Conclusions about the detrital sedimentary rocks regarding their magnetic properties must rely in part on knowledge of the ferric oxide minerals present. These minerals may be present in the coarse fraction of the rock as black detrital grains or the weathering products thereof, or in the matrix of the rock as inherited products of weathering in the source area and/or as weathering products thereof, or as chemically precipitated iron oxide cement. The genesis of the black grains and the aphanitic red pigment in a given red bed must be completely understood before these particles may be used for paleomagnetic work. Information about the geomagnetic pole position dated by a deposit is given only by the particles oriented at the time of deposition, or those derived by weathering from particles so oriented. The problems of red bed pigmentation are so manifold that current information and opinions cannot provide a unifying explanation. Most of the red pigment is probably inherited hematitic clay, yet some of the ferric oxides apparently have been redistributed in colloidal form after deposition, and some of it may be altered diagenetically. The resultant geomagnetic data are therefore secondary and do not indicate primary pole positions.

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