Microfossil and Nannofossil Image Gallery

by Keith Abineri, UK

 

Introduction

Microfossils and nannofossils have been very much in the news recently. For example, there is still a hot debate over whether the microscopic features found in an Antarctic meteorite originating from Mars are evidence of past life on that planet. Linked to these debates and the search for extraterrestial life is the question 'how small can a living organism be?'. Australian researchers who recently found what are believed to be the smallest living nannobacteria in rocks deep beneath the earth's surface may force scientists to review how they define the smallest living organism.

These debates revolve around organisms or their fossilised remains visible under the electron microscope, but many microfossils and nannofossils can be observed by amateur microscopists using modest optical microscopes and simple preparation techniques i.e. without the need to prepare thin rock sections.

To illustrate this, shown below is an image gallery of a selection of microfossils and nannofossils that can be found in rocks of the Dorset coast, Southern England. Many are typical of rocks of this type that can be found elsewhere. The fossils can provide evidence of the habitat and climate type that was present when the microscopic organisms died and slowly fossilised.

The images were taken not of the rocks but of cellulose peels of prepared rock surfaces, a technique that is well within the scope of the amateur microscopist/geologist. Cellulose peels are prepared by painting the rock surface with a lacquer, that when dry can give a faithful replica of a rock surface (a 'peel') down to the tiniest structures, as well as some removal layers of rock material. The rock can be stained or unstained prior to making the peel to clearly show certain structure types. Keith Abineri's earlier articles explain the technique in more detail and what can be deduced from the fossils found.

Image gallery - specimen locations and image details are in the Appendix.

Terms underlined are explained in the Glossary.

 

Fig. 1: Globigerinid forams, other forams, sponge fragments, calcispheres and nannofossils in chalk. Stained cellulose lacquer peel, examined under PPL brightfield illumination. It shows both thin removed layer images and replica images. The absence of any blue or mauve staining indicates aerobic conditions during the deposition of the chalk, in common with other Upper Chalk microfossils and nannofossils. Size of the large foram chamber = ca. 93 mm. Limiting resolution of nannofossils = ca. 2 mm.

Fig. 2: Large damaged foram section, calcispheres, chalk nannofossils etc. in chalk. Stained cellulose lacquer peel, examined under PPL brightfield illumination. It shows both thin removed layer images and replica images. Length of foram chambers = ca. 110 mm. Limiting resolution of nannofossils = ca. 2 mm.

 

 

Fig. 3: Chalk calcisphere section on a background of damaged coccoliths and other nannofossils. Stained cellulose lacquer peel, examined under PPL illumination. The absence of any blue or mauve staining indicates again aerobic conditions during the deposition of the chalk. The diameter of the calcisphere, shown here, including the complex outer layer, is ca. 42 mm. The limiting resolution of the coccoliths and nannofossils is about 1 mm.

Fig. 4: The fine structure of the chalk is shown here, including partly buried and damaged coccoliths and other nannofossils. Stained cellulose lacquer peel, examined under PPL brightfield illumination. The absence of any blue or mauve staining indicates once more aerobic conditions during the deposition of the chalk. The size of the coccoliths, other nannofossils and fragments range from <l mm to 9.3 mm in diameter.

 

 

Fig. 5: Coccoliths and coccolithophores, including some buried in kerogen. Unstained cellulose lacquer peel, examined under PPL brightfield illumination. The picture shows both thin removed layer images and replica images. The three centre coccolithophores range from ca. 14 to 16 mm in diameter, and the coccoliths on their surfaces are about 4 to 5 mm in diameter. The numerous free coccoliths in the field range from about 2 to about 5 mm in diameter.

 

Fig. 6: Coccoliths and coccolithophores buried in kerogen and partly not covered. Unstained cellulose lacquer peel, examined under PPL brightfield illumination. The picture shows both thin layer images and replica images. The large uncovered coccolithophore in the lower left-hand field has a diameter ca. 23 mm. There are indications of similar features buried in the dark kerogen in the right-hand field. (See figure (7)).
Fig. 7: This shows features from the field in Figure (6), but using XPL illumination to indicate the optical figures of coccoliths and coccolithophores. Note the pale yellow colour of the objects embedded in kerogen (lower image). The thick kerogen layer appears very dark. Uncovered objects show bright white optical figures. The diameter of the largest buried coccolithophore in the right-hand field of Fig. 7 is here also ca. 23 mm (upper image). Note also from comparison between figures (6) and (7) that some of the coccoliths in the left-hand field are replica images.

