IMPORTANCE OF CLAY IN IRON TRANSPORT AND SEDIMENT REDDENING: EVIDENCE FROM REDUCTION FEATURES OF THE ABO FORMATION, NEW MEXICO
Iron-bearing sand and silt grains, which are generally regarded to be the principal source of iron for hematite precipitation in red beds, are uncommon (average <1%) in the Abo Formation. Where present these grains are not significantly altered in either red host rock or in the white reduction features. Therefore, detrital iron-bearing clays are the primary source of iron in the Abo Formation. Although compositionally variable, the clay-rich areas contain a mean of 8.4% FeO(total) in the host rock and a mean of 4.6% FeO(total) in reduction spots. Low whole rock iron values of the Abo Formation relative to other red bed units is consistent with clay being the principal iron source. The Abo Formation may represent a clay dominated end member in a continuum of red beds in which the iron needed for reddening is derived from clays and coarser iron bearing framework grains.