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Stratigraphic Forward Modelling of Lacustrine Carbonates in a Tectonically Active Basin

Abstract

Since the recent discoveries of pre-salt oil fields on offshore Brazil, there has been increased interest on understanding the controlling factors that lead to the formation of microbial carbonates. Stratigraphic forward modelling is a useful tool to test hypotheses derived from outcrop studies of analogue microbial strata. Data from Upper Jurassic to Lower Cretaceous (Purbeck Fm) lacustrine carbonates outcropping in Southern England is used to generate a numerical forward model to assess the importance of the different genetic processes involved. New depositional models developed for the lower Purbeck suggest palaeobathymetry played an important role in distribution of the various carbonate facies while seismic data show that normal faulting was likely active during deposition of these carbonates. In addition, initial palaeotopographic maps show that these faults could be controlling position of lake margins. A preliminary 3D forward model based on Carbo-CAT (Burgess, 2013) can simulate deposition from several carbonate factories in a tectonically active environment. The geological processes included are subsidence on normal faults, lake level oscillations, water depth and position-dependent carbonate production rates, facies clustering and migration, and sediment transport. We are using the new forward model to better understand how the accumulation of microbial carbonates is influenced by active normal faulting. Initial results will be presented showing how carbonate deposystems respond to various active fault and relay ramp configurations.