Neumeier U. (1999) Experimental modelling of beachrock cementation under
microbial influence. Sedimentary Geology, v. 126, p. 35-46.
doi:10.1016/S0037-0738(99)00030-5
Abstract
A laboratory model has been developed, which reproduces natural conditions
of beachrock formation. These include the porosity of beach sand, tidal
movements (alternation of phreatic and vadose conditions), temperature,
evaporation, illumination, and water composition (sea-water, with a control
of following parameters: salinity, Ca, Mg, SCO2, pH, CaCO3
saturation).
The conditions of two beachrocks from the Red Sea (Egypt) and Shark Bay
(Australia) have been simulated, and the influence of the micro-organism population
(undetermined) sampled in these beachrocks was observed for 3-4 months. In
the experiments inoculated with micro-organisms, biomineralization produced
characteristic crystals of various forms from 1-20 µm in size. The
precipitates resemble the micritic cements of natural beachrocks. On the
contrary, precipitation was much less developed in the control experiments
under nearly sterile conditions.
These results confirm the importance of microbial activity during beachrock
formation. The first micritic cement, which seems to control cementation
and produce the initial consolidation, is formed under a strong microbial
influence in or near a biofilm covering the grain surface. The presence of
this micritic cement is necessary for the development of the subsequent prismatic
cement, which probably results from an abiotic precipitation during higher
fluid circulation.
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