Everything about Microfossil totally explained
Micropaleontology (also sometimes spelled as
micropalaeontology) is that branch of
paleontology which studies microfossils.
Microfossils are
fossils generally not larger than four
millimeters, and commonly smaller than one millimeter, the study of which requires the use of light or electron
microscopy. Fossils which can be studied with the naked eye or low-powered magnification, such as a hand lens, are referred to as
macrofossils. Obviously, it can be hard to decide whether or not some organisms should be considered microfossils, and so there's no fixed size boundary.
For example, some colonial organisms, such as
bryozoa (especially the
Cheilostomata) have relatively large
colonies, but are classified on the basis of fine skeletal details of the tiny individuals of the colony. Most bryozoan specialists tend to consider themselves
paleontologists, rather than
micropaleontologists, but many micropaleontologists also study bryozoa.
In another example, many fossil
genera of
Foraminifera, which are protists, are known from shells (called "tests") that were as big as coins, such as the genus
Nummulites.
Microfossils are a common feature of the
geological record, from the
Precambrian to the
Holocene. They are most common in deposits of
marine environments, but also occur in brackish water, fresh water and terrestrial
sedimentary deposits. While every
kingdom of
life is represented in the microfossil record, the most abundant forms are
protist skeletons or cysts from the
Chrysophyta,
Pyrrhophyta,
Sarcodina,
acritarchs and
chitinozoans, together with
pollen and
spores from the
vascular plants.
Micropaleontology can be roughly divided into four areas of study on the basis of microfossil composition: (a)
calcareous, as in
coccoliths and
foraminifera, (b)
phosphatic, as in the study of some
vertebrates, (c)
siliceous, as in
diatoms and
radiolaria, or (d)
organic, as in the
pollen and
spores studied in
palynology.
This division reflects differences in the mineralogical and chemical composition of microfossil remains (and therefore in the methods of fossil recovery) rather than any strict
taxonomic or
ecological distinctions. Most researchers in this
field, known as
micropaleontologists, are typically specialists in one or more
taxonomic groups.
Calcareous microfossils
Calcareous [CaCO3] microfossils include
Coccoliths,
Foraminifera, Calcareous
dinoflagellates, and
Ostracods (seed shrimp).
Phosphatic microfossils
Phosphatic microfossils include
Conodonts (tiny oral structures of an extinct chordate group), some
scolecodonts ("worm" jaws),
Shark spines and teeth, and other
Fish remains (collectively called "
ichthyoliths").
Siliceous microfossils
Siliceous microfossils include
Diatoms,
Radiolaria,
Silicoflagellates,
phytoliths, some
scolecodonts ("worm" jaws), and
spicules.
Organic microfossils
The study of
organic microfossils is called
palynology. Organic microfossils include
pollen,
spores,
Chitinozoans (thought to be the egg cases of marine invertebrates),
Scolecodonts ("worm" jaws),
Acritarchs,
Dinoflagellate cysts, and
fungal remains.
Methods
Sediment or rock samples are collected from either cores or outcrops, and the microfossils they contain extracted by a variety of physical and chemical laboratory techniques, including sieving, density separation by
centrifuge, and chemical digestion of the unwanted fraction. The resulting concentrated sample of microfossils is then mounted on a slide for analysis, usually by light microscope. Taxa are then identified and counted. The very large numbers of microfossils that a small sediment sample can often yield allows the collection of statistically robust datasets which can be subjected to
multivariate analysis. A typical microfossil study will involve identification of a few hundred specimens from each of ten to a hundred samples.
Applications of Micropaleontology
Microfossils are especially noteworthy for their importance in
biostratigraphy. Since microfossils are often extremely abundant, widespread, and quick to appear and disappear from the stratigraphic record, they constitute ideal
index fossils from a biostratigraphic perspective. In addition, the
planktonic and
nektonic habits of some microfossils gives them the added bonus of appearing across a wide range of
facies or paleoenvironments, and having near-global distribution making bio
stratigraphic correlation even more powerful and effective.
Microfossils also provide some of the most important records of global environmental change on long-timescales, particularly from deep-sea sediments. Across vast areas of the ocean floor the shells of planktonic micro-ogranisms sinking from surface waters provide the dominant source of sediment and they continuously accumulate (typically at rates of 20-50m/million years). Study of changes in assemblages of microfossils and of changes in their shell chemistry (e.g oxygen isotope composition) are fundamental to research on climate change in the geological past.
In addition to providing an excellent tool for
sedimentary rock-body dating and for paleoenvironmental reconstruction – heavily used in both
petroleum geology and
paleoceanography – micropaleontology has also found a number of less orthodox applications, such as its growing role in
forensic police investigation or in provenancing archaeological artefacts.
Further Information
Get more info on 'Microfossil'.
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