390px, Sketch of a hypothetical peneplain formation after an orogeny. In

geomorphology Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or ...

and

geology Geology () is a branch of natural science concerned with Earth and other Astronomical object, astronomical objects, the features or rock (geology), rocks of which it is composed, and the processes by which they change over time. Modern geology ...

, a peneplain is a low-relief

plain In geography, a plain is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands ...

formed by protracted

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...

. This is the definition in the broadest of terms, albeit with frequency the usage of peneplain is meant to imply the representation of a near-final (or penultimate) stage of

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

during times of extended

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

stability. Peneplains are sometimes associated with the cycle of erosion theory of William Morris Davis, but Davis and other workers have also used the term in a purely descriptive manner without any theory or particular genesis attached. The existence of some peneplains, and peneplanation as a process in nature, is not without controversy, due to a lack of contemporary examples and uncertainty in identifying relic examples. By some definitions, peneplains grade down to a

base level In geology and geomorphology a base level is the lower limit for an erosion process. The modern term was introduced by John Wesley Powell in 1875. The term was subsequently appropriated by William Morris Davis who used it in his cycle of erosion ...

represented by

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardis ...

, yet in other definitions such a condition is ignored. Geomorphologist

Karna Lidmar-Bergström Karna Lidmar-Bergström (born 1940) is a Swedish geologist and geomorphologist known for her study of Pre-Quaternary landforms in Sweden and Norway. In 2004 she was elected into the Royal Swedish Academy of Sciences.pediplains among peneplains. While peneplains are usually assumed to form near sea level it has also been posited that peneplains can form at height if extensive sedimentation raises the local base level sufficiently or if river networks are continuously obstructed by tectonic deformation. The peneplains of the

Pyrenees The Pyrenees (; es, Pirineos ; french: Pyrénées ; ca, Pirineu ; eu, Pirinioak ; oc, Pirenèus ; an, Pirineus) is a mountain range straddling the border of France and Spain. It extends nearly from its union with the Cantabrian Mountains to ...

and

Tibetan Plateau The Tibetan Plateau (, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau () or as the Himalayan Plateau in India, is a vast elevated plateau located at the intersection of Central, South and East Asia covering most of the Ti ...

may exemplify these two cases respectively. A common misconception about peneplains is that they ought to be so plain they are featureless. In fact, some peneplains may be hilly as they reflect irregular deep

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movement ...

, forming a plain grading to a base level only at a grand-scale.

Types of peneplains

There are various terms for landforms that are either alternatives to classical peneplains, a sub-set of peneplains or partially overlap with the term. The last is the case of planation surfaces that may be peneplains or not, while some peneplains are not planation surfaces. In their 2013 work Green, Lidmar-Bergström and co-workers provide the following classification scheme for peneplains: #

Planation surface In geology and geomorphology a planation surface is a large-scale surface that is almost flat with the possible exception of some residual hills. The processes that form planation surfaces are labelled collectively planation and are exogenic (ch ...

s ## Pediplain ## Inselberg plain ## Etchplain #Hilly relief ##Etched hilly relief Rhodes Fairbridge and Charles Finkl argue that peneplains are often of mixed origin (polygenetic), as they may have been shaped by etchplanation during periods of humid climate and pediplanation during periods of arid and semi-arid climate. The long time spans under which some peneplains evolve ensures varied climatic influences. The same authors do also list marine abrasion and

glacial erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dist ...

among processes that can contribute in shaping peneplains. In addition, epigene peneplains can be distinguished from exhumed peneplains. Epigene peneplains are those that have never been buried or covered by sedimentary rock. Exhumed peneplains are those that are re-exposed after having been buried in sediments. The oldest identifiable peneplain in a region is known as a primary peneplain. An example of a primary peneplain is the

Sub-Cambrian peneplain The sub-Cambrian peneplain is an ancient, extremely flat, erosion surface ( peneplain) that has been exhumed and exposed by erosion from under Cambrian strata over large swathes of Fennoscandia. Eastward, where this peneplain dips below Cambria ...

in southern Sweden.

Pediplains

The peneplain concept is often juxtaposed to that of pediplain. However authors like

Karna Lidmar-Bergström Karna Lidmar-Bergström (born 1940) is a Swedish geologist and geomorphologist known for her study of Pre-Quaternary landforms in Sweden and Norway. In 2004 she was elected into the Royal Swedish Academy of Sciences.Lester Charles King Lester Charles King (1907–1989) was an English geologist and geomorphologist known for his theories on scarp retreat. He offered a very different view of the origin of continental landscaping than that of William Morris Davis. Studying at univ ...

held them as incompatible landforms arguing that peneplains do not exist. King wrote: :''A peneplain in the Davisian sense, resulting from slope reduction and downwearing, does not exist in nature. It should be redefined as "an imaginary landform."'' According to King the difference between pediplains and Davis’ peneplains is in the history and processes behind their formation, and less so in the final shape. A difference in form that may be present is that of residual hills, which in Davis’ peneplains are to have gentle slopes, while in pediplains they ought to have the same steepness as the slopes in the early stages of erosion leading to pediplanation. Given that the coalesced

pediments Pediments are gables, usually of a triangular shape. Pediments are placed above the horizontal structure of the lintel, or entablature, if supported by columns. Pediments can contain an overdoor and are usually topped by hood moulds. A pedime ...

of the pediplains form a series of very gentle concave slopes, a difference with Davis' understanding of peneplains may lie in the fact that his idealized peneplains had very gentle convex slopes instead. However, Davis' views on the subject are not fully clear. Contrary to this view Rhodes Fairbridge and Charles Finkl argue that the precise mechanism of formation (pediplanation, etc.) is irrelevant and that the term peneplain has been used and can be used in a purely descriptive manner. Further, alternation of processes with varying climate, relative

and biota make old surfaces unlikely to be of a single origin.

Preservation and destruction of peneplains

Peneplains that are detached from their base level are identified by either hosting an accumulation of sediments that buries it or by being in an uplifted position. Burial preserves the peneplain. Any exposed peneplain detached from its baselevel can be considered a

paleosurface In geology and geomorphology a paleosurface is a surface made by erosion of considerable antiquity. Paleosurfaces might be flat or uneven in some cases having considerable relief. Flat and large paleosurfaces —that is planation surfaces— have ...

or paleoplain. Uplift of a peneplain commonly results in renewed erosion. As Davis put it in 1885: :"the decrepit surface must wait either until extinguished by submergence below the sea, or regenerated by elevation into a new cycle of life" Uplifted peneplains can be preserved as fossil landforms in conditions of extreme

aridity A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most a ...

or under non-eroding cold-based

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...

ice. Erosion of peneplains by glaciers in shield regions is limited. In the

Fennoscandian Shield The Baltic Shield (or Fennoscandian Shield) is a segment of the Earth's crust belonging to the East European Craton, representing a large part of Fennoscandia, northwestern Russia and the northern Baltic Sea. It is composed mostly of Archean an ...

average glacier erosion during the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million year ...

amounts to tens of meters, albeit this was not evenly distributed. For glacier erosion to be effective in shields a long "preparation period" of

under non-glacial conditions may be a requirement. Silicification of peneplain surfaces exposed to sub-tropical and tropical climate for long enough time can protect them from erosion.

Notes

References

{{reflist, 2 Geomorphology Erosion landforms Fluvial geomorphology

Types of peneplains

Pediplains

Preservation and destruction of peneplains

See also

Notes

References