ABSTRACT

Anhydrite nodules are known from, or have been interpreted to have formed in, geologic environments that range from near surface to several hundred meters of burial depth. Anhydrite nodules from the Upper Devonian Leduc Formation in the subsurface of Alberta, Canada, have feeder channels of anhydrite and contain inclusions of bitumen-stained wall rock, indicating that these nodules formed after oil migration and hence at depths of probably more than 2500-3000 m. These new findings indicate that anhydrite nodules can form at burial depths ranging from nearly zero to several thousand meters, and that the mere presence of anhydrite nodules has no particular significance genetically (displacive or replacive) or paleoenvironmentally (sabkha, subaqueous, etc.). The origin of anhydrite nodul s in any particular area can often be determined by means of petrographic and/or geochemical criteria.