An in situ geotechnical tool, the piezocone penetrometer, was used to study an offshore site in the Canadian Beaufort Sea for geological and geotechnical purposes. Five stratigraphic units are identified in the Mackenzie Trough. Marine clay of Unit A shows a very linear cone response, indicating a uniform lithology and simple stress history. Units B through E, which underlie Unit A, show more complex responses, indicating lithologic variation and more complex stress history related to delta progradation and transgression. The cone data and, in particular, the pore-pressure response enable the recovery of continuous and detailed sedimentological data, including bed thickness, graded bedding, and thinning and fining-upward sequences. This paper describes the use and interpretation of the penetrometer tool for sedimentological study and presents a case study of the Mackenzie Trough, Beaufort Sea, where the tool was applied. The interpreted piezocone profiles are shown to correlate directly with the seismic data and collected samples. Based on experience gained in the study area of Mackenzie Trough, methods are described for improving marine field procedures with the use of the piezocone penetrometer in a geological site investigation.