Origin and significance of clay minerals in Mesozoic shales of the Scotian Basin

Abstract

Upper Jurassic–Lower Cretaceous shales of the Scotian Basin, offshore Nova Scotia, are a primary source of hydrocarbons and of the basinal fluids that affected diagenesis of sandstone reservoirs. This study documents and interprets variability in provenance, early diagenesis and burial diagenesis of clay minerals. A total of 108 shale samples from 16 wells in the Scotian Basin were analyzed with X‐ray diffraction using bulk random sidepack and <2 μm oriented mounts. The observed uniformity of clays present, including abundant mixed‐layer clays, reflects detrital supply from the Canadian Shield and the Appalachian orogen, followed by trends of burial diagenesis known in other basins. Climate variability is masked by diagenetic processes. Enhanced supply from the Meguma Terrane in the Hauterivian‐Aptian is marked by higher Mg chlorite and muscovite, erosion of volcanic products yielded smectite, whereas rapid denudation of inboard metamorphic terranes is recorded in the Albian by higher illite crystallinity.