Quaternary Geology and Till Geochemistry, Wapiti Map Area (NTS 83L)

This report provides the current data and interpretations concerning the surficial geology and till geochemistry of the Wapiti map area (NTS 83L). Work on the project was suspended during the second year due to reprioritizing of staff effort.

The area encompasses the transition zone from the Interior Plains to the Eastern Cordillera, with elevation rising from about 525 m (1720 ft) in the northeast to 2455 m (8050 ft) in the southwest. Four physiographic regions can be defined: the Wapiti Plains, the Alberta Plateau Benchlands, the Rocky Mountain Foothills, and the Rocky Mountains.

The surficial geology is shown on a 1:250 000 scale map, compiled by Andriashek (1983) based on unpublished work by A. Twardy and L. Bayrock. The main surficial materials are till, glaciolacustrine sediment, weathered bedrock and, to a lesser extent, glaciofluvial sediment. The till includes units deposited by Laurentide (Continental), Cordilleran, and Rocky Mountain ice sheets.

The ice-flow direction, from the Rocky Mountain, Cordilleran and Laurentide glacial centres, and the relationships between the various lobes are poorly understood. Field examination of the pebble to boulder fraction indicates that the till units are characterized by 1) clasts of green metaconglomerate and low-grade greenish grey schist, plus granite and other igneous rocks (mixed Laurentide and Cordilleran sources), in the northwest; 2) clasts of grey carbonate (Rocky Mountain or Cordilleran source) in the west and southwest; 3) mainly quartzite and igneous (primarily granite) clasts (Laurentide source) in the east; 4) abundant well-rounded quartzite clasts, incorporated from the underlying Tertiary gravel deposits, in parts of the centre and south; 5) boulders of low-grad schist (?earlier Cordilleran source) at three sites, in the south-central part of the area; and 6) a boulder of low-grade metamorphic rock, perhaps phyllite, in the southeast (source uncertain).

The majority of the samples were collected from areas accessible by road, although a few were obtained using a helicopter to reach less accessible sites. Most of the samples collected are from till, although a few are from bedrock, lacustrine, colluvial or fluvial units. At each site, a 2 to 3-kg sample was collected from below the top of the C soil horizon (at a depth of about 2 m) for geochemical and carbonate analysis of the less than 0.063 mm fraction and texture analysis of the less than 2 mm fraction. Field data recorded at each site included information on the general sampling environment and observations on the colour, texture, moisture content and mineralogy of the till.

The matrix fraction (<0.063 mm="" or=""><230 mesh)="" was="" analyzed="" by="" flame="" atomic="" absorption="" spectrometry="" (aa)="" for="" ag,="" cd,="" co,="" cu,="" fe,="" li,="" mn,="" mo,="" ni,="" pb,="" v,="" zn,="" and="" (for="" a="" few="" samples)="" mg,="" and="" by="" instrumental="" neutron="" activation="" analysis="" (inaa)="" for="" ag,="" as,="" au,="" ba,="" br,="" cd,="" ce,="" co,="" cr,="" cs,="" eu,="" fe,="" hf,="" ir,="" la,="" lu,="" mo,="" na,="" ni,="" rb,="" sb,="" sc,="" se,="" sm,="" sn,="" ta,="" tb,="" te,="" th,="" w,="" u,="" yb,="" zn,="" and="" zr.="" the="" results="" are="" shown="" as="" a="" series="" of="" element="" distribution="">

There is a good correlation between Ce, La, Sm and Th. The concentrations for this group of elements are low in the southwest quadrant and high in the southeast quadrant. There is also a strong correlation between Cr and Sc. These two elements, with three exceptions, show higher concentrations in the southwest-central part of the area and predominantly low concentrations in the southeast quadrant.

There is also a strong correlation between Co, Cu and Ni, with the correlation between Co and Cu being slightly weaker. Sites with high concentrations (>75 per cent) of this group of elements occur primarily in the north half of the area, except for two small clusters of sites with high concentrations in the southwest quadrant.