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Periodicities in natural remanent magnetization and palaeoclimatic records detected by walsh spectra
Authors:J G Negi  R K Tiwari
Institution:(1) Theoretical Geophysics Group, National Geophysical Research Institute, 500 007 Hyderabad, India
Abstract:The time series consisting of nonsinusoidal Natural Remanent Magnetization (NRM) and palaeoclimatic variations for the past two million years have been spectrally examined by using a new Walsh transform technique. The results show statistically significant periodicities (at 95% confidence level) of approximately 92,000 years; 43,000 years and 21,000 years in the ensemble spectra of the NRM intensity (mineralogic) variations. These NRM periodicities are remarkably close to the well-known Milankovitch cycles. The ensemble spectra of palaeoclimatic records reveal only 41,000 years statistically significant (95%) periodicity corresponding to the obliquity cycle. The study suggests that NRM variations in deep sea sediments probably are more sensitive recorders of ldquopalaeoclimatic memoryrdquo than the oxygen isotope variations.
Keywords:Walsh spectra  natural remanent magnetization  palaeoclimate  orbital cycles
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