Jp. Hodych et S. Bijaksana, CAN REMANENCE ANISOTROPY DETECT PALEOMAGNETIC INCLINATION SHALLOWING DUE TO COMPACTION - A CASE-STUDY USING CRETACEOUS DEEP-SEA LIMESTONES, J GEO R-SOL, 98(B12), 1993, pp. 22429-22441
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.