J. Kropp^a, W. von Bloh^a and T. Klenke^b

Geol. Rundsch. 85, 857-863 (1996)

^aPotsdam Institute for Climate Impact Research (PIK), Telegrafenberg, P.O. Box 60 12 03, D-14412 Potsdam, Germany.

^bInstitute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, P.O. Box 2503, D-26111 Oldenburg, Germany

Abstract

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 (CAM). Calcite is traced out in the model by virtual calcium distribution patterns obtained from runs under different assumptions concerning sediment-intrinsic conditions. For justification of the CAM, real calcium distribution patterns, documented by scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDX), are quantitatively compared with the virtual patterns on the basis of multifractal analyses. The formation of high magnesian calcite as a consequence of biogenic anaerobic decomoposition of organic matter starts at certain initial calcite domains. In this stage an inhomogeneous and multifractal calcium distribution is characteristic. Nearly complete remineralization of organic matter leads to monofractal behavior of generalized fractal dimensions (D_B(q)=1.84). The CAM results confirm that calcite formation is a self-determining morphogenetical process and diffusive transport procsesses of reactants within the mat affect the biogenic calcite formation.

Keywords: Microbial mats, Calcite, Fractal, Multifractal, Tidal sediments, Cellular automaton