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Angular unconformity. An angular unconformity is an unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers. [6] The whole sequence may later be deformed and tilted by further orogenic activity. A typical case history is ...
[10] [11] The contact between the overlying Tapeats Sandstone and the folded and faulted Nankoweap Formation is a prominent angular unconformity that is part of the Great Unconformity. [7] Uranium-lead dating of detrital zircons from the Nankoweap Formation indicate the presence of zircon grains in approximately the 800–770 Ma age range. This ...
The surface of this angular unconformity truncates dipping strata comprising the folded and faulted Unkar Group. Though this surface is typically a plane, differential erosion of the tilted strata of the Unkar Group left resistant beds of the upper layer Cardenas Basalt and the middle layer Shinumo Quartzite as ancient hills, called monadnocks .
Any angular unconformity is proof that a tectonic phase took place between the deposition of the layers below and on top of it. It is important to know if the tectonic phase was a longer event or if it was local or regional. Tectonic phases can be important events that affected large areas. The Alleghenian orogeny in North America (during the ...
An unconformity is a break in the normal progression of sedimentary deposits, where newer deposits are lain on top of older. The example Hutton discovered is known as an angular unconformity in which a sharp change in younging direction can be seen in the orientation of bedding planes .
Cross-cutting relationships can be used to determine the relative ages of rock strata and other structures. Explanations: A – folded rock strata cut by a thrust fault; B – large intrusion (cutting through A); C – erosional angular unconformity (cutting off A & B) on which rock strata were deposited; D – volcanic dike (cutting through A, B & C); E – even younger rock strata (overlying ...
Throughout the majority of it extent, the Tonto Group lies unconformably on underlying Precambrian rocks forming the Great Unconformity. This contact is either an angular unconformity truncating tilted strata of the Grand Canyon Supergroup or a nonconformity cut into the crystalline Vishnu Basement Rocks. The base of the Tonto Group consists of ...
Explanations: A – folded rock strata cut by a thrust fault; B – large intrusion (cutting through A); C – erosional angular unconformity (cutting off A & B) on which rock strata were deposited; D – volcanic dyke (cutting through A, B & C); E – even younger rock strata (overlying C & D); F – normal fault (cutting through A, B, C & E).