-Five overlapping sections from the thick Neoproterozoic to early Cambrian sediments of western Mongolia were analysed to yield a remarkable carbon-isotope, strontium-isotope and small shelly fossil (SSF) record. Chemostratigraphy suggests that barren limestones of sequences 3 and 4, which lie above the two Maikhan Uul diamictites, are post-Sturtian but pre-Varangerian in age. Limestones and dolomites of sequence 5, with Boxonia grumulosa, have geochemical signatures consistent with a postVarangerian (Ediacarian) age. A major negative 8 13

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Organic matter of vegetal and (or) bacterial origin in the Earth's crust under the conditions of hypergen esis carries two functions: destructive, providing decomposition and dissolution of primary minerals, and creative, which controls incorporation of mineral ized organic remnants in the composition of new hypergene formations. Biomineral interactions and their role in mineral formation are related to one of the most important problems of the twenty first century in mineralogy [1,2]. It has become much more evident that bacteria occur in all environments and on all sur faces and that they actively participate in rock weath ering, material transportation, sedimentation, and diagenesis. Biofilms and cyan bacterial mats play an important role in the processes of mineral formation as well [3]. Additional support for these facts was obtained during study by a scanning (SEM) and trans mitting (TEM) electron microscopy, thermal analysis, and IR spectroscopy of fireproof clay from the Latn enskoe deposit; as a result, the interaction between organic and inorganic materials during their forma tion was originally discovered.The deposit is located in 15 km to the west of Vor onezh in the Don-Veduga-Devitsa interfluves. Clay composes oval lenses with a width of several hundred meters and a length of a few kilometers; it occurs in the middle part of the section of sand-gravel alluvial deposits of Aptian age. The thickness of productive horizon ranges from n to 40 m; the average thickness of proper fireproof clay is 3-4 m. Clay is mainly com posed of kaolinite, the concentration of which is 70-90%. Terrigenous hydromica and quartz, as well as authigenous montmorillonite and gibbsite, usually occur as admixtures. Five lithological types and seven technological types of clay (LT O-LT U) applied in fireproof, ceramic, cement, and other productions are distinguished on the deposit. Color is one of the main lithological signs of fireproof clay from the Latnenskoe deposit. Depending on the concentration of carbon aceous material, thte color varies from light gray in the best clay (LT O) to black in carbonaceous clay (LT U). According to the production volume, clays from the Latnenskoe deposit occupy the leading place in the market of fireproof raw materials in Russia [4,5].The presence of two genetic varieties of kaolinite is established in all lithological types of clays: terrigenous redeposited from washing of weathering and authige nous crusts deposited under the influence of organic matter. Authigenous kaolinite was formed by the flow ing mode in the reduced acid medium of the lakeswamp environment as a result of successive replace ment of hydromica by montmorillonite, and the latter by kaolinite and gibbsite. Newly formed kaolinite is represented by vermicular crystals [4]. The role of organic matter in this process is not still clear. Was it only the reaction environment of the mineral forma tion or at the same time the matrix for pseudomor phous replacement by aluminosilicate minerals? In the latter case, we should consider...

We review the development ofBacterial Paleontology and consider its relevance ofthe rapidly emerging field of Astrobiology. We present electron microscopic images of fossil bacteria in different states of preservation in Earth rocks and Astromaterials.

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