Stratigraphy - Wikipedia
Stratigraphy, from Latin stratum + Greek graphia, is the description of all rock or attributes in order to establish their distribution and relationship in space and Formal stratigraphic terminology uses unit-terms that are defined and named. The relationship of lithostratigraphic units to other kinds of stratigraphic units is A body of rocks that is defined and recognized on the basis of its lithologic. Stratigraphy is a key concept to modern archaeological theory and practice. Modern excavation Stratigraphic relationships are the relationships created between contexts in time, representing the chronological order in which they were.
The designation of a stratotype type section or type locality on which the unit is based and which may be used by interested scientists as a reference. Publication in a recognized scientific medium. Definition, characterization, and description.
Name see section 3. Stratotypes or other standards of reference. Gives the geographic location and geologic setting of the stratotype with an indication of accessibility, maps, and markers, both artificial and natural. For units of the type for which it is impractical to use stratotypes as standards, reliance is placed on the accurate description and illustration of those features that constitute the diagnostic criteria of the unit. Description ofunit at stratotype or type locality.
Geographic extent; regional variations in thickness, lithostratigraphy, biostratigraphy or other properties; nature of boundaries away from the type; criteria to be used in identifying and extending the unit over the area of its presence. Correlation with other units. References to the literature. Special requirements for establishing subsurface units. The same rules of procedure used for outcrop sections apply to subsurface units established on the basis of exposures in mines, tunnels or from sections penetrated in wells.
Stratotypes in well sections are designated by well depths and on well logs and in cores, if available. The following data are desirable for establishing subsurface units: Designation of well or mine. The name of the well or mine and geographic location using conventional oil field or topographic nomenclature. Lithologic and paleontologic logs of the well or wells, and maps and cross sections of the mine, in written and graphic form with the boundaries of the new unit and its subdivisions.
Geophysical Logs and Profiles. A depository should be an institution with the proper curatorial facilities and assurance of perpetuity where the materials are available for study.
The location of the depository for materials from the stratotype well, tunnel or mine should be given. Naming of stratigraphic units.
- Stratigraphy (archaeology)
The names of most formal stratigraphic units consist of an appropriate geographic name combined with an appropriate term indicating the kind and rank of the unit, e. La Luna Formation, except for some terms that were established in the early history of stratigraphy. The formal name of a biostratigraphic unit is formed from the names of one or more appropriate fossils combined with the appropriate term for the kind of biostratigraphic unit, e.
Geographic component of names of stratigraphic units i. Geographic names should be derived from permanent natural or artificial features at or near which the stratigraphic unit is present. A name should be on standard published maps of the pertinent political jurisdiction. Where such names are not available, the place from which the name is derived should be described and shown on an appropriately scaled map accompanying the description of the new unit.
Short names are preferable to long or compound names. The name of the stratigraphic unit should be exactly the same as the name of the geographic feature after which it is named.
Spelling of Geographic Names. The spelling of the geographic component of the name of a stratigraphic unit should conform to the usage of the country of origin. The spelling of the geographic component, once established, should not be changed. The rank or lithologic component may be changed when translated to a different language.
International Stratigraphic Guide
Some degree of dating objects by their position in the sequence can be made with known datable elements of the archaeological record or other assumed datable contexts deduced by a regressive form of relative dating which in turn can fix events represented by contexts to some range in time. For example, the date of formation of a context which is totally sealed between two datable layers will fall between the dates of the two layers sealing it. However the date of contexts often fall in a range of possibilities so using them to date others is not a straightforward process.
Here we can see 12 contexts, each numbered with a unique context number and whose sequence is represented in the Harris matrix in fig B.
A horizontal layer Backfill of the wall construction trench sometimes called construction cut A horizontal layer, probably the same as 1 Construction cut for wall 2 A clay floor abutting wall 2 Fill of shallow cut 8 Shallow pit cut A horizontal layer, probably the same as 9 Natural sterile ground formed before human occupation of the site Trample in the base of cut 5 formed by workmen's boots constructing the structure wall 2 and floor 6 is associated with.
If we know the date of context 1 and context 9 we can deduce that context 7, the backfilling of pit 8, occurred sometime after the date for 9 but before the date for 1, and if we recover an assemblage of artifacts from context 7 that occur nowhere else in the sequence, we have isolated them with a reasonable degree of certainty to a discrete range of time.
In this instance we can now use the date we have for finds in context 7 to date other sites and sequences. In practice a huge amount of cross referencing with other recorded sequences is required to produce dating series from stratigraphic relationships such as the work in seriation. Resources Stratigraphy is the study of layered materials strata that were deposited over time. The basic law of stratigraphy, the law of superposition, states that lower layers are older than upper layers, unless the sequence has been overturned.
Stratified deposits may include soils, sediments, and rocks, as well as man-made features such as pits and postholes. The adoption of stratigraphic principles by archaeologists greatly improved excavation and archaeological dating methods. By digging from the top downward, the archaeologist can trace the buildings and objects on a site back through time using techniques of typology i. Object types, particularly types of pottery, can be compared with those found at other sites in order to reconstruct patterns of trade and communication between ancient cultures.
When combined with stratification analysis, an analysis of the stylistic changes in objects found at a site can provide a basis for recognizing sequences in stratigraphic layers. Archaeological stratigraphy, which focuses on layers created by man, was derived largely from the observations of stratigraphic geologists and geomorphologists. A geomorphologist studies stratigraphy in order to determine the natural processes, such as floods, that altered and formed local terrain.
By comparing natural strata and man-made strata, archaeologists are often able to determine a depositional history, or stratigraphic sequence—a chronological order of various layers, interfaces, and stratigraphic disturbances.
By this method, archaeologists can illustrate the strati-graphic sequence of a given site with a single diagram. Such a diagram, showing the different layers with the oldest at the bottom and the youngest at the top, may cover 3, years. The diagram also records finds such as pits, post holes, and burials that may have belonged to a single period. The archaeologist may also document the site with notes about the relationships of stratigraphic units and soil composition. History of stratigraphy The basic principles of stratigraphy were developed primarily by geologists in the nineteenth century.