxia—in coral skeletons using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Studying Paleozoic microfossils presents challenges due to the high degree of induration of ancient rocks, which makes it difficult to extract fragile microfossils intact. Retrieving calcareous fossils from limestone matrices is an especially demanding task. Chapter 1 details the methodology for extracting dacryoconarids from different rock types. It evaluates the potential of surfactants and freeze-thaw processing as alternative chemical and mechanical techniques for disaggregating the rock matrix, comparing their effectiveness to the traditional boiling method. Results indicate that matrix composition is a crucial factor when selecting surfactants, as certain surfactant types exhibit differing potential for effective disaggregation. The highest fossil yield across all rock types was achieved using sodium bicarbonate. Chapter 2 investigates the body size trends in dacryoconarids from the Appalachian Basin during the Late Devonian punctata carbon isotope perturbation. A nearly complete stratigraphic section spanning the late Givetian to middle Frasnian stages was sampled along Eighteen Mile Creek in western New York to assess temporal changes in dacryoconarid assemblage diversity and body size. To reconstruct regional environmental conditions and explore potential drivers of the observed size trends, published geochemical proxy datasets from nearby outcrops, drill cores, and global compilations were integrated. While short-term fluctuations in both adult and initial chamber volumes occur between sampling horizons—potentially reflecting preservational biases or variations in local nutrient availability—there is a long-term trend of decreasing adult volume throughout the interval. Evolutionary trajectory modeling indicates that the long-term reduction in adult volumes is unlikely to be the result of random processes. An analysis of taxonomic composition reveals that this shift is primarily driven by a general decrease in assemblage volume over time, rather than the selective loss of large-bodied taxa in response to local environmental stressors. Furthermore, a correlation with reconstructed regional temperature data, based on published conodont apatite δ¹⁸O records, suggests that long-term warming may have contributed to body size reductions, consistent with the Temperature–Size Rule. Chapter 3 focuses on the development of a protocol for measuring in situ I/Ca ratios in coral skeletons using LA-ICP-MS. Corals serve as time-resolved archives of seawater conditions, and the I/Ca ratio may be a useful proxy for hypoxia exposure. Laser ablation enables high-resolution analysis at a faster rate than traditional methods. However, no standard reference materials currently exist for iodine analysis in carbonates using this technique. Through experiments quantifying measurement precision, this study establishes the powdered Porites coral reference material, JCp-1, as a suitable standard compared to a synthetic standard MACS-3. Optimized instrumental and laser parameters for accurate I/Ca measurements were also established. Line scans across skeletal structures reveal significant spatial variation in I/Ca ratios, highlighting the need for careful sampling to avoid potential biases in proxy interpretation.

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Open Access

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