1. Introduction to Microfossils
palaeoenvironmental interpretation, dating and correlation of rock units

2. Home
Micro-zooplankton - protozoans feeding on phytoplankton and organic detritus in the water
Phytoplankton - the lowest level in the food web
Microfossils - the remains of once living bacteria, protist, plants and animals
Benthic organisms - live at or within the sediment
Other microfossils - what were they?

3. Microfossils Microfossils
Microfossils comprise the remains of once living bacteria, protists, plants and animals and in some cases fragments of larger organisms (e.g., conodonts). These fossils are so small that we need a microscope to study them.   Based on their test composition, microfossils are commonly divided into;
non-mineralized (organic-walled) forms
mineral-walled forms
Non-mineralized forms
Some microfossils with non-mineralized tests are remarkably resistant to microbial as well as chemical attack and to a certain extent to the effects of temperature and pressure after burial.   These are called palynomorphs. They represent the most resistant group of microfossils, and include some dinoflagellate cysts, spores and pollen.
Why are mineral-walled microfossils less resistant than organic-walled groups? 
Upper: Conodont elements Lower: A dinoflagellate cyst

4. Microfossils Mineral-walled microfossils
Diatoms and radiolarians have silica tests, whereas coccoliths and most fossil foraminifera have tests made up of calcium carbonate.   Consequently, the preservation of these mineral-walled microfossils depends on the acidity and other geochemical properties of the depositional and subsequent diagenetic environment.   Why are microfossils useful in biostratigraphy?
Upper right: Coccolithophorid Left: A rock basically containing diatoms and therefore called diatomite Lower right: Diatom

5. Microfossils Biostratigraphy
Advantages of using microfossils in biostratigraphy:
They possess a shell or a test, which is so robust that they are not easily destroyed after their deposition.
Many groups have a short stratigraphic range.
They are numerous in small (a few grams) sediment or rock samples.
They have a widespread occurrence.
Most groups have a high species diversity and are sensitive environmental indicators.
The same group of microorganisms may inhabit a wide range of environments from the abyss to the upper intertidal zone, even between small sand grains on the beach. Diatoms and foraminifera are examples of groups comprising both planktic and benthic forms.
The main bulk of microfossils are remains of marine organisms. Some groups of diatoms are freshwater species, whereas pollen and spores represent the parent plants and their environment on land even when they are found in marine sediments.
Which groups represent the lowest trophic level?
Upper: Planktic foraminifera Lower: A silica assemblage with diatoms and radiolaria

6. Phytoplankton Phytoplankton
Most of the primary production in aquatic environments are accounted for by the following phytoplankton or microplankton groups:
Dinoflagellates
Diatoms
Coccolithophorides (calcareous nannoplankton)
Dinoflagellates and diatoms are commonly comparable in size but generally larger than calcareous nannofossils. Their preservable parts make up most of the fossil phytoplankton record.   Do you know the important phytoplankton groups?
Coccolithophores
Upper: A coccolithophoride Lower: A silica assemblage with diatoms and radiolaria

7. Phytoplankton, dinoflagellates
Dinoflagellates are unicellular organisms (generally µm long). Most species are equipped with two dissimilar flagella, which enable them to actively move around in the water column in search for optimal light and nutrient conditions.   Feeding Some are plant-like (autotrophic) some are animal-like (heterotrophic) some are both (mixotrophic).   The autotrophic species contain chloroplasts and therefore produce organic compounds by photosynthesis.   The heterotrophic species ingest other organisms for food.   The mixotrophic may feed both like plants and animals.
These differences in feeding strategies have made the group difficult to place systematically. Now they are placed with protists and in the family Dinophyceae.
  Where do they live?
Upper: Drawing of a living dinoflagellate Lower: A living dinoflagellate

8. Phytoplankton, dinoflagellates
Environment The majority of species are marine but they are also common in freshwater lakes, ponds, rivers and other aquatic media.   Most dinoflagellate species seem to be cosmopolitan or to be restricted to wide latitudinal bands.   Cysts Although the motile cells of dinoflagellates are abundant and wide ranging, it is the resistant resting cyst, which leaves a fossil record. Cysts form following sexual reproduction within the formerly motile cell and contain food as oil and starch etc. This makes the cysts viable for several years even within the sediment.
Do they all fossilize?
Upper: Living dinoflagellate Lower: Dinoflagellate cyst

