| 项目编号: | 1520674
|
| 项目名称: | Collaborative Research: Reversal frequency versus ancient field strength: Clues from the Jurassic and Cretaceous |
| 作者: | Lisa Tauxe
|
| 承担单位: | University of California-San Diego Scripps Inst of Oceanography
|
| 批准年: | 2014
|
| 开始日期: | 2015-08-15
|
| 结束日期: | 2018-07-31
|
| 资助金额: | USD282237
|
| 资助来源: | US-NSF
|
| 项目类别: | Standard Grant
|
| 国家: | US
|
| 语种: | 英语
|
| 特色学科分类: | Geosciences - Earth Sciences
|
| 英文关键词: | average field strength
; magnetic field strength
; reversal rate
; sample
; rapid reversal
; magnetic field
; geomagnetic field
; low field strength
; ancient field strength
; individual reversal
; field strength
; few reversal
|
| 英文摘要: | Much progress has been made in our understanding of the variation of Earth's magnetic field strength through geological time, but some rather fundamental and far-reaching questions remain. One key question bears on the relationship between magnetic field strength and its tendency to change sign in a process known as reversing. Records of individual reversals clearly show that they are associated with low magnetic field strength. This observation lead to the hypothesized relationship of average field strength with reversal rate in which periods with few reversals (e.g., the Cretaceous Normal Superchron) would have higher average field strengths and periods with rapid reversals (e.g., the Jurassic Quiet Zone) would have lower average field strengths. While existing data provide some support for the existence of a long period of reduced average field strength in the Jurassic (the Mesozoic Dipole Low, or MDL), the recovery from the state of extremely rapid reversals apparently was not accompanied by a recovery in field strength; the low field strengths apparently persisted well into the Cretaceous, long after reversal rates returned to 'normal'. The problem is that nearly all of the data on which the MDL hypothesis is based are based on poorly documented data from Armenia, published in the 1980s. High quality data derived from modern paleointensity experiments combined with direct radiometric dates from the Jurassic and Cretaceous are essential to resolve whether and for how long the geomagnetic field was depressed during the Mesozoic. The PIs will be collaborating with Armenian scientists, and will collect samples in Armenia. ISE is providing co-funding for travel.
Funding from this grant will allow the team to resample the key Armenian baked contacts and new data will help constrain the age and nature of the termination of the Mesozoic Dipole Low. Additionally, high quality age data from the Armenian arc sequences in which there are marine sediments interbedded with datable lava flows may allow direct calibration of the Jurassic biostratigraphic time scale, a period in which such calibration is rare. Samples will be collected from the Mesozoic arc sequences exposed in Armenia and samples will be subjected to complete paleointensity experiments whereby the original thermal remanent magnetization (TRM) is progressively replaced by a TRM induced in the laboratory under known conditions of the applied magnetic field. Such data, along with checks for chemical alteration and non-ideal behavior provide the basis for determining the ancient field strength. Successful samples will be radiometrically dated using the 39Ar/40Ar method. Samples will also be subjected to a host of rock magnetic tests designed to characterize the suitability of the samples for paleointensity experimentation. |
| 资源类型: | 项目
|
| 标识符: | http://119.78.100.158/handle/2HF3EXSE/93637
|
| Appears in Collections: | 影响、适应和脆弱性
气候减缓与适应
|
|
There are no files associated with this item.
|
| Recommended Citation: | |
Lisa Tauxe. Collaborative Research: Reversal frequency versus ancient field strength: Clues from the Jurassic and Cretaceous. 2014-01-01.
|
|
|