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The rare and unusual minerals from several Leg 34 sediment samples shed light on processes that contributed these minor but important minerals to pelagic sediments. A ubiquitous biotiteorthopyroxene-amphibole association reflects a slow, continuous, presumably worldwide input from intermediate volcanoes, thus creating a low-level background concentration of intermediate magma detritus which must be clearly exceeded before inferences can be drawn about the inception of nearby island arc or continental margin volcanism (Andean in the present case). Basaltic detritus, composed of augite, palagonite, fibropalagonite, and smectite aggregates presumably derived from sideromelane, is most simply explained by local input from basement exposures on the sea floor. However, this explanation is not readily adapted to all occurrences, largely for lack of an adequate mechanism of transport, so that an appeal to supplementary eolian input from distant sources may be necessary. Even eolian input is difficult to prove, however, without carefully controlled quantitative studies. Authigenic minerals include phillipsite and clinoptilolite, whose variable degrees of crystal development probably reflect growth rates; Mn micronodules, composed largely of todorokite, which thus indicates redox potentials in the sediments less than those is the overlying bottom waters; and dolomite, formed by kinetically controlled unmixing of unstable magnesian calcite skeletal debris to low-Mg calcite and dolomite, with minor contribution of Mg from connate fluids, volcanic detritus and diffusion from the overlying water mass. The metalliferous sediments of the Bauer Deep are composed largely of amorphous Fe oxide particles ("RSOs") with which, by virtue of a low sedimentation rate," one finds relatively high concentrations of eolian dust (intermediate and basic volcanic detritus); authigenic minerals (Mn micronodules, phillipsite, and barite); and fish debris. The RSOs have widely varying physical properties, including density, which constrain any hypothesis of origin. A smectite-rich object from the Oligocene at Site 321, originally described as "bentonite," is tentatively identified as a fragment of a calcareous algal mat which was broken from its place of growth in shallow water (in the photic zone) and rafted over Site 321, where it sank rapidly below the CCD to the sea floor where, prior to and during burial, the calcite was replaced by a poorly crystallized smectite. If so, and if the mat grew on the Galapagos Rise, the rise crest was much shallower than heretofore suspected.

Rare and Unusual Minerals and Fossils(?) in Sediments of Leg 34