Anthracology

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Anthracology (from the Greek anthrax , coal ') refers to the science of analyzing charcoal .

General

Anthracology as a sub-area of paleobotany or archaeobotany includes the determination methods for charred wood and the description of the morphological properties of charcoals of various origins. Anthracological investigations allow conclusions to be drawn about the composition of the vegetation and thus the ecology and climatic conditions. The information obtained in this way about the flora and habitat of the area from which the investigated charcoal originates, as well as the possible role of humans in this area, are among other things the basis for archaeological research. Anthracology or charcoal analyzes are also a sub-area of wood anatomy .

Significance for archeology

By means of charcoal analyzes, the type of charred wood is determined mainly in archaeological contexts in order to obtain information about facts about vegetation history. Additional information is derived from accompanying circumstances such as the location of the charcoal. An absolute dating of the archaeological excavation horizons is possible using the radiocarbon method if the charcoal particles are large enough .

Capturing the pieces of charcoal in archaeological contexts

The collection of the charcoal particles or the direct selection is to be preferred in order to avoid the comminution of these during the sludge , since they must be of sufficient size for determination as well as for radiocarbon dating . The documentation of the detection situation is used for later evaluation, as additional information can be derived from it. The documentation includes a description of the suspected type of deposit such as blown air-flow coal, charcoal from fireplaces or hearths, entire layers of fire, floods or particles that have been carried over. In addition, the packaging of the charcoal should be done without mechanical impact and protected from mechanical impact during storage and transport, so that it is not subsequently comminuted and then recorded separately, since quantitative surveys can also be made.

Archaeological application example Baaz

The archaeological site of Baaz in south-west Syria, excavated between 1999 and 2004, provided researchers with botanical remains from the time when humans turned from hunters and gatherers to arable farmers and ranchers.

The reason for this change in lifestyle is probably to be found in a chain of factors. A factor often cited is climate change in the Middle East at the time. A climatic change could have optimized the conditions for those plants to which our cultivated plants can be traced. Accordingly, climate change would have encouraged the development of agriculture and animal husbandry.

In Baaz, macrobotanical samples could be taken from seven main archaeological horizons and collected using various sampling methods. They provided information about the vegetation history of the site.

Since it can be assumed that charcoal samples from archaeological horizons are representative of the occurrence of wood plants in the investigated area for the period of the investigated horizon, the percentages of charcoal surveys in the samples were evaluated as an indicator of tree population. In addition, the archaeobotanical investigation of the species community at that time revealed a bush-steppe vegetation for the time of possible climate change. Indications of poplars and willows, which were most likely used as firewood, obtained from anthracological surveys, can be attributed to the local permanently humid conditions of the Jaba'deen wadis below Baaz.

The results of the investigation of the material from the horizons, which contained relatively smaller amounts of charcoal, seem to speak for the rarity of wood plants in the Pleistocene at this location.

In addition, further archaeobotanical investigations revealed that Baaz was outside the range of wild grain during the Younger Dryas and the early Holocene . The effects of climate change, which could have led to the increased occurrence of annual grasses as the forerunners of the later grains, are therefore not detectable for Baaz.

Visual appraisal and preparation of specimens

For the visual examination of charcoal in general, binocular magnifying glasses with a magnification of up to 50: 1 and incident light microscopes of up to 400: 1 are used. To examine fracture surfaces in incident light, the coals must be broken transversely to the longitudinal axis . Since a successful determination of the type of wood is only possible if the pieces are precisely oriented, this can be precisely specified with the aid of a scalpel under the magnifying glass when creating breaks . It should be noted, however, that cut surfaces are generally unsuitable for a determination. Both reflected and transmitted light images can be used for the photographic documentation of the structures. The latter requires the production of sections made from embedded specimens . As matrix has polymethylmethacrylate proven because this has approximately the same hardness as the embedded object.

With the aid of sections, dimensional changes in tissues and in the cell wall that have arisen during the charring can be recognized during the analysis. The anatomical properties of the woods are more clearly visible.

