The use of titania polymorphs as indicators of mesodiagenesis during hydrocarbon charge

Abstract

Authigenic titania (TiO2) minerals are observed in the Upper Jurassic-Lower Cretaceous pro-deltaic reservoir sandstones of the Scotian Basin. Although diagenetic rutile is rare, relatively large amounts of diagenetic anatase and brookite are present. Anatase is mostly early diagenetic whereas brookite is usually late diagenetic and is abundant in reservoir sandstones above the free-water level. The availability and mobility of Ti during late diagenesis is attributed to the dissolution of Ti-bearing minerals enhanced by Ti complexes formed from hydrocarbon-rich and highly saline fluids. This study suggests that the precipitation of late diagenetic brookite, rather than anatase or rutile, may be due to the incorporation of Fe and V during hydrocarbon charge and the presence of Cl− in circulating fluids. In addition, the chemical composition, timing and distribution of the diagenetic titania polymorphs relative to other diagenetic minerals further constrains the overall paragenetic evolution of the basin, and thus illustrates the relationship between titania minerals, hydrocarbon charge and fluid conditions in the basin.