Editing Unconformity (section)

===Angular unconformity===
[[File:Angular unconformity.jpg|thumb|120px|Angular unconformity]]
An angular unconformity is an unconformity where horizontally parallel [[stratum|strata]] of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers.{{sfn|Boggs|2006|pp=404-405}}  The whole sequence may later be deformed and tilted by further [[orogeny|orogenic]] activity. A typical case history is presented by the Briançonnais realm (Swiss and French Prealps) during the Jurassic.<ref>Septfontaine M. (1984): Le Dogger des Préalpes médianes suisses et françaises - stratigraphie, évolution paléogéographique et paléotectonique.- Mém. Soc. Helv. Sci. Nat., vol. 97, 121 p. (Birkhäuser éd.)</ref><ref>Septfontaine M. (1995): Large scale progressive unconformities in Jurassic strata of the Prealps South of lake Geneva: interpretation as synsedimentary inversion structures. Paleotectonic implications. Eclogae geol. Helv., 88:3 553–576.</ref>
<!--[[File:Briançonnais modèles 7F.jpg|thumb|alt= modèles palinspastiques|Block diagrams and profiles of Palinspastic Alps (Briançon sl) Middle Jurassic]][[File:Discordances successives Jurassique Préalpes.jpg|thumb|Successive angular unconformities and fans on the margin N-Briançon, affecting 650m of sediment during 50 Ma; Dogger-Malm, Chablais Alps (Suisse, France).]]-->

Angular unconformities can occur in [[ash fall]] layers of [[pyroclastic rock]] deposited by volcanoes during [[explosive eruption]]s. In these cases, the hiatus in deposition represented by the unconformity may be geologically very short – hours, days or weeks.