Speleothems

Lascu_Feinberg_Figure1

Conceptual model of the processes affecting the magnetism of speleothems (Lascu and Feinberg, 2011).

My interest in the magnetism of speleothems (chemical sediments from cave environments) is driven by the impetus to find the ideal, yet elusive paleomagnetic recorder. Such recorder would lock in the geomagnetic field signal instantaneously, provide a measurable, continuous, high-­resolution time series of geomagnetic variation, and have excellent age control, with respect to both accuracy and precision.

Unfortunately none of the traditional archives (volcanic rocks, marine and lake sediments, or archeological artifacts) encompass all of these traits; consequently paleomagnetic data generally suffer from resolution and reliability issues. In light of recent advances in the theory of acquisition of depositional remanence, as well as in sensitivity and resolution of next-generation magnetometers, I am working to contribute to the establishment of this archive as candidate for the ideal geomagnetic recorder.

Speleothems incorporate magnetic minerals in their structure as they precipitate from carbonate-rich drip waters, so they are poised to acquire a natural magnetic remanence of detrital origin. A major advantage in using speleothems is the minimal time lag between the deposition of magnetic particles and their encapsulation in the speleothem structure. Speleothems should therefore “freeze” Earth’s magnetic field signal instantaneously, and capture time series of geomagnetic activity at high resolution, which may be dated with very high precision using U-series radiometric techniques

Records of small-scale fluctuations in the Earth’s magnetic field are scarce, but would be very valuable in the effort to constrain the processes in the Earth’s outer core that generate them, which are not well understood. In addition, the mineralogy, grain size, and abundance of magnetic minerals can be used to reconstruct the history of environmental changes associated with speleothem formation, and compared to traditional speleothem paleoclimate proxies, such as isotopic records.

Papers

Lascu, I. and Feinberg, J. M., 2011, Speleothem magnetism, Quaternary Science Reviews 30, p. 3306-3320, doi:10.1016/j.quascirev.2011.08.004.

Lascu, I., Feinberg, J. M., Dorale, J. A., Cheng, H.  and Edwards, R. L., 2016, Age of the Laschamp excursion determined by U-Th dating of a speleothem geomagnetic record from North America,  Geology 44, p.139-142, doi:10.1130/G37490.1.

Feinberg, J. M., Lascu, I., Lima, E. A. and Weiss, B. P., Dorale, J. A., Alexander Jr., E. C., and Edwards, R. L., Magnetic detection of paleoflood layers in stalagmites, in preparation.

Strauss, B. E., Strehlau, J. H., Lascu, I., Dorale, J. A., Penn, R. L. and Feinberg, J. M., 2013, The origin of magnetic remanence in stalagmites: Observations from electron microscopy and rock magnetism, Geochemistry, Geophysics, Geosystems 14, p. 50065025, doi:10.1002/2013GC004950.