A varve is an annual layer of
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
or
sedimentary rock
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
.
The word 'varve' derives from the
Swedish
Swedish or ' may refer to:
Anything from or related to Sweden, a country in Northern Europe. Or, specifically:
* Swedish language, a North Germanic language spoken primarily in Sweden and Finland
** Swedish alphabet, the official alphabet used by ...
word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as ''Hvarfig lera'' (varved clay) on the first map produced by the
Geological Survey of Sweden
Geological Survey of Sweden ( sv, Sveriges geologiska undersökning, SGU) is a Swedish government agency that was founded in 1858 dealing with questions about the nature of the geological and mineral management in Sweden. The institution has the ...
in 1862.
Initially, "varve" referred to each of the separate components comprising a single annual layer in
glacial lake
A glacial lake is a body of water with origins from glacier activity. They are formed when a glacier erodes the land and then melts, filling the depression created by the glacier.
Formation
Near the end of the last glacial period, roughly 10,0 ...
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
s, but at the 1910 Geological Congress, the Swedish geologist
Gerard De Geer
Baron Gerard Jacob De Geer (20 November 1858 – 24 July 1943) was a Swedish geologist who made significant contributions to Quaternary geology, particularly geomorphology and geochronology. De Geer is best known for his work on varves. In 1890 D ...
(1858–1943) proposed a new formal definition, where varve means the whole of any annual sedimentary layer. More recently introduced terms such as 'annually laminated' are synonymous with varve.
Of the many
rhythmite
A rhythmite consists of layers of sediment or sedimentary rock which are laid down with an obvious periodicity and regularity. They may be created by annual processes such as seasonally varying deposits reflecting variations in the runoff cycle, b ...
s in the geological record, varves are one of the most important and illuminating in studies of past
climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
. Varves are amongst the smallest-scale events recognised in
stratigraphy
Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sedimentary and layered volcanic rocks.
Stratigrap ...
.
An annual layer can be highly visible because the particles washed into the layer in the spring when there is greater flow strength are much coarser than those deposited later in the year. This forms a pair of layers—one coarse and one fine—for each annual cycle. Varves form only in
fresh
Fresh or FRESH may refer to:
People
*DJ Fresh (born 1977), UK-based drum and bass artist
*DJ Fresh (producer), US-based R&B producer born Marqus Brown
Arts, entertainment, and media Films
* ''Fresh'' (1994 film), a crime film
* ''Fresh'' (200 ...
or
brackish
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...
water, because the high levels of salt in normal sea water
coagulate
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism o ...
the clay into coarse grains. Since the saline waters leave coarse particles all year, it is nearly impossible to distinguish the individual layers in salt waters. Indeed, clay
flocculation
Flocculation, in the field of chemistry, is a process by which colloidal particles come out of suspension to sediment under the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from pr ...
occurs at high
ionic strength
The ionic strength of a solution is a measure of the concentration of ions in that solution. Ionic compounds, when dissolved in water, dissociate into ions. The total electrolyte concentration in solution will affect important properties such as ...
due to the collapse of the clay
electrical double layer
A double layer (DL, also called an electrical double layer, EDL) is a structure that appears on the surface of an object when it is exposed to a fluid. The object might be a solid particle, a gas bubble, a liquid droplet, or a porous body. The D ...
(EDL), which decreases the
electrostatic repulsion
Electrostatics is a branch of physics that studies electric charges at rest ( static electricity).
Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for ambe ...
between negatively charged clay particles.
History of varve research
Although the term varve was not introduced until the late nineteenth century, the concept of an annual rhythm of deposition is at least two centuries old. In the 1840s,
Edward Hitchcock
Edward Hitchcock (May 24, 1793 – February 27, 1864) was an American geologist and the third President of Amherst College (1845–1854).
Life
Born to poor parents, he attended newly founded Deerfield Academy, where he was later principal, ...
suspected laminated sediment in North America could be seasonal, and in 1884
Warren Upham
Warren Upham (March 8, 1850 – January 29, 1934) was an American geologist, archaeologist, and librarian who is best known for his studies of glacial Lake Agassiz.