9. Phytoplankton, dinoflagellates
Fossil cysts Overall about 10 % of the present day living dinoflagellate species may produce geologically preservable cysts. Most cyst-forming dinoflagellates appear to be coastal/neritic.   Stratigraphic use
Dinoflagellate cysts (or dinocysts) are of considerable value in the biostratigraphy of marine strata since the Late Triassic.
They have allowed detailed subdivision of many parts of the stratigraphic record and have been particularly useful for oil exploration in strata where calcareous microfossils are not abundant.
Do you know the other important phytoplankton groups?
Diatoms
Coccolithophores
Do you know of any other microfossil groups with a planktonic mode of life but at a higher trophic level?
Dinoflagellate cyst

10. Phytoplankton, diatoms
Diatoms are unicellular algae which are characterized by an external skeleton (a frustule) comprising two valves, one overlapping the other like the lid of a pillbox. The size range of frustules is generally µm.   The frustules are made of opaline silica. They are usually either circular (centric) or elliptical (pennate) in valve view. They are commonly very intricate and varied, and their patterns and types of ornamentation form the basis of nearly all diatom taxonomy.   Environment They live practically everywhere where light and moisture occur, including virtually all marine, brackish, and freshwater environments as well as soils, ice, and attached to rocks and other substrates within spray or splash zones.   Unlike dinoflagellates and calcareous nannoplankton, the vegetative cells of diatoms lack flagella. Thus, diatoms are passively dispersed by currents in the surface layers of the ocean.   But where do they thrive?
Upper: Drawing of centric diatom Middle: Drawing of pennate diatom Lower: Photo of a live diatom

11. Phytoplankton, diatoms
Fertile waters
Diatoms seem to thrive in more turbulent waters than dinoflagellates, i.e. where physical mixing brings nutrients to them.
Generally, high abundance of diatoms correlates strongly with waters of high nitrate and phosphorous concentrations.  
Beneath these fertile waters sediments on the sea floor consist of abundant diatoms, commonly referred to as diatom oozes.
Stratigraphic use 
Diatoms are the primary means of correlating high-latitude deep-sea sediments.
The oldest reliable record of diatoms is from the Early Jurassic (Toarcian) but abundant, well-preserved assemblages do not occur until the Early Cretaceous (Aptian-Albian).
Do you know the other important phytoplankton groups?
Dinoflagellates
Coccolithophores
Do you know of any other microfossil groups with a planktonic mode of life but at a higher trophic level?
Upper: Centric diatom, valve view Lower: Centric diatom, side view

12. Phytoplankton, coccolithophores
Coccolithophores are unicellular and predominantly autotrophic nannoplankton (commonly 5-60 µm in size). The cell is surrounded by protective armour of tiny calcareous scales called coccoliths (3-15 µm in diameter).
The most common coccoliths in the microfossil record are the so-called heterococcoliths. The majority comprise discs of elliptical or circular outline constructed of radially arranged plates, enclosing a central area which may be empty, crossed by bars, filled with a lattice or produced into a long spine.
These tiny coccoliths are abundant in marine sediments, particularly in zones of oceanic upwelling or of pronounced vertical mixing. Although the majority of the species are marine, some are adapted to fresh and brackish waters.
Stratigraphic use 
Coccoliths are useful for biostratigraphic correlations of post-Triassic rocks.
Do you know the other important phytoplankton groups?
Dinoflagellates
Diatoms
Do you know of any other microfossil groups with a planktonic mode of life but at a higher trophic level?
Upper: Coccolith Lower: Drawing of a coccolithophorid

13. Micro-zooplankton Micro-zooplankton
Radiolaria and planktic foraminifera are marine heterotrophic protozoans. They commonly feed on phytoplankton and organic detritus in the water column and are called micro-zooplankton.   What are the characteristic features of radiolaria?
What are the characteristic features of planktic foraminifera?
Upper: Planktic foraminifera assemblage Lower left and right: Radiolaria

14. Micro-zooplankton, radiolaria
Radiolaria are marine protozoans. Most species possess skeletons in the size range µm and the fossil forms are made of opaline silica. These polycystine radiolarians are usually divided into Spumellaria and Nassellaria.
Morphology
Spumellaria skeletons are spherical, whereas Nassellaria skeletons are nonspherical and usually with a bilateral symmetry.
The simplest spumellarian or nassellarian skeleton is a spicule.
The more advanced forms of radiolaria have lattice skeletons with complex geometry. Some consist of several spherical lattice skeletons, one inside the other, whereas some lattice skeletons have the shape of a bell. Many skeletons have spines, which may be simple or branched.
Similarity to sponge spicules
Both spumellarian and nassellarian spicules can be distinguished from most sponge spicules since the radiolarian spicules are solid and do not possess the central space common to sponge spicules.
How is their life strategy?
Upper: Spumellaria Lower: Nassellaria

