Palaeomagnetism of the Jurassic Navajo Sandstone from South‐western Utah

Summary A combination of petrographic and magnetic studies indicates that the Navajo Sandstone carries a stable secondary magnetic moment and arguments are given for believing this to have been recently acquired. It therefore follows that haematite is more mobile in permeable sandstones than has generally been thought. The results suggest that the Jurassic palaeomagnetic pole for North America, based largely on preliminary work by Runcorn and Collinson & Runcorn from the same formation and similar red‐bed lithologies, is based on rocks with a present‐day component of magnetization. The virtual poles reported by DeBoer or Helsley & Steiner may be the best representations of the North American Jurassic palaeomagnetic pole position. A petrographic study indicates that the investigation of the Navajo Sandstone as a means of detailing the behaviour and detailing a part of the polar wandering curve for North America is not feasible. However, a residuum of the original Jurassic component may be seen in the reversely magnetized sites. There probably exist similar residue in the normally magnetized sites, but these Jurassic residues are much less clearly defined.