CALCITE FORMATION IN MICROBIAL MATS - MODELING AND QUANTIFICATION OF INHOMOGENEOUS DISTRIBUTION PATTERNS BY A CELLULAR-AUTOMATON MODEL AND MULTIFRACTAL MEASURES

The evolution of early diagenetic calcite cements in microbial mats of recent supratidal sediments of the southern North Sea is modeled in a two-dimensional microscale approach by a cellular automaton model (CA M). Calcite is traced out in the model by virtual calcium distribution patterns obtained from runs under different assumptions concerning se diment-intrinsic conditions. For justification of the CAM, real calciu m distribution patterns, documented by scanning electron microscopy co upled with energy-dispersive Xray spectrometry (SEM/EDX), are quantita tively compared with the virtual patterns on the basis of multifractal analyses. The formation of high magnesian calcite as a consequence of biogenic anaerobic decomposition of organic matter starts at certain initial calcite domains. In this stage an inhomogeneous and multifract al calcium distribution is characteristic. Nearly complete remineraliz ation of organic matter leads to monofractal behavior of generalized f ractal dimensions (D-B(q)congruent to 1.84). The CAM results confirm t hat calcite formation is a self-determining morphogenetical process an d diffusive transport processes of reactants within the mat affect the biogenic calcite formation.