Abstract: Origin of chlorite rims in reservoir sandstones of the Lower Missisauga Formation, offshore Nova Scotia

Diagenetic chlorite rims on quartz grains preserve porosity and permeability by preventing the formation of secondary, pore-filling quartz overgrowths in wells from the Venture and Thebaud fields. Elsewhere, such chlorite rims have been interpreted as early diagenetic related to a high input of iron (Fe) from rivers or volcanic activity, or alternatively to later diagenesis by basinal fluids. The purpose of this study is to evaluate which of these hypotheses is applicable to the Scotian Basin. It has been suggested that detrital altered ilmenite is responsible for the unusually high titanium (Ti) content of Cretaceous shale in the Scotian Basin and might be an important source of labile Fe. A set of 45 sandstone samples from conventional cores was analyzed for mineralogy in thin section, mineral composition by electron microprobe, whole-rock chemistry, and mineralogy of the <2 μm fraction by X-ray diffraction. This petrographic data has been integrated with facies description of conventional core and with wireline log data. Electron microprobe analysis shows that the chlorite rims are Fe rich and resemble chamosite in composition. Seven sandstone types are distinguished: 1) well-sorted with chlorite rims; 2) well-sorted with chlorite rims and pore-filling clays; 3) carbonate-cemented; 4) partially dissolved carbonate-