Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. Stratigraphy, a branch of Geology, studies rock layers and layering ( stratification) In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period of time as another horizon at some other section. The fossils are useful because sediments of the same age can look completely different because of local variations in the sedimentary environment. Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of For example, one section might have been made up of clays and marls while another has more chalky limestones, but if the fossil species recorded are similar, the two sediments are likely to have been laid down at the same time. Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and Marl or Marlstone is a Calcium carbonate or lime -rich mud or Mudstone which contains variable amounts of Clays and Aragonite Chalk (ʧɔːk is a soft white porous Sedimentary rock, a form of Limestone composed of the Mineral Calcite. Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3
Ammonites, graptolites and trilobites are index fossils that are widely used in biostratigraphy. Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda phylum Graptolites (Graptolithina are Fossil colonial Animals known chiefly from the Upper Cambrian through the Lower Carboniferous ( Mississippian Trilobites ("three-lobes" are extinct Arthropods that form the class Trilobita. Index fossils (also known as guide fossils or zone fossils are Fossils used to define and identify geologic periods (or faunal stages Microfossils such as acritarchs, chitinozoans, conodonts dinoflagellate cysts, pollen, spores and foraminiferans are also frequently used. Micropaleontology (also sometimes spelled as micropalaeontology) is that branch of Paleontology which studies microfossils Acritarchs are small organic Fossils present from approximately to the present Chitinozoa (singular chitinozoan plural chitinozoans are a Taxon of flask -shaped organic walled marine Microfossils produced Conodonts are extinct chordates resembling eels classified in the class Conodonta. The dinoflagellates are a large group of Flagellate Protists Most are marine Plankton, but Pollen is a fine to coarse powder consisting of microgametophytes ( pollen grains) which produce the male Gametes (sperm cells of In Biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions The Foraminifera, ("Hole Bearers" or forams for short are a large group of Amoeboid Protists with reticulating Pseudopods fine Different fossils work well for sediments of different ages; trilobites, for example, are particularly useful for sediments of Cambrian age. Trilobites ("three-lobes" are extinct Arthropods that form the class Trilobita. The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with To work well, the fossils used must be widespread geographically, so that they can occur in many different places. They must also be short lived as a species, so that the period of time during which they could be incorporated in the sediment is relatively narrow. The longer lived the species, the less accurate the correlation, and so fossils that evolve rapidly, such as ammonites, are favoured over forms that evolve much more slowly, like nautiloids. Nautiloids are a group of marine Mollusks in the subclass Nautiloidea, which all possess an external shell the best-known example being the modern Nautiluses
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Fossils as a basis for stratigraphic subdivision
Concept of stage
A stage is a major subdivision of strata, each systematically following the other each bearing a unique assemblage of fossils. Therefore, stages can be defined as a group of strata containing the same major fossil assemblages. French palaeontologist Alcide d'Orbigny is credited for the invention of this concept. Palaeontology redirects here For the Scientific journal, see Palaeontology (journal. Alcide Charles Victor Marie Dessalines d'Orbigny ( September 6, 1802 - June 30, 1857) was a great French naturalist He named stages after geographic localities with particularly good sections of rock strata that bear the characteristic fossils on which the stages are based.
Concept of zone
In 1856 German palaeontologist Albert Oppel introduced the concept of zone (also known as biozones or Oppel zone). Carl Albert Oppel (1831&ndash1865 was a German Paleontologist. A zone includes strata characterised by the overlapping range of fossils. They represent the time between the appearance of species chosen at the base of the zone and the appearance of other species chosen at the base of the next succeeding zone. Oppel's zones are named after a particular distinctive fossil species, called an index fossil. Index fossils are one of the species from the assemblage of species that characterise the zone.
The zone is the fundamental biostratigraphic unit. Its thickness range from a few to hundreds of metres, and its extant range from local to worldwide. Biostratigraphic units are divided into six principal kinds of biozones:
- Taxon range biozone represent the known stratigraphic and geographic range of occurrence of a single taxon.
- Concurrent range biozone include the concurrent, coincident, or overlapping part of the range of two specified taxa.
- Interval biozone include the stata between two specific biostratigraphic surfaces. It can be based on lowest or highest occurrences.
- Lineage biozone are strata containing species representing a specific segment of an evolutionary lineage.
- Assemblage biozones are strata that contain a unique association of three or more taxa.
- Abundance biozone are strata in which the abundance of a particular taxon or group of taxa is significantly greater than in the adjacent part of the section.
Index fossils
To be useful in stratigraphic correlation index fossils should be:
- Independent of their environment
- Geographically widespread (provincialism/isolation of species should be avoided as much as possible)
- Rapidly evolving
- Abundant (easy to find in the rock record)
- Easy to preserve (Easier in low-energy, non-oxidized environment)
- Easy to identify
See also
External links
Biostratigraphic Lithostratigraphic Column Generator
Lithostratigraphy is a sub-dicipline of Stratigraphy, the geological Science associated with the study of strata or rock layers Chronostratigraphy is the branch of Stratigraphy that studies the age of rock strata in relation to Time. In Geology tectonostratigraphy refers either to rock sequences in which large-scale layering is caused by the stacking of thrust sheets or nappes in areas of Thrust tectonicsDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic