If the geological record was 100% complete and there were no breaks in sedimentation, the stratigrapher's job would be an easy one.However, breaks in sedimentation do occur and when this happens, geologists' refer to this missing strata as an unconformity.
This is shown below: The Angular Unconformity The strata A to E was deposited first, tilted, subjected to erosion (peneplained) and submerged.Strata X to Z were laid down horizontally on top of the older beds.This activity was selected for the On the Cutting Edge Exemplary Teaching Collection Resources in this top level collection a) must have scored Exemplary or Very Good in all five review categories, and must also rate as “Exemplary” in at least three of the five categories.Prior to the availability of radiocarbon dates (and when there is no material suitable for a radiocarbon date) scientists used a system of relative dating.Often when geologists examine rock outcrops like the one illustrated above they are interested in not only the types of rocks present, but the order in which they formed.
When they put events in chronological order like they use Relative Dating.Absolute dating entails laboratory analysis of rock samples that will take a longer time.further, the dating results will still have to be cross-checked with mapping data.These ages have been derived from relative dating and absolute dating (radiometric dating) of rock layers and fossils.(a) Relative Dating This technique uses principles of stratigraphy (rock strata) and the study of fossils (palaeontology) to determine the relative ages of rocks and sediments. Field geologists' rely on a number of simple techniques for dating rocks and constructing geological successions. The Law of Strata Identified by Fossils is a little bit more complex.The plane or junction, marked by the thick green line, between both sets of strata is the unconformity.