Biography
Warren Upham was born in Amherst, New Hampshire and attended Dartmouth ...
postulated that light-dark laminated couplets represented a single year's deposition. Despite these earlier forays, the chief pioneer and populariser of varve research was Gerard De Geer. While working for the Geological Survey of Sweden, De Geer noticed a close visual similarity between the laminated sediments he was mapping, and
tree-rings. This prompted him to suggest the coarse-fine couplets frequently found in the sediments of glacial lakes were annual layers.
The first varve
chronology
Chronology (from Latin ''chronologia'', from Ancient Greek , ''chrónos'', "time"; and , '' -logia'') is the science of arranging events in their order of occurrence in time. Consider, for example, the use of a timeline or sequence of events. I ...
was constructed by De Geer in
Stockholm
Stockholm () is the Capital city, capital and List of urban areas in Sweden by population, largest city of Sweden as well as the List of urban areas in the Nordic countries, largest urban area in Scandinavia. Approximately 980,000 people liv ...
in the late 19th century. Further work soon followed, and a network of sites along the east coast of Sweden was established. The varved sediments exposed in these sites had formed in glaciolacustrine and glacimarine conditions in the Baltic basin as the last ice sheet retreated northwards. By 1914, De Geer had discovered that it was possible to compare varve sequences across long distances by matching variations in varve thickness, and distinct marker laminae. However, this discovery led De Geer and many of his co-workers into making incorrect correlations, which they called 'teleconnections', between continents, a process criticised by other varve pioneers like
Ernst Antevs
Ernst Valdemar Antevs (November 20, 1888 – May 19, 1974) was a Swedish-American geologist and educator who made significant contributions to Quaternary geology, particularly geomorphology and geochronology.
Ernst Valdemar Antevs was born on a ...
.
In 1924, the Geochronological Institute, a special laboratory dedicated to varve research was established. De Geer and his co-workers and students made trips to other countries and continents to investigate varved sediments. Ernst Antevs studied sites from
Long Island
Long Island is a densely populated island in the southeastern region of the U.S. state of New York (state), New York, part of the New York metropolitan area. With over 8 million people, Long Island is the most populous island in the United Sta ...
, U.S.A. to
Lake Timiskaming
Lake Timiskaming or Lake Temiskaming (french: Lac Témiscamingue) is a large freshwater lake on the provincial boundary between Ontario and Quebec, Canada. The lake, which forms part of the Ottawa River, is in length and covers an area of a ...
and
Hudson Bay
Hudson Bay ( crj, text=ᐐᓂᐯᒄ, translit=Wînipekw; crl, text=ᐐᓂᐹᒄ, translit=Wînipâkw; iu, text=ᑲᖏᖅᓱᐊᓗᒃ ᐃᓗᐊ, translit=Kangiqsualuk ilua or iu, text=ᑕᓯᐅᔭᕐᔪᐊᖅ, translit=Tasiujarjuaq; french: b ...
, Canada, and created a North American varve chronology.
Carl Caldenius
Carl Caldenius (1887–1961), until 1920 known by the surname Carlzon, was a Swedish Quaterany geologist and geotechnical engineer. He is mostly known for his geochronological work in Patagonia.
Caldenius worked as geotechnical engineer for the ...
visited
Patagonia
Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...
and
Tierra del Fuego
Tierra del Fuego (, ; Spanish for "Land of the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla G ...
, and Erik Norin visited central
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
. By this stage, other geologists were investigating varve sequences, including Matti Sauramo who constructed a varve chronology of the last deglaciation in
Finland
Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
.
1940 saw the publication of a now classic scientific paper by De Geer, the ''Geochronologia Suecica'', in which he presented the Swedish Time Scale, a floating varve chronology for ice recession from
Skåne
Scania, also known by its native name of Skåne (, ), is the southernmost of the historical provinces (''landskap'') of Sweden. Located in the south tip of the geographical region of Götaland, the province is roughly conterminous with Skåne C ...
to
Indalsälven
Indalsälven is one of Sweden's longest rivers with a total length of 430 kilometers. Among its tributaries are Kallströmmen, Långan, Hårkan and Ammerån. A total of 26 hydropower plants are placed along its course, making it the third mo ...
