The Biostratigraphie (from ancient Greek βίος bios "life"; stratigraphy : "layers customer" from the Latin stratum "layer" and -graphy ) is a branch of stratigraphy in the geology . It deals with the structure and the relative chronological determination of rock units with the help of fossils .
After Nicolaus Steno had already recognized in the 17th century that the spatial arrangement of rock layers on top of one another actually corresponds to a temporal sequence of rock formation one after the other ( see: stratigraphic principle ), and Georges de Cuvier at the end of the 18th century spread the knowledge that it was in the In the course of the earth's history there have been repeated extinctions of biological species , William Smith used the principle of fossil tracking with great success in his geological mapping of England around the year 1800 . Around 1810, Leopold von Buch coined the term “ Leitfossil ” for the fossils that were particularly suitable for this purpose .
By 1830, Charles Lyell divided the tertiary in southern France, Gérard-Paul Deshayes the sequence of rocks in the Paris Basin and Heinrich Georg Bronn the Italian tertiary using fossils . In the subdivision of the former primary system in 1838, by comparing the underlying and overlying fossil contents, lithologically very different, spatially widely separated rock layers were interpreted as temporally equivalent deposits. The forerunner of the concept of zone, introduced by Alcide d'Orbigny in 1852 as the étage , still describes the biostratigraphic basic unit of the structure using fossils as “biozone”. In addition to the originally used for structuring fossil groups ( Ortho chronology ) were gradually through paleontological working stratigraphers other fossil groups ( Para chronology harnessed). In modern biostratigraphy, since the second half of the 20th century, classifications by series of factually seamlessly traceable, phylogenetic lines ( evolutionary series) have been sought. A new development is the use of all fossil individuals that have been collected horizontally and assigned to a taxon by computer-aided processes.
The principle of fossil succession
Fossil sequence means the occurrence of fossils in a very specific, unchangeable and recognizable vertical arrangement within a sequence of rocks. In connection with animal and vegetable remains, one also speaks of faunal or flora sequences .
The principle of fossil succession (also known as the "key fossil principle") states that a certain fossil community is replaced by another socialization in a certain area over time. Once a fossil disappears from a sequence of rocks, it never returns in the sequence. This principle distinguishes biostratigraphy from lithostratigraphy , because, unlike fossils, certain rocks can appear again and again in practically identical form in the course of the rock sequence. It not only enables the correlation of certain rock strata over long distances, even if their original storage conditions have been disturbed and altered by subsequent tectonic events , but also the relative dating of the strata to one another and the prediction of which strata can be expected at which location in the subsurface.
Long before the publication of Charles Darwin's theory of evolution , the observation of the sequence of fossils in the rocks suggested that the development of living beings does not run cyclically, like the cycle of rocks , but in a directed, fundamentally irreversible process, for every stage The history of the earth can be defined by a unique, unprecedented and never recurring socialization of fossil organisms.
Procedures and concepts
The basic unit of biostratigraphy is the biozone . The term zone was introduced by Albert Oppel as a refinement and conceptual clarification of the étage by Alcide Dessalines d'Orbigny . As a chronological unit, the biozone describes a period of time based on the lifespan of a biological species and as a stratigraphic term the newly formed rocks within this period of time. In the past, analogous to the species , higher taxonomic units were also used to classify them according to their phylogenetic existence. The period of time based on the duration of existence of a species was called a stage .
Modern biostratigraphy rarely uses higher taxonomic categories than those of the biological species . This corresponds to the fact that the international recommendations do not keep any biostratigraphic categories in stock above the zone. In contrast to traditional usage, units based on genera or families have recently been called zones.
Different, strictly separate concepts are used, which are defined by taking into account the times of species development and extinction (or the appearance or disappearance in the rock sequence) of a single taxon or a combination of several taxa. A differentiated, concrete unit always consists of at least the name of the taxon (or taxa) and the term “zone” or “biozone”. The G. kugleri zone in the border area Palaeogene / Neogene describes the (reach) zone established by the foraminifera species Globorotalia kugleri . An example of a highly taxonomized zone is the Lagenida zone , a subunit of the lower Badenium (a local time stage for the central Paratethys Sea), which is characterized by the Lagenida, an order of foraminifera.
The phylo-zone comprises the duration of existence of a delimited species within an evolutionary series of developments. It begins with the appearance of the eponymous species and ends with the appearance of the successor taxon. Such a structure requires precise knowledge of the development series. To understand such a series of developments, it is important to know why the individual links can be observed at all in this density and what the inner and / or outer "drives" of the constant change of form are. This concept enables the stable differentiation of zones for an extremely short period of time. An example of this is the division of the Upper Devonian by platform conodonts of the genus Palmatolepis .
A range zone represents the section of the temporal, stratigraphic and geographical occurrence of one or more taxa. A further distinction is made here between:
- Taxon range zone
- Overlap zone
- Interval zone
- Socialization zone
- Frequency zone
The concept of the taxon range zone largely corresponds to that of the key fossil .
A bio-horizon is a biostratigraphically established area in a rock. Each point on the surface represents the time of a paleontologically perceptible change or event (environmental event ). There is often a close connection between sedimentological and paleontological findings.
The fossils that serve as stratigraphic markers are called guide fossils . Good index fossils are as frequent as possible, facies-independent, well fossil-conservable and short-lived taxa.
Classically, biostratigraphy is carried out with marine invertebrates. Marine sediments are much more common in the rock tradition than terrestrial sediments, and many marine organisms have hard parts that have a high fossil conservation potential. Important macro-conductive fossils in the Paleozoic are brachiopods and goniatites , in the Mesozoic ammonites i. e. S. (order Ammonitida ) and mussels .
Vertebrates are much rarer in the fossil record than invertebrates and therefore rather not typical key fossils. Vertebrate biostratigraphy is mainly applied to terrestrial sediments. Thus Therapsid the most important index fossils in Perm the Karoo Basin . Rodent teeth are the most important key fossils in terrestrial sediments of the Cenozoic era (see also → ELMMZ Neogen ).
The advantage of microbiostratigraphy is that microfossils usually occur much more frequently and in larger numbers in sediments. In addition, some groups also occur in terrestrial sediments. Important key fossils in the Old Paleozoic are acritars , in the younger Paleozoic conodonts , in the Mesozoic foraminifera and coccoliths . Ostracodes are particularly important in terrestrial sediments .
Pollen and spores
Pollen and spores from land plants, so-called palynomorphs, also meet the requirements of good index fossils and are therefore suitable for biostratigraphy. They are widely drifted by the wind and are therefore also found in marine sediments.
- ↑ Lehmann 1977: 205
- ↑ Rudwick 1979, p. 16.
- ↑ a b Lehmann 1977, p. 413.
- ↑ Steininger & Piller 1999, p. 9.
- ↑ Lehmann 1977, p. 255.
- ↑ Lehmann 1977: 270
- ^ Sadler & Cooper 2003.
- ↑ Stanley 2001, p. 12.
- ↑ Müller 1992, p. 25.
- ↑ Schweigert 2005.
- ↑ Müller 1992, p. 237.
- ↑ Steininger & Piller 1999: 10
- ↑ Stainford & Lamb 1981.
- ^ Sandberg & Ziegler 1990.
- ↑ Steininger & Piller 1999: 10-14
- ↑ Steininger & Piller 1999, p. 14.
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