CAN REMANENCE ANISOTROPY DETECT PALEOMAGNETIC INCLINATION SHALLOWING DUE TO COMPACTION - A CASE-STUDY USING CRETACEOUS DEEP-SEA LIMESTONES

We studied 35 Cretaceous limestone specimens from five Pacific plate D eep Sea Drilling Project sites. Inclination I(N) of the natural remane nce is on average 17-degrees shallower than the average 44-degrees exp ected paleofield inclination I. Anhysteretic remanence (ARM) applied i dentically to various axes was found to be weakest (ARM(min)) perpendi cular to bedding and strongest (ARM(max)) parallel to bedding. The ave rage ARM(min)/ARM(max) of 0.87 as well as the inclination shallowing o f 17-degrees likely originated from sediment compaction rotating the l ong axes of magnetite grains toward the bedding plane. This origin is theoretically and experimentally consistent with the average fractiona l compaction of 0.6 experienced by our sediments (estimated from their porosity). A compaction origin is also supported by the significant c orrelation found between tan I(N)/tan I and ARM(min)/ARM(max). The cor relation line's slope of 2.3 +/- 0.7 agrees with theory, taking into a ccount our observation that ARM given perpendicular to the long axes o f magnetite grains has on average approximately 0.37 times the intensi ty of ARM given axially. These results suggest that compaction-induced inclination shallowing may be detected in a suite of fine-grained mag netite-bearing sediments by looking for a correlation between tan I(N) , and ARM(min)/ARM(max) (having shown that ARM anisotropy is foliated in the bedding plane). This correlation line's prediction of I(N) when ARM(min)/ARM(max) = 1 should estimate I corrected for inclination sha llowing.