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ASSIGNMENT ON GEY 402 (MICROPALEONTOLOGY)
BY
EDEOGHO ORUAROGHENE
12/SCI14/009
AFE BABALOLA UNIVERSITY
ADO EKITI
EKITI STATE
ASSIGNMENT QUESTION
EXPLAIN THE FOLLOWING
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CALCEROUS MICROFOSSILS
CALCEROUS NANNOFOSSILS
SILICEOUS MICROFOSSILS
PHOSPHATIC MICROFOSSILS
CALCEROUS MICROFOSSIL
Calcerous microfossils include coccoliths, foraminifera, calcerous dinoflagellete cycsts and
ostracods. They have shells composed of calcite or aragonite. These organisms are present in
most marine and in sme nonmarine environments. At great oceanic depths characterized by low
temperature and high hydrostatic pressure, however, calcerous remains are largely or completely
dissolved. The depth below which this occurs which varies in different oceangraphic settings is
termed carbonate compensation depth (CCD)
There are three principal types of calcerous microfosils: calcerous foraminifera, ostracods and
calcerous nannofosils.
CALCEROUS FORAMINIFERA: calcerous foraminifera are a group f unicellular organism
that secrete a riid calcite or aragonite shell. Fossils of these forms are found in sediments of
brackish to marine origin from Silurian to Holocene in age. Most are benthic but a significant
group in the late Mesozoic and Cenozoic are planktonic forms.
Some stratigraphically important foraminifera developed complex internal structures and these
include the fusulinids ( pennyslvanian to permain )n and several groups of so called larger
foraminifera ( Triassic to Holocene) they occur primarily in carbonate or fine-grained clastic
rocks and are excellent time markers.
Because many species have limited and well-known environmental ranges, they are excellent
paleobathymetric and paleoenvironmental indicators, especially in younger phanerozoic rocks.
OSTRACODS
Osctracods are microscopic crustaceans whose fossils are found in cambrain to Holocene
rcks. They occur in most marine and nonmarine depositional environments and are
generally excellent environmental indicators. The paleontologic application of ostracods
is limited because ;
 They are rare in many sections
 Many species are endemic to local basins, so their age and environmental range
are porly understood. Ostracods typically have rapid eveolutionary rates and are
useful biostratigraphic tools in sme situation:
 In Paleozoic sequences
 In marine environments where wide-ranging species are presen
 For local stratigraphy in basins of limited extent
 In lacustrine environments, where they frequently one of the few microfossils
present.
Ostracods may also indicate thermal maturation of source rocks.
CALCEROUS NANNOFOSSILS
Calcerous nannofossils are extremely small objects less than 25microns produced by planktonic
unicellular algae. As the nameimplies, they are made of calcium carbonate. Nannofossils first
appeared during the Mesozoic era and have persisted and evolved through time. The function of
the calcerous plates, even in living form is uncertain. One extant group that produces
nannofossils is the cocclithophorans, planktonic golden brown algae that are very abundant in the
worlds oceans. The calcerous plates accumulates on the ocean floor, become buried beneath
layer layers and are preserved as nannofossils. Some chalks such as those comprising the White
Cliffs of Dover are composed almost entirely of nannofossils.
Calcerous nannofossils include both fossil coccoliths and nannoliths. Coccoliths are minute
(˂25µm) calcite objects produced by unicellular marine plants (golden-brown algae). The origin
of nannoliths is uncertain, but these calcite bodies are associated with fossil coccolihts
assemblages in marine sediments and are also organic salt derived.
Calcerous nannofossils are an excellent biostratigraphic tool because of their rapid evolution and
geographic dispersal (I.e their entire life cycle is in photic zone of the ocean) as well as their
varied and distinct morphologies. The oldest known calcerous nannofossils are late Triassic; they
are crucial microfossil group in calibrating the Jurrassic-Holocene marine record. Relatively little
has been published about the palegeographic distributins of calcerous nannofossils; less is known
about their exact paleoenvironmental preferences, although they have been shown occasionally
to penetrate into shallow marine environments. Their main industrial application is their
calibration to published time scales and sequence stratigraphic records, especially the association
of high abundance with condensed marine sections.
Calcareous nannofossils are fossil remains of golden-brown, single-celled algae that live in the
oceans. Because they are plants, they require sunlight, so they float near the surface of the water.
There are billions of them living in the oceans today, and they are eaten by anything that is
bigger than they are. They are one of the primary organisms at the base of the food chain. These
algae make tiny calcite platelets inside their cells, and these platelets (the calcareous nannofossils
or nannos for short) move to the surface of the cell. The platelets fall off the cell and slowly drift
down to the bottom of the ocean. These platelets are replaced by new ones that constantly are
forming within each cell. As these platelets land on the bottom of the ocean, they are slowly
covered up with remains of other plants and animals and bits of mud and sand that have washed
out with the rivers of the world. At this point they are part of a mud or marl or sandy clay.
Eventually, there are many sediments on the ocean bottom, and their weight is enough so that the
lowest sediments are squeezed enough to become rocks. Chalks are composed almost entirely of
nannofossils
Calcareous nannofossils are the most useful age indicator for marine sediments from the Jurassic
(205 million years) to the Recent because of their rapid rate of evolution and wide geographic
distribution. The first appearance datums (FAD's) and last appearance datums (LAD's) for
calareous nannofossil species usually occur at the same horizon globally and often can date
sediments to accuracies of one million years or less. Accurate dating of sedimentary deposits has
many practical applications.
