Characterising the orosirian earth system
Abstract/Contents
- Abstract
- The Orosirian Period (2.05 to 1.8 billion years ago; Ga) is bookended by two remarkably contrasting intervals in Earth history. The preceding Great Oxidation Event (GOE) spanned ca. 2.5 to 2.05 Ga, and marks the first sustained oxygenation of Earth's atmosphere. The end of the GOE has been hypothesised as a so-called 'oxygen overshoot', with oxygen levels declining across the termination of the event. Closely associated with the GOE is the Lomagundi-Jatuli Excursion (LJE), Earth's longest-duration, largest-magnitude positive carbon isotope excursion, canonically interpreted to represent a period of elevated organic carbon burial. Following the Orosirian Period is an interval informally referred to as the 'mid-Proterozoic' or 'boring billion', spanning ca. 1.8 to 0.8 Ga. This interval has been broadly characterised by geologists and geochemists as recording stasis in the Earth system, with relatively stable levels of atmospheric oxygen and gross primary productivity, a mild, non-glacial climate, and ecosystem stability. While these two intervals have been subject to considerable study, the intervening Orosirian Period has been largely overlooked, in spite of potentially recording a transition between these two extremes. To better understand the Orosirian Period, field work and a suite of geochemical techniques were conducted on sedimentary rocks collected from northern Canada and Europe. Chapter One applies carbon isotope chemostratigraphy and U-Pb geochronology of volcanic zircons to establish a time-calibrated, high-resolution carbon isotope curve through the Orosirian. Chapter Two applies barium and multiple sulphur isotope ratios, as well as triple oxygen isotope anomalies, to diagenetic barite crystals in the Belcher Group to constrain gross primary productivity across the end-GOE transition. Chapter Three is a study of carbon isotope ratios in the Labrador Trough to better constrain the conclusion of the LJE within the succession. Chapter Four applies iron speciation to shale samples collected from the Belcher Group to constrain oxygenation of the local water column during deposition of the Belcher Group. Finally, Chapter Five uses molybdenum isotope ratios and rare earth elements (plus yttrium) of carbonate sedimentary rocks to constrain changes in ocean oxygenation across the end-GOE, both on a global and local scale. Overall, this thesis demonstrates that the Orosirian Period was a dynamic interval that is critical for understanding the transition out of the GOE/LJE and the onset of stable conditions that persisted through much of the Proterozoic
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2020; ©2020 |
| Publication date | 2020; 2020 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Hodgskiss, Malcolm Stewart William |
|---|---|
| Degree supervisor | Sperling, Erik |
| Thesis advisor | Sperling, Erik |
| Thesis advisor | Swanson-Hysell, Nicholas |
| Thesis advisor | Payne, Jonathan L |
| Degree committee member | Swanson-Hysell, Nicholas |
| Degree committee member | Payne, Jonathan L |
| Associated with | Stanford University, Department of Geology. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Malcolm S. W. Hodgskiss |
|---|---|
| Note | Submitted to the Department of Geology |
| Thesis | Thesis Ph.D. Stanford University 2020 |
| Location | electronic resource |
Access conditions
- Copyright
- © 2020 by Malcolm Stewart William Hodgskiss
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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