An Organic Geochemical Approach to Understanding Microbial Community Dynamics During Paleoenvironmental Transitions

• Main Author: Martinez, Aaron Matthew
• Other Authors: Love, Gordon D
• Format: Other/Unknown Material
• Language: English
• Published: eScholarship, University of California 2020
• Subjects: Geobiology; Geochemistry; Geology; Environmental transitions; Lipid biomarkers; Stable isotopes; Greenland; Greenland Sea
• Online Access: https://escholarship.org/uc/item/496775tt

Organic geochemistry provides a way to explore the dynamics of past life on the Earth without requiring the preservation of discrete macrofossils. In particular, lipid biomarker analysis and stable isotope analyses, combined with sedimentological, paleontological, and other geochemical background, can be utilized to understand biogeochemical cycles as well as the sources and preservation of organic matter. These, in turn, may help unravel questions such as the distribution of primary producers during mass extinctions, hydrological dynamics of ancient rift systems, and the interactions of local environments on global carbon and climate systems. Throughout this dissertation, I will walk through time to discrete events in the history of life on Earth. Through lipid biomarker, isotope, and complimentary techniques I characterize past paleoenvironments to understand transitions occurring in the biosphere, and vice versa. We will begin at one of the great mass extinctions, the End Devonian Hangenberg Crisis. Using a mix of geochemical techniques, I locate this mass extinction within the Cleveland Shale Member of the Ohio Shale, then show that there is a stable microbial community of primary producers throughout the event, despite devastating losses occurring in the macrofaunal clades. Then, we fast forward to the Jurrasic, where we use a suite of environmentally relevant lipid biomarkers to constrain the hydrologic history of an ancient rift lake system and make inferences about environmental variables such as pH and salinity. Lastly, I explore some nuances of Cenozoic carbon cycle dynamics by unraveling the depositional history of organic matter at a high-latitude, nearshore marine basin and find that significant amounts of complex terrigenous materials were continuously sequestered into the early-middle Eocene Norwegian-Greenland Sea.