A Multi-scale Analysis Of Microbialite Facies Of Shark Bay, West Australia, With Numerical Forward Modelling

The occurrence of stromatolites in the geological record can be dated from 3,500million years ago. These stromatolites can develop in different environments such asmarine and nonmarine, hypersaline and normative saline. Many details of theircomposition, diverse morphology, and biology have been studied, but their growthpatterns and environmental forcing are still poorly understood due to their widedistribution in time and space. Furthermore the petrophysical properties ofstromatolites are rare studied.The stromatolites, living in hypersaline marine environments of Hamelin Pool atShark Bay, Western Australia, provide a unique opportunity to insight the significantevolution of stromatolites and their reservoir properties. This study focuses on thegrowth patterns and environmental forcing of stromatolites in different scales, andhopefully improves our understanding and insight into the dynamic processes ofmicrobialites resulting from different environmental factors. The study also illustratesthe value of numerical modelling in complementing and extending carbonateheterogeneity studies. The results of the study show that these stromatolites aremainly controlled by temperature and salinity variation, sea-level fluctuations,siliciclastic supply and directional wave action. The water level oscillation appears tobe a significant control on the growth rate of stromatolite. The stromatolite withdifferent initial topography has different growth rate in the same period. Besides themicrobial growth space is controlled by the change of sea level, and is characterizedby the lateral trend of migration. Stromatolites at similar depths all have similar relief.In addition, the result of seismic scale implies that the characteristics of stromatolitereef are flat top and "lens shape" in the bottom, two wings of stromatolite reef aresymmetrical or asymmetric characteristics. The rapid rise of relative sea level causedby climate warming and the increase rate of sediment supply would lead to the deathof microbialites. According to the simulations of porosity and permeability in different scales, theresults indicate that the relationship between the original porosity/ permeability andthe growth rate of microbialites is approximate direct ratio in vertical direction. Inhorizontal direction, the permeability of principal axis is influenced by the wavedirection.