Relationship between remagnetization, magnetic fabric and deformation in Paleozoic carbonates

We have studied the magnetic fabric of Paleozoic carbonates from numerous sites in the North American midcontinent, for comparison with paleomagnetic behavior and calcite twinning strains. Sites carrying a Kiaman remagnetization have significantly lower anhysteretic remanent magnetization (ARM) anisotropy (less than 3%) than other sites. Minimum axes of ARM ellipsoids are distributed in a vertical plane trending approximately SE-NW. This trend is very similar to the orientation of Alleghenian layer-parallel shortening, as inferred by mechanical twinning in calcite. Sites lacking a Kiaman overprint invariably have steeply-oriented minimum ARM axes and relatively strong anisotropy, whereas the most strongly remagnetized sites have nearly horizontal minima and weak anisotropy. These observations suggest that diagenetic/authigenic magnetites formed independently of any pre-existing fabric of precursor sulphides and host rock, and that the magnetic fabric of the whole midcontinent was at least partially affected by Alleghenian syn-orogenic activity.