A 200 Kyr Pleistocene lacustrine record from the Valles Caldera insight: from environmental magnetism and paleomagnetism
Linda Donohoo-Hurley, John W. Geissman, Peter J. Fawcett, Tim Wawrzniec, and Fraser Goff

Abstract:

An ~80 m section of lacustrine sediment cored from the Valles Caldera (VC-3) was deposited over three glacial and two interglacial periods in the mid-Pleistocene. An Ar/Ar age determination of 552 + 3 ka for an ash layer at 76 m depth and major transitions recorded by multiple proxies outside this study have been combined to suggest that core VC-3 was deposited during marine isotope stages (MIS) 14 to MIS 10, including glacial terminations VI (533 ka) and V (424 ka). Alternating field demagnetization response resolves positive inclination magnetizations from samples through most of the core, consistent with Brunhes normal polarity. Three short intervals of shallow to negative inclination magnetizations may partially record geomagnetic polarity events at ~406 ka (11α), ~536 ka (14 α) and the Big Lost excursion (~580 + 8 ka). Remanent magnetization in these sediments is principally carried by a range of multidomain to pseudo-single domain ferrimagnetic particles. Sedimentary deposits of glacial period 5 are typified by higher remanent magnetization and susceptibility values and interglacial times are characterized by lower intensity values. Anomalously high magnetic susceptibility and/or rock magnetic intensities measured from 48 m to 43 m are most likely due to the formation of new magnetic phases (i.e., greigite) over a lithologically distinct interval with preserved shallow mud cracks.


Citation:

  1. Donohoo-Hurley, Linda; Geissman, John W.; Fawcett, Peter J.; Wawrzniec, Tim; Goff, Fraser, 2007, A 200 Kyr Pleistocene lacustrine record from the Valles Caldera insight: from environmental magnetism and paleomagnetism, in: Geology of the Jemez Region II, Kues, Barry S.; Kelley, Shari A.; Lueth, Virgil W., New Mexico Geological Society, Guidebook, 58th Field Conference, pp. 424-432.

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