Magnetic fabric results from DSDP Holes 380A (Black Sea) and 524 (South Atlantic) sediment cores: A case study for the comparison between low and high field torque magnetometer measurements

Magnetic fabric (anisotropy) measurements have been made on samples of Quaternary sediments from DSDP Hole 380A (Black Sea) and Tertiary and Cretaceous nannofossil oozes, marls and volcanoclastic sandstones from the Southeast flank of the Walvis Ridge at Hole 524, recovered during Legs 42B and 73 of the International Program of Ocean Drilling (IPOD). The fabric was determined by means of both a low field and a high field torque magnetometer.The overall results from the low field measurements are similar to those from the high field measurements. The results from both sets of measurements indicate the existence of a NE-SW lineation at Hole 380A and a NW-SE lineation at Hole 524. For Hole 380A some of the individual parameters show slight differences in values for the low field and high field torque measurements while for Hole 524 these individual parameters compare favourably and indicate an approximately one-to-one correspondence. In general the fabric is better defined at Hole 524 than at Hole 380A. Anisotropy measurements sometimes were found to be greatly affected by the shape of the sample. This apparent shape-effect appears to be more prevalent in the high field than in the low field measurements. In addition, for Holes 380A and 524 some samples show deformational-style fabric characteristics on one instrument and depositional-style characteristics on the other. The reasons for these differences and how the effects on the anisotropy data can be removed or minimised are described in this paper.