Synchronous authigenic albite and dolomite formation in carbonates

Understanding the drivers of authigenic mineral formation in low permeability carbonate reservoirs is critical to model sedimentary basin history and to predict reservoir quality. The aim of this study is to define a mechanism that explains the curious juxtaposition of authigenic albite and dolomite observed in the Austin Chalk Formation. It is proposed that the formation of these authigenic phases was contemporaneous and was directly controlled by the mobilisation of cations from the smectite to illite transition. The observations presented here suggest a strong interdependence between the presence of clay mineral rich lithofacies and the formation of authigenic albite and dolomite. The growth of these authigenic phases was inhibited by supply limitations in a closed geochemical system. Similarly, cation mobility curtailment through the gradual destruction of porosity and permeability during mechanical compaction, chemical compaction (stylolite formation) and clay mineral alignment reduced fluid flow from the clay mineral rich lithofacies into the surrounding facies, further restricting the mineral growth. Most of the authigenic albite and dolomite crystal growth aligns with the early and peak smectite to illite transformation at relatively low temperatures during burial. The formation of authigenic albite and dolomite in the Austin Chalk thus provides a unique window into the controls of authigenic albite and dolomite growth in fine-grained carbonate systems. This detailed analysis identifies thin clay mineral rich interbeds as a first-order control on the formation of authigenic phases in a fine-grained carbonate system.