PETROGRAPHY OF THE CARDIUM SANDSTONES IN THE RICINUS, CAROLINE, AND GARRINGTON FIELDS, ALBERTA

Abstract

<p>Seventy-nine thin sections were prepared from cores of the Upper Cretaceous Cardium sandstone, obtained from wells in the Ricinus, Caroline and Garrington fields in Alberta. Petrography of each thin section was studied to determine if any comparisons could be made between sands of differing fields, or between the Upper (A) Lower (B) sands of the same field. Two sandstone types have been determined based upon modal percentages of three major mineral constituents. A chert rich sublitharenite generally contains 60% chert,30% quartz, and 10% unstable rock fragments. A chert poor sublitharenite contains 70% quartz, 15% chert and 15% unstable rock fragments. The chert sublitharenite were coarse grained to conglomerate, poorly sorted, with subround to rounded grains. The chert poor sublitharenite were fined grained, well sorted, and contained subangular to angular gralns. Within the Caroline and Garrington fields, the Upper and Lower sands can be distinguished on the basis that the former is of the fine grained, chert poor sublitharenite type, and the latter is of the conglomeratic chert rich sublitharenite type of sandstone. The Lower Garrington sand can be distinguished from the Lower Caroline sand, because the Lower Garrington sand tends to be more chert rich. Similarly, the Upper Garrington sand and the Upper Caroline sand can be distinguished on the basis that the Upper Garrington sand contains a greater abundance of unstable rock fragments. The Upper sands of the Caroline and Garrington fields can not be distinguished from the Ricinus sand, whereas the Lower sands can, as they tend to be richer in chert, and are coarse grained to conglomeratic in grain size. The cementing sequence of; siderite, calcite and silica (in chronological order) was observed in all of the sands. Variations in cement abundances were a function of both depth and grain size. The deeper sands such as In the Ricinus field were predominantly silica cemented. The shallower sands tended to be siderite cemented, as did all those coarse grained to conglomeratic sands.</p>