Breakability

The breakability of charcoal allows conclusions to be drawn about the type of wood, because charcoals can be broken in different ways. In the analysis, this property can provide an informative contribution to the result, but it can also lead to false conclusions as a result of mechanical effects after the rescue, as this can increase the (apparent) number of items used as an assessment criterion. The breakability can be quantified as compressive strength or via breaking stress values ​​in bending tests. Differentiated and qualitative statements are also possible on the fracture behavior and fracture result of coal from different types of wood, differentiated according to tree species and anatomical origin.

Tangential and radial breaks allow the wood to be determined. The orientation of the direction of break is crucial here. In softwood , the tangential and length shrinkage can be recognized, for example, by the so-called court pits .

Wear resistance

Differences in stress in the history of a piece of charcoal must be taken into account. They can provide insights that will help determine the type of coal and its route to the site. A fluvial alluvial process, for example, shows very different stresses than an aeolian deposit. The rolling of pieces of charcoal with the movement of the water on a lake bed or, to a greater extent, in the shallow water zone in the bank area leaves traces that contribute to the determination in addition to species and individual-specific factors. The traces on the coal pieces caused by rolling in the water provide valuable information on the sedimentation process and thus on the conditions that prevailed when the respective layer was formed.

Not only the rolling in the water leads to more or less rounded edges and corners. Coal pieces are already mechanically influenced by rolling in a fireplace. A scheme was drawn up for the traces left by such stress, according to which pieces of coal can be assigned to different tree species.

nature

The nature of the fracture surface also provides information that makes it easier to determine. For example, water movements or the mechanical effect of stepping on the charcoal (rolling) can be responsible for the fragmentation and shrinkage of the charcoal. Therefore, charcoal analysis requires sedimentological work, i.e. H. the consideration of sedimentological aspects. There are differences in the sensitivity to mechanical effects of different tree species. The factors that have an effect on the charcoal allow statements to be made about the layer formation in a sedimentological interpretation.

Taphonomy

Within archaeobotany, the phenomena listed under the term taphonomy are of fundamental importance. This term encompasses all processes and influences that affect an object after it has been deposited or an organism after its death. In addition to the chemical reactions that take place during the charring process, the swelling of pectins and mechanical effects from the outgassing of volatile constituents and water vapor also lead to partial deformations in the wood. However, the microstructure is retained. The factors on which this depends are the type of wood, density, microstructural features, fungus destruction, size, shape, moisture content and the heating and combustion temperature of the fire causing the charring.

Special features of the interpretation

In the area of ​​smaller sample stocks, the number of species always increases with the number of pieces, which is why this must be taken into account when compiling the proportions of charcoal. For example, for the study of the history of vegetation, it is sufficient to first identify a few pieces, the type of which is typical for the respective form of vegetation.

Fungal hyphae are clearly detectable in charcoal. They are indicators of another telling fact. Wood is usually attacked in a damp environment after it has died. On the other hand, the wood must represent an environment that is conducive to the fungus and has very specific properties. It is more likely to thrive where the plant's toxic defense substances are only present in low concentrations. The presence and degree of fungal infestation can thus enable indirect cultural and historical interpretations such as the use of fallen wood versus felled wood.

For example, micro-charcoal fragments in the sediments of lakes can provide information about the extent of forest destruction by fires.

Comparison of anthracology with palynology

Compared to palynology (pollen analysis), anthracological studies have the disadvantage that they only document wood plants. Herbs are also used in pollen analyzes, but with the disadvantage that wind-pollinated plants are overrepresented in quantitative surveys. Their pollen can also have been transported over great distances. Pollen diagrams therefore give a broader picture of the vegetation, although the catchment area is sometimes difficult to narrow down. In contrast, the results of the anthracology reflect the (used) wood spectrum, but this mostly from a very small catchment area.

literature

Individual evidence

  1. ↑ K. Deckers, S. Riehl, E. Jenkins, A. Dodonov, AN Simakova, NJ Conard: Vegetation development and human occupation in the Damascus region of southwestern Syria from the Late Pleistocene to Holocene ( Memento des Originals from November 12, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 751 kB). 2009, pp. 329-340.  @1@ 2Template: Webachiv / IABot / www.geo.uni-tuebingen.de
  2. ↑ RTJ Cappers, S. Bottema, H. Woldring, H. van der Plicht, H.-J. Streurman: Modeling the emergence of farming: implications of the vegetation development in the Near East during the Pleistocene-Holocene transition. 2002, pp. 3-14.