Stratigraphy (archeology)
The recording of the stratigraphy of an archaeological finding is a scientific method of archeology and helps with the relative age determination of deposits. Its object is the detectable during an excavation in a vertical profile sequence of Straten ( lat. Stratum , Pl. Strata to sternere "spread", "layer") caused by natural and anthropogenic (deposits as well as construction landfill trench shaft, Well, post hole , leveling, backfilling, etc.). The sequence of the strata itself is also referred to as archaeological stratigraphy .
Research history background
The Danish natural scientist Nicolaus Steno (Niels Stensen) laid the basis of stratigraphic observations in geology with the Stratigraphic Basic Law in 1669 . The knowledge of Glossopetrae (fossil shark teeth, so-called "tongue stones") from the Danish collection helped him to assess marine sedimentary rocks . While in Florence in 1666, he was allowed to dissect a shark recently caught on the coast. When examining the teeth, he came to the conclusion that the Glossopetrae are fossilized shark teeth. From this he concluded that the "tongue stones" embody marine deposits and therefore the surrounding sedimentary rock is of marine origin. Steno is therefore considered to be the founder of stratification in historical geology .
Another major player was the English engineer and geologist William Smith (1769–1839). When building canals in southern England, he could see a recurring sequence of layers with the fossils they contained. His discovery laid the foundation for the chronological strate correlation using the associated fossils. So Smith recognized that two strates with the same number of fossils of the same type must be at the same time.
The Scot Sir Charles Lyell (1797–1875) also played a crucial role in the history of stratigraphy. In his famous three-volume Principles of Geology , he established a relationship between fossils found in layers and living things today. He showed that in older strata a lower number of fossils can be identified with the species living today and vice versa: the number of fossils identifiable with the species living today is significantly greater in younger strata. With the knowledge of Nicolaus Steno, William Smith and Charles Lyell, the geological basis for stratigraphy was created.
The English geologist James Hutton (1726–1797), who formulated the principle of actualism , should also be mentioned. This principle says that the geological processes that are observed today can basically not differ from those that were at work in earlier geological times. Thus, based on current observations, conclusions could be drawn about past geological activities and processes. Hutton called the time between individual stratigraphic activities unconformity or interface . Of course, since geological epochs were measured in millions of years, this caused controversy with the biblical notion that the world was 6,000 years old. This dispute was resolved by the invention of radiometric dating , which measures the time or duration of the interfaces just mentioned.
During the 19th century, the principle of stratigraphy was used in connection with cultural layers. The Danish archaeologists Christian Jürgensen Thomsen (1788–1865), Jens Jacob Asmussen Worsaae (1821–1885) and Gabriel de Mortillet (1821–1898), but also the excavator Trojas Heinrich Schliemann (1822–1890) and the Egyptologist, were pioneers and archaeologist Flinders Petrie (1853-1942). Thus stratigraphy was also anchored in archeology.
Axioms of Stratigraphy
There are four laws in stratigraphy, first formulated specifically for archeology by Edward Harris in 1979:
- The law of superposition
- The law of original horizontality
- The law of original continuity
- The law of stratigraphical succession
The Steno law of storage states that in the process of deposition, layer after layer follows and thus the upper layers are younger than the lower if the sequence of layers is undisturbed.
The law of primordial horizontality states that unconsolidated soil tends to orient itself horizontally, mainly due to gravity.
The law of original continuity states that each layer is bounded by a natural surface shape or gradually tapering off to thin ends.
These first three rules were formulated in the geology of Nicolaus Steno, but the fourth law was developed in archeology. It expresses that a layer to be examined is determined by its position between the upper (younger) and lower (older). Thus, any relationship to other strata can be neglected, since only the stratigraphic units that are in direct contact with the stratum to be examined are of importance for it.
Stratification and Strata
stratification
The process of stratification has two components: erosion and accumulation . Loose rocks always erode downwards and collect in a deposit basin (accumulation), which limits the strata that form as a result. Such boundaries can be beds of old rivers, military trenches, and walls and walls of houses.
However, new layers are created not only through natural processes, but also through human activities such as digging. If you dig a hole in the ground, you pile up the shoveled earth, which in turn erodes over time and spreads horizontally. The archaeological stratification is thus an interplay of natural processes of erosion and deposition and human changes in the landscape.
In stratification, nature always seeks the paths with the least resistance. Soft, unconsolidated material erodes first, with the process running faster the easier it is for a material to erode. Strata of human origin depend solely on people's cultural preferences. You are not bound by this rule. Humans can ignore the limitation of the deposit basins already mentioned (and create their own by digging). Nature is unable to do this. It must follow the topographic conditions and contours (exceptions include volcanic eruptions ). It is a process by which particles are transported downwards towards the seas. The natural transport of geological material thus depends on gravity. For example, rocks break out of a larger formation and fall down. Further erosion as well as wind and water forces carry away smaller fragments of this rock until these also lose their energy and the particles themselves come to rest. So when the transport ends, the deposit begins.
Another example is the gradual crumbling of walls. If these disintegrate and collapse on their own or if a trench is filled by erosion, nature is the transporter of this material to the deposition site. However, when a trench is filled with household waste, people are transporting it.