15. Micro-zooplankton, radiolaria
Feeding strategy
Radiolarians employ a broad range of trophic strategies and this explains their exceptionally wide distribution within the marine water masses.
Many radiolarians live in symbiosis with zooxanthella (unicellular algae) which, through their photosynthesis, provide the radiolarians with food.
Stratigraphic use
The polycystine radiolarians have the longest geologic range (Cambrian to Holocene), the widest biogeography (pole to pole, surface to abyss), and the most diverse taxonomy of the well-preserved micro-zooplankton.
Do you know the other group of micro-zooplankton ?
- Foraminifera
Radiolaria

16. Micro-zooplankton, foraminifera
Foraminifera are protozoans with a test consisting of one or more chambers each interconnected by an opening (foramen) or several openings (foramina).
The most prominent feature which distinguishes foraminifera from other protists is that they possess granuloreticulopodia, which are fine, thread-like, pseudopodia that anastomose (splitt and rejoin) and have granular texture  when viewed with light microscope.
Foraminifera comprise both planktic and benthic forms.
Planktic foraminifera
Planktic foraminifera are entirely marine and they generally range in size between 60 µm and > 1 cm. Their calcium carbonate test consists of chambers, which commonly are inflated and added in different kinds of spiral shape as they grow. They have a spiny to smooth surface texture.
Where do we find planktic foraminifera?
Modern planktic foraminifera

17. Micro-zooplankton, foraminifera
Environment
Living foraminifera have their maximum abundance in euphotic, near-surface waters between 10 and 50 meters. They are intolerant of brackish water. Many are cosmopolitan and occur in broad latitudinal belts generally related to the temperature and the major ocean current systems. Some species are so abundant that their dead shells make up a large proportion of the deep ocean “ooze”. In the present day abyssal North Atlantic the ooze is about 75% foraminifera and 25% coccoliths.
Stratigraphic use
Extending back to the mid Jurassic, the geologic record of planktic foraminifera shows them to have undergone frequent phases of diversification, notably in the mid- and late-Cretaceous, Palaeocene, mid-Eocene, and early- and mid- Miocene. Many species have short stratigraphic ranges and the succession of overlapping species ranges makes them an extremely useful tool in biostratigraphy.
Do you know the othor group of micro-zooplankton?
- Radiolaria  
Do planktic foraminifera have a benthic relative?
Planktic foraminifera

18. Benthic organisms Benthic organisms
Both diatoms and foraminifera include benthic as well as planktic species.   Being autotrophic, utilizing the sunlight, benthic diatoms are restricted to the photic zone.   In contrast, benthic foraminifera have a wide range of feeding strategies and some may therefore live in the dark and deepest parts of the oceans.
What is the test of benthic foraminifera made of?
Upper right: Benthic foraminifera Lower right: Live (stained) benthic foraminifera Left: Pennate diatom, which in general are benthic

19. Benthic organisms, foraminifera
Benthic foraminifera Most fossil species of benthic foraminifera have a test (shell) composed either of calcium carbonate or foreign (often detrital) particles held together with a cement, which is partly or entirely organic. The former are called calcareous and the latter agglutinated foraminifera.   The test morphology of benthic foraminifera is extremely varied. Chambers may be single or multiple, arranged in rows or spirals, or in a range of complex patterns. Most are < 500 m in size.
But where do we find benthic foraminifera?
Water
Foraminifera
Sediment
Right: Suspension feeding benthic foraminifera
Left: Modern benthic foraminiferal assemblage

20. Benthic organisms, foraminifera
Environment Benthic foraminifera are more or less ubiquitous in marine sediments from the most extreme intertidal marsh to the deepest trenches of the ocean, and they often form a very important component of the meiofauna.   Their high diversity and abundance, and their sensitivity to environmental change and disturbance make them excellent proxies for palaeoecological and palaeoenvironmental interpretations.
Stratigraphic use Although their geological record ranges from the Cambrian to Recent, benthic foraminifera with hard tests were scarce until the Devonian when calcareous walls first became common.   Benthic foraminifera tend to be more restricted in distribution than planktic ones but provide useful schemes for local- and sometimes for intercontinental correlations.   Do you know any other groups of microfossils?
Upper: Modern benthic foraminifera Lower: Carboniferous benthic foraminifera

