Fossil Foraminifera in Herault (Alveolina) Limestone

Cactusdave · Post by **Cactusdave** » Mon Mar 02, 2015 8:14 am

The general quality of the images of living freshwater and marine organisms on this site is amazing, in fact for some images, I have simply run out of superlatives. So for a change I thought I'd show some images of marine life that is dead, very dead, in fact fossilised. I recently acquired a slide with a label that said section of Alveolina limestone, Herault, France. The maker's name, J. How and address in London, places its manufacture to the 1880s. The section is simply glued to the slide, probably with Canada Balsam and has been produced by grinding. There is no coverslip. The section contains abundant Foraminifera fossils in matrix and is named after the most abundant species present, Alveolina. The limestone was laid down in the Eocene epoch, roughly, 35-40 million years ago. I am no expert at naming the fossils, but using this reference (in French) http://planet-terre.ens-lyon.fr/image-d ... -10-13.xml , I can hopefully recognise some of the forams. present.

The section was examined with coaxial incident polarised light using an Ortholux 1 with Ultropak incident light attachment and X6.5 Ultropak objective. The photoeyepiece was a Leitz Vario-Orthomat zoom http://www.photomacrography.net/forum/v ... 294c#51190 . The camera was a Sony NEX 5N afocally coupled via a T-mount and a reversing ring to the filter mount of a Minolta 45mm prime lens attached to the camera with a Minolta to Sony E-mount adapter. This setup gives minimal vignetting (< 10%) at the lowest zoom settings on the Vario-Orthomat of X5 and X6.3 which disappears at X8. Maximum zoom is X12.5.

For comparison transmitted polarised light +/- retarder images were taken on a Nikon Diaphot with a Leitz X2.5 planachromat objective. A Canon 5D mkII was attached to the front SLR port which employs a built in X2.5 relay lens.

Alveolina, incident polarised light, field width approximately 2mm

Same specimen with polarised transmitted light and a retarder.

Alveolina (top), miliolid foram. underneath, part of an Orbitolites at the bottom.

Similar area in transmitted polarised light plus retarder. Crop from a five image stitch.

Opertorbitolites incident polarised light.

Opertorbitolites, transmitted polarised light.

More images to follow.

Beatsy · Post by **Beatsy** » Mon Mar 02, 2015 2:35 pm

Really interesting set. Loads of species names I've literally never heard of - ever.

Quite a striking difference (improvement) with transmitted polarised and retarder too. What does the retarder add in this situation? Contrast?

carlos.uruguay · Post by **carlos.uruguay** » Mon Mar 02, 2015 6:51 pm

Awesome !! Many many thanks thanks for sharing !!

Cactusdave · Post by **Cactusdave** » Tue Mar 03, 2015 1:36 am

Thanks Beatsy and Carlos.

Beatsy, the role of polarisation is a bit different between the incident and transmitted light situations. For incident light it is pretty much essential in a situation like this. Without polarising the incident light there is excessive reflection and glare from the mineral surface. I think wetting the surface might help further with this, but the surface is very absorbent and I was concerned about damaging this very old slide.
With the transmitted light situation, polarised light gives better contrast and detail than non polarised light in my system. Putting a retarder in as well is a matter of choice really. it maybe helps a little with contrast, but in some of these images it does pick up some colour from other minerals in the section, which, in a pretty monochrome/yellowish sample, gives a bit of additional interest.

Cactusdave · Post by **Cactusdave** » Tue Mar 03, 2015 2:07 am

As promised, a few more pictures.

Orbitolites, polarised incident light.

Orbitolites, polarised transmitted light with a retarder. Cropped from a 27 image stitch.

Not sure if this pair are Alveolina in TS or someting else. Transmitted polarised light with retarder. HDR image produced from 6 individual images using Fusion free version.

A couple of stitched transmitted polarised light images with retarder which give a better overview of the section, showing just how packed it is with fossils.

Crop from a 27 image image.

Alternative crop.

Jacek · Post by **Jacek** » Tue Mar 03, 2015 5:17 am

very interesting

gpmatthews · Post by **gpmatthews** » Tue Mar 03, 2015 5:30 am

Fascinating images, David!

Cactusdave · Post by **Cactusdave** » Wed Mar 04, 2015 2:38 am

Thanks Graham. It was interesting to try to find ways to photograph this section successfully. Ultimately, transmitted light gave good and informative images, but it was revealing to compare them with what was visible on the surface of the section with reflected light. I have recently been looking at some thin sections of bones from the Lower Permian amphibian Eryops, again comparing transmitted and incident light. Very different, but sort of complementary views are produced.

Marek Mis · Post by **Marek Mis** » Wed Mar 04, 2015 6:06 am

Very interesting images ! The second and the last one are my favourite. The watching organisms which were living millons years ago before the man became one of the Earth inhabitants is always very exciting. Thank you for sharing.

Marek

Cactusdave · Post by **Cactusdave** » Thu Mar 05, 2015 5:16 am

Thanks Marek. I really should post some of my images of fossil bone sections. Some of the dinosaur (Iguanodon) sections show remarkable preservation of recognisable bone structure

Charles Krebs · Post by **Charles Krebs** » Thu Mar 05, 2015 7:29 pm

A different and fascinating subject. Nicely done!

RogelioMoreno · Post by **RogelioMoreno** » Fri Mar 06, 2015 7:49 am

Very interesting set!

Rogelio

Cactusdave · Post by **Cactusdave** » Tue Mar 10, 2015 3:28 am

Thanks Charles and Rogelio. It certainly makes a change to see the fossil remains of a bunch of protozoa that are long, long dead.