High resolution environmental magnetism of short sediment cores from Lake Tekapo, New Zealand

Quinn, Alissa N. (Alissa Nicole)

U-channel samples from two lake sediment cores (L-1397 and L-1398) collected by NIWA in 1991 from Lake Tekapo, New Zealand, have been used for an environmental magnetic study. Lithostratigraphic analysis was carried out on the cores, which contain turbidites and laminae that are interpreted to be varves. A varve count gave an age of 353 years before 1991 for L-1397 and 303 years before 1991 ,for L-1398. High-resolution magnetic measurements of natural remanent magnetisation intensity and magnetic susceptibility, and a stepwise alternating field demagnetisation were performed on the u-channels. Declination, inclination and mean destructive field down through the core were obtained from a principal component analysis of orthogonal component projections at 1 cm intervals. An age model was constructed and a sedimentation rate of 6.2 mm/year determined for Lake Tekapo. Natural remanent magnetisation intensity has been plotted against age in attempt to compare cyclicity within the data to paleoclimatic events. The occurrence of two turbidites has been correlated to large paleoseismic events within the South Island in 1861 and 1888 respectively. The cyclicity of declination is the same as the cyclicity of natural remanent magnetisation intensity, suggesting an annually resolvable record of fluctuations in the intensity of the Earth's magnetic field has been obtained. Declination and inclination have been used to reconstruct secular variation for the last 300 years for the Lake Tekapo area.

viii, 62 leaves : ill., maps ; 30 cm. + 1 CD-ROM (4 3/4 in.)

2004Quinn