. Ragnar Lidén made the first attempts to link this time scale with the present day. Since then, there have been revisions as new sites are discovered, and old ones reassessed. At present, the Swedish varve chronology is based on thousands of sites, and covers 13,200 varve years.
In 2008, although varves were considered likely to give similar information to
dendrochronology
Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed. As well as dating them, this can give data for dendroclimatology, the study of climate and atmos ...
, they were considered "too uncertain" for use on a long-term timescale. However, by 2012, “missing” varves in the
Lake Suigetsu
is a lake in the Hokuriku region of Honshu, Japan, which is one of the Mikata Five Lakes located in Mihama and Wakasa, Fukui Prefecture (west-central Honshu), close to the coast of the Wakasa Bay in the Sea of Japan. Since 1993, it has been a ...
sequence were identified in the Lake Suigetsu 2006 Project by overlapping multiple cores and improved varve counting techniques, extending the timescale to 52,800 years.
Formation
Varves form in a variety of
marine
Marine is an adjective meaning of or pertaining to the sea or ocean.
Marine or marines may refer to:
Ocean
* Maritime (disambiguation)
* Marine art
* Marine biology
* Marine debris
* Marine habitats
* Marine life
* Marine pollution
Military
* ...
and
lacustrine
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
depositional environments from
season
A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and pol ...
al variation in
clastic
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...
, biological, and chemical sedimentary processes.
The classic varve
archetype
The concept of an archetype (; ) appears in areas relating to behavior, historical psychology, and literary analysis.
An archetype can be any of the following:
# a statement, pattern of behavior, prototype, "first" form, or a main model that ot ...
is a light / dark coloured couplet deposited in a
glacial lake
A glacial lake is a body of water with origins from glacier activity. They are formed when a glacier erodes the land and then melts, filling the depression created by the glacier.
Formation
Near the end of the last glacial period, roughly 10,0 ...
. The light layer usually comprises a coarser laminaset, a group of conformable laminae, consisting of
silt
Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when ...
and fine
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
deposited under higher energy conditions when meltwater introduces sediment load into the lake water. During winter months, when meltwater and associated suspended sediment input is reduced, and often when the lake surface freezes, fine
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
-size sediment is deposited forming a dark coloured laminaset.
In addition to seasonal variation of sedimentary processes and deposition, varve formation requires the absence of
bioturbation
Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a pr ...
. Consequently, varves commonly form under
anoxic
The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts:
* Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...
conditions.
A well-known marine example of varved sediments are those found in the Santa Barbara basin, off
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
. Another long record of varved sediments is the palaeo-lacustrine record of the Piànico–Sèllere Basin (southern Alps). Here, the detrital layer part of each varve was used as a proxy for 771 palaeofloods which occurred over a period of 9.3 thousand years during an interglacial period in the Pleistocene.
See also
*
*
*
References
Further reading
* De Geer, G. (1940), ''Geochronologia Sueccia Principles''. Kungl. Svenska Vetenskapsakademiens Handlingar, Tredje Serien. Band 18 No.6.
* Lowe, J.J. and Walker, M.J.C. (1984), ''Reconstructing Quaternary Environments''. Longman Scientific and Technical.
* Sauramo, M. (1923), ''Studies on the Quaternary varve sediments in southern Finland''. Comm. Geol. Finlande Bulletin 60.
*
Wohlfarth, B. (1996), The chronology of the Last Termination: A review of radiocarbon-dated, high-resolution terrestrial stratigraphies. ''Quaternary Science Reviews'' 15 pp. 267–284.
{{commons category, Varved Clay
Incremental dating
Sedimentary rocks
Climatology
Sedimentology
fi:Lustosavikronologia