What Is Varve Chronology?
The various dating techniques available to archaeologists determine an approximate date range, which, in the cases of varve analysis and dendrochronology. Chronology: Relative and Absolute Dating methods .. However, instead of the limitations, varve analysis can be used indirectly for archaeological dating. The technique which has been used most frequently to do this in glacial varve sequences is radiocarbon (14C) dating. In Sweden, varve sequences may be.
Beyond the limits of glaciers and ice-sheets, extensive layers of outwash sands and gravels were deposited; where these deposits occur in lakes they are called varves. The periglacial zone around the margin of an ice sheet has permanently frozen subsoil, and is occupied by cold-loving plants and animals.Anthropology optional for UPSC - Dating methods like relative and absolute dating for finding age
Erosion was mainly brought about by solifluxion. The low temperatures and the constant freezing and thawing also affect the soil; these frost effects are called cryoturbation. Particularly characteristic are ice-wedges, polygonal cracks in the ground frequently recognizable in air photographs.
They were caused by the shrinking of the ground at low temperatures and the filling of the cracks with water, which subsequently expanded on freezing to open the crack still further. The last two million years have been marked by a series of such glaciations. Broad correlations between the glaciation schemes in different parts of Europe and North America exist.
This gradually gave way to the First Interglacial Gunz-Mindel Period lasting about 60, years in which warm conditions again prevailed. Dendrochronology - The age of wooden objects can be determined by means of Dendrochronology or tree ring analysis. It determines the calendar years of tree-ring formation and the felling dates of trees, which helps to determine the age of wooden objects with a great precision.
Dendrochronology has therefore become well established in the field of archaeology, art history and cultural heritage. The method depends on the fact that trees growing in temperate zones have clearly defined annual rings of growth.
As these tree rings represent annual growth, merely by counting rings one can count the age of the tree and hence its association.
This dating method with latest methodological advances helps us in defining the calendar year in which the tree-rings were formed and in interpreting such dating in terms of the age of a wooden object. Despite many difficulties found for ESR dating of bones and carbonates, tooth enamel dated by Electron Spin Resonance ESR has been proven as a reliable method in its application to fossil teeth and quartz.
Both of the latter materials have allowed dating of Early and Middle Pleistocene sites which are not datable using other methods. In particular, recent discoveries of human remains in Western Europe have been proposed to be sites of the earliest arrival of humans there, and have been dated to the Early Pleistocene by Electron Spin Resonance ESR using quartz and tooth enamel.
Electron Spin Resonance ESR method can be applied to different types of samples in various environments; its contribution to the elaboration of a chronostratigraphic frame is of a great importance for the understanding of the Homo erectus dispersals out of Africa and especially for the first settlements in Europe.
Varve dating - Oxford Reference
Palaeomagnetic Dating - It is an important means of crosschecking the dates based on the constantly shifting nature of the earth magnetic field, both in direction and intensity. The measurement of the earth's magnetic field in several places of the world for centuries has shown that it varies with time.
A number of studies have shown that a record of past magnetic field in the form of angles of declination and dip can be trapped in baked clay. When clay is heated to a certain degree, the magnetic elements of baked clay realign themselves along lines dictated by the intensity and character of the magnetic field of the earth at that time.
On cooling the magnetic elements are frozen and can be recorded as long as the clay is preserved. This is called remnant magnetism. When records of past angles of declination and dip have been kept it is possible to compare the values of historic records and arrive at the date of archaeological specimens of fired clay.
Fluxgate, Spinner magnetometer, Super-conduction magnetometer are the instruments used for measuring magnetic remenence. The method was used in Great Britain by Aitken in detail.
It has also been used in Japan and Arizona. In India the method is applied in dating Karewa sediments in Kashmir. The reliability of the application of the method depends on certain conditions such as The availability of good records of change of magnetic paths near the prehistoric sites, Occurrence of series of already dated baked clay in the area against which objects of unknown dates can be dated, Availability of archaeological samples which are found in their place of first occurrence.
What is Varve Chronology?
Fire places and kiln thus provide best samples for dating. Varve analysis - Varve analysis, one of the oldest dating methods which demonstrate seasonal variation and also reflect the climatic conditions of ancient time. The word varve in Swedish means annual layers of sediments deposited at the bottom of the lakes by the runoff from melting glacial ice. The method is based on the relative thickness of the varves and their comparison to the new sections as in tree ring analysis.
Formation of varves depends on climatic variation. In summer when ice melts coarse sediments deposits at the bottom and in winter when the lake is frozen, the finer sediments deposit at the top. It is possible to measure the relative thickness of the varves and obtain a series to which one can compare and correlate new sections as they are discovered. The application of varve dating is restricted by several factors. First, it is because varve accumulation occurs only to glacial areas of the world.
Second, many of the Pleistocene glacial areas has receded nowadays and affecting the supply of sediments. Therefore outside Scandinavia it is difficult to find continuous sequence of varves reaching the present. The longest sequence known goes back only 17, years.
Third, the varves may form frequently rather than annually depending on the pattern of the melting. However, instead of the limitations, varve analysis can be used indirectly for archaeological dating.
In North America, Ernst Antevs has made several attempts to relate Pleistocene geological formations in the American Southwest to events that produced varves in the northern parts of North America. Fission Track Technique - This technique dates material ranging from 20 years to 1,, years before the present.
Fission track dating is based upon the fact that over geological time spontaneous fission of uranium impurities produces minute sub- microscopic damage trails in the most insulating solids, both long period of time. As the damage sites are permanent, a simple count of their number allows an age to be measured. The density of track depends on the uranium content as well as the age of the sample i. The sample is immersed in the proper chemical reagent, which allows rapid attack of the narrow regions of damage and slower dissolution of the adjacent unchanged material.
Varve - Wikipedia
Such treatment are used to create etch pits of optical size, each one making a single fission site. The method requires sufficient uranium to produce a track density, which can be counted within reasonable time.
Amino Acid Racemisation Technique Amino Acid Racemisation, a method of absolute dating applied to human fossils is developed very recently. This is based on the fact that all living organisms have L-amino acid in their protein and after death, and over a long period of time all the L-amino acids except glycine undergo change called racemisation and became non protein D-amino acid.
The proportion of these D-amino acids increases with time. Thus the age of the skeletal materials that are found in archaeological sites can be estimated by determining the amount of change, racemisation that has occurred. ByDe 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.
- varve dating
- Principles of Prehistoric Archaeology. Chronology: Relative and Absolute Dating methods
- Varve analysis
Inthe 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 IslandU. By this stage, other geologists were investigating varve sequences, including Matti Sauramo who constructed a varve chronology of the last deglaciation in Finland.
Since then, there have been revisions as new sites are discovered, and old ones reassessed.