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

Introduction to Microfossils

palaeoenvironmental interpretation, dating and correlation of rock units

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

MicrofossilsMicrofossils- - the remains of once living the remains of once living bacteria, protist, plants and bacteria, protist, plants and animalsanimals

Benthic organismsBenthic organisms- live at or within the - live at or within the sedimentsediment

PhytoplanktonPhytoplankton- the lowest level in the food - the lowest level in the food web web

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Other microfossilsOther microfossils- what were they?- what were they?

Micro-zooplanktonMicro-zooplankton- protozoans feeding on - protozoans feeding on phytoplankton and organic phytoplankton and organic detritus in the waterdetritus in the water

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

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;

1. non-mineralized (organic-walled) forms 2. mineral-walled forms

Upper: Conodont elementsLower: A dinoflagellate cyst

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?

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

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: CoccolithophoridLeft: A rock basically containing diatoms and therefore called diatomiteLower right: Diatom

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Microfossils

Biostratigraphy Advantages of using microfossils in biostratigraphy:

1. They possess a shell or a test, which is so robust that they are not easily destroyed after their deposition.

2. Many groups have a short stratigraphic range.

3. They are numerous in small (a few grams) sediment or rock samples.

4. They have a widespread occurrence.5. 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 foraminiferaLower: A silica assemblage with diatoms and radiolaria

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Phytoplankton

PhytoplanktonMost of the primary production in aquatic environments are accounted for by the following phytoplankton or microplankton groups:

1. Dinoflagellates2. Diatoms 3. 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 Do you know the important phytoplankton groups?phytoplankton groups?

– Dinoflagellates – Diatoms– Coccolithophores

Upper: A coccolithophorideLower: A silica assemblage with diatoms and radiolaria

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Phytoplankton, dinoflagellates

DinoflagellateDinoflagellates are unicellular organisms (generally 20-150 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 dinoflagellateLower: A living dinoflagellate

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Microfossils

Phytoplankton

Micro-zooplankton

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EnvironmentThe 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 dinoflagellateLower: Dinoflagellate cyst

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils


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 useDinoflagellate 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 Do you know the other important phytoplankton groups?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

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Phytoplankton, diatoms

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 10-100 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 diatomMiddle: Drawing of pennate diatomLower: Photo of a live diatom

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Phytoplankton, diatoms

Fertile watersDiatoms 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).


– Dinoflagellates

– Coccolithophores


Upper: Centric diatom, valve viewLower: Centric diatom, side view

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Phytoplankton, coccolithophores

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.


– Dinoflagellates

– Diatoms


Upper: Coccolith Lower: Drawing of a coccolithophorid

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

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 What are the characteristic features of planktic foraminifera?of planktic foraminifera?

Upper: Planktic foraminifera assemblageLower left and right: Radiolaria

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Micro-zooplankton, radiolaria

Radiolaria Radiolaria are marine protozoans. Most species possess skeletons in the size range 50 - 200 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

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

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 Do you know the other group of micro-zooplankton ?micro-zooplankton ?

- Foraminifera- Foraminifera

Radiolaria

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Micro-zooplankton, foraminifera

ForaminiferaForaminifera 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 foraminiferaPlanktic 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

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

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 Do you know the othor group of micro-zooplankton?micro-zooplankton?

- Radiolaria - Radiolaria

Do planktic foraminifera have a benthic relative? Planktic foraminifera

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

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 foraminiferaLower right: Live (stained) benthic foraminiferaLeft: Pennate diatom, which in general are benthic

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Benthic organisms, foraminifera

Benthic foraminiferaMost 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?

Sediment

Water

Foraminifera

Right: Suspension feeding benthic foraminifera

Left: Modern benthic foraminiferal assemblage

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

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.

Upper: Modern benthic foraminiferaLower: Carboniferous benthic foraminifera

Stratigraphic useAlthough 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?

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Other microfossils, conodonts

Other microfossilsThe strangest microfossils look like teeth or chewing device, and are called condonts.

ConodontsConodonts are tooth-like fossils typically less than a millimeter long. Four basic shapes can be distinguished:

1. Simple cones2. Bars3. Blades4. Platforms

Fragments of condont elements

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?

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Other microfossils, pollen and spores

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:

1. Shape2. Apertures3. Wall-structure4. Size

What can we learn from pollen analysis?

Upper: A blooming tree spreading pollen Lower left and right: Pollen

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Microfossils

Phytoplankton

Micro-zooplankton

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Other microfossils

Other microfossils, pollen and spores

EnvironmentPollen 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

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

General information

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 http://www.learningjournals.net. About the author

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

About the module

Title: Introduction to microfossils

Responsible teacher: Professor Elisabeth Alve

Written by: Professor Elisabeth Alve and Dr. scient. Thor A. Thorsen

E-mail:[email protected]@geologi.uio.no

Responsible institution:

University of Oslo

Department of Geology

P.O. Box 1047 Blindern

0316 Oslo

Norway

www.geologi.uio.no

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

FAQ

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

References

Brasier, M.D., 1980. Microfossils. George Allen & Unwin, London, 193 pp.

Lipps, J.H. (ed.), 1993. 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.

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Microfossils

Phytoplankton

Micro-zooplankton

Benthic organisms

Other microfossils

Summary

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:

1. Mineral-walled microfossils; diatoms, coccoliths, radiolaria, foraminifera, conodonts.

2. 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:

1. Phytoplankton – autotrophic, photosynthesising primary producers living in the surface water (dinoflagellates, diatoms, coccolithophorids).

2. Micro-zooplankton – heterotrophic protozoans commonly feeding on phytoplankton and organic detritus in the water column (radiolaria, foraminifera).

3. Benthic organisms – comprising both autotrophic and heterotrophic groups living at or within the sediment surface (diatoms, foraminifera).

4. Other microfossils – stem from larger organisms (conodonts, pollen, spores).

You should now be ready for the module:

The use of biostratigraphy

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

Documents

microfossils useful

animals microfossils

main bulk of microfossils

groups of diatoms

important phytoplankton

sediment phytoplankton

following phytoplankton

organicwalled groups