 

Fig. 8: Numerous coccoliths including some embedded in a layer of kerogen. Unstained cellulose lacquer peel, examined under PPL brightfield illumination. The picture shows both thin removed layer images and replica images. The numerous coccoliths have diameters in the range from ca. 3.0 to 6.0 mm. The most detailed images appear to be those coccoliths embedded in the kerogen.
Fig. 9: A complex field including coccoliths and coccolithophores, some of which are embedded in kerogen, together with some fusain and pyrites, as well as a replica of part or a fragment of wood. Partly stained cellulose lacquer peel, examined under PPL brightfield illumination. The complex picture shows both thin removed layer images and replica images. Some of the staining was probably inhibited by the presence of kerogen. The coccoliths ranged in diameter from ca. 3.0 to 6.5 mm. Note the small area of ferroan calcite associated with the wood fragment. The diameter of the distinct coccolithophore, embedded in kerogen, at the central area of the right-hand field is ca. 14 mm. The diameters of its surface coccoliths are approximately 4.7 mm.

Glossary

Aerobic : in the presence of oxygen.
Anaerobic : in the absence of oxygen.
Calcareous nannofossils : Nannofossils largely composed of calcium carbonate. Many forms belong to the Coccolithophyceae.
Calcispheres : Minute hollow microfossils and nannofossils of calcareous composition. Found frequently in chalk and limestone sediments. They have existed in differing forms since the Devonian Period (circa. 380 million years ago).
Coccoliths : minute calcium carbonate platelets secreted by coccolithophores which bear them as surface plates.
Coccolithophore : a unicellular planktonic organism of uncertain type (protozoan or algae?). Currently assigned the phylum Haptomonada.
Ferroan Calcite : crystalline calcium carbonate with a very small proportion of the calcium displaced by iron(II) in the crystal lattice. This occurs under anaerobic environments.
Forams : Foraminifera. A class of protozoa that form calcareous shells. (See articles in the Micscape on-line library by Brian Darnton).
Fusain : carbonaceous material derived from decaying vegetation or wood.
Globigerinid forams : a foram of the genus Globigerina.
Kerogen : A solid complex organic material which yields petroleum type hydrocarbons under heat and pressure.
Microfossil : a fossil or fossil fragment that can only be seen with a microscope.
Nannofossil : fossils of minute planktonic organisms, especially calcareous unicellular algae.
Period: Jurassic - ca. 218 - 144 million years ago; Cretaceous - ca. 144 - 65 million years ago.
Pyrites : a most widespread sulphide of iron. A sure sign of anaerobic sediments.
Removed layer images : actual rock material removed from rock surface by peel, e.g. kerogen, calcite etc.
Replica images : images fromed by "printing" by cellulose lacquer; produce no XPL images.
Staining : in the absence of iron (II) no Prussian Blue is formed and indicates aerobic conditions.
PPL : plane polarised light (plane polarising filter in the substage only)
XPL : cross polarised light (plane polarising filter both in the substage and the eyepiece aligned at right angles for maximum extinction).


Appendix

Details of the specimen locations and objective used.
(Objective 40X - N.A. 0.65; objective 100X oil-immersion - NA 1.25).

Figure (1) and Figure (2).
From the Cretaceous, Upper Chalk, Actinocamax Quadratus Zone. Map Reference SY.851.802. West of Arish Mell on the cliff, Dorset coast. (Objective 40X).
Figure (3) and Figure (4).
From the Cretaceous, Upper Chalk, Actinocamax Quadratus Zone Map Reference SY.851.802. West of Arish Mell on the cliff, Dorset coast. (Objective 100X).
Figure (5).
From the Jurassic, Kimmeridge Clay, Rope Lake Head Stone Band. Map Reference SY.926.775. Rope Lake Head, West of Hounstout Cliff, Dorset coast. (Objective 100X).
Figure (6) and Figure (7).
From the Jurassic, Kimmeridge Clay, Maple Ledge Shales. Map Reference SY. 908.790. East of Gaulter Gap, Kimmeridge Bay, Dorset coast. (Objective 100X).
Figure (8) and Figure (9).
From the Jurassic, Kimmeridge Clay, Rope Lake Head Stone Band. Map Reference SY.926.775. Rope Lake Head, West of Hounstout Cliff, Dorset coast. (Objective 100X).

Editor's note: Some of the quality of the author's original 35mm slides is lost in the scanned and compressed web images. Comments to the author are welcomed, who can be contacted directly at the address below or comments can be passed on via the Micscape Editor, see magazine index contact..

Keith Abineri. 42 West Borough, Wimborne, Dorset BH21 1NQ, UK. Tel. 01202 885547

 

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