About This Item
Share This Item
Excellent exposures of Upper Cretaceous rocks in the central Foothills of Alberta reveal a lateral and vertical succession of marine shale, littoral and near-shore sandstones, and lagoonal to deltaic sediments. The interpretation of the depositional environments is based on comparisons with Recent sediments and on various physical criteria such as areal patterns, structures, and textures. In addition, paleontological data also provide useful information. The intertonguing of deposits records shifting shorelines related to the slowly regressing sea. Delineation of the ancient shorelines suggests areas in which potential reservoir rock may have formed and is important in future petroleum exploration.
Several units are interpreted as having formed in the transitional environment. Some of the sandstones, particularly those of the Cardium formation, are similar to those associated with barrier islands and represent the littoral and upper part of the epineritic environments. The sandstones are finely laminated, show reworking by organisms, and generally are well sorted. They have a linear distribution, extending for hundreds of miles along the Foothills. Associated with those sand bodies are carbonaceous sediments believed to represent lagoonal and marsh deposits. They include coarse-grained sandstone that presumably formed in stream channels, suggesting the presence of a deltaic complex. The abundance of carbonaceous debris and thin coal seams attest to widespread and recurring swamp conditions.
The marine shales are separated into several types, each characterizing a specific zone of deposition. Those formed in an oxidizing environment, presumably above wave base, contain glauconite and siderite. Shales formed below wave base were in a reducing environment that favored the development of pyrite and the diagenetic alternation of calcite to dolomite.
End_of_Article - Last_Page 549------------