Clumped and Intramolecular Isotopic Perspectives on the Behavior of Organic and Inorganic Carbon in the Shallow Crust and Deep Biosphere

Author: Lloyd, Max Kaufmann

Year: 2018

Degree: Dissertation (Ph.D.)

Advisor: Eiler, John M.

Committee Members: Sessions, Alex L.; Rossman, George Robert; Orphan, Victoria J.; Eiler, John M.

Option: Geochemistry

DOI: 10.7907/Z96T0JV5

Abstract

Although the upper crust is the most accessible swath of the subsurface, the geochemical processes therein are challenging to observe. Here, I use site-specific and ‘clumped’ isotope analyses (where multiple rare, heavy isotopes are bound in single molecules) of carbonates and organic solids to explore petrology, brittle tectonics, diagenesis, and biodegradation in the shallow crust. In carbonates, I employ contact aureoles, regional metamorphic terranes, thermal and geochemical models, and high-pressure experiments, to extract nuanced thermal and chemical histories. In the organic realm, I develop new methods to measure the clumped 13C – 2H composition of methoxyl groups (R – O – CH3) from kerogen, lignin, and other complex organic substrates. This work expands the field of clumped isotope geochemistry into the realm of solid compounds, and enables new, site-specific isotopic perspectives on the shallow crustal transformations of organic carbon substrates and the microbial assemblages that live on them.

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