THE GRAVIMETER IN STUDIES OF BURIED VALLEYS

Abstract

In glaciated areas, variation in density and thickness of the drift or of members within it is often an important cause of gravity anomalies. This can be utilized whenever the drift is the principal object of attention, such as in prospecting for ground water. Trends of gravity lows near Kindersley, Saskatchewan, some with amplitude of one milligal, appear to be connected with buried valleys formerly occupied by the South Saskatchewan River and its tributaries. Calculation from detailed gravimeter traverses and comparison with borehole samples give estimates of the thickness and density contrasts of the fill in the valleys. These indicate a low‐density sand section with a thickness of up to 250 ft and a density contrast of 0.27 gm/cc for the buried valley of the South Saskatchewan River; and a low‐density silt section with a thickness of up to 400 ft and a density contrast of 0.25–0.35 gm/cc for a buried tributary valley. Density measurements indicate that contrasts within the drift can be as large as those between bedrock and drift. It is thus possible to detect buried valleys which have been cut entirely into drift, as well as those cut into bedrock.