MS-13-P-2876 Microscopic methods for the study of biomineralization in ancient sedimentary rocks and modern marine sediments.

Biomineralization (the formation or accumulation of minerals by living organisms) can be "biologically induced" (BIM) and "biologically controlled" (BCM) (Lowenstam, 1981; Mann, 1983). To determine the role of biomineralization in the litho- and ore genesis comprehensive studies of Cimmerian oolitic iron ore (N22, Kerch iron pool) and modern silty-clayey marine sediments (QIV, White Sea) were carried out. To study of biomineral formation at the micro- and ultra-micro level comprehensive laboratory tests were performed: a) light microscopy of samples in thin sections; b) Scanning electron microscopy (SEM); b) electron-probe microanalysis (EPMA). BCM in Cimmerian oolitic iron ores may be detected already at the macro level. It is represented by carbonate biominerals made of large (5-7 cm) shells of mollusks and detritus (Fig.1a). Light microscopy showed that calcite-siderite detritus has microfibre structure (Fig.1c). SEM-images show that the shell detritus consists of alternating layers of calcite with different ultramicrostructures (Fig.1c-d). In marine sediments (Fig.2a) BCM is presented by opal. It was discovered as a result of light microscopy of thin sections (Fig.2b,e). It was confirmed by SEM and EPMA. Opal composes fragments of flint shells of diatoms (Fig.2f-g), silicoflagellate skeletons (Fig.2h) and the spicules of siliceous sponges (Fig.2c-d). BIM in oolitic- and pisolitic iron ores resulted in the formation of various oxides and hydroxides of iron. Microscopic analysis of the ores reported presence of such iron biominerals as hematite and goethite, which compose the basic structural elements of ore – oolites, oolite-like formations and cement (Fig.1). Iron biomorphic formations (Fig.1h,j,k) and silicate (Fig.1g,l) biomorphic formations of different shapes found by SEM in the oolitic and pisolitic iron ores, may be an indirect proof of iron and silicate bacteria involvement in iron ore process. In marine sediments BIM is found in the form of framboidal pyrite aggregates. Pyrite framboids are recorded in samples of sediment already in the light microscopy of thin sections (Fig.2b,i). SEM help to visualize framboidstructure and different shape of individual crystallites - globular shape, pentagonal dodecahedron, octahedral and pseudocubic shape (Fig.2j-l). Pyrite framboids often formed on the diatom shells surface residues or inside them (Fig.2i-k). The results of these studies are necessary not only for understanding of biogenic substances role in the formation of sedimentary rocks and ores, but also for the reconstruction of paleoenvironment of sedimentary deposits.
References
Lowenstam H A (1981) Minerals formed by organisms. Science 211:1126-1131
Mann S (1983) Mineralization in biological systems. Struct Bonding 54:125-174