Gossip meeting “Microfossils”

Saturday 14th November 2020

Pam Hamer hosted this meeting and began with an overview of microfossils in a PowerPoint presentation that included what a microfossil is, where to find them, how to find them and how to look at them. Microfossils include parts of macro fossils (such as teeth, protective plates or shell fragments), juveniles of species, Foraminifera, Radiolaria and diatoms. They also include coccoliths, pollen and seeds, which are not easy for amateurs to observe.

Click the arrows to move through the slides. Click the symbol at bottom right for a larger version.

In the following discussion, suggested locations for microfossils included Oamaru diatomite, Achmelvich Bay on the west coast of Scotland, a diatomite mine on Skye, Cromer Cliffs, Hunstanton North Sands and Dog’s Bay in County Galway. Pam emphasised that you should not hammer cliffs – all of her samples were taken from material that had detached naturally.

Members asked where to find the special sides for microfossils, and here are 3 sources in the UK:

Microfossil slidesMicrofossil slides

Chris Green started looking at forams when he retired about 8 years ago, and he used a PowerPoint presentation to show a selection of photographs of live and dead specimens from all around the British Isles, habitats (beaches, bays, estuaries and chalk pits) and old ships that trawled the ocean floor to collect specimens. If you find white deposits on a beach, Chris recommended an old credit card to scrape up a sample. Chris explained how he collects and processes samples, boiling them, floating them, drying them, sieving them and using a stereomicroscope to examine them. Chris cautioned that you should use microfossil slides that are acid-free; he makes his own from archival materials. To pick up the smallest specimens, Chris uses a brush with all except one or two bristles removed. One of the first books was On the Recent Foraminifera of Great Britain by William Crawford Williamson. A satisfactory classification has only been available for about 30 years. The protoplasm is mainly confined to one chamber.

Various foramsVarious forams

Tràigh Nam beach, Isle of MullTràigh Nam beach, Isle of Mull

Sorting foramsSorting forams

Click the arrows to move through the slides. Click the symbol at bottom right for a larger version.

Paul Smith concentrated on diatoms in his PowerPoint presentation. The study of diatoms seems to have paralleled the development of achromatic and better objectives, as enthusiasts wanted to be able to see smaller and smaller dots. They are found in almost any damp or wet habitat. They are made of silica, and various dangerous chemicals are used to remove detritus, calcium deposits and protoplasm and make the tests visible. Modern diatoms can be cleaned with bleach or enzyme washing powder. Normal mounting media with a refractive index of around 1.5 make diatoms hard to see, although phase contrast can help. All sorts of mounting media with high refractive indices have been used to make the features visible, even strange ones such as white phosphorus dissolved in carbon disulfide, and realgar (arsenic sulfide). Modern mountants include Pleurax and Naphrax. Paul explained a method of making slides of diatom strews on coverslips, using card and sticky tape to hold the coverslip (diatoms down) just above the glass slide. Paul then showed some photomicrographs of fossil Oamaru diatoms mounted in this way, and a diatom arrangement by W. A. Firth. Diatomite can be broken down by repeatedly freezing and thawing it.

Diatom arrangement by W. A. FirthDiatom arrangement by W. A. Firth

Click the arrows to move through the slides. Click the symbol at bottom right for a larger version.

Pam Hamer reminded us that the Club’s slide collection contains lots of slides of foraminifera and diatoms from various parts of the world, and that the whole collection is being digitised so that it can be made available on the website.

Foraminifera slides in the collectionForaminifera slides in the collection

Foraminifera slides in the collectionForaminifera slides in the collection

Diatom slides in the collectionDiatom slides in the collection

Diatom slides in the collectionDiatom slides in the collection

We need more volunteers to transcribe the data from photographs of the slides into an Excel spreadsheet. If you can help, please contact Pam Hamer.

There are several papers in the Journal (which is available on a USB drive) on work done on diatoms and forams by Quekett members, for example:

Paper on Oamaru diatomsOn a Fossil Marine Diatomaceous Deposit from Oamaru, Otago, New Zealand by E. Grove & G. Sturt

Number of forams in chalkOn the Estimation of the Numbers of Foraminifera found in Chalk by M. C. Cooke

Alan Wood couldn’t find a suitable photomicrograph to help publicise this gossip meeting on Facebook and Twitter, so he looked through his slide collection and discovered a slide of radiolarian fossil earth from Barbados, made by Brian Darnton. He used his Olympus BH2-DCD dark-ground condenser and SPlanApo 10× objective to take this photo with his Canon EOS 5D Mark II and EOS Utility, combining seventy images at 0.002 mm intervals in Zerene Stacker.

Radiolarian fossil earth from BarbadosRadiolarian fossil earth from Barbados

Alan eventually found a close-up photograph of foraminiferous sand from Dog’s Bay in County Galway, Ireland, taken with a macro lens:

Foraminiferous sand from Dog’s BayForaminiferous sand from Dog’s Bay

Report by Alan Wood

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