ABSTRACT

The Meadow Lake escarpment in northwest Saskatchewan is an erosional lineament that originated during the sub-Devonian unconformity interval. At that time, Silurian, Ordovician and 1000 feet of Cambrian rocks were removed from the area north of the escarpment. During the sub-Devonian interval the Saskatchewan plains formed an elevated area (Prairie Plateau) which was attacked by active erosion from the north. This erosion was apparently stopped along the slightly arcuate trend of the Meadow Lake escarpment.

The earliest marine Devonian, the Lower Elk Point of the Ulsterian series, approached from the north and northwest but did not extend over the Prairie Plateau, which remained a positive area until Winnipegosis, Erian time.

The escarpment has been projected east and west, following the erosional northern margin of the Ordovician carbonates. The eastern projection has a trace parallel over 120 miles with an important Precambrian fault system, the Kisseynew lineament of the Flin Flon area. It is suggested that this lineament, which ties in across the shield with the boundary between the Precambrian Churchill and Superior provinces, provides the tectonic background and hinge line, which gave the linear character to the escarpment. It is a belt of faults, thrusted from the north, accompanied by north-south trending faults of later date, with vertical as well as horizontal movements.

Factual proof of faults in the Precambrian subsurface of the Meadow Lake area is not found, but there are indications that suggest faulting. Both salt solution and movements along reactivated Precambrian faults are possible interpretations, in addition to the effect of the hinge line, which controls the regional picture.

The Lower Elk Point is pre-Ashern Devonian of the Ulsterian series, not present in the Williston Basin. It has assumed counterparts in many pre-Winnipegosis, post-Silurian formations in Western Canada, which are mostly non fossiliferous. An ostracod fauna (Woileria and Welleriopsis) in the Lower Elk Point suggests an age relation with the fossiliferous (Abibibi) limestone group of the James Bay Lowland, which, according to recent publications, belongs to the Onesque-thaw stage of the Ulsterian series, which correlates with the Lower Devonian Coblenzian of Europe (Cooper 1942).

A number of formations of questionable age, which appear to be possible equivalents of the Lower Elk Point, have been outlined on a framework map. It is hoped that this map may be of assistance in visualizing to some extent, the source, environment and basin structure during the first Devonian transgression of the Ulsterian seas.