21. Other microfossils, conodonts
The strangest microfossils look like teeth or chewing device, and are called condonts.
Conodonts
Conodonts are tooth-like fossils typically less than a millimeter long. Four basic shapes can be distinguished:
Simple cones
Bars
Blades
Platforms
Conodonts were probably parts of a chewing apparatus in a very primitive vertebrate animal. The conodont animal was a small (30-40 mm long) predatory swimmer. So far, only very few individuals have been found in the fossil record, whereas the conodont elements are common.
Stratigraphic use
Useful biostratigraphic markers in Cambrian to Triassic marine deposits.
Most people know of pollen, but do we find them in the fossil record?
Fragments of condont elements

22. Other microfossils, pollen and spores
Pollen are produced in large numbers. In the spring we may see it as yellow “dust” on the water.
Pollen from seed plants and spores from vascular land plants are very common as fossils. Their size generally range from about ten to a few hundred microns. The morphology of pollen grains and spores can be described according to their:
Shape
Apertures
Wall-structure
Size
 What can we learn from pollen analysis?
Upper: A blooming tree spreading pollen Lower left and right: Pollen

23. Other microfossils, pollen and spores
Environment
Pollen and spores are produced in large numbers and can be carried over long distances by wind or water before they settle down and get deposited.
Where the ecology of the parent plant is known, pollen and spores can be utilized for palaeoecological and palaeoenvironmental studies.
In marine deposits, they can give us a clue about the distance to land.
Stratigraphic use
Pollen and spores are valuable stratigraphic markers in terrestrial, lacustrine, fluviatile, and deltaic sediments.
They are particularly helpful in correlating continental and nearshore marine deposits of Devonian or younger age.
How can we summarize the use of microfossils?
Pollen

24. General information About the author Title:
Introduction to microfossils
Teacher(s):
Elisabeth Alve
Assistant(s):
Thor A. Thorsen, Tore Joranger & Tania Hildebrand-Habel
Abstract:
In this module you will be introduced to the most important groups of micofossils and their stratigraphic use.
4 keywords:
Micropalaeontology, biostratigraphy, microfossils, palaeoenvironment
Topic discipline:
Biostratigraphy
Level: 2
Prerequisites:
Basic knowledge of biostratigraphy
Learning goals:
Learn about the different types of microfossils and their use in biostratigraphy.
Size in megabytes:
2.8 Mb
Software requirements:
Microsoft Powerpoint XP
Estimated time to complete:
30 min
Copyright information:
The author has copyright to the module and use of the content must be in agreement with the responsible author or in agreement with
About the author

25. About the module Title: Introduction to microfossils
Responsible teacher:
Professor Elisabeth Alve
Written by:
Professor Elisabeth Alve and Dr. scient. Thor A. Thorsen
Responsible institution:
University of Oslo
Department of Geology
P.O. Box 1047 Blindern
0316 Oslo
Norway

26. FAQ
Not implemented

27. References
Brasier, M.D., Microfossils. George Allen & Unwin, London, 193 pp.
Lipps, J.H. (ed.), Fossil Prokaryotes and Protists. Blackwell Scientific Publications, Oxford, 342 pp.
Stanley, S.M., 1998, Earth system history, W.H. Freeman and Company, New York, 615 pp.

28. Summary You should now be ready for the module:
Microfossils provide valuable information on the history of life and how the environments have changed through time. The evolution of species gives us a powerful tool to characterize and correlate rock units.
In this module you have been introduced to the most important groups of micofossils and their stratigraphic use. Based on the composition of their test, they are commonly divided into:
Mineral-walled microfossils; diatoms, coccoliths, radiolaria, foraminifera, conodonts.
Organic-walled microfossils also known as palynomorphs; dinoflagellate cysts, pollen and spores.
For palaeoecological reasons, this introduction to microfossils presents them according to habitat and life stragegy:
Phytoplankton – autotrophic, photosynthesising primary producers living in the surface water (dinoflagellates, diatoms, coccolithophorids).
Micro-zooplankton – heterotrophic protozoans commonly feeding on phytoplankton and organic detritus in the water column (radiolaria, foraminifera).
Benthic organisms – comprising both autotrophic and heterotrophic groups living at or within the sediment surface (diatoms, foraminifera).
Other microfossils – stem from larger organisms (conodonts, pollen, spores).
You should now be ready for the module:
The use of biostratigraphy