Strata
There are two types of man-made strata: horizontal and vertical strata. Vertical strata can be walls or walls, for example. All three types of layers, the natural horizontal, the man-made horizontal and the vertical layers have in common that they all have an upper and an original (lower) surface. However, vertical strata not only have horizontal surfaces but also surfaces that are vertical. Edward Harris warns in his book Principles of Archaeological Stratigraphy (1979) against digging trenches around these vertical strata during an archaeological excavation, as this would destroy the vertical relationships. This is because stratigraphic relationships between layers are created by the deposition of new layers on top of existing layers. The deposits that lie on the vertical surface of the upright strata therefore also have relationships. So all stratigraphic units have areas.
Boundary and Surface Contours
There are two types of contours that a layer has. The boundary contours and the surface contours . The former are contours that define the spatial extent of a stratigraphic unit in horizontal and vertical dimensions. Surface countours, on the other hand, show the topographic relief of the surface of a layer. However, this type of contour is generally only shown in plans, not in profiles. Furthermore, all stratigraphic units have a certain position in the sequence of a stratigraphy. This position provides a relative age as compared to the other units in the same sequence. However, the exact age of a layer, which is measured in years, often cannot be determined without datable artifacts. Chronological data, like a stratigraphic unit, cannot change its position in the stratigraphic sequence. However, much of such data appears to be inconsistent with the rest of the sequence. The already mentioned Edward Harris gives a simple example of this, which was formulated by the Scotsman Sir Charles Lyell:
“Even in cities, such as Venice and Amsterdam, it cannot be laid down as universally true, that the upper parts of each edifice, whether of brick or marble, are more modern than the foundations on which they rest, for these often consist of wooden piles, which may have rotted and been replaced one after the other, without the least injury to the building above; meanwhile, these may have required scarcely any repair, and may have been constantly inhabited. "
“Even in cities like Venice and Amsterdam, it cannot be taken as a general rule that the upper parts of every building, whether brick or marble, are newer than the foundations on which they rest, as these are often made of wooden stakes could be rotten and replaced one at a time without the slightest damage to the building above; which during this time hardly required any repairs and could remain permanently inhabited. "
In this example, the foundation appears newer than the structure of the house above. This problem can also occur in stratigraphy.
The interface
A basic distinction is made between three types of interfaces , which are explained in this chapter. The layer interface refers to the surfaces of a layer that have been deposited horizontally and the vertical surfaces of an upright layer. The extent of the layer interface is usually just as large as that of the layer itself. These interfaces have the same stratigraphic relations as their layers, which is why they are given the same number in drawn profiles and recorded as part of the deposits. With upstanding layer interfaces , no surface contours can be recorded, only boundary contours . Horizontal layer interfaces, on the other hand, have both boundary and surface contours . Both types of the layer interface characterize the time that has passed between the creation of a certain layer and its covering.
The feature interface arises from the destruction of existing deposits. They have their own stratigraphic relations, surface and boundary contours , and should therefore be given their own number when creating a profile of the associated stratigraphy.
Horizontal feature interfaces are associated with upright strata and mark the levels on which such strata have been destroyed.
Vertical feature interfaces, on the other hand, are the result of digging pits and trenches. The layers at the bottom of the pit are on a lower level than other contemporaneous deposits outside the pit. Thus, these layers at the bottom of a pit or a trench are related to other stratigraphic units of a much more recent period.
The period interface is, in simple terms, the interface or the “boundary” between two periods or phases. This can be, for example, settlement phases, prehistoric, historical, constructive and deconstructive phases.
Correlation, phasing and stratigraphic sequences
correlation
Strata can be related in three ways. Two layers can either have no direct contact at all, be on top of one another, or they can occur as parts of the same original layer that was separated, for example, by a trench. These relations can be represented in a stratigraphic profile or more clearly and thus more easily with the help of the so-called Harris matrix .
However, not all relations between all strates have to be recorded in a Harris matrix. According to the law of stratigraphical succession, only the relationships with the layer above and below are relevant for a stratum. Thus, the Harris matrix can be reduced to the essentials.
Phasing and stratigraphic sequences
The aim of a stratigraphic investigation is to create a so-called sequence. This is nothing other than examining the existing strategies, relating them to one another and finally recording them. Stratigraphic sequences are represented by means of profiles. Once a sequence has been recorded, the phase position or the division of the sequence into periods can be started. Strata that belong together are summarized in phases that represent a geohistorical or cultural-historical period, for example the period in which a certain culture settled at a certain point (settlement period) or in which another event took place, such as the excavation a ditch or the like.
See also
literature
- Manfred KH Eggert : Prehistoric Archeology. Concepts and Methods. 3rd, completely revised and expanded edition. Francke, Tübingen et al. 2008, ISBN 978-3-8252-2092-1 ( UTB - Archeology 2092).
- Edward C. Harris: Principles of Archaeological Stratigraphy. Academic Press, London et al. 1979, ISBN 0-12-326650-5 ( Studies in Archaeological Science ).
- Ronald E. Martin: Taphonomy. A process approach. Cambridge University Press, Cambridge et al. 1999, ISBN 0-521-59171-6 ( Cambridge Paleobiology Series 4).
- Ulrike Sommer: On the emergence of archaeological find associations. Attempt at a taphonomy. In: Elke Mattheusser: The geographical orientation of ceramic houses. Habelt, Bonn 1991, ISBN 3-7749-2526-7 , pp. 51-193 ( Studies on settlement archeology . 1 = University research on prehistoric archeology 6).
Web links
- http://www.archeoworld.de/Ausgrabung3.htm - detailed description of stratigraphy in archeology
- Stratigraphy as a contribution to relative chronology