Present Structure

Present Structure of Old Crow Basin

As previously indicated, the Old Crow Basin is a shallow depression originating in early to mid Tertiary time (Morrell and Dietrich 1993). Lawrence (1973) classified the Old Crow Basin as a "tectonically deformed cratonic margin type", or in other words, a bowl- or crater-shaped depression formed by movement of earth plates at the edge or margin of a major tectonic plate.

Morrell and Dietrich (1993) interpret the information provided by seismic studies as indicating that there are two subbasins to the Old Crow Basin which are aligned with the orientation of the major syncline in the area. (A syncline is a structure in which the layers or strata form a downward curve). The subbasins contain relatively thick sediments from the Tertiary Period.

A 1973 gravity survey of the Old Crow Flats suggests that the subbasins are bounded by faults and contain between 1.8 and 4 km of Mesozoic and Cenozoic rocks. The southern basin lies east-west just below 68^o 00' N and is 45 km long and 20 km wide. The northern subbasin is similar in size but narrower (12 km wide) and lies parallel to the southern subbasin. Timber Hill, the ridge separating the two subbasins, is likely composed of the Carboniferous Kayak Formation or older rocks beneath thin Quaternary cover (Morrell and Dietrich 1993). The structure that separates the two subbasins is named the Timber Ridge anticline.

The structure of the Old Crow Basin from north to south is shown in Figure 3.7. The east-west structure of the mountains on the north side of Vuntut National Park is shown in Figure 3.8. Although these figures date from 1993 or earlier, they provide the most useful and easy to understand overall picture of the suggested structure of the Old Crow Basin.

The many square or rectangular and oriented lakes (oriented in a northwest-southeast direction) of the Old Crow Flats have led to the theory that the lakes have a "fault-block" origin. Price (1968) suggests the formation of the lakes is due to subsidence over fault or fissure blocks. Also, Hughes (1972) reports that deposits of sand, gravel, and silt along the Old Crow River extend below bedrock, suggesting that warping or faulting of the bedrock must have contributed to the formation of the lowlands. Based on the appearance of a small fault on the upper part of a seismic section across the northern subbasin of the Old Crow Basin, Morrell and Dietrich (1993) suggest that this shallow fault is "on trend with" the straight shore line of a nearby lake, thus supporting Allenby's (1989) suggestion that the rectangular lake outlines of Old Crow Flats are partially controlled by faults. However, there is not a great deal of supporting evidence and this theory is not generally accepted (Lane pers. comm. 2000). Other theories have been proposed concerning the origin of these shallow lakes, including the affect of prevailing winds, and surface processes related to patterned ground and permafrost (see "Geomophology" for further discussion of this topic).