Unconformities

Return to [Index]
Unconformities are breaks in a sedimentary sequence. They may separate sequences with angular discordance -- where the rocks below are folded or tilted; or they may separate sequences with no angular discordance -- a disconformity representing a period of non-deposition or erosion; or the upper rocks may lie on igneous rocks or metamorphic rocks with no obvious layering -- nonconformities.

Angular unconformities


91_001. Hutton's unconformity; Devonian Old Red Sandstone on upturned Silurian slates.  Siccar Point, Scotland.
This was the first recognized unconformity and played a crucial role in Hutton's work.


57_106. Unconformity of Permian conglomerate and sandstone on steeply dipping Silurian sandstone.  Richardson Mountains, Northwest Territories, Canada. [67.993579,-136.915284]


57_107. Detail of section close to of 56_106. Permian sandstone on steeper dipping Silurian sandstone.
Richardson Mountains, Northwest Territories, Canada [67.993579,-136.915284]


64_227. Proterozoic basal conglomerate on Archaean gneiss.  Weekeroo, South Australia. [-32.178867,140.212097]


67_136. Unconformity of Cambrian sandstone on Precambrian gneiss. North of Kingston, Ontario, Canada. [44.300559,-76.415634]


85_026. Angular unconformity between Proterozoic red beds and horizontal Cambrian Tapeats sandstone.
On the other side of the canyon, the Tapeats lies on Vishnu schist -- a non-conformity.
Kaibab Trail, Grand Canyon, AZ. [36.09136,-112.090166]


85_129. Cambrian quartzite resting on Torridonian sandstone.  Inchnadamph, Assynt, NW Highlands, Scotland.  [58.18132,-5.008764]
The hammer lies just beneath the unconformity, in this view there is no angular discordance, but the lower sandstone is nearly horizontal, while the Cambrian quartzite dips at about 10 degrees east -- away from camera. The tilt on the lower sandstone was removed when the Cambrian was tilted.


91_024. Triassic breccia on tilted Carboniferous Limestone. Barry Is, Glamorgan, Wales. [ST112665;  51.389248,-3.279594]
The breccia runs across the middle of the photo. The Carboniferous limestone strikes across the lower part and dips to the left. The light gray Triassic limestone at the top has prominent joints at a high angle to bedding.


91_027. Another view of the Triassic breccia on tilted Carboniferous Limestone. Barry Is, Glamorgan, Wales. [ST112665;  51.389248,-3.279594]


67_100_8. Cliff of upturned Tertiary sands overlain by Pliocene conglomerate.  Sellick Beach, South Australia. [-35.348008,138.439293]

Nonconformities


85_029. View from Panorama Point. Non-conformity of Proterozoic sandstone lying on Vishnu schist.
Kaibab Trail, Grand Canyon, AZ. [36.094134,-112.090552]


85_030. Non-conformity of Cambrian Tapeats sandstone lying on Vishnu schist.   Kaibab Trail, Grand Canyon, AZ. [36.094134,-112.090552]


85_032. Non-conformity of Cambrian Tapeats sandstone lying on Vishnu schist.   Kaibab Trail, Grand Canyon, AZ. [36.094134,-112.090552]


85_155. Nonconformity of Proterozoic Stoer Group on Lewisian gneiss. Chlachtoll, NW Highlands, Scotland. [NC038271; 58.188953, -5.339307]


85_238. Nonconformity of Torridonian on Lewisian .  Inchnadamph, Assynt, NW Highlands, Scotland. [58.184578,-5.051680]

Return to [Index]