A relict, in
geology
Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...
, is a structure or mineral from a parent
rock that did not undergo
metamorphic change when the surrounding rock did, or a rock that survived a destructive geologic process.
Some
geologic processes are destructive or transformative of structures or minerals, and when a process is not complete or does not completely destroy certain features, the left-over feature is a relict of what was there before. For example, relict
permafrost
Permafrost () is soil or underwater sediment which continuously remains below for two years or more; the oldest permafrost has been continuously frozen for around 700,000 years. Whilst the shallowest permafrost has a vertical extent of below ...
is an area of ancient permafrost which remains despite a change in climate which would prohibit new permafrost from forming or it could be a fragment of ancient soil or sediment found in a younger
stratum
In geology and related fields, a stratum (: strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ...
. A relict
sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
is an area of ancient sediment which remains unburied despite changes in the surrounding environment. In
pedology, the study of
soil formation and classification, ancient soil found in the geologic record is called a
paleosol
In Earth science, geoscience, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The definition of the term in geology and paleontology is slightly different from its use in soil science.
In geo ...
, material formed in the distant past on what was then the surface. A relict paleosol is still found on the surface, and yet is known to have been formed under conditions radically different from the present climate and topography.
In
mineralogy
Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical mineralogy, optical) properties of minerals and mineralized artifact (archaeology), artifacts. Specific s ...
, a relict mineral is a surviving mineral from a parent rock that underwent a destructive or transformative process. For example,
serpentinite is a kind of rock formed in a process called
serpentinization
Serpentinization is a hydration and Metamorphic rock, metamorphic transformation of ferromagnesian minerals, such as olivine and pyroxene, in mafic and ultramafic rock to produce serpentinite. Minerals formed by serpentinization include the Serp ...
, in which a host mineral produces a
pseudomorph, and the original mineral is eventually replaced and/or destroyed, but is still present until the process is complete.
Within
geomorphology
Geomorphology () is the scientific study of the origin and evolution of topographic and bathymetric features generated by physical, chemical or biological processes operating at or near Earth's surface. Geomorphologists seek to understand wh ...
a relict landform is a
landform
A landform is a land feature on the solid surface of the Earth or other planetary body. They may be natural or may be anthropogenic (caused or influenced by human activity). Landforms together make up a given terrain, and their arrangement ...
that took form from geomorphic processes that are not active at present. In a
Scandinavia
Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...
n context, this is often meant to imply that relict landforms were formed before the
last glaciation and survived it under cold-based parts of the
ice sheet
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...
.
estimated that 95% of
mid-latitude landforms are relict.
See also
*
References
{{reflist
Geology