For example, calcareos nannofossils have been used successfully to help map both the surface
and subsurface geographic extent of lithologic units, particularly in regions with complex facies
patterns like New Jersey and Alabama. They also are used in regional geologic studies to
correlate time-equivalent but lithologically distinct deposits form state to state and region to
region.
Calcareous nannofossils have been used in forensic studies. For example, clay scraped from the
shoes of a murder suspect in England contained calcareous nannofossil species that were unique
enough to lead the police to the scene of the crime. Calcareous nannofossils have been used to
determine the origin of building stones for Medieval churches in Denmark and to check
authenticity of paintings. In Norway, which has no native chalk, calcareous nannofossils were
used to determine the origin of white chalk that was used to prepare the surfaces of Medieval
wooden sculptures and panels before painting.
SILICEOUS MICROFOSSILS
Siliceous microfossils are protists with shells constructed of opaline (amorphous) silica. There is
no intense dissolution of siliceous remains in the deep ocean. Sediments deposited below the
carbonate compensation depth are commonly enriched in silica by removal of the carbonate,
sometimes to the point of forming siliceous oozes. With subsequent remobilization of the silica,
deep-sea cherts may be formed. Siliceous microfossils are subject to burial diagenesis and
become rare at great well depths except when recrystallized, preserved in nodules or concretions,
or replaced by pyrite or calcite.
There are three major groups of siliceous microfossils: radiolarians, diatoms, and
silicoflagellates.
Typical radiolarians.
Radiolarians are planktonic protists that occur primarily in open marine, deep-water settings.
They are useful time indicators and are found in rocks of Cambrian to Holocene age. They may
be the only common microfossils in abyssal environments, commonly forming radiolarian oozes.
Radiolarian chert, the product of silica diagenesis, is fairly widespread in the geologic record.
Radiolarians are common in some marine source rocks.
DIATOMS
Diatoms are photosynthesizing protists that occur in both marine and nonmarine environments.
Marine diatoms range from Upper Jurassic or Lower Cretaceous to Holocene and are particularly
useful for age and environmental determinations in the upper Cenozoic. Nonmarine diatoms
range from Eocene to Holocene and also are useful in the upper Cenozoic. These microfossils
can be a major rock-forming group, forming sedimentary rock (diatomites) consisting primarily
of diatoms. Diatomaceous sediments, when altered by burial diagenesis, are converted to
siliceous shale, porcellanite, and chert. Such rocks can serve as sources and fractured reservoirs
for hydrocarbons (e.g., Monterey Formation of California). The changes in rock properties
associated with silica diagenesis permit seismic definition of silica phase transformation zones in
the subsurface (e.g., bottom-simulating reflector).
Typical diatoms.
SILICOFLAGELLATES
Silicoflagellates are another group of planktonic photosynthesizing marine protists; they
commonly occur with diatoms. Silicoflagellates range in age from Cretaceous to Holocene.
Although not as common as diatoms, they are useful time indicators, particularly in the upper
Cenozoic. As a group, they were much more abundant during the early and middle Cenozoic
than today. They have been used to estimate marine paleotemperatures in the late Tertiary and
Quaternary.
Typical Silicoflagellates.
PHOSPHATIC MICROFOSSILS
Phosphatic microfossils, notably conodonts, are composed of crystallites of calcium phosphate
(apatite) embedded in an organic matrix. There is one type of stratigraphically significant
phosphatic microfossils (conodonts); but fish teeth, of less practical utility, are found in some
marine strata.
Typical conodonts.
Conodonts are extinct toothlike microfossils composed of calcium phosphate whose biological
affinities, while poorly understood, lie with chordates. Conodonts are widely distributed in
marine rocks of Cambrian through Triassic age. They are excellent indicators of time and
thermal maturity especially in carbonates, where other methods of evaluating organic thermal
maturity are less successful. Conodonts are commonly used as zonal indices for the latest
Cambrian through Triassic because they were abundant, evolved rapidly, and were widespread
geographically. Although found in most marine rocks, conodonts are most efficiently recovered
from the insoluble residues of carbonates dissolved in weak acids or from easily disaggregated
shales.
Individual conodonts vary greatly in morphology, and taxonomy was originally based on the
morphology of these individual specimens. While conodonts are common, the preserved remains
of the soft-bodied animal that bore them are extremely rare. Based on a few preserved wholeanimal specimens discovered recently (e.g., conodonts appear to have been located in the
cephalic area and may have functioned as teeth. However, the conodont animal apparently bore
many conodonts of differing shapes and morphologies, based on the study of the very rare
whole-animal specimens and rare bedding-plane groupings of conodonts representing individual
animals.
APPLICATION OF MICROFOSSILS
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, as well as having near-global
distribution, making biostratigraphic correlation even more powerful and effective.
Microfossils, particularly from deep-sea sediments, also provide some of the most important
records of global environmental change on long, medium or short timescales. Across vast areas
of the ocean floor, the shells of planktonic micro-organisms sinking from surface waters provide
the dominant source of sediment, and they continuously accumulate (typically at rates of 20-50
million per million years).
In addition to providing an excellent tool for sedimentary rock 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 determining the provenance of
archaeological artefacts.
Micropaleontology is also a tool of Geoarchaeology used in archaeological reconstruction of
human habitation sites and environments. Changes in the microfossil population abundance in
the stratigraphy of current and former water bodies reflect changes in environmental conditions.
Naturally occurring Ostracods in freshwater bodies are impacted by changes in salinity and pH
due to human activities. When correlated with other dating techniques, prehistoric environments
can be reconstructed.