Thesis
Major and trace element analysis of the late Cambrian SPICE Event from the Rhinehart A-1 Core, Dallas County, IA
University of Iowa
Master of Science (MS), University of Iowa
Summer 2023
DOI: 10.25820/etd.006941
Abstract
The Steptoean Positive Carbon Isotope Excursion (SPICE) represents a major perturbation to the global carbon cycle during which carbon isotope (δ13Ccarb) values reach up to +4-5‰ in Upper Cambrian strata spanning several paleocontinents. This prominent global shift in δ13Ccarb is accompanied by biotic turnovers and upheavals in other biogeochemical cycles. New high-resolution trace metal and rare earth element data from the SPICE in central Iowa reveal significant enrichments of these elements that are consistent with changing marine redox conditions and a substantial increase in primary production around the event onset. Both of these factors play a critical role in attempting to decipher the dominant control(s) and sequence of events responsible for driving such a large biogeochemical event. These redox proxies cannot be applied to the global oceans; however, the relationships shown here between metal enrichment, nutrient cycling, deoxygenation of marine settings, and the onset of a widespread carbon cycle perturbation resemble those observed during other Phanerozoic biogeochemical events, ultimately serving as critical models when evaluating the biogeochemical signals preserved here as well as shedding more light on the evolution of the ocean-atmosphere-biosphere system.
Details
- Title: Subtitle
- Major and trace element analysis of the late Cambrian SPICE Event from the Rhinehart A-1 Core, Dallas County, IA
- Creators
- Gwen Leann Barnes
- Contributors
- Bradley D Cramer (Advisor)Jessica R Meyer (Committee Member)David W Peate (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Geoscience
- Date degree season
- Summer 2023
- DOI
- 10.25820/etd.006941
- Publisher
- University of Iowa
- Number of pages
- x, 59 pages
- Copyright
- Copyright 2023 Gwen Leann Barnes
- Language
- English
- Date submitted
- 07/24/2023
- Description illustrations
- illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references (pages 40-50).
- Public Abstract (ETD)
- Earth’s global carbon cycle, which is linked to climate, and oceans have undergone several significant changes throughout history. These changes are preserved in the rock record of marine sediments. Carbon has two stable isotopes, 12C and 13C, and we measure the ratio of these two carbon species from marine rocks as 13C/12C to give us the carbon isotope record, δ13C, of the oceans. Sudden changes in the carbon cycle appear as “excursions” in the δ13C record where δ13C values rapidly increase or decrease over a short interval of time. This study investigates an event known as the Steptoean Positive Carbon Isotope Excursion, or the SPICE event, that occurred ~494 million years ago and is reflective of an extreme change in the global carbon cycle as well as the biology and chemistry of the oceans. The changes are reflected by a positive carbon isotope excursion, a global mass extinction of marine fauna, the depletion of oxygen from the global oceans, and changes in trace metal concentrations in marine sediments. The causes of these events are still unknown, but we can better understand the driving mechanisms by measuring the concentrations of certain elements preserved in ocean sediments. Some elements behave differently under oxic versus anoxic conditions (e.g., are trapped in the sediment when no oxygen is present or remain dissolved in the ocean when there is oxygen), and others are incredibly useful for photosynthetic microorganisms. Our study documents an influx of biologically important nutrients near the beginning of the SPICE, which is consistent with a substantial increase in primary production around this time. An increase in primary productivity would deplete the oxygen in the oceans, which would allow for the enhanced burial of organic carbon. This is important because the continued expansion of oxygen depletion permits more organic carbon burial, which is thought to cause the positive change in carbon isotope values, as well as the sedimentary enrichment of metals that we also see here. On a broader scale, better understanding the causes of these events will provide us with insight into future climate change.
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984454318902771
Metrics
24 Record Views