The geochemistry of deep sea sediments from the Indian Ocean and the stability of their smectite, palygorskite and zeolite phases

Sayad, Pooran (1984) The geochemistry of deep sea sediments from the Indian Ocean and the stability of their smectite, palygorskite and zeolite phases. University of Southampton, Doctoral Thesis, 396pp.

Record type: Thesis (Doctoral)

Abstract

Cretaceous to Quaternary sediments cored in Deep Sea Drilling Project Legs 22, 23, 24, 25 and 26 in the Indian Ocean were studied. Chemical analyses of zeolites (phillipsite (phill) + clinoptilolite (clin)), palygorskite (paly), mixed layer illite/smectite (MLIS) isolated from the sediments and bulk sediments were performed by Energy Dispersive X-ray and a-probe techniques. Bulk chemistry element-comparisons (i.e. Ti vs. Al, Cr vs. TiO2 and Fe/Ti vs. Al/(A1+Fe+Mn) indicated the basaltic and silicic volcanic material contribution to the sediments. The sediments contain authigenic minerals: mainly phillipsite (Miocene and younger), clinoptilolite (Cretaceous to Miocene), mixed layer illite/smectite and palygorskite. Palygorskite, mixed layer illite/ smectite and clinoptilolite assemblages are present in Cretaceous sediments. Biogenic silica is relatively abundant everywhere. Opal-CT formed from dissolved radiolaria, diatoms and sponge spicules is mainly associated with clinoptilolite. Phillipsite and mixed layer illite/smectite, with a high percentage of expandable layer, are thought to be derived from volcanic glass, whereas palygorskite can form from mixed layer illite/smectite. In the absence of detrital mixed layer illite/smectite (i.e. MLIS with a low percentage of expandable layer) authigenic mixed layer illite/smectite (i.e. MLIS with a high percentage of expandable layer) results from the alteration of volcanics and becomes a sink for Mg2+. On moving into more siliceous interstitial waters on burial, clinoptilolite could format the expense of mixed layer illite/smectite and silica. In the presence of detrital mixed layer illite/smectite, Mg2+ released from the alteration of volcanics (plus additional Mg2+ from sea water, or hydrothermal solutions or Mg-bearing minerals) could react with mixed layer illite/smectite to form palygorskite. Clinoptilolite could then form at the expense of palygorskite on moving into more siliceous interstitial waters on burial. The suggested reactions are: 1. MLIS(authigenic) + Silica(biogenic and/or volcanic) - clin 2. Phill + Silica(biogenic and/or volcanic) clin 3. MLIS(dejal)4- Silica (biogenic and/or volcanic) ~: paly 4. Paly + Silica(biogenic and/or volcanic) -~ clinReactions 1, 2 and 4 show negative free energies of reaction, whereas reaction 3 is almost at equilibrium using activity data for ions in interstitial waters.Thermodynamically, phillipsite, palygorskite and mixed layer illite/ smectite are unstable relative to clinoptilolite, which is favoured by high silica concentrations. The stability diagrams indicated that high Mg z+ and pH, and low to high silica, are necessary for palygorskite formation compared with mixed layer illite/smectite and clinoptilolite.

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