Abstract

Aerial photographs of North America show a great abundance of north-south and east-west lineaments, caused by the man-mode cultivation pattern. There are, however, also a great number of natural lineations in the same directions. These are particularly evident within the Cordillera, in granites of Lower Cretaceous age, and near their contacts. Similar lineament trends are also present in the Caroline area of Alberta. A field inspection shows that the lineaments are minor topographic depressions and their photo expression is caused by soil tonal and vegetal changes along the lineaments.

A lineament study in the Caroline area, Alberta, covered 1.404 square miles, and 24,129 lineaments were recorded. Their average length is 0.78 miles (1.25 km), and a distinct maximum occurs at 0.5 miles (0.8 km). The density is 17.2 lineaments/mile² (7 lineaments/km²), or 13.2 miles of lineaments/mile² (8.2 km/km²). These lineaments are defined as “meso-fractures,” whereas lineaments longer than 2 miles are defined as “macro-fractures.”

A high macro-fracture density indicates the “Caroline Arch.” Devonian reef growth had the tendency to prefer the flanks of this arch. The arch rose by 200 feet (61 meters) in late Paleozoic-early Mesozoic time, as shown by the truncation of Carboniferous formations. The paleotopography on the Paleozoic surface is very well mapped by the density of meso-fractures. A N 45° E trending “Raven Horst” rose at the time of erosion on the Paleozoic surface and a gas field was discovered at its updip portion.

Macro-fractures are interpreted as basement fractures which propagate upward particularly well in areas of uplift. Meso-fractures are interpreted to be caused mainly by differential compaction.