Paleomagnetic inclination errors in sediments cored from a Gulf of Mexico salt dome—An indicator of ancient sea level?

A paleomagnetic study of piston-cored sediments was done in conjunction with a high-resolution seismic reflection study of a salt dome on the upper continental slope in the northern Gulf of Mexico. Seismic data showed that late Pleistocene sediment layers are exposed around the bank and tilted up to 8° by the diapiric uplift. Cores were taken on the flanks of the bank to test the use of paleomagnetism in measuring the tectonic tilt of the sediments. After structural corrections, results from six cores agreed with the geocentric axial dipole inclination for the site, but four other cores displayed significantly shallowed inclinations. Moreover, several cores showed linear trends of inclination shallowing, increasing downcore. The anomalous results are from the summit of the bank and suggest a relation to subaerial exposure during a sea-level lowstand. We think that the shallow inclinations were caused by compaction, but that the linear trends resulted from rehydration of the sediments after exposure by erosion.