The Holocene History of the North American Flux lobe: New Constraints From Fish Lake, Harney County, Oregon
Thursday, 17 December 2015: 11:20
300 (Moscone South)
To constrain the Holocene history of the North American flux lobe we present new relative paleointensity (RPI) and paleomagnetic secular variation (PSV) data from Fish Lake, Harney County Oregon. Located high on Steens Mt, Fish Lake (42° 44' 15" N, 118° 38' 57" W, 2,246.7 m) is the largest of several lakes in the Fish Lake glacial valley. Cored along with Pate Lake in the summer of 2012, sediment from four offset holes were cored to a maximum depth of 9 m using a UWITEC coring system. Field based magnetic susceptibility insured that a completely duplicated sediment sequence was recovered. Computer tomographic scans confirmed the quality of the recovered sediment and allowed precise mapping of overlapping sequences. Additional physical properties data, along with Pb-210, radiocarbon dating and discrete tephra layers, including Mazama, tightly constrain this sequence from -0.06 to 14 ka. Progressive alternating field demagnetization of u-channel samples demonstrate that a consistently strong, stable, and low coercivity magnetization is preserved, with low MAD values both before and after deconvolution. Inclinations vary around expected values for the site latitude, with no evidence for inclination shallowing as suggested in previous studies. Declination was reconstructed by initially rotating the declination of each drive to a mean of zero, then further rotating to achieve maximum alignment of overlapping sections, followed by a final rotation of the entire sequence base upon a 400 yr historical model calibration. Remanence is normalized using ARM acquisition, ARM demagnetization, and IRM demagnetization and agreement between these suggests that RPI is preserved. RPI from Fish Lake provides a previously missing proxy for the North American flux lobe that invites comparison with other high quality, high resolution, and independently dated paleomagnetic and archeomagnetic records from the NE Pacific to Europe; allowing us to tease out modes of variability of a large part of the geomagnetic field.