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Biological alteration of aluminosilicates and biogenic silica during sedimentation and burial, with particular reference to the role of bacteria

Objective


The methodology involved in fixing and sample preparation from the deep sea environment has been perfected.
The interpretation of fossil structures found was aided by observation of the microbial-particle interactions.
Microbes from deep sea South Atlantic sediments were found to be rarely preserved.

During this work, methodology has been perfected for fixing and sample preparation of mixed organic particulate sediments for scanning and transmission electron microscope studies.
Observation of microbial particle (mineral or biosiliceous) interactions in experiments using coastal sediments has greatly aided the interpretation of the fossil structures found in the ancient South Atlantic diatom oozes. Ubiquitous active microbial particle interaction was found in the sense that microbially produced exopolymeric material (EPM) covers almost all surfaces and that particles are bound within the EPM, as well as by fibrils emanating from the bacteria.
The study of deep sea South Atlantic sediments demonstrated that microbes are rarely preserved in this environment. Possibly the blobby flakes and smooth cement, common in most types of sediment, are vestiges of an organic conditioning film. Silicified bacteria, and their associated EPM were found only in the almost purely diatomaceous layers of a single location. The organic material seems to have been passively impregnated with silica. It is proposed that the unusual 3.5 Myear long M Miocene hiatus contributed to this silicification.
It is concluded that diagenesis is not a purely physicochemical process and that silica diagenesis can be bacterially mediated.
Bacterial influence on the alteration and neoformation of silicates in a volcanic sediment could not be determined although it is implied.

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