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Abstract:
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This study was undertaken to explain why silica is preserved in the oceans, which are undersaturated in silica. Ion probe, electron probe and SEM analysis of the surface chemistry of radiolarians (a siliceous microfossil) and analysis of data about their geographic distribution were performed to answer this question.
It was found that a number of factors contribute to radiolarian preservation. A metallic coating consisting of Al, Ni, Mg, Cu, Fe, Co, Mn, Mo, Cr, Zn and Ba exists on the surface of all radiolarians. The composition of this coating varies with geographic location and depth in the water column. It also varies between live and dead water column samples. High aluminum content in the coating of sediment samples may inhibit silica dissolution. Anoxic basin conditions also aid silica preservation.
Analysis of the geographic distribution of radiolarians which are indicators of particular oceanographic conditions showed that they are preserved in restricted zones in the oceans. Surface, warm water dwelling radiolarians are shown to be preserved in the equatorial region. Intermediate and deep, cold water dwelling radiolarians exhibit cosmopolitan distributions in the sediments with enhancement under oceanographic convergences and divergences. |
