Conference proceeding
Dating the Laschamp excursion; why speleothems are valuable tools for constraining the timing and duration of short-lived geomagnetic events
American Geophysical Union Fall Meeting, Vol.2015
American Geophysical Union 2015 fall meeting
12/2015
Abstract
Short-lived geomagnetic events are reflections of geodynamo behavior at small length scales. A rigorous documentation of the anatomy, timing, duration, and frequency of centennial-to-millennial scale geomagnetic events can be invaluable for theoretical and numerical geodynamo models, and for the understanding the finer dynamics of the Earth's core. A critical ingredient for characterizing such geomagnetic instabilities are tightly constrained age models that enable high-resolution magnetostratigraphies. Here we focus on a North American speleothem geomagnetic record of the Laschamp excursion, which was the first geomagnetic excursion recognized and described in the paleomagnetic record, and remains the most studied event of its kind. The geological significance of the Laschamp lies chiefly in the fact that it constitutes a global time-synchronous geochronological marker. The Laschamp excursion occurred around the time of the demise of Homo neanderthalensis, in conjunction with high-amplitude, rapid climatic oscillations leading into the Last Glacial Maximum, and precedes a major supervolcano eruption in the Mediterranean. Thus, the precise determination of the timing and duration of the Laschamp would help in elucidating major scientific questions situated at the intersection of geology, paleoclimatology, and anthropology. Here we present a geomagnetic record from a stalagmite collected in Crevice Cave, Missouri, which we have dated using a combination of high-precision 230Th ages and annual layer counting using confocal microscopy. We have found a maximum duration for the Laschamp that spans the interval 42,250-39,700 years BP, and an age of 41,100 + or - 350 years BP for the height of the excursion. During this period relative paleointensity decreased by an order of magnitude and the virtual geomagnetic pole was located at southerly latitudes. Our chronology provides the first robust bracketing for the Laschamp excursion, and improves on previous age determinations based on (super 40) Ar/ (super 39) Ar dating of lava flows, and orbitally-tuned sedimentary and ice-core records.
Details
- Title: Subtitle
- Dating the Laschamp excursion; why speleothems are valuable tools for constraining the timing and duration of short-lived geomagnetic events
- Creators
- Ioan Lascu - University of CambridgeJoshua M FeinbergJeffrey A DoraleHai ChengR. Lawrence Edwards
- Resource Type
- Conference proceeding
- Publication Details
- American Geophysical Union Fall Meeting, Vol.2015
- Conference
- American Geophysical Union 2015 fall meeting
- Publisher
- American Geophysical Union
- Alternative title
- AGU 2015 fall meeting
- Language
- English
- Date published
- 12/2015
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240795802771
Metrics
2 Record Views