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Multi-scale modelling of microbial lacustrine carbonates with Carbo-CAT and Mounds3D
Two numerical forward stratigraphic models are used to explore the origin of carbonate lacustrine strata characteristics at various scales. The large-scale model (Carbo-CAT; Burgess, 2013) focuses on exploring kilometre scale carbonate stratal heterogeneity developing in extensional settings. New developments include spatial distribution of dissolved carbonate in water controlling carbonate production and subsidence produced by various 3D fault configurations. The small-scale model (Mounds3D) investigates the controls on microbial mound development in the metre to decametre scale. Modelled microbial growth includes precipitation and trapping and binding processes. These are affected by energy, slope and spatial distribution of the microbial community. The model incorporates a depth-averaged hydrodynamic model to assess the impact of transported sediment deposition, erosion and trapping and binding in mound development.
Numerical experiments using these models show the complex relationship between initial conditions, processes and resulting stratal geometry. For example, large-scale models of carbonate systems developing over relay ramps show that their size, shape and facies distribution is controlled by the combined effect of varying basement surface, the platform ability to keep up with relative water-level rise and sediment transport processes. The tests performed with the small-scale model show that, although the initial bathymetry exerts a first order control on initial location of microbial mounds, the dynamic behaviour of the systems suggests that mound spacing is also controlled by local variations on the hydrodynamic and depositional conditions.
