Age of the Laschamp excursion determined by U-Th dating of a speleothem geomagnetic record from North America

The Laschamp geomagnetic excursion was the first short-lived polarity event recognized and described in the paleomagnetic record, and to date remains the most studied geomagnetic event of its kind. In addition to its geophysical significance, the Laschamp is an important global geochronologic 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 coeval with a major supervolcano eruption in the Mediterranean. Thus, precise determination of the timing and duration of the Laschamp excursion would help in elucidating major scientific questions situated at the intersection of geology, paleoclimatology, and anthropology. Here we present a North American speleothem geomagnetic record of the Laschamp excursion that is directly dated using a combination of high-precision 230Th dates and annual layer counting using confocal microscopy. We have determined a maximum excursion duration that spans the interval 42,250-39,700 yr BP, and an age of 41,100 ± 350 yr BP for the main phase of the excursion, during which the virtual geomagnetic pole was situated at the southernmost latitude in the record. Our chronology provides the first age bracketing of the Laschamp excursion using radioisotopic dating, and improves on previous age determinations based on 40Ar/39Ar dating of lava flows, and orbitally-tuned sedimentary and ice-core records.This project was funded by NSF-EAR grant 1316385, a University of Minnesota McKnight Land Grant Professorship to JMF, and ERC grant 320750. Confocal microscopy was performed at the University of Minnesota Imaging Centers. We are grateful to John Geissman, Brad Singer, and James Channell for their constructive reviews. This is Institute for Rock Magnetism contribution 1506.This is the author accepted manuscript. The final version is available from the Geological Society of America via http://dx.doi.org/10.1130/G37490.

Uranium-series Chronology and Environmental Applications of Speleothems

An increasing number of scientists recognize the value of speleothems1 as often extremely well-preserved archives of information about past climate, vegetation, hydrology, sea level, nuclide migration, water-rock interaction, landscape evolution, tectonics and human action. Well-constrained data are required to document pas

A High-Resolution Absolute-Dated Late Pleistocene Monsoon Record from Hulu Cave, China

Oxygen isotope records of five stalagmites from Hulu Cave near Nanjing bear a remarkable resemblance to oxygen isotope records from Greenland ice cores, suggesting that East Asian Monsoon intensity changed in concert with Greenland temperature between 11,000 and 75,000 years before the present (yr. B.P.). Between 11,000 and 30,000 yr. B.P., the timing of changes in the monsoon, as established with 230Th dates, generally agrees with the timing of temperature changes from the Greenland Ice Sheet Project Two (GISP2) core, which supports GISP2\u27s chronology in this interval. Our record link North Atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer East Asian Monsoon originates

Decoding Last Interglacial sea-level variations in the Western Mediterranean using speleothem encrustations from coastal caves in Mallorca and Sardinia: A field data - model comparison

U-Th ages of phreatic overgrowths on speleothems in coastal caves of the Western Mediterranean record high sea level positions during marine isotope stage (MIS) 5e of the last interglacial.While relative sea level (RSL) on the southeastern coast of Mallorca stood w2.6 m above present sea level (apsl) during MIS 5e, it stood w4.3 m apsl at this time in northwestern Sardinia. The difference between the two sites during MIS 5e and the deviation from the eustatic sea level trend during the Holocene was investigated using the numerical code SELEN. The offset between the eustatic curve and those pertaining to the two sites principally reflect the vertical deformations and geoidal variations in response to meltwater loading. As Sardinia is closer to the center of the Mediterranean basin, the hydro-isostatic component of RSL is enhanced here compared to Mallorca, which results in a modeled offset ofw60 cm between the two sites. This result is qualitatively useful as it provides a partial reconciliation for the site differences. However, the need for refinement in the model is also recognized, as it does not match the observation based on UeTh dating of speleothem overgrowths in Mallorca that sea level there has remained stable for the past 2800 years. Overall, the results of the study first suggest that both sites largely track the eustatic sea level curve, and second suggest that glacial isostatic adjustment is a viable mechanism to reconcile some, if not most, of the relatively small elevation difference of MIS 5e sea level observed at Mallorca and Sardinia, although minor tectonic adjustments cannot be ruled out in explaining some low-amplitude local variation