Download assignment on gey 402(micropalentology - abuad lms

ASSIGNMENT ON GEY 402(MICROPALENTOLOGY/
PALAECOLOGY)
BY
WATEGIRE DANIELLA
MATRIC NUMBER: 12/SCI14/025
JANUARY 2016
AFE BABALOLA UNIVERSITY, ADO EKITI
FACULTY OF SCIENCE
DEPARTMENT OF GEOLOGY
QUESTION: Write short notes on the following and their application in
hydrocarbon;
 Calcareous microfossils
 Calcareous nannofossils
 Siliceous microfossils
 Phosphatic microfossils
QUESTION 1
CALCAREOUS MICROFOSSILS
Calcareous microfossils have shells composed of calcite or aragonite. These organisms are
present in most marine and in some nonmarine environments. At great oceanic depths
characterized by low temperature and high hydrostatic pressure, however, calcareous remains are
largely or completely dissolved. The depth below which this occurs, which varies in different
oceanographic settings, is termed the carbonate compensation depth (CCD).
There are three principal types of calcareous microfossils: calcareous foraminifera, ostracods,
and calcareous nannofossils.
Calcareous foraminifera
Calcareous foraminifera are a group of unicellular organisms (protists) that secrete a rigid calcite
or aragonite shell (or test). Fossils of these forms are found in sediments of brackish to marine
origin from Silurian to Holocene in age. Most are benthic (bottom dwelling), but a significant
group in the late Mesozoic and Cenozoic are planktonic (floating) forms.
Some stratigraphically important foraminifera developed complex internal structures and,
frequently, large test size. Studied primarily in thin section, these include the fusulinids
(Pennsylvanian to Permian) 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.
Figure 1 shows some typical calcareous foraminifera.
Ostracods
The Ostracoda are one of the most successful crustacean groups with approximately 8000 living
species. Ostracods are generally small, ranging in length from 0.1 to 32 mm (that's smaller than
a poppy seed to the size of a meatball). As indicated by its name, Gigantocypris a planktonic
ostracod, is by far the largest member of this group reaching up to 32 mm. Gigantocypris's
pelagic life style (continuously swimming in the open water) sets it apart from many other
ostracods as well. Most other ostracods are found crawling on or burrowing into the sediments at
the bottom of the ocean or lakes. A few species, for example Mesocypris sp., are also found
crawling around in moist terrestrial habitats such as mosses. In these habitats, they feed on dead
organic material, suspended organic particles, microscopic plants, or they are predators.
Ostracods consist of little more than a head. They have the typical five pairs of appendages on
their head but only 1-3 pairs of appendages on the rest of the body. Their bivalved carapace may
cause you to mistake them for tiny clams or mussels, thus the common name of "mussel
shrimp". The two part, hinged carapace encloses the entire body, similar to the branchiopod
Conchostraca. However, their appendages distinguish them from the conchostracans. Another
feature that differentiates these groups is a lack of growth rings on the carapace. Ostracods shed
the carapace with each molt, whereas the conchostracans simply add material to the carapace as
they grow.
The ostracods have the most complete fossil record of any of the crustaceans.
Ostracods are microscopic crustaceans whose fossils are found in Cambrian to Holocene rocks.
They occur in most marine and nonmarine depositional environments and are generally excellent
environmental indicators. The paleontologic application of ostracods is limited because (1) they
are rare in many sections and (2) many species are endemic to local basins, so their age and
environmental ranges are poorly understood. Ostracods typically have rapid evolutionary rates
and are useful biostratigraphic tools in some situations:

In Paleozoic sequences

In marine environments where wide-ranging species are present

For local stratigraphy in basins of limited extent

In lacustrine environments, where they are frequently one of the few microfossils present
Ostracods may also indicate thermal maturation of source rocks.
ostracods
Calcareous nannofossils
The term calcareous nannofossils includes 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 coccoliths
assemblages in marine sediments and are also organically derived.
Calcareous nannofossils are often widespread, abundant and well preserved in marine sediments
in the geological record and are therefore a very useful biostratigraphic tool. Made of
calcium carbonate, they can often be found in vast numbers, sometimes forming the major
constituent of a particular rock e.g. the White Cliffs of Dover. Living and fossil nannoplankton
are also important in the study of climate change and in palaeoceanographic and
palaeoecological research.
Calcareous nannofossils are an excellent biostratigraphic tool because of their rapid evolution
and geographic dispersal (i.e., their entire life cycle is in the photic zone of the ocean) as well as
their varied and distinct morphologies. The oldest known calcareous nannofossils are Late
Triassic; they are a crucial microfossil group in calibrating the Jurassic-Holocene marine record.
Relatively little has been published about the paleogeographic distributions of calcareous
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.
QUESTION 2
CALCAREOUS NANNOFOSSILS
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. Nannofossils also occur in other sedimentary lithologies The
calcite platelets are preserved in the rocks and are the fossils that paleontologists study.
Calcareous nannofossils have been living in the world's oceans for at least 200 million years
(from the Triassic Period), and they have evolved and changed constantly over time.
Biostratigraphy - 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 proctical applications. For example, calcareos nannofossils have been used
succuesfully to help map both the surface and subsurface geographic extent of lithologic units,
particulary 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.
QUESTION 3
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
Radiolarians
Figure 1 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
Figure 2 Typical 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 subsurfac
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.
QUESTION 4
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.
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. This recent information has led to more accurate multielement species concepts.