**Stratigraphic Unconformities: Review of the Concept and Examples from the Middle-Upper Paleozoic and Examples from the Middle-Upper Paleozoic**

**Stratigraphic Unconformities: Review of the Concept** 

DOI: 10.5772/intechopen.70373

Pavel Kabanov Pavel Kabanov Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.70373

#### **Abstract**

Only about 10% of geologic time is imprinted in sedimentary strata and the rest is hidden in non-depositional or erosional surfaces called unconformities. Stratigraphic unconformities (disconformities) are principal bounding surfaces in sequence stratigraphy, which a geologist would easily identify in the outcrop but frequently overlook in the subsurface unless core is available. The proportion of disconformities that are misidentified or overlooked in subsurface stratigraphy is quite large, which puts a warning sign on simplistic sequence stratigraphic models. The amount of time imprinted in disconformities can be evaluated using relative weathering maturity of the subaerial profile, cyclostratigraphic calibration, absolute dating, and biostratigraphy. However, using biostratigraphy alone is never enough as biostratigraphic gaps tend to fill with increasing data coverage. Identification of paleo-vadose zones and subaerial exposure profiles is regarded as critical for finding stratigraphic unconformities and is the only approach in strata where geophysically mappable fluvial systems are absent. Drowning unconformities are carbonate platform drowning surfaces that usually produce distinct reflection horizons and have better stratigraphic value in the subsurface than platform-embedded subaerial unconformities. This discussion is supported by examples of subaerial disconformities from the Devonian, Carboniferous, and Permian of Canada and Russia and with an example of a geographically extensive mid-Devonian drowning unconformity from Northwestern Canada.

**Keywords:** disconformities, paleosols, paleokarsts, vadose alteration, erosion, drowning unconformities, sequence stratigraphy, subsurface identification

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
