| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | April 10, 2019 |
| Latest Amendment Date: | April 10, 2019 |
| Award Number: | 1916698 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Dena Smith-Nufio
dmsmith@nsf.gov (703)292-7431 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2018 |
| End Date: | August 31, 2022 (Estimated) |
| Total Intended Award Amount: | $91,191.00 |
| Total Awarded Amount to Date: | $91,191.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
3227 CHEADLE HALL SANTA BARBARA CA US 93106-0001 (805)893-4188 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
Rm 3227 Cheadle Hall Santa Barbara CA US 93106-2050 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Sedimentary Geo & Paleobiology |
| Primary Program Source: |
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| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The Great Unconformity (GU) represents one of the largest gaps of time in the rock record. Since it is followed by the Cambrian Radiation, one of life's most significant increases in biodiversity and complexity, it has long been thought that these phenomena are linked. Geoscientists have proposed that the GU was caused by large-scale erosion of Earth's crust. As rocks weathered and dissolved, an element critical to life, phosphorous, was released and carried to the ocean by rivers. The increase in phosphorous is proposed to have spurred photosynthesis among cyanobacteria, which then increased the oxygen content of the ocean and atmosphere. This oxygenation was perhaps the fuse that led to the Cambrian Radiation since complex life requires oxygen. Despite the GU's potential role in one of life's most important transformations, very little is known about when and where it occurred. Determining when the GU developed and the size of the last erosion event that lead to its formation are critical for identifying viable mechanisms for life and environmental change during this pivotal interval of Earth history. This research project is making use of advances in zircon and titanite (U-Th)/He methods to decipher GU development. Results are directly testing hypotheses that relate continental erosion to oxygenation and the explosion of life. The project is also advancing scientific and technological understanding through the training of undergraduate and graduate students and K-12 teachers.
It has been proposed that the erosion below the Great Unconformity occurred as the result of supercontinental breakup, Snowball Earth glaciation, or global eustasy, and may have delivered bio-limiting nutrients to the ocean that fueled the Cambrian Radiation. However, the timing, proposed global synchroneity, and magnitude of the Great Unconformity have not been previously tested or constrained. Recent advances in (U-Th)/He thermochronology allow access to the thermal histories required to unravel the history of this iconic feature. This project will acquire zircon and titanite (U-Th)/He data for samples along two transects across two different cratonic margins. Study sites will be targeted to fully exploit Neoproterozoic and Cambrian geologic constraints, which will be vital for narrowing the range of viable thermal histories to enable discrimination between GU formation models. The results will dramatically improve constraints on the Neoproterozoic cooling history of each margin, which will be used to test competing models for GU development and significance.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The Great Unconformity is a major gap in the rocks record in North America between unfossiliferous Precambrian rocks and fossiliferous Cambrian to Ordovician strata. It has been previously proposed that Neoproterozoic glacial events (Snowball Earth) drove major erosion that fertilized the oceans, lubricated subduction zones, and defined the Great Unconformity. The major goals of our proposed work were to test this hypothesis by constraining the timing, magnitude, and spatial heterogeneity of erosion that lead to development of the Great Unconformity with zircon, titanite, and apatite (U-Th)/He data from multiple regions across North America. We found that the erosion under the Great Unconformity is highly variable in both space and time, which is inconsistent with the hypothesis of glacial erosion. Instead, our data suggest that regional tectonics and dynamic topography associated with mantle convection instead drove variable erosion in space and time. In addition, analysis of the preserved sedimentary record on North America suggests that it is not a faithful recorder of global sea-level, but instead a biased record of tectonics and mantle dynamics (which do contribute to global sea-level). These results were published in top journals in our field including GEOLOGY and PNAS, and other papers are in preparation associated with this work. The grant also supported the training of two PhD students who are prepared to join the workforce. These students also gained experience in community outreach by developing and teaching a multi-week class on Earth History and geochemistry for high school students, and by developing a museum exhibit.
Last Modified: 09/26/2022
Modified by: Francis A Macdonald
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