**7. Conclusion: a word of caution**

It is generally accepted that the unconformities collectively record about 90% of the geologic time in its stratal expression. Stratigraphic unconformities are critical surfaces in sequence stratigraphy, but their identification remains largely the art of a visual rock assessment. Subaerial exposure profiles with paleosols are most common expression of non-eroded disconformities, but gamma and other conventional log signatures of even thick pedogenic claystones tend to stay at the background of host strata, and the majority of these surfaces do not coincide with surfaces of lithological change that would produce impedance contract for a seismic survey. Although major surfaces with prominent paleokarsts, erosion relief, lateritic mantles, and/or system of incised channels are certainly correlated, it has to be admitted that straightforward and universal technique to identify disconformities in coreless subsurface sections does not exist.

Stratigraphic unconformities included in table of formations are usually biased to those surfaces that were identified in outcrop, and their correlation may be undermined by a blank zone of unknown surfaces below and above, especially when dealing with non-cored intervals in the subsurface. This bias improves with increasing knowledge on the stacking pattern and ranking of measured disconformities.

Stratigraphic breaks diagnosed in old times and supported by missing faunal zones (e.g., sub-Canol hiatus of Mackenzie Corridor) are prone to dissolution or narrowing with increasing accuracy of biostratigraphic framework and absolute dating. Robustness of identified hiatuses should be confirmed with signatures of subaerial exposure or erosion.

Drowning unconformities are drowning surfaces specific for carbonate platforms. Usually, such surfaces produce vivid reflection horizons, and in the subsurface, they frequently have better stratigraphic value than platform-embedded subaerial disconformities.
