The role algobacterial mat in accumulation of silicon in sedimentary rock of hydrothermal sources is investigated. It is shown, that formation of this rock is result of influence of three factors: the content a plenty of silicon in water of a source (up to 400 mg/L); growth algobacterial mat in a stream of water of a source; the formation and accumulation of gas bubbles under layers of algobacterial mat. Gas acts from punctures of a bottom of a stream of a source and raises separate site slayers of mat. Height of such eminences are about 5 cm above a surface of a level of a stream. In these eminences there is an evaporation of hydrothermal water and accumulation of silicon. Result of this process – formation of siliceous plates on current of hydrothermal stream. These siliceous plates include strings of cyanobacteria. Authors name such rock filled with biota, biosilicite. Thickness of deposits under algobacterial mat reach up to 30 cm in area of a hydrothermal source. The received data help to decipher conditions sedimentation of the most ancient hydrothermal systems.
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