A disconformity is a specific type of hiatus wherein the layers above and below an erosional boundary have the same orientation (often horizontal). Given that rock layers above and below an unconformity surface have the same orientation (strike and dip), disconformities may be difficult to recognize. However, as with all unconformities, disconformities involve a significant time gap-- typically on the order of tens of millions of years!
Refer to the photograph presented below. Note that all of the units above the Grand Canyon Series are horizontal, beginning with the Cambrian Bright Angel Shale through the uppermost Kaibab Formation. Yet, a significant disconformity exists between the Cambrian Muav Limestone and the Mississippian Redwall Limestone.
Refer to your geologic time scale and determine the approximate time missing as well as the geologic periods.
