MEASUREMENT OF THE DEGREE OF SMOOTHING IN SEDIMENT PALEOMAGNETIC SECULAR VARIATION RECORDS - AN EXAMPLE FROM LATE QUATERNARY DEEP-SEA SEDIMENTS OF THE BERMUDA RISE, WESTERN NORTH-ATLANTIC OCEAN

Replicate paleomagnetic secular variation (PSV) records for the last 1 5,000 yr have been recovered from two deep-sea sediment gravity cores on the Bermuda Rise, western North Atlantic Ocean. The records have be en correlated using several different parameters and dated by correlat ion to a nearby piston core which has a high-resolution C-14 chronolog y. The PSV records are systematically subdued with respect to the expe cted local magnetic field variability during the Holocene, when sedime ntation rates were about 10 cm/kyr. During the Late Pleistocene, when sedimentation rates were a factor of 2-3 higher, the PSV variability w as significantly larger. We attribute this to smoothing of the PSV rec ords by a depositional/post-depositional remanence (DRM/PDRM) acquisit ion process with a 10-20 cin lock-in interval. The degree of PSV smoot hing was evaluated by comparing the VGP angular dispersion and vector spectral content of the Bermuda Rise cores with high-resolution PSV re cords from North America and Great Britain. These results suggest a 50 % reduction in the DRM/PDRM recording of vector variability during the Holocene on the Bermuda Rise, with most of the PSV reduction occurrin g for features of less than 2000 yr in duration. We can reproduce the subdued PSV pattern with a mathematical model that simulates the site DRM/PDRM remanence acquisition process. Finally, the replicate gravity cores document that PSV records may be reproducible on a local scale, even though they only retain a low-pass filtered record of true magne tic field variability.