About This Item
Share This Item
The term unconformity is applied to first-order discontinuities which bound major continental framework sequences. Regional and interregional identity and continuity of most unconformities have remained unappreciated because: (1) they normally are erased in many areas by later degradation; (2) empirical criteria are inconsistently developed and commonly obscure the unconformities; (3) most empirical criteria do not make it possible to distinguish between unconformities and countless small-magnitude discontinuities; (4) conventional stratigraphy is depositionally, but not degradationally, oriented; (5) unconformably separated sequences commonly are erroneously equated and thus mistakenly interpreted as facies; (6) miscomprehension of the base-level concept has resulted in ailure to relate episodically contemporaneous marine, non-marine, and volcanic successions; (7) individual unconformities are too commonly conceived to be of a single type rather than to represent several or all types; (8) diagnostic faunas commonly are absent from critical strata; and (9) many biostratigraphic standards are inadequate to define unconformities.
Failure to recognize these obstacles has led in many cases to the fallacious expedient of interpreting events directly from the unconformity-riddled and thus degradationally fragmented stratal record. As a result, the occurrence of alternating interregional depositional and degradational episodes generally has remained unappreciated, and many conventional interpretations are erroneous.
Because all unconformities have certain phenomena in common, particularly in regard to their manner of development, and because the beds above and below an unconformity repeatedly have certain relations to one another and to the unconformity separating them, certain axioms and corollaries can be stated that apply specifically to unconformities. It is believed that analytical procedures devised and carried out in the light of these axioms and corollaries provide a systematic basis for the interpretation of unconformities and for their distinction from the myriads of minor breaks.
End_of_Article - Last_Page 640------------