Analysis of well log data from Cenozoic basin fill of the Deer Lodge Valley, southwestern Montana, provides evidence for identifying paleosols and paleosol stacks in the subsurface. The paleosol stacks are continental sequence boundary markers and appear as several relatively thin, high-velocity/high-density zones within basin fill. Zone thickness ranges from 1 to 1.5 m; zones are stacked to thicknesses of up to 15 m. Density varies within the zones by as much as 0.6 g/cm³, and differs by as much as 0.9 g/cm³ from material immediately above these zones. Velocity differs by as much as 10 ft/ms from the overlying material and causes bright reflections on seismic sections. Synthetic seismograms are used to tie well log and seismic data.

Basing our interpretation upon well log data and well cuttings analyses, we determined the high-velocity/high-density zones to be limestone. The pedogenic origin of the limestone is shown by (1) well cutting chips from the high-velocity/high-density zones that exhibit pedogenic features associated with calcic paleosols, (2) paleosol horizonation interpreted from well log analysis, (3) the absence of minerals normally associated with lacustrine deposits, and (4) comparison with surface paleosol exposures.