The Geological Survey of Canada owns and operates "slim hole" geophysical sondes and recording equipment for use in PVC cased boreholes in unconsolidated overburden. Such holes are commonly drilled and cased for overburden stratigraphic or geotechnical studies related to on-going GSC projects. These boreholes have been located in various parts of Canada and in a variety of differing material types, including glacial, fluvial and lacustrine deposits. Most (but not all) sediments are of Quaternary age. The compilation is offered as a guide to the geophysical response of overburden materials for users planning geophysical surveys in a particular area, and also as a teaching resource for near-surface applied geophysical education programs.

Borehole geophysical logs database

An interactive map view provides access to the database of borehole logs. Clicking on a borehole site on the map will return an image of the log for that location.

GSC geophysical logs are generally found in clusters on the location map of Canada, resulting from concentrations associated with GSC projects. Hence by using the zoom function, one can inspect the areal distribution of boreholes within a project area. By clicking on a borehole location, a template of available logs will appear. This template includes a generalized geological log.

• Geonics EM-29
  • inductive conductivity
  • magnetic susceptibility
  • natural gamma

• IFG
  • temperature
  • spectral gamma-gamma density

• Downhole seismic (P and S wave velocities)
  • sidewall-locking geophones
  • hydrophone arrays

Natural gamma

For many of the holes shown in this compilation, the outside hole diameter was in the range of 15 cm, the inside diameter of the PVC casing was 6.5 cm, and the holes were grouted with low activity cement/mud mixtures or with sand. Under these conditions, for the GSC gamma sonde at 2.5 cm/sec logging rate, the following guidelines can be used:

• background (or massive ice): 10-15 cps
• coarse sand/gravel: 15-50 cps
• dominantly fine sand: 50-80 cps
• dominantly silt: 80-130 cps
• clay: 130-200 cps

Spectral gamma-gamma density log

Since no calibration of density vs count rate is available for this tool for densities in the range of typical soils and in PVC cased boreholes, the data is plotted in this compilation in the form of counts/sec. The results can be used in a qualitative manner only to infer variations in soil density. In many of the holes in this compilation, where a well-defined groundwater table exists, this physical boundary is evident as a large deviation (towards high count rates) in the log.

Spectral gamma-gamma ratio log

The spectral gamma-gamma ratios shown in the compilation have low and high energy windows as indicated, and have been smoothed using a Savitsky-Golay smoothing function.

Temperature and temperature gradient logs

The temperature gradients shown in this compilation have been smoothed using a Savitsky-Golay smoothing function.

Detailed geological descriptions can be obtained via the listed contact personnel:

• J.A. Hunter
• S.E. Pullan
• R.L. Good
• M. Douma