HR: 1340h
AN: GP53B-1216    [Abstracts]
TI: A Rockmagnetic and Palaeomagnetic Record of two Glacial Lakes in the Wind River Range, Wyoming, U.S.A.
AU: * Geiss, C E
EM: christoph.geiss@trincoll.edu
AF: Trinity College, Department of Physics, 300 Summit St., Hartford, CT 06106-3100, United States
AU: Dorale, J A
EM: jeffrey-dorale@uiowa.edu
AF: The University of Iowa, Department of Geoscience, Trowbridge Hall North Capitol St., Iowa City, IA 52242, United States
AU: Dahms, D
EM: dennis.dahms@uni.edu
AF: University of Northern Iowa, Department of Geography, ITTC 205, Cedar Falls, IA 50614- 0406, United States
AB: We analyzed four cores from Louis Lake (42.596 ° N,108.846 ° W, 2610 m elev.) and nearby Fiddlers Lake (42.6312 ° N, 108.8786 ° W, 2868 m elev.), two glacial lakes in the Wind River Range of Wyoming. The lakes were dammed by lateral moraines and hold the possibility of long records of mid-continental climate change. Due to the lack of dateable material towards the base of the cores it is impossible to establish a precise maximum age for both records. We use comparisons of magnetic secular variation with other sites from the Western and Midwestern United States to constrain the age of these lakes as well as rock magnetic analyses to obtain a paleoenvironmental record. Glacial sediment in both lakes is characterized by inorganic, sometimes varved deposits containing high concentrations of coarse-grained (MD) ferrimagnetic minerals (high values of magnetic susceptibility, ARM and IRM, low ARM/IRM ratios). The post-glacial sediments at Fiddlers Lake contain mostly organic material with low concentrations of fine-grained (SD and finer) ferrimagnetic minerals (low values of magnetic susceptibility, ARM and IRM, high ARM/IRM ratios). In contrast, post glacial sediments at Louis Lake are more strongly magnetized containing a higher proportion of detrital material leading. Bulk susceptibility and IRM are still controlled by the presence of abundant organic material, bulk ARM and ARM/IRM ratios, however remain high, indicating the abundance of fine (SD) magnetic minerals. Paleomagnetic analyses show that all samples are demagnetized in fields below 80 mT and that all glacial samples as well as the post-glacial samples from Louis lake yield stable paleomagnetic directions. Holocene samples from Fiddlers Lake were too weakly magnetized to have their NRM analyzed. Both inclination and declination records from both lakes are consistent and paleosecular variations can be used to correlate the records of both sites. Both lakes show several pronounced dips in inclination and a shift in declination in the glacial sediments that can be correlated with other paleomagnetic records and constrains the maximum age of both lake records to approximately 15 - 20 ka B.P.
DE: 0458 Limnology (1845, 4239, 4942)
DE: 1512 Environmental magnetism
DE: 1522 Paleomagnetic secular variation
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting