Sandstone petrography of the Nanushuk Group and Torok Formation

Abstract

Surface and subsurface samples of sandstone from the Lower and Upper Cretaceous Nanushuk Group and the Lower Cretaceous Torok Formation were examined to determine the textural and mineralogical factors that might indicate their source and affect reservoir characteristics. The samples were collected from scattered outcrops (samples number 1075 through 5475), from measured sections in the western and central outcrop belts, and from the subsurface. The stratigraphic sections in the Nanushuk Group range in depositional setting from fluvial through deltaic to shallow marine and show variations in texture, composition, and diagenetic alteration. Sampling was not systematic; rather, it concentrated on the coarser grained, thicker sandstone beds, which are of greater interest from the standpoint of provenance and potential petroleum reservoirs; most surface samples examined were from the fluvial and deltaic regimes; the thicker beds were frequently sampled at several horizons. Modal analyses were performed on a total of 199 thin sections, and observations on the textural details were